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Improving type 2 diabetes mellitus glycaemic control through lifestyle modification implementing diet intervention: a systematic review and meta-analysis.

García-Molina, Laura [email protected] Lewis-Mikhael, Anne-Mary Riquelme-Gallego, Blanca Cano-Ibáñez, Naomi Oliveras-López, María-Jesús Bueno-Cavanillas, Aurora

European Journal of Nutrition Jun2020, Vol. 59 Issue 4, p1313 16p.

English

*HEALTH behavior *MEDICAL care *MEDLINE *TYPE 2 diabetes *PATIENTS *WEIGHT loss *EVIDENCE-based medicine *TREATMENT effectiveness *GLYCEMIC control BEHAVIOR modification GLYCOSYLATED hemoglobin INFORMATION storage & retrieval systems META-analysis ONLINE information services PRIMARY health care SYSTEMATIC reviews (Medical research)

Diet; Glycaemic control; Lifestyle intervention; Meta-analysis; Systematic review; Type 2 diabetes mellitus

Purpose: Type 2 diabetes mellitus represents a significant health problem. Many studies have reported that intensive nutritional intervention by itself or in addition to medications is the best method to improve glycaemic control in type 2 diabetes mellitus. However, in clinical practice, dietary education is not implemented as an integral part in the management of type 2 diabetes mellitus. The purpose of this systematic review and meta-analysis is to analyse the scientific evidence concerning the role of nutritional intervention in the glycaemic control of type 2 diabetes mellitus. Methods: We searched Pubmed, Scopus, Cochrane Library and Web of Science databases from inception till

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May 2019 for randomised controlled trials (RCTs) that include dietary interventions in the management of patients with type 2 diabetes mellitus. Results: A total of 28 studies were included. Our results demonstrated that lifestyle interventions significantly lowered glycosylated haemoglobin (HbA1c) levels compared to the usual care for patients with type 2 diabetes mellitus, overall weighted mean difference, WMD = − 0.51 (− 0.67, − 0.35). Strategies combining individualized and group-based activities were the most effective, WMD = − 0.95 (− 1.24, − 0.66). Most of stratified analyses did not totally resolve heterogeneity, but improvement in HbA1c levels has been consistently observed. Conclusions: The available evidence from RCTs shows that lifestyle intervention is more effective than the standard care regarding the glycaemic control of type 2 diabetic patients, particularly when there is a weight loss. It is time to translate this evidence to the primary health care practice. The protocol of the present systematic review was registered in PROSPERO, registration number CRD42018090469. ABSTRACT FROM AUTHOR

Department of Preventive Medicine and Public Health, University of Granada, Avenida de la Investigación, 11, 18016, Granada, Spain; CIBER Epidemiología y Salud Pública (CIBERESP), Avenida Monforte de Lemos, 3-5, 28029, Madrid, Spain; Department of Obstetrics and Gynecology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada; High Institute of Pubic Health, Alexandria University, 165 El-Horreya Avenue – El-Ibrahimia, Alexandria, Egypt; Fundación para la Investigación Biosanitaria de Andalucía Oriental (FIBAO), Avenida de Madrid, 15, 18018, Granada, Spain; Department of Molecular Biology and Biochemical Engineering, University Pablo de Olavide, Carretera de Utrera, Km 1, 41013, Seville, Spain; Instituto de Investigación Biosanitaria de Granada (ibs.Granada), Servicio Andaluz de Salud/Universidad de Granada, Avenida de Madrid, 15, 18018, Granada, Spain

14366207

Publication Type: Article Update Code: 20200519

143245203

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Improving type 2 diabetes mellitus glycaemic control through lifestyle modification implementing diet intervention: a systematic review and meta- analysis

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Purpose: Type 2 diabetes mellitus represents a significant health problem. Many studies have reported that intensive nutritional intervention by itself or in addition to medications is the best method to improve glycaemic control in type 2 diabetes mellitus. However, in clinical practice, dietary education is not implemented as an integral part in the management of type 2 diabetes mellitus. The purpose of this systematic review and meta-analysis is to analyse the scientific evidence concerning the role of nutritional intervention in the glycaemic control of type 2 diabetes mellitus. Methods: We searched Pubmed, Scopus, Cochrane Library and Web of Science databases from inception till May 2019 for randomised controlled trials (RCTs) that include dietary interventions in the management of patients with type 2 diabetes mellitus. Results: A total of 28 studies were included. Our results demonstrated that lifestyle interventions significantly lowered glycosylated haemoglobin (HbA_1c) levels compared to the usual care for patients with type 2 diabetes mellitus, overall weighted mean difference, WMD = − 0.51 (− 0.67, − 0.35). Strategies combining individualized and group-based activities were the most effective, WMD = − 0.95 (− 1.24, − 0.66). Most of stratified analyses did not totally resolve heterogeneity, but improvement in HbA_1c levels has been consistently observed. Conclusions: The available evidence from RCTs shows that lifestyle intervention is more effective than the standard care regarding the glycaemic control of type 2 diabetic patients, particularly when there is a weight loss. It is time to translate this evidence to the primary health care practice. The protocol of the present systematic review was registered in PROSPERO, registration number CRD42018090469.

Keywords: Diet; Glycaemic control; Lifestyle intervention; Meta-analysis; Systematic review; Type 2 diabetes mellitus

Electronic supplementary material The online version of this article (10.1007/s00394-019-02147-6) contains supplementary material, which is available to authorized users.

