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Global warming: is weight loss a solution?

A Gryka, J Broom and C Rolland

Centre for Obesity Research and Epidemiology, Faculty of Health and Social Care, Robert Gordon University, Aberdeen, UK

The current climate change has been most likely caused by the increased greenhouse gas emissions. We have looked at the major greenhouse gas, carbon dioxide (CO2), and estimated the reduction in the CO2 emissions that would occur with the theoretical global weight loss. The calculations were based on our previous weight loss study, investigating the effects of a low-carbohydrate diet on body weight, body composition and resting metabolic rate of obese volunteers with type 2 diabetes. At 6 months, we observed decreases in weight, fat mass, fat free mass and CO2 production. We estimated that a 10 kg weight loss of all obese and overweight people would result in a decrease of 49.560 Mt of CO2 per year, which would equal to 0.2% of the CO2 emitted globally in 2007. This reduction could help meet the CO2 emission reduction targets and unquestionably would be of a great benefit to the global health.

International Journal of Obesity (2012) 36, 474–476; doi:10.1038/ijo.2011.151; published online 26 July 2011

Keywords: global warming; carbon dioxide; weight loss

Introduction

Climate change resulting from the mean rise in temperature

over the last 100 years has been widely discussed.1 It has been

accepted by the majority of scientists that the change is being

caused by the anthropogenic increase in greenhouse gas

emissions. Greenhouse gases in the atmosphere impair the

earth’s cooling processes, which results in the global rise in

temperature.1 The major greenhouse gas is carbon dioxide

(CO2), which mostly comes from burning of fossil fuels (gas,

oil, coal and other solid fuels). Other sources of CO2 emissions

include iron and steel production, cement manufacture, solid

waste combustion or petrochemical production. In 2007,

burning of fossil fuels and cement manufacture caused

emission of 30 649.36 Mt CO2 globally. 2 Across the world,

fossil fuels are combusted to provide energy to generate

electricity, for transport, business, agriculture and industry. If

the current emissions are not reduced, the global temperature

may rise by 2–7 1C by the end of the century, depending on

the models used.3 This in turn may cause the extinction of

many species, irreversible changes in the ecosystems and

environmental disasters like storms, wildfires, droughts or

floods. Such prognoses bring governments to set targets

for the reduction of CO2 production and support the search

for alternative energy sources.

Humans, apart from indirectly producing CO2 through

the use of fossil fuels and the industry, also produce CO2 during respiration. Consequently, global CO2 emissions

depend on the size of the population. In addition, due to

the fact that CO2 production is proportionate to body mass,

heavier individuals produce more (based on our data, for

every kg of body mass lost, resting metabolic rate (RMR)

dropped by about 18 kcal per day and there was a 1%

reduction in CO2 produced). The post-industrial changes to

human lifestyle and diet have resulted in an obesity

epidemic. Although the knowledge of obesity mechanisms

is quickly expanding and novel obesity treatments are being

developed, the situation on a world population level has

not improved. With the countless unsuccessful efforts to

tackle the obesity problem, it is more and more evident that

the global modification of today’s lifestyles and environ-

ments may be the only possible solution to the obesity

epidemic.

In light of the growing literature on the link between

obesity, type 2 diabetes (T2DM), coronary artery diseases and

climate change,4–8 we thought it would be interesting to

discuss the effect of the global reduction of body mass, in

particular of those individuals who are obese and overweight

on worldwide CO2 emissions. It is clear that an omnipresent

weight loss of all obese and overweight population is as

improbable in the short term as global warming is inevitable

if no action is taken. However, it is essential to model the

effect of population weight loss on CO2 emissions. We have

assumed a 10 kg weight loss, based on our observations as

well as other studies using a low carbohydrate diet for a

6-month period.9 Received 17 December 2010; revised 2 June 2011; accepted 24 June 2011;

published online 26 July 2011

Correspondence: Dr C Rolland, Centre for Obesity Research and Epidemiology,

Faculty of Health and Social Care, Robert Gordon University, St Andrew Street,

Aberdeen, AB25 1HG UK.

