In some studies of large numbers of people, researchers have found that people with the lowest death rates had a body mass index (BMI) solidly in the overweight range. This finding has led to the so-called “obesity paradox”, meaning that while we generally think that being overweight is unhealthy, being a little overweight might be healthier than being of normal weight. A new study shows that the obesity paradox can’t possibly be true.
When researchers declare something a paradox, it means that some piece of data doesn’t agree with their theories. For example, the French paradox refers to the fact that the French eat a diet high in saturated fat, yet have low rates of cardiovascular disease. The French paradox is easily solved if you discard the idea that saturated fat causes heart disease.
A paradox is nature’s way of telling you that you’re wrong.
The obesity paradox can be characterized as follows:
… numerous studies have documented an obesity paradox in which overweight and obese people with established CV disease, including HTN, HF, CHD, and peripheral arterial disease, have a better prognosis compared with nonoverweight/nonobese patients.
The paradox can be resolved either by concluding that being overweight isn’t really unhealthy, or that the data showing that is wrong.
The main confounding factor in the obesity paradox is likely to be reverse causation, meaning that in this case, poor health causes weight loss. If it did, then the category of normal BMI would include people who were in worse health than people who weighed more.
And we do know that poor health can cause weight loss. Smokers also weigh less than non-smokers, and are in worse health.
The study looked at over 296,000 people in the UK Biobank database. Only people non-smokers who were healthy at baseline were included.
Result: no obesity paradox. Risk of cardiovascular disease rose starting at a BMI of about 22. Other studies have found that a BMI of about 22 or even lower is the healthiest, so this latest study adds evidence.
Of interest, being underweight had a higher risk than being overweight/obese. That’s likely due to low muscle mass.
The obesity paradox is due to confounding due to smokers and those with ill health being included in the category of normal BMI.
Another way to investigate the obesity paradox and to clarify the dangers of obeisty is through the use of lifetime maximum BMI, rather than BMI at time of enrollment.
Using lifetime maximum BMI, not only is there is no obesity paradox, but risks of overweight/obesity are much higher.
Using BMI at survey, an estimated 5.42% of deaths were attributable to the combination of overweight and obesity, whereas using maximum BMI, the attributable risk was substantially greater, at 32.58%.
Well-controlled studies, which exclude smokers and other unhealthy people at baseline, show that the health risks of being overweight rise monotonically with increasing weight. There is no obesity paradox, and being overweight is bad for health. Full stop.
Other studies using maximum lifetime BMI substantially increase our estimates of the detrimental effects of overweight/obesity on health.
For those few people who have a BMI >25 due to a high muscle mass, rest assured that the aspect of high BMI that causes problems is not muscle, but fat, especially visceral fat.
Stay lean, my friends.