Introduction Type 2 diabetes mellitus represents a significant worldwide public health problem. It is mainly a consequence of the currently experienced sedentary lifestyle and the marked increase in obesity all over the world [[ 1]]. Type 2 diabetes mellitus is associated with high morbidity and mortality [[ 2]], as it is the main cause of kidney insufficiency, [[ 4]–[ 6]] blindness, [[ 7]] and non-traumatic amputations [[ 8]]. Also, it represents a fundamental risk factor for cardiovascular disease, the leading cause of mortality in diabetic patients [[ 9]]. Thus, type 2 diabetes mellitus not only reduces quality of life, but also decreases life expectancy, on average 8 years less than the non-diabetic population [[10]]. On the other hand, type 2 diabetes mellitus implies very high health expenditures, reaching more than 383,000 million dollars per year in Europe only, [[11]] and still more if indirect costs are included. Both direct and indirect costs increase when diabetes complications occur [[12]–[16]].

Health education interventions are comprehensive programmes that health care providers deliver to patients aimed at improving patients' clinical outcomes through the increase and maintenance of health behaviour [[17]]. Concerning the role of health education interventions in diabetic patients, the "Look Ahead study" demonstrated an effect of intensive lifestyle intervention on glycated haemoglobin as well

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as initial improvements in most cardiovascular risk factors [[18]]. The "PREDIMED study" reported a decrease in the incidence of type 2 diabetes mellitus in high-risk cardiac patients implementing a Mediterranean Diet enriched in extra virgin olive oil or nuts compared to the control group who were only advised to follow a low fat diet [[19]]. This study also demonstrated the efficacy of nutritional intervention in improvement of glycaemic control [[20]].

The American Diabetes Association's Standards of Medical Care in Diabetes [[21]] focus on diet and physical exercise for the management of diabetes. "Lifestyle management and psychosocial care are the cornerstones of diabetes management", mostly in overweight and obese diabetic patients. However, there is poor application and maintenance of lifestyle modification actions. In spite of the clear recommendations on a healthy diet and increased physical activity, lack of relevant applications of these guidelines in the primary health care system has been highlighted [[22]]. Important advancements of antidiabetic medications and the emergence of new drugs in recent years have led to poor development of relevant strategies for lifestyle modification [[24]]. There are no special resources allocated to this goal or specific training for primary health care practitioners and nurses.

The aim of the present systematic review and meta-analysis is to analyse the available scientific evidence regarding the role of lifestyle-related interventions based on diet modification in the glycaemic control of type 2 diabetes mellitus patients. Our specific goals are to demonstrate if there is sufficient evidence that would justify implementing specific lifestyle modification strategies by the primary health care units for the management of type 2 diabetes patients and to identify the most effective ones.

Methods

Protocol and registration The present systematic review and meta-analyses are written applying the PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health interventions [[25]]. The protocol of the present systematic review was registered in PROSPERO with the registration number CRD42018090469, available in: https://www.crd.york.ac.uk/PROSPERO.

Eligibility criteria

Search strategy We have searched several electronic databases (PubMed, Scopus, Cochrane Library and Web of Science) from inception of each till May 2019. This is in addition to hand searching references of relevant systematic reviews as well as the included articles. The research question using PICO strategy is: P-type 2 diabetes mellitus patients; I-lifestyle intervention based on diet modification; C-usual diabetic care; O-HbA levels at the end of the intervention. Our search strategy was randomised controlled studies carried out on adults with type 2 diabetes mellitus where the intervention encompasses lifestyle modification including diet with or without physical activity. There were no restrictions regarding socioeconomic, geographic, or racial/ethnic characteristics of the study population. Also, there was no

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language restriction. Only studies published as full texts were eligible for reviewing; abstracts that did not have full texts were excluded for our concerns about sub-optimal bias assessment. The search strategy included different combinations of a number of terms: "type 2 diabetes mellitus", "diabetes control", "dietetic intervention", "lifestyle intervention", "nutrition education", "dietetic pattern", "behaviour intervention", "medication", "control group" and "clinical trials". On the other hand, we excluded the terms "type 1 diabetes mellitus" and "T1DM".

Inclusion and exclusion criteria This systematic review considered for inclusion any RCT that assesses a lifestyle intervention (based on diet, nutritional education and/or physical activity) in type 2 diabetes mellitus population. The primary outcomes were HbA at different follow-up periods to measure the glycaemic control of type 2 diabetes mellitus. Exclusion criteria were ( 1) study designs other than RCTs, ( 2) type 1 diabetes mellitus population, prediabetics, gestational diabetes mellitus, ( 3) types of interventions other than lifestyle modification.

Data collection and risk of bias Two reviewers (LG-M and BR-G) independently screened the titles and abstracts, reviewed the full texts for study selection, extracted data and assessed the quality of the included articles. A piloted extraction form was used to extract the data and included: first author, publication year, journal name, study settings, sample size, characteristics of the participants, mean of follow-up durations, body mass index (BMI) of the included sample, type and nature of intervention, inclusion of physical activity in the intervention, diabetes mellitus evolution time, inclusion of motivational or psychoeducational elements in the intervention, staff who delivered the intervention, number of visits, duration of visits, data on the blood glucose levels of the participants, HbA mean and standard deviation before and after the interventions, variables adjusted for, and risk of bias. Authors were contacted for relevant data that were not provided in the manuscripts.

Any discrepancy between the two reviewers regarding article inclusion and data collection was resolved first by discussion followed by taking the opinion of a third researcher. Assessment of methodological quality of included studies was carried out using Cochrane risk of bias tool for RCTs (RoB 2) [[26]]. The tool is structured into five domains including bias arising from the randomisation process; bias due to deviations from intended interventions; bias due to missing outcome data; bias in measurement of the outcome; and bias in selection of the reported results.