E-mail: [email protected]

International Journal of Obesity (2012) 36, 474– 476 & 2012 Macmillan Publishers Limited All rights reserved 0307-0565/12

www.nature.com/ijo

Methods

The calculations in the current paper are based on an

observed decrease of resting metabolic rate that occurred

with weight loss in our recent study. The intervention

involved 6 months on a low-carbohydrate, high-protein diet

and included 25 obese volunteers (13 females, 12 males) with

poorly controlled (glycated haemoglobin (HBA)1c47.5%) T2DM (ISRCTN20400186). CO2 production and body com-

position were assessed at baseline and 6 months. The CO2 production was measured using the Quark RMR (Cosmed,

Rome, Italy). Body composition was measured by air-

displacement plethysmography (Bod Pod, Life Measurement

Inc., Concord, CA, USA). The majority of the variables were

not normally distributed; hence, the Wilcoxon signed-rank

test was used to investigate the 6-month changes in weight,

fat mass (FM), fat-free mass (FFM) and CO2 production.

Analyses were performed with SPSS, version 17.0 (SPSS Inc.,

Chicago, IL, USA).

Results and calculations

The dietary composition of participants on a low-carbohy-

drate/high-protein diet is outlined in Table 1. As expected,

the total energy of the diet was significantly lower during the

study than at baseline. According to our recommendations,

the total amount of carbohydrate, both as grams per day and

as a percent of daily total energy, was lower during the study

than at baseline. Additionally, the amount of protein

increased from 22% to about 30% of total energy levels,

but did not change when expressed in grams per day.

After 6 months of the weight loss programme, we observed

a decrease in weight, FM, FFM and CO2 production (Table 2).

The 6-month change in CO2 production was positively

correlated with the changes in weight (r¼0.506; P¼0.0.12) and FM (r¼0.517; P¼0.011). The majority of weight lost was attributed to a decrease in FFM (Table 2), reflecting the

higher protein content of the diet, which was about 30% of

energy intake (Table 1). Weight loss achieved by implement-

ing a normal- or a low-protein diet (that is, 10–15% of

energy), could perhaps induce a higher loss of FFM than a

high-protein diet. Consequently, such a diet would cause an

even bigger drop in RMR and CO2 production, but would not

be beneficial to the health of the individual losing weight.

On the basis of the current data, for every 1 kg of body

mass lost, the CO2 production would decrease 3.2 ml min �1.

Therefore, an individual who lost 10 kg would produce 32 ml

of CO2 less every minute. This would equal to 168 12 l

(33.04 kg) of CO2 less in a year, compared with what would

be produced without weight loss. In 2008, the global number

of obese and overweight adults over 20 years old was 1.5

billion.10 If all those individuals lost 10 kg and sustained it

for a year, the reduction in CO2 emissions would be 49.56 Mt

CO2 per year. This would equate to 0.2% of CO2 emitted

globally in 2007 by burning of fossil fuels and the

manufacture of cement.2 Analogously, a 5-kg weight loss of

all overweight and obese people would reduce global CO2 emissions by only 0.1%.

Discussion

Our calculations have shown that a 10-kg weight loss of all

overweight and obese people would translate into a 0.2%

Table 1 Changes in diet composition during the low-carbohydrate/

high-protein weight loss programme (n¼25)

Baseline 6 months Change P-valuea

Energy

Kcal 1845±74 1194±21 �594±600 0.001

Carbohydrate

g per day 164±69 50±25 �108±74.1 o0.001 % Total energy 41±9 22±11 �17.8±12.0 o0.001

Protein

g per day 87±33 79±28 �5.3±32.2 0.882 % Total energy 22±7 30±8 7.9±7.5 o0.001

Fat

g per day 80±44 68±20 �16.4±37.1 0.573 % Total energy 38.5 50.0 10.0±13.9 0.015

Values are expressed as mean±s.d. aSignificance level of the difference between baseline and 6 months, Wilcoxon signed-rank test.

