Intended for healthcare professionals

CCBYNC Open access

Rapid response to:

Feature Christmas 2014: Gastroenterological Tracts

When somebody loses weight, where does the fat go?

BMJ 2014; 349 doi: (Published 16 December 2014) Cite this as: BMJ 2014;349:g7257

Rapid Response:

Expanding globesity continues to present many novel challenges to society, from combusting crematoria (1) to wider trolleys and longer endoscopes in hospitals (2). As we approach New Year, with its cyclically futile outbreak of good intentions, we wondered if the article in the Xmas BMJ (3) might unwittingly provide yet another excuse to defer impending dietary restraint - this time on account of saving the planet?

Altruistic adiposity by selflessly putting one's own health at risk to save countless others from the ravages of climatic, not calorific, tsunamis. After all, if, by losing 10 Kg of fat, this then led to the liberation of 8.4 Kg of carbon dioxide (volatile carbon as CO2.), with its attendant environmental impact, would we not all be much better off by remaining somewhat plumper but cooler?

To test this hypothesis we used contemporary UK data for CO2 production from fossil fuels, from the National Health Survey (from PHE (4)), and from the Office for National Statistics. If we now make a series of approximations and assumptions, as follows

(a) 83% of UK population is >15 years of age which is 52.3 million people.
(b) For every 10 Kg of fat lost, 8.4 kg (84%) is volatile carbon as CO2. See (3).
(c) The average man in England in 2013 was 5ft 9in (175.3cm) tall and weighed 13.2 stone (83.6kg). BMI of 27.3 but their ideal weight was 75 Kg (BMI 24.5). Average weight loss needed therefore is 8.6 Kg per man.
(d) The average woman in England weighed 11 stone (70.2kg) and was 5ft 3in tall (161.6cm). BMI 27.Ideal weight 64 Kg (BMI 24.5). Average weight loss needed 6.2 Kg per woman.
(e) Weight loss down to ideal weight over 12 months (at a very modest monthly rate, and perfectly achievable)
(f) 50% men and 50% women
(g) A grand national total of 387 million Kg of fat lost over the year.
(h) Which equates to 325 million Kg of volatile CO2 generated - this is 0.325 million metric tonnes of CO2
(i) Total carbon fuel burning-related emissions of volatile CO2 in 2013 was 464.3 million metric tonnes of CO2
(j) So the additional amount of volatile CO2 produced in this really most unlikely "mass contraction and shrinkage" annus mirabilis would be just an additional 0.07% of the carbon fuel contribution to CO2 emissions in that same year.

It seems to us therefore that the excuse of remaining portly as a noble gesture to help protect the planet is just plain old hot air. Thinner waistlines will not lead to more wastelands. Tightening the belt will not destroy the veld. So, come January 1st, let's all now plan to get into some serious fat loss secure in the knowledge that we can help ourselves without harming others. Just one more wafer-thin mince pie........

David Goldsmith and Eric P Heymann


(1) Last accessed 18.12.14

(2) endocrine-today/%7B39256858-e05c-4804-90ba-b5318394a4be%7D/health-care-community-responding-to-obesity-epidemic. Last accessed 18.12.14

(3) BMJ 2014;349:g7257

(4) _ for_england. Last accessed 18.12.14

Competing interests: No competing interests

18 December 2014
David J Goldsmith
Eric P Heymann (Cantonal University Hospital of Vaud (CHUV) Lausanne, Switzerland)
Guy's and St Thomas' Hospitals