Synthesis of data and statistical analysis We have primarily pooled the results of the included studies based on the longest duration of follow-up of the diabetic patients for each study. We have used the means and standard deviations reported by the authors for HbA levels for the intervention and control groups at the end of the intervention/standard care. For studies that did not provide standard deviations, we calculated them from the 95% CI provided by the authors. The effect estimates of included studies were summarized and presented as forest plots. We applied a random-effects model owing to the expected heterogeneity

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between studies [[27]]. Heterogeneity was assessed using Cochran's Q statistic and quantified using the I statistic [[28]].

To investigate potential sources of heterogeneity between studies, subgroup analyses were conducted, stratifying by potential variables that we have set a priori that included: length of follow-up of participants, quality of the articles (overall quality and by different quality components), sample size, region and setting of the RCTs. We also stratified articles based on the different characteristics of the interventions, type of intervention (individual, group based, or including both individualized and group- based components), inclusion of a motivational/psychoeducational component, inclusion of diabetes self-management educational intervention, inclusion of physical activity in the intervention, number of visits of each intervention, total number of hours of the intervention and involvement of a nutritionist. Moreover, we stratified studies by differences between intervention and control groups regarding post- intervention weight loss. We used the difference in the change in BMI, and grouped the studies as no difference, low, moderate and high differences. When the BMI variation is equal in both groups or lower in the intervention group than in the control group, we considered it as no difference. The difference between the intervention and control groups was considered low, moderate or high when the decrease in BMI was higher among the intervention group by 0.20, 0.2–0.8, or > 0.8 points, respectively. Stratification was also conducted based on characteristics of the participants including their BMI and the average duration in years since the diagnosis of diabetes. To examine the robustness of the study results and to evaluate the disproportionate influence that a specific study may impose on the combined summary statistics, we recalculated pooled estimates after deleting one study at a time in a sequential manner. We have applied a priori planned sensitivity analyses by excluding low-quality studies as well as studies providing outliers. We also conducted sensitivity analyses after undergoing subset analyses to determine the effects of specific studies on the overall pooled estimates. Statistical analysis was conducted using Stata v.14 software (Stata Corp., 2015, College Station, TX, USA).

Results

Study selection Search results are shown in Fig. 1 (PRISMA Flow diagram showing the selection process of the studies included in the systematic review and meta-analysis). A total of 2408 articles were identified from the initial search in the different databases. 608 articles remained after eliminating duplicates and irrelevant articles by title, followed by excluding 450 articles based on the abstract. After reviewing full text, we excluded 35 articles that did not include lifestyle intervention, another 35 articles that lacked randomisation and 54 that did not provide data about HbA or relevant data at follow-up. Finally, eight articles were excluded for not including type 2 diabetes population. Lastly, we identified two articles from hand searching included articles' references. In total, 28 records were systematically reviewed.

Graph: Fig. 1 PRISMA Flow diagram showing the selection process of the studies included in the systematic review and meta-analysis

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Study characteristics The main characteristics of the 28 studies that we systematically reviewed are summarized in Table 1. All are RCTs with lifestyle interventions and were conducted in different countries, nine studies from the Americas, [[29]–[37]], eight from Europe, [[38]–[45]], eight from Asia, [[46]–[53]], one from New Zealand [[54]] and two from Africa [[55]]. In total, 9 studies were published before 2010 and 19 after this year.

Summary of included studies

Study, first author, year

Initial population (final population)/follow-up

Type of intervention Personnel conducting intervention

Major findings: HbA basal and after follow-up (mean ± SD)

Al-Shookri 2012 [46]

N: 200 (170) T2D, 30– 70 years/6 months

Individualized intervention; interval: basal, week 2 and week 2–4; duration: 3 h in total; regarding behavioural goals for diet, eating and exercise

Dietitian, nurse, health educator and physician

IG: 10.3 (1.8)–9 (1.8)–9.5 (1.4); CG: 10.2 (2.4)–9.4 (2)– 9.8 (1.8)

Ali 2012 [40] N: 48 (46) T2D, HbA > 53 mmol/mol, not on insulin, on oral medication > 18 years/12 months

Individualized intervention; interval: monthly (first 2 months) and every 3 months for the 12 months; regarding regular monitoring and lifestyle intervention

Pharmacist IG: 8.2 (1.65)–6.6 (0.59); CG: 8.1 (0.97)–7.5 (0.64)

Alonso- Domínguez 2019 [45]

N: 204 (175) T2D, HbA ≥ 48 mmol/mol, 25-70 years/12 months

Group intervention; duration: 3 h; regarding healthy diet, culinary techniques, food labelling, smartphone application and physical activity

Nurse IG: 6.9 (1.2)–6.8 (1.0)–6.9 (1.1); CG: 6.8 (1.2)–6.8 (1.1)– 7.0 (1.3)

Andrews 2011 [38]

N: 593 (579) T2D (diagnosed 5-8 months), > 30 years, HbA < 86 mmol/mol, BMI > 25/12 months

Individualized intervention; interval: every 3 months and monthly with nurse; duration: 7.5 h; Regarding diet and physical exercises

Dietitian, nurse and physician

IG: Diet 6,64 (0.93)– 6.57 (1.06)–6.55 (0.95)/Diet + PA 6,69 (0.99)–6.60 (1)–6.65 (0.93); CG: 6.72 (1.02)–6.86 (1.02)–6.81 (0.91)