Table 2 Changes in weight, fat mass, fat-free mass, resting metabolic rate

and CO2 production, during the low-carbohydrate/high-protein weight loss

programme (n¼25)

Baseline 6 months Change P-valuea

Weight (kg)

Males (n¼12) 117.7±19.5 108.0±20.9 �9.7±6.4 0.001 Females (n¼13) 104.6±22.2 94.2±22.1 �10.4±7.8 o0.001 Total 110.9±21.6 100.8±22.2 �10.1±7.0 o0.001

FM (kg)

Males 50.3±13.0 41.1±12.9 �9.2±5.2 o0.001 Females 54.1±17.6 45.7±19.8 �8.8±7.8 0.001 Total 52.4±15.7 43.4±16.5 �9.0±6.5 o0.001

FFM (kg)

Males 67.3±11.8 67.0±12.0 �0.3±1.7 0.266 Females 50.5±7.4 49.3±7.3 �1.6±1.4 o0.001 Total 59.0±12.8 58.1±13.3 �0.9±1.7 0.001

RMR (kcal per day)

Males 2267±451 2033±420 �234±181 0.001 Females 1845±428 1572±345 �274±306 0.002 Total 2048±81 1793±442 �254±250 o0.001

CO2 production (ml min �1)

Males 258±56 220±45 �37±33 0.001 Females 201±47 173±42 �27±37 0.013 Total 226±58 195±50 �31±34 o0.001

Abbreviations: FFM, fat-free mass; FM, fat mass; RMR, resting metabolic rate.

Values are expressed as mean±s.d. aSignificance level of the difference between baseline and 6 months, Wilcoxon signed ranks test.

Global warming and weight loss A Gryka et al

475

International Journal of Obesity

reduction in the global CO2 emissions. This percentage

seems small; however, we have looked at personal produc-

tion only. Had we accounted for additional reductions in

CO2 emissions that would likely accompany weight loss, for

example decreases in transport costs, and smaller amounts of

food consumed as suggested by Edwards and Roberts,11 the

total estimated decreases in CO2 production would have

been greater. It could also be argued that the decrease in CO2 production, which accompanies weight loss, would mimic

the benefits of decreasing global population.

The theoretical global weight loss would also be of great

health benefit; halving the risks of developing T2DM and

obesity-related cancers, improving glycemic control in those

with T2DM, and finally improving blood pressure and lipid

profiles.12 Such changes would bring the significant reduc-

tions of healthcare costs and also improvements in general

quality of life.

The targets for CO2 emissions, as specified in the Kyoto

Protocol Reference Manual, vary for different countries and

regions of the world. The UK Low Carbon Transition Plan

suggests lowering the emissions by 18% from the 2008 levels,

or 95.9 Mt CO2 per year, by 2020. 13 A 10-kg weight loss of all

overweight and obese in the UK would account for over 1%

of the CO2 emission reduction target by 2020. 14–16

This estimation was only possible when a number of

assumptions were made. First, we assumed that weight loss

in overweight people would result in the same change in FM

and CO2 production as in the obese. Second, we assumed

that obese and overweight, but otherwise healthy people,

would show the same change in CO2 production with weight

loss, as did obese people with T2DM. Finally, it has been

shown that people with T2DM have higher RMR than those

without,17 and therefore, our calculations may be slightly

overestimated. However, if significant loss of FFM occurred

with weight loss (as may be the case with normal- or low-

protein diets), the decrease in RMR could have been higher,

in which case the current estimations would underestimate

it. Present calculations were not designed to accurately

reflect potential impact of global weight loss on climate

disruption, but to signal an opportunity for addressing

individual, global and environmental benefits of weight loss.

Health and climate change issues seem to be closely

related in the perspective of our future. We agree with

Wilkinson et al.,18 who stated that policies to reduce carbon

emissions and climate change will improve health and well-

being of the people. The opposite should also be true;

tackling lifestyle-related health problems should have a

positive effect on the environment. Universal moderate

weight loss of the overweight and obese would result in an

equivocal influence on the world carbon emissions with

possible effects on climate disruption. Nevertheless, this

relatively small amount could help to meet the CO2 emission

reduction targets and unarguably would be of great benefit

to the human’s health. Moreover, the shift from seeing

weight loss as beneficial for an individual’s health to also

being beneficial for the planet may change attitudes toward

healthy lifestyle. If such benefits were persuasive to govern-

ments across the world, a significant impact on global

warming might be achieved as a consequence.

Conflict of interest

The authors declare no conflict of interest.

Acknowledgements

We thank A Stewart for reading of the manuscript and

critical comments. The study of low-carbohydrate diet was

supported by the Go Lower Company.

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