August 03, 2016

Being fat does NOT kill you

An absolutely fascinating study just out in JAMA. Those authoritarian Swedes with their detailed tracking of their population have made possible what would normally be an almost inconceivable study of obesity.  They have done a study which controls for genetic factors.  There are lots of twin registers around but Sweden has such a big one that the researchers were able to look for a needle in a haystack and find it.

They wanted to find not only identical twins with obesity but twins where one was much fatter than the other. As soon as I saw that design, I scoffed mentally and said they would be lucky to find half a dozen of those -- a completely useless sample size.  But because the researchers were loking at a nationewide database, they found, not half a dozen suitable pairs but 4046:  A brilliant sample size that allows great confidence in the results.  Most unusual in medical research.

The full results are below and they are striking.  Decades of medical wisdom have been knocked into a cocked hat.  With twins you have the perfect controls.  Whatever you find is NOT genetic.  It is due to lifestyle and environment.  So this data is miles more conclusive than all previous studies of the question.  And there was NO difference in lifespan or heart attacks according to how fat you were.  Even if you ate your head off all your life, you lived just as long as if you had adopted a so-called "healthy" diet.  I have been saying for a long time that there is no such thing as a "healthy" diet and this is strong reinforcement of that view.

The fatties in the study WERE slightly more likely to get diabetes but there has long been an association between over-eating and diabetes so that is not too surprising.  You can mostly control diabetes just by eating less. The important thing is that the diabetes did NOT kill them.

So this study is a body-blow to the obesity "war".  We have the strongest evidence possible that obesity does not kill you.  So what will be the outcome?  Will articles about diet vanish from our newspapers?

Thay should vanish.  But they won't.  The study will be tucked into the back of the minds of a lot of obesity researchers but nothing will change overnight.  The obesity "war" will go on as before.  Eventually, however, some notice will be taken of the study.  Researchers will mention it and GPs will learn of it and patients with weight concerns will be quietly assured that they don't have to be too bothered about their weight.  There will always be social reasons to stay slim -- fat is unattractive -- but medical reasons will be downplayed.


Risks of Myocardial Infarction, Death, and Diabetes in Identical Twin Pairs With Different Body Mass Indexes

Peter Nordström et al.

ABSTRACT

Importance:  Observational studies have shown that obesity is a major risk factor for cardiovascular disease and death. The extent of genetic confounding in these associations is unclear.

Objective:  To compare the risk of myocardial infarction (MI), type 2 diabetes, and death in monozygotic (MZ) twin pairs discordant for body mass index (BMI).

Design, Setting, and Participants:  A cohort of 4046 MZ twin pairs with discordant BMIs (difference >0.01) was identified using the nationwide Swedish twin registry. The study was conducted from March 17, 1998, to January 16, 2003, with follow-up regarding incident outcomes until December 31, 2013.

Main Outcomes and Measures:  The combined primary end point of death or MI and the secondary end point of incident diabetes were evaluated in heavier compared with leaner twins in a co-twin control analysis using multivariable conditional logistic regression.

Results:  Mean (SD) baseline age for both cohorts was 57.6 (9.5) years (range, 41.9-91.8 years). During a mean follow-up period of 12.4 (2.5) years, 203 MIs (5.0%) and 550 deaths (13.6%) occurred among heavier twins (mean [SD] BMI, 25.9 [3.6] [calculated as weight in kilograms divided by height in meters squared]) compared with 209 MIs (5.2%) and 633 deaths (15.6%) among leaner twins (mean [SD] BMI, 23.9 [3.1]; combined multivariable adjusted odds ratio [OR], 0.75; 95% CI, 0.63-0.91). Even in twin pairs with BMI discordance of 7.0 or more (mean [SE], 9.3 [0.7]), where the heavier twin had a BMI of 30.0 or more (n = 65 pairs), the risk of MI or death was not greater in heavier twins (OR, 0.42; 95% CI, 0.15-1.18). In contrast, in the total cohort of twins, the risk of incident diabetes was greater in heavier twins (OR, 2.14; 95% CI, 1.61-2.84). Finally, increases in BMI since 30 years before baseline were not associated with the later risk of MI or death (OR, 0.97; 95% CI, 0.89-1.05) but were associated with the risk of incident diabetes (OR, 1.13; 95% CI, 1.01-1.26).

Conclusions and Relevance:  In MZ twin pairs, higher BMI was not associated with an increased risk of MI or death but was associated with the onset of diabetes. These results may suggest that lifestyle interventions to reduce obesity are more effective in decreasing the risk of diabetes than the risk of cardiovascular disease or death.

JAMA Intern Med. Published online August 01, 2016. doi:10.1001/jamainternmed.2016.4104




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