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Study, first author, year

Initial population (final population)/follow-up

Type of intervention Personnel conducting intervention

Major findings: HbA basal and after follow-up (mean ± SD)

Bender 2017 [36]

N: 45 (45) T2D (non- insulin dependent), ≥ 18 years, BMI > 23, own smartphone with internet access/6 months

Individualized intervention; interval: monthly, with not intervention in month 5; regarding diet, physical exercises, and lifestyle balance

Research investigators

IG: 7.39 (0.82)–6.9 (0.67)–7.1 (0.98); CG: 7.44 (0.93)–7.3 (1)–7.1 (1.2)

Coppell 2010 [54]

N: 104 (94) T2D, < 70 years, diagnosed 9 months before the study, and two of: hypertension, dyslipidaemia, overweight or obesity/6 months

Individualized and group intervention; interval: every 2 weeks (month 1), monthly (first 5 months) and group session (in the first 2 months); regarding intensive dietary intervention

Dietitian IG: 8.9 (1.4)–8.4 (1.0); CG: 8.6 (1.3)– 8.6 (1.2)

Debussche 2012 (41)

N: 398 (319) T2D, > 18 years/12 months

Individualized intervention; interval: every 3 months; regarding lifestyle intervention, diet and physical activity

Dietitian, nurse and exercise physiologist

IG: 10.0 (2.2)–8.2 (1.6); CG: 10.3 (2.2)–8.3 (1.5)

Debussche 2018 [55]

N: 151 (140) T2D, HbA ≥ 64 mmol/mol, 30–80 years/12 months

Group intervention; interval: every 3 months. duration: 6 h; regarding cardiovascular risk factors, food intake, exercise and insulin management

Peer educators IG: 10.6 (1.8)–9.5 (2.0); CG: 10.8 (1.9)–10.6 (1.75)

Diabetes study group 2004 [29]

N: 362 (317) T2D (at least 1 year), HbA > 58 mmol/mol, ≥ 18 years/36 months

Individualized and group intervention; regarding diet, exercise, self-care behaviours, and strategies to improve self-care education

Dietitian and nurse

IG: 9.54 (0.12)–8.29 (0.12)–8.17(0.11)– 8.11 (0.11)–7.92 (0.13); CG: 9.66 (0.13)–8.94 (0.15)– 8.86 (0.14)–8.82 (0.13)–8.7 (0.15)

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Study, first author, year

Initial population (final population)/follow-up

Type of intervention Personnel conducting intervention

Major findings: HbA basal and after follow-up (mean ± SD)

Ferreira- Grillo 2016 [32]

N: 137 (127) T2D, 18– 80 years, HbA > 53 mmol/mol, 12 months

Group intervention; interval: weekly for 2 weeks and reinforcement meetings at months 4 and 8; duration: 10 h; regarding diabetes risk factors, healthy diet and exercise, pharmacological therapy, chronic diabetes complications, and foot care

Nurse IG: 8.8 (1.9)–8.7 (1.9)–8.6 (2.1)–8.7 (1.7); CG: 9.2 (2.1)– 9.3 (2.1)–9.5 (2.3)– 9.2 (2.2)

Fiore-Scain 2009 [31]

N: 104 (104) T2D (not on insulin therapy), 25–75 years/12 months

Group intervention; interval: weekly; duration: 8 h; regarding diet, physical exercises, self-monitoring, and foot care

Nurse IG: 6.8 (1.5)–6.5 (1.3)–6.4 (1.0)–6.4 (1.3)–6.5 (1.3); CG: 6.7 (1.4) 6.7 (1.1)– 6.8 (1.4)–6.9 (1.5)– 6.9 (1.4)

Goudswaard 2004 [39]

N: 58 (50), T2D (needing to start insulin), HbA ≥ 53 mmol/mol, 39–75 years/18 months

Individualized intervention; interval: every 3–6 weeks; duration: 2.5 h; regarding lifestyle education and management of blood glucose

Nurse IG: 8.2 (1.1)–7.2 (1.3)–7.8 (0.9); CG: 8.8 (1.5)–8.4 (1.7)– 8.2 (1.4)

Islam 2018 [37]

N: 336 (271), T2D HbA ≥ 48 mmol/mol, 21–75 years/6 months

Individualized and group intervention; interval: monthly; duration: 13 h; regarding nutrition, healthy eating and physical activity.

Community health workers

IG: 7.8 (1.3)–7.6 (1.2); CG: 8.0 (1.5)– 8.0 (1.6)

Kattelmann 2009 [33]

N: 114 (104) T2D, 18– 65 years/6 months

Group intervention; interval: monthly; duration: 13.5 h; regarding dietary intervention and meal plans

Dietitian IG: 8.9 (0.4)–8.4 (0.3) CG: 8.6 (0.3)– 8.5 (0.3)

Khanna 2014 [35]

N: 75 (49) T2D, HbA > 64 mmol/mol/3 months

Telephone individualized intervention; interval: basal, month 3 and telephone intervention by two calls weekly; regarding the importance of minimizing high-glycaemic index foods in diet

Telephone nutrition support system

IG: 9.2 (1.9)–9.1 (2.1); CG: 8.9 (1.3)– 8.5 (1.5)

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Study, first author, year

Initial population (final population)/follow-up

Type of intervention Personnel conducting intervention

Major findings: HbA basal and after follow-up (mean ± SD)

Kim 2003 [51]

N: 50 (36) T2D, HbA > 53 mmol/mol/3 months

Telephone individualized intervention; interval: twice a week (month 1) and weekly (month 2 and 3); duration: 6.5 h; regarding education and reinforcement of diet, exercise and medication adjustment recommendations

