Week 5 assignment CI

Answers Rubric for Assignment 5 Bazzano et al.

# Questions Answers Points

1. Title of article, Journal name, and your name Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial Annals of Internal Medicine Your name

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2. What is the research question addressed in this study? What are the effects of a low-carbohydrate diet compared with a low-fat diet on body weight and cardiovascular risk factors?

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3. Identify the dependent variable(s) Cardiovascular disease risk factors, body weight 5 4. Identify the independent variable(s) Type of diet: low-carbohydrate vs. low-fat diet 5 5. What is the research design used? Randomized parallel group trial. Cohort is also correct if included in the

answer since all RCTs are by definition a couple of cohorts followed over time.

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6. What type of sampling design was used? Convenience or volunteer sampling 5 7. Describe the intervention. Was it adequately described?

Note: for the purpose of this article, since it’s a parallel design, it does not matter which diet is labeled as intervention or comparison. Technically, the low-carb diet is the intervention.

Both diets and details for the intervention were adequately and clearly described. Low-carb diet: maintain an intake of digestible carbohydrate (total carbohydrate minus total fiber) of less than 40 g/d. weekly meetings with a dietitian for 1st 4 weeks, followed by small group counseling sessions every other week for the next 5 months (a total of 10 sessions) and monthly for the last 6 months of the intervention.

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8. Describe the control or comparison condition. Was it adequately described?

Both diets and details for the intervention were adequately and clearly described. Low-fat diet: maintain less than 30% of daily energy intake from total fat (with <7% from saturated fat) and 55% from carbohydrate, based on National Cholesterol Education Program guidelines; weekly meetings with a dietitian for 1st 4 weeks, followed by small group counseling sessions every other week for the next 5 months (a total of 10 sessions) and monthly for the last 6 months of the intervention.

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9. Were the participants fully informed about the nature of the research?

Yes. Each participant signed an approved consent form. Consent forms usually have all the components to help participants be fully informed about the study.

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10. Was ethical permission granted for the study? Yes. The study was approved by the Institutional Review Board at Tulane University.

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11. Were randomization procedures adequately explained? Describe them.

Yes. Participants were assigned to one of the two diet groups using a computer-generated, blocked randomization, stratified by sex.

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12. Does the article provide evidence that randomization was successful - that is, it resulted in groups that were comparable prior to the intervention?

Yes. Table 1 shows that the two groups were similar on demographic characteristics and cardiovascular risk factors.

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13. Was the study longitudinal? How many data collection Yes, the study followed participants over one year. There were four data 5

points were there? collection points: at baseline and at 3, 6, and 12 months. 14. Was blinding used? If yes, who was blinded - and was this

adequate? If not, is there an adequate rationale for failure to blind/mask?

Outcome assessors (data collectors) were blinded to the diet group assignment. Dietitians were not blinded to the study hypothesis. This may have resulted in potential differences in dietary counseling. Training, detailed scripts, and intermittent observations were used to minimize any differences. No rationale is provided to why the dieticians were not blinded to the study hypothesis. Obviously, participants were not blinded. That would not be possible because each group had to follow the recommended dietary intake so they knew the type of diet they were on.

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15. What are the results of the study? Did the results answer the research question(s)?

Overall, a low-carbohydrate diet resulted in greater weight loss and reduction in cardiovascular risk factors than a low-fat diet among obese black and white adults. Table 3 reports the detailed results for the low- carb (LC) vs. the low-fat (LF) diets (please note that only differences between the two groups that had p-values <.05 are considered significant differences that can be attributed to the program and not chance): - Body weight: LC lost more weight than LF - Waist circumference: LC lost more waist circumference at 3 and 6 months but no significant differences between the two groups at 12 months. - Lean mass: LC group gained more lean mass - Fat mass: LC group lost more fat mass at 6 and 12 months - Cholesterol: no significant differences in total and LDL. For HDL (the good cholesterol), there were significant increases for the LC group relative to the LF group at 6 and 12 months. - Triglycerides: LC decreased more at the 3 data collection points - Blood pressure, plasma glucose, insulin, serum creatinine: no decreases or significant differences - C-reactive protein level: LC reduced more at 6 and 12 months - 10-year Framingham risk score: LC improved their score, i.e., reduced it.

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16. Was outcome data reported even for treatment group members who did not complete the program (intention-to- treat analysis)? If not, what was the rationale? If not applicable, indicate that in your answer.

There were several individuals who did not complete the program (10, 11, and 7 at 3, 6, and 12 months, respectively) as shown in Figure 1. However, in Table 3, results were reported only for those who completed the programs. No rationale was provided. The most common is the difficulty and cost of tracking down people who are lost to follow-up. We also don’t know if those lost to follow-up are different from those who completed the program.

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17. What were the study limitations? (1) Self-reported dietary information may be subject to memory and recall issues; (2) dietitians were not blinded to the study hypothesis; (3)

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no CVD clinical end points (example a fatal or non-fatal CVD event such as a heart attack) ; (4) multiple statistical tests were performed, potentially resulting in statistical significance due to chance; (5) generalizability is limited to situations where intensive and repeated dietary counseling is available; (6) the characteristics of those lost to follow-up are not reported.

18. Do you consider the outcomes measured to be important policy or practical outcomes? Were they measured over a long enough period?

With obesity prevalence reaching epidemic proportions and with CVD being the number one cause of death, it is important to assess different types of diets and their impact on body weight and CVD risk factors. A one-year time period is reasonable to see changes in the outcome measures used. A 3-months period would have been too short to see the effect of dietary changes on some of the cardiovascular risk factors.

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