Not everyone who smokes gets lung cancer. That doesn't exonerate cigarettes nor does it create a "tobacco paradox." There is no obesity paradox either. But given the attention the notion is getting of late, we clearly seem to think there is, so let's sort it out.
The obesity paradox refers to the fact that sometimes being heavier — even being overweight or slightly obese — is associated with lower, rather than higher, death rates. Severe obesity is consistently, uncontroversially, and unparadoxically bad for health, so it's not part of the discussion.
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There has long been attention to the obesity paradox concept, even when it wasn't referred to by that name. Colleagues of mine, for instance, have long made the point that it's possible to be fat and fit and that being fit but fat is better than being unfit and lean. That is true, and the relatively small number of people who are truly fit and somewhat fat nonetheless explain away some portion of the paradox.
We have also long known that all varieties of obesity are not created equal. The common measure of weight status at the population level, the body mass index (BMI), is a very crude metric. It tells about weight for height but can't say anything about whether the pounds in question are comprised of fat or muscle, or where they are distributed. Being heavy is not harmful to health; athletes with lots of muscle tend to be heavy. Being overly fat is the hazard.
But being fat is only a hazard when fat is in the wrong places. The right places, the places where a body can safely store fat, are the hips, thighs, and buttocks in particular. When weight accumulates there, as it does most often in pre-menopausal women, it is referred to as the gynoid or "pear" pattern of obesity. We have long known this is unassociated with harmful metabolic effects.
In contrast, weight accumulation around the middle, which tends to predominate in men and women after menopause, is associated with fat accumulation in the liver, insulin resistance, and the metabolic syndrome. This android or "apple" pattern of obesity clearly is harmful much of the time, but only about half of the overweight or obese population is in this camp.
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We have also long known that just as some people can be heavy but healthy, others can be morphologically lean but metabolically fat. That sounds complicated at first, but perhaps an image can make it quite simple: think Kermit the frog. Kermit is a pretty little guy but with a bit of a paunch.
As it turns out, there are whole populations, such as Indians, who are prone to gaining weight around the middle, even while their BMI is well under the red line. This can result in insulin resistance and diabetes at BMIs that qualify as "healthy" but clearly are not. An excess of fat around the middle is potentially quite harmful at a BMI of 20 (normal), just as a BMI of 28 (overweight) is potentially harmless if it is the result of muscle or of fat stored in the pear pattern, below the waist.
The party line, which I fully support, is that obesity is indeed a health hazard. In fact, I consider it a public health menace of the first order. The obesity paradox is that excess weight can at times be helpful. The above considerations go a long way toward annulling the obesity paradox concern.
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If obesity is a health hazard, we prove it statistically by showing worse health outcomes among heavier people. But statistics represent effects in groups, not individuals. So, if some heavy people are healthy – either because they have fat in harmless places, have a lot of muscle and/or are fat but fit – they will make obesity look less harmful than it is; the lack of harm among them will be mixed up with the harmful effects among others and dilute the apparent effect for the population as a whole. Since the statistical harms of obesity we can perceive are despite this dilution, they are actually more severe than they seem among the at-risk individuals.
Also of importance is that the obesity paradox literature is almost exclusively about years in life, rather than life in years. In other words, obesity may not always increase mortality, but the evidence that it increases morbidity is overwhelming. The evolution of adult onset diabetes into Type 2 diabetes, a condition affecting children as well as adults, is a clear and compelling demonstration of the impact of obesity on illness.
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But none of these is the most important reason the obesity paradox isn't one. That reason is the one that's most self-evident: People who die are, most often, old and sick. And people who are old and sick tend to be losing weight, not gaining it.
My fellow physicians and I know that one of the more worrisome signs among our older patients is steady weight loss, particularly in the absence of an obvious reason. Usually the reason we find is bad news. It can be social isolation and poor nutrition resulting from being housebound. It can be an occult cancer. It can be the gradual failure of a vital organ. Generally, though, it's nothing good.
In contrast, we rarely have to worry about our older patients gaining weight. Chronic and serious illness tends to go the other way.
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This well-established fact of medicine suggests that, among older people, keeping some meat on them bones would tend to be a good thing. And that, really, is what the obesity paradox is all about. Older people who manage to stay overweight or slightly obese despite being older tend to do better. I don't find this at all surprising,as it may simply mean the converse: older people who are doing better tend to hang onto their weight.
But could this mean that obesity is harmless or even beneficial to us all? Absolutely not. Even as the obesity paradox has been grabbing the spotlight, a study was published in the American Journal of Public Health showing that obesity was causing more, not less, death than we ever thought. The new research indicates an astounding 1 in 5 premature deaths in the U.S. is a result of obesity, and among some ethnic groups, it's an incredible 1 in 3.
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What's different about this study? The investigators accounted for birth cohort. Consider that people in their 60s, 70s or 80s today who are overweight or slightly obese grew up at a time when childhood obesity was quite rare. These people likely gained weight over the years and became overweight as they aged. As compared to older people who are wasting away, they are healthier, not sicker. And they have not been subject to obesity their whole lives – it's a relatively recent development for most of them.
But in today's world, childhood obesity is rampant. When today's kids reach their 70s, some of them will have been obese for 65 years. So the question is: Will they ever reach their 70s in the first place? The new study adds urgency to that question. It shows that the mortality from obesity is rising over time as successive birth cohorts experience obesity over ever greater portions of their lifespan. What obesity is doing among older people today may seriously underestimate its toll among those subject to its influence over many decades.
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Weight isn't really what matters, of course. Health is what matters, and weight is just a marker, and not always a very good one. But in general, where there is more obesity, there are more dangers to health. That is especially true when obesity develops early in life, as is now more norm than exception.
Being heavy isn't always harmful. Older people who hang onto their body mass are generally better off than older people who start wasting away. But such things do not a paradox make. We should not allow a penchant for controversy to distract us from a danger that is clear, all but omnipresent, and eminently fixable. We can get out of the dark wood, but only if we see the forest through all these trees.
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Hungry for more? Write to eatandrun@usnews.com with your questions, concerns, and feedback.
David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011 and is president-elect of the American College of Lifestyle Medicine. His latest book, "Disease Proof: The Remarkable Truth About What Makes Us Well," was released in September.