Dietitian, nurse and physician

IG: 8.8 (1.2)–7.6 (1); CG: 8.2 (0.8)–8.8 (0.9)

Ko 2004 [47]N: 180 (178) T2D, HbA = 64–97 mmol/mol, 35–75 years/12 months

Individualized intervention; interval: every 3 months; duration: 2.5 h; regarding cardiovascular risk factors education: smoking, obesity, diet, exercise, glycaemic control, and dyslipidaemia

Physician and nurse

IG: 8.6 (1.6)–8.1 (1.5); CG: 8.4 (1.2)– 8.2 (1.4)

Ménard 2005 [30]

N: 72 (61) T2D, 30–70 years, HbA > 64 mmol/mol/18 months

Individualized intervention; interval: monthly; regarding diet, physical exercises, and information on managing diabetes, hypertension and hyperlipidaemia

Physician IG: 9.1 (1.0)–7.5 (1.0)–8.1 (1.2)/CG: 9.3 (1.0)–8.6 (1.3)– 8.6 (1.3)

Mollaoğlu 2009 [48]

N: 50 (50) T2D, 18–65 years/2 months

Individualized and group intervention; interval: basal and monthly. regarding diet and exercise

Nurse IG: 9.5 (1.7)–7.5 (1.3); CG: 9.7 (1.6)– 9.6 (1.6)

Muchiri 2015 [56]

N: 82 (76) T2D, 40–70 years, HbA > 64 mmol/mol/12 months

Group intervention; interval: weekly, monthly and bi-monthly; duration: 26.5 h; regarding diet and information on managing diabetes, and vegetable gardening

Dietitian IG: 10.80 (1.80)– 9.67 (0.29)–9.80 (0.30); CG: 11.40 (2.20)–10.3 (0.29)– 10.40 (0.30)

Rygg 2012 [44]

N: 146 (133) T2D, > 18 years/12 months

Group intervention; interval: every 1 or 2 weeks; duration: 15 h; regarding lifestyle intervention and diabetes management

Dietitian and nurse

IG: 7.1 (1.4)–7.0 (1.2)–7.2 (1.2); CG: 6.9 (1.3)–7.1 (1.3)– 7.2 (1.4)

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Study, first author, year

Initial population (final population)/follow-up

Type of intervention Personnel conducting intervention

Major findings: HbA basal and after follow-up (mean ± SD)

Sharifirad 2011 [49]

N: 100 (97) T2D (at least 1 year), > 60 years/3 months.

Individualized intervention; interval: weekly and telephone calls in week 4 and 8; duration: 4.5 h; regarding frequency of meals, use of fat and simple sugars and use of fruits and vegetables

Dietitian IG: 7.7 (0.97)–7.33 (0.95); CG: 7.81 (0.98)–7.76 (0.8)

Spencer 2011 [34]

N: 183 (136) T2D, > 18 years/6 months

Individualized and group intervention; interval: one educational session and home visits every two weeks. regarding healthy lifestyle and diabetes self- management activities

Community health workers

IG: 8.6 (8.1, 9.2)– 7.8 (7.3, 8.3); CG: 8.5 (8.0, 9.1)–8.5 (8.0, 9.1)

Thors- Adolfsson 2006 [43]

N: 101 (88) T2D (at least 1 year), ≤ 75 years, HbA = 48–86 mmol/mol/12 months

Group intervention; duration: 2.5 h; regarding diet, physical activity, medication, and foot care

Nurse and physician

IG: 7.4 (1.0)–7.3 (1.3); CG: 7.1 (0.8)– 7.4 (1.1)

Trouilloud 2013 [42]

N: 120 (99) T2D, 20– 80 years/3 months.

Group intervention; interval: daily; duration: 24 h; regarding diet, physical activity, medication, and problem solving

Dietitian, nurse, physical activity counsellor and diabetologist

IG: 7.61 (1.45)–6.87 (1.17); CG: 7.47 (1.16)–7.29 (1.04)

Yuan 2014 [50]

N: 88 (76) T2D, > 18 years/3 months

Group intervention; interval: weekly; duration: 16 h; regarding healthy eating, being active, problem solving and reducing risk

Dietitian IG: 6.97 (0.915)– 6.77 (0.76); CG: 7.03 (1.04)–7.11 (1.3)

Zhang 2018 [52]

N: 1004 (978) T2D, 18–65 years/24 months

Individualized and group intervention; interval: monthly. regarding lifestyle intervention based on diet and exercise, self-monitoring blood glucose and educational group chat

Dietitian, nurse, exercise specialist, endocrinologist, behavioural therapist, and pharmacist

IG: 7.86 (1.2)–6.91 (0.7); CG: 8.15 (1.5)–7.78 (1.3)

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Study, first author, year

Initial population (final population)/follow-up

Type of intervention Personnel conducting intervention

Major findings: HbA basal and after follow-up (mean ± SD)

Zheng 2019 [53]

N: 60 (60) T2D, HbA ≥ 48 mmol/mol/3 months

Individualized and group intervention; duration: 3 h. regarding diabetes knowledge, nutrition and individualized exercise guidance

Dietitian IG: 8.30 (1.02)–6.34 (0.87); CG: 8.48 (0.40)–8.53 (0.72)

N number, IG intervention group, CG control group, T2D type 2 diabetes mellitus

Characteristics of participants The sample size ranged from 45 to 1004 participants. Studies included in our systematic review and meta-analysis applied different criteria for inclusion of the type 2 diabetic patients. All the studies included only adults with mean age ranging between 50 and 67 years old. Concerning BMI, the highest mean was 35.1 m /kg in the study of Coppell et al. [[54]]. None of the selected studies included hospitalized patients or diabetics with complications as diabetic nephropathy, dementia, cognitive alterations, and mental disorders. Participants were recruited from primary health care centres in 11 studies [[32]–[34], [37], [39], [43]–[46], [50], [56]], from hospitals or diabetes clinics in 15 studies [[29]– [31], [35], [38], [41], [47]–[49], [51]–[55]] and was not specified in only 2 articles [[36], [40]]. Fourteen studies set a minimum HbA level for participation [48–64 mmol/mol (6.5–8%)] [[29], [32], [35], [37], [39], [43], [45], [47], [51], [53], [55]]; however, there was no statistically significant differences between these means and HbA means of the participants in the studies that did not consider a specific HbA level in their inclusion criteria. Four articles set other inclusion criteria as medication (not starting insulin therapy, not on oral medication) [[31], [36], [39]] while one study only included diabetic patients that have two of the following conditions: hypertension, dyslipidaemia, overweight or obesity [[54]].

Characteristics of interventions Nine studies aimed to examine the effect of individualized lifestyle interventions on the control of blood glucose levels of the included type 2 diabetes mellitus population [[30], [36], [38]–[41], [46], [49]], two studies aimed to evaluate the effect of telephone-based lifestyle interventions [[35], [51]] while ten studies aimed to examine the effect of group-based lifestyle interventions [[31]–[33], [42]–[45], [50], [55]]. Finally, seven studies assessed the effect of both individualized and group-based lifestyle interventions [[29], [34], [48], [52]–[54]]. The length of the interventions and follow-up ranged from 2 months to 36 months; less than 4 months (n = 7) [[35], [42], [48]–[51], [53]], between 4 and 6 months (n = 6) [[33], [36], [46], [54]], between 7 and 12 months (n = 11) [[31], [38], [40], [43]–[45], [47], [55]] and more than 12 months (n = 4) [[29], [39], [52]]. The interventions were carried out by only dietitians/nutritionists in six studies [[33], [49], [53], [56]], and by nutritionist in collaboration with other health professionals (mainly nurses and/or physicians) in nine studies [[29], [35], [38], [41], [44], [46], [51]]. In eight studies, the intervention was carried out by nurses and/or physicians [[30]–[32], [39], [43],

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[45], [47]]; in the study of Ali et al. [[40]], the intervention was carried out by a pharmacist, and in three studies [[34], [37], [55]] by community health workers. Finally, the study of Bender et al. was carried out by technical researchers whose training background was not specified [[36]]. Most of the studies included physical activity (n = 23) as part of the intervention, only five did not include any [[35], [40], [49], [56]]. Control groups received the standard conventional diabetes care in all the included RCTs.

Risk of bias in the included studies We have assessed the quality of the studies included in our systematic review and meta-analysis according to Cochrane risk of bias tool for randomised trials (RoB 2) [[26]]. No included studies were blinded, which is expected due to the type of the intervention that involved lifestyle modifications through personal interviews, telephone calls, etc. Figure S-1 provides the estimated risk of bias of the included studies that were classified as "low" for 7 studies, "with some concern" for 10 studies and "high risk" for the remaining 11 RCTs, based on the RoB 2 tool.

Synthesis of results The results of the meta-analysis show an overall weighted mean difference (WMD) equal to − 0.51 (− 0.67, − 0.35) for post-intervention HbA levels when comparing lifestyle intervention groups to the usual diabetic care controls (Fig. 2). These results are significant (p = 0.000) but show high heterogeneity (I = 91.7%; p = 0.000). Undergoing sensitivity analysis, we removed the two outliers (Zheng et al. and Mollaglu et al.), but there was no significant change in the observed heterogeneity. To address the observed heterogeneity, we stratified the studies by many variables including the duration of follow-up (Fig. 3). The results revealed homogeneity for studies with a follow-up period of 4–6 months and those that measured the HbA levels after more than 12 months of follow-up. The WMD of post-intervention HbA levels increased with the increase in follow-up duration, from − 0.20 (− 0.34, − 0.05), (I = 18.5%, p = 0.293) for follow-up of 4–6 months, to − 0.36 (− 0.56, − 0.16), (I = 73.0%; p = 0.000) when the follow-up length is 7–12 months and − 0.79 (− 0.88, − 0.71), (I = 28.8%, p = 0.239) for patients followed up for more than 12 months. A slightly greater effect than the latter was observed when pooling the results provided for 2–3 month follow-up, − 0.87 (− 1.55, − 0.20), but high heterogeneity was observed in this group (I = 92.4%; p = 0.000).

Graph: Fig. 2 Meta-analysis of the effect of lifestyle interventions on the glycaemic control of type 2 diabetes patients (pooling the weighted mean differences of HbA1c levels after the longest duration of follow-up for each study)

Graph: Fig. 3 Stratifying studies by duration of follow-up

According to the type of intervention, it was interesting to notice that the pooled results of studies that assessed individualized lifestyle intervention as well as those that applied solely group-based lifestyle intervention showed lower WMD than studies that applied both individualized and group-based interventions, − 0.95 (− 1.24, − 0.66) (I = 91.6%; p = 0.000) (Fig. S-2). On the other hand, studies that included diabetes self-management as part of the intervention showed higher WMD: − 0.71 (− 0.89, −

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0.54) but higher heterogeneity (I = 86.2%; p = 0.000) (Fig. 4) than studies where the intervention encompassed diet and physical activity, WMD: − 0.24 (− 0.37, − 0.11) (I = 47.1%; p = 0.036).

Graph: Fig. 4 Stratifying studies by the presence or absence of diabetes self-management as part of the applied lifestyle intervention

Basal and post-intervention BMIs were provided by 20 studies. When stratifying by differences in weight loss between intervention and control groups (Fig. 5), we found that interventions which led to greater weight loss (a difference in the decrease in BMI between the intervention and control groups greater than 0.8) showed the higher pooled effects on the glycaemic control of the diabetic patients. Besides, stratifying by differences in the change in the BMI between intervention and control groups, heterogeneity was resolved for all the three groups of studies that showed a higher change in BMI for the intervention group versus the control group.

Graph: Fig. 5 Stratifying studies by differences between intervention and control groups regarding post- intervention changes in body mass index (BMI)

Risk of bias across studies Although we have synthesized only data referring to type 2 diabetes populations, there was still some variability in the characteristics of the participants of the included RCTs. Differences include time since development of diabetes mellitus, ethnicity and socioeconomic background. When we stratified by diabetes evolution time, we found the greatest effect of the intervention on those diagnosed for less than 3 years and those with a diagnosis of diabetes of more than 10 years.(Fig. S-3). On the other hand, means of age of the studied populations ranged between 50.7 and 67.0, but when we stratified by age mean at the beginning of the study, the effect was similar, WMD: − 0.42 (− 0.59, − 0.24) (I = 60.1%; p = 0.007) for patients older than 58 years, and WMD: − 0.56 (− 0.78, − 0.34) (I = 93.8%; p = 0.000), for patients younger than 58 years. Analysing the effect of the BMI, the heterogeneity was partially resolved in patients with BMI between 27 and 30 m /kg (Fig. S-4). Nevertheless, the degree of glycaemic control of the participants at the start of the trial could be a source of bias, as the baseline HbA levels differed between the included studies and it ranged from 51 mmol/mol in the study of Fiore-Scain [[31]] to 86 mmol/mol in the study of Debussche et al. [[41]].

Discussion

Summary of evidence After systematically reviewing and synthesizing the available data, our results show that lifestyle interventions might be superior to the standard diabetic care in glycaemic control reflected on the reduction of post-intervention HbA levels. Besides, the results suggest that the impact of lifestyle interventions is stronger when it encompasses both individualized and group-based activities, and when the intervention comprises diabetes self-management education (refers to interventions that also include information and skills for people to manage their diabetes, as monitoring blood sugar levels, problem

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solving and taking medication) and/or physical activity advice. However, these outcomes must be interpreted with caution given the heterogeneity that was observed when we primarily pooled the results of the retrieved data. In spite of some differences in PICO questions, previously published meta- analyses about lifestyle and health educational interventions have showed significant reduction in HbA levels for the intervention groups, yet authors have been concerned with the heterogeneity observed between the studies [[57]–[60]]. Regarding the method of assessment of glycaemic control, HbA was used in all the studies and accordingly we have chosen to use weighted mean differences in the meta- analyses [[61]]. For follow-up time, it was different among the included studies and, therefore, we have considered that thoroughly in our analysis.

To address sources of heterogeneity, we have taken into consideration several variables related to the study design. These variables included duration of follow-up, sample size, type of intervention (individualized/group based), personnel involved in the intervention, the inclusion of self-management of diabetes and/or physical activity, as well as the number of visits and hours of direct contact with patients, and the quality of the included studies [[26]]. Despite stratifying studies by all these variables, we have only been able to detect homogeneity among studies with prolonged follow-up (18 months or more) or those with intermediate follow-up (4–6 months). Also, we found homogeneity when pooling results of studies with 50–100 participants, but not for those with less than 50 participants or more than 100.

The more interesting results were observed when stratifying by the differences between intervention and control groups regarding post-intervention decrease in BMI. The heterogeneity between studies was resolved when the weight lost was greater for the intervention group. Also, we observed higher intervention effects as the differences in weight loss between the intervention and the control groups increased. As overweight and obesity are strongly related to type 2 diabetes mellitus [[21]], and weight loss leads to metabolic control [[24]], the effect of lifestyle interventions on the glycaemic control of DM is likely to be mediated by weight loss. The interpretation of this finding could also be that weight loss is a correlate of the quality of the applied nutritional intervention.

We have also tried to explain the observed heterogeneity between studies based on the expected variability of the characteristics of the participants. Accordingly, we stratified studies by BMI, diabetes evolution time, baseline HbA levels at the start of the intervention, and the health care facility type (primary versus secondary). These analyses did not identify a clear source of heterogeneity. However, studies with less heterogeneity were those that selected patients with diabetes progression time between 3 and 10 years (ten studies), or with lower BMI (27–30 m /kg) (eight studies).

In spite of heterogeneity, the pooled effect was higher when the intervention comprised diabetes self- management education, a finding previously reported by another meta-analysis [[59]]. This could be attributed to a weak health care system and/or a worse basal diabetic management. However, we did not find differences in the baseline levels of HbA for groups with or without diabetes self-management education. On the other hand, we found a stronger effect of the interventions for studies with smaller

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sample size, which is expected due to the possibility of close interaction with the personnel delivering the intervention as well as the higher frequency of visits in case of small sample sizes. This could be explained by the specific nature of diabetes management that requires frequent contact with health care staff to maintain and reinforce appropriate lifestyle modification [[62]]. Also, the pooled effect was higher when combining different approaches in the interventions. Accordingly, multi-component interventions, including advice on diet, physical activity and diabetes self-management skills might provide the most efficient management of type 2 diabetes. It has been suggested that health education delivered by a team of educators and reinforced by regular contact with health care staff, may help in the improvement of glycaemic control reflected on HbA levels [[63]]. The benefit of this strategy could be delivered in the primary care centres [[64]]. Cradock et al. analysed lifestyle intervention characteristics associated with better glycaemic control. They reported an inverse effect of duration of follow-up [[60]]. We also found a higher pooled effect for studies shorter than 3 months, but we cannot rely on this finding due to the high observed heterogeneity. However, we found an increasing WMD with the increase in the duration of follow-up of the patients and results were retrieved from homogenous studies; WMD: − 0.79 (− 0.88, − 0.71), (I = 28.8%, p = 0.239) for the longest duration of follow-up (18–24 months).

Regarding participant characteristics, the benefit of intervention was more pronounced in participants who were diagnosed as type 2 diabetics since more than 10 years or when patients were recruited from hospitals or specialized health care centres. Again, our results must be carefully interpreted due to the high observed heterogeneity. Furthermore, we expected a greater effect of the intervention on those with poorly controlled diabetes (reflected on HbA baseline levels). This is supported by Pillay et al. [[59]] as they have reported a greater effect of nutrition interventions on patients with HbA baseline levels greater than 53 mmol/mol. Also Franz et al. [[65]], in a meta-analysis including RCTs and observational studies dealing with type 1 and type 2 diabetic patients, observed a more pronounced effect of lifestyle modification on participants with less controlled diabetes reflected on their baseline HbA levels. In our study, stratification by HbA baseline levels (below or above 58 mmol/mol) showed no relevant differences, but the WMD was higher for patients with longer diabetes evolution time. This might suggest poor lifestyle interventions in the standard diabetic care [[66]]. On the other hand, contrary to our expecting a greater effect on overweight and obese people, we found a greater WMD when study participants were below 27 m /kg of BMI which is opposite to results highlighted by Gummesson et al. [[67]]. Regarding health care facilities, results showed that those recruited from specialized health care centres had a better response. We attribute this to the fact that hospital follow- up implies complex diabetic cases and a greater risk of complications and thus higher patient compliance. Also, it might be related to the intensity of the intervention and the follow-up, and/or higher quality of studies carried out in the hospitals [[68]]. However, stratifying by the quality of studies did not resolve heterogeneity or modify the pooled effect size.

It is interesting to point out that, compared with usual diabetic care, an additional lifestyle intervention had a statistically significant consistent effect on HbA levels. Despite recommendations of Standards of Medical Care in Diabetes: "All individuals with diabetes (both diabetes mellitus type 1 and type 2) should be offered a referral for individualized medical nutrition therapy, preferably provided by a registered dietitian" [[21]], this is not clearly applied and nutritional intervention is scarcely implemented.

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Since patients with type 2 diabetes are diagnosed and managed at the primary health care level, they have no access to specialized medical nutritional therapy. Primary health care nurses and physicians are neither well trained in nutritional advice nor have enough time to spend with each patient. It should be noted that it was observed that the participation of qualified dietitians in nutritional interventions is deficient in the assessed RCTs. In Spain, as in many parts of the world, nutritionists are not part of the primary care teams, and often, the dietary intervention is delegated to nursing staff without specific training. This, together with limited time to attend each patient, makes health education on lifestyle modification quite defective in the primary health care units [[66], [69]].

Limitations The main limitation is the variability in the contents of the applied interventions. This is an expected limitation when addressing lifestyle interventions.

Despite applying a meticulous method for excluding studies that have interventional modalities other than lifestyle modification, inevitable differences in the interventional approaches might explain the observed heterogeneity. This diversity was observed in the health educational contents, intensity, duration, staff in charge, etc. Despite detecting some of the potential sources of heterogeneity, it was not possible in some analyses to have a clear explanation for it. Also, we were not able to consider compliance to pharmacological treatment due to lack of data. On the other hand, standard care in the control groups included some sort of health education on lifestyle modifications that might explain the small overall effect detected when comparing the intervention to the standard care groups.

Conclusions Our results show that lifestyle interventions significantly improve the glycaemic control of type 2 diabetes mellitus, particularly when there is a weight loss greater than 5% of initial BMI, when the intervention includes diabetes self-management education, combines individual and group sessions, and/or extends over a longer time period. These results can be applied in improving the management of type 2 diabetes mellitus. This could have an impact, not only on the glycaemic control of diabetes, but also on other risk factors for cardiovascular diseases.

Funding The research leading to these results has received funding from the CIBER Epidemiología y Salud Pública (CIBERESP/CB06/02/1014).

Acknowledgements The first author would like to acknowledge support by the CIBER Epidemiología y Salud Pública (CIBERESP/CB06/02/1014). The authors especially thank the co-authors for their collaboration and effort in this systematic review and meta-analysis.

Compliance with ethical standards

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Conflict of interest The authors declare that there is no duality of interest associated with this manuscript.

Electronic supplementary material Below is the link to the electronic supplementary material.

Graph: Supplementary material 1 (DOCX 544 kb)

• BMI

Body mass index

HbA

Glycosylated haemoglobin

• RCTs

Randomised clinical trials

• WMD

Weighted mean difference

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By Laura García-Molina; Anne-Mary Lewis-Mikhael; Blanca Riquelme-Gallego; Naomi Cano-Ibáñez; María-Jesús Oliveras-López and Aurora Bueno-Cavanillas

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