Pure Genius

Q&A: When it's good to be fat

Q&A: When it's good to be fat

Posting in Design

In multiple studies crossing many different diseases, those who are overweight have a significantly higher survival rate than normal-weight people suffering from the same illnesses.

In the 1940s the Framingham Heart Study launched and brought to the forefront the serious health risks of obesity. This study became the gold standard long-term research that says the higher your weight the more likely you are to develop all kinds of serious illnesses from heart disease to high blood pressure. And ever since doctors' first order of business is to have patients lose the weight.

But during the last decade a curious discovery casts doubt over that recommendation to lose weight. In multiple studies crossing many different diseases it seems that those who are overweight or moderately obese have a significantly higher survival rate than normal-weight people suffering from the same illnesses. For instance in a recent study out of the Feinberg School of Medicine at Northwestern University scientists found that normal-weight patients are twice as likely to die from Type 2 diabetes as overweight or obese patients.

To find out more, SmartPlanet spoke with Harriet Brown, a journalist and author who has written extensively about weight issues and has been closely following the emergence of this "obesity paradox." Brown's latest book is Brave Girl Eating: A Family's Struggle With Anorexia.

What is the “obesity paradox”?

It’s a finding that has come up in study after study across many fields. And it’s not something anyone has been looking for. In fact it has been very surprising.

And it’s this: For people with certain chronic diseases the higher their body mass index, or BMI, [one's body mass divided by their height squared] up to a certain point, the better they do. They seem to do better surviving with the illness. It typically doesn’t hold as true at the extreme end of obesity, maybe over BMI 40. For those who are mild to moderately obese and people who are of normal weight, their risk for survival is a little bit elevated.

Can you give us a sense of the BMI ranges?

Yes. BMI is like a blunt instrument. So normal is considered 18.5 to 25. Overweight is 25 to 30. Moderate obesity is 30 to 35-ish, sometimes up to 40. And above 40 is often considered severe obesity.

In your research you came across a study that found that diabetes patients of normal weight are twice as likely to die than those who are overweight or obese by those measurements.

Yes. It was by a diabetes researcher who wondered why normal weight people get Type 2 diabetes. Because the major risk factor for Type 2 has always been considered obesity. And in trying to answer that question, she discovered this other paradox.

It wasn’t something she expected to find. And in fact she had to check it a number of times to make sure it was right. One of the classic confounding variables in these things is that people at the very end of their lives tend to be losing weight. So you’ve got people who are very ill and about to die mixed in there and that’s going to skew your findings. So she analyzed for that. And she analyzed for smoking which will artificially suppress people’s weight. No matter what she analyzed for she kept coming back to this finding.

So we might be on the verge of a paradigm shift?

One of the things that flummoxed me about this was that I talked to a dozen researchers all of whom had uncovered some type of obesity paradox, and verified it, and validated it, and acknowledged it. Yet every one of them still said to me, “You know we still think it’s a good idea for people to lose weight when they are diagnosed with these illnesses.” Despite the fact that there have actually been studies, with heart failure for example, showing that those who lose weight do worse than the patients who don’t lose weight.

It’s so deeply ingrained that they could not bring themselves to say that it might be okay not to lose weight.

What are the plausible explanations about why they’ve been finding this trend?

Well genetics is one. One of the theories is that there are different genetic variants of some of these illnesses and if you are normal weight when you develop say diabetes or heart failure, you basically get a different gene variant of the illness than you do if you are overweight or obese. And that gene variant is more severe and therefore people don’t do as well.

That sort of shocks me. How do they know that?

You know, it kind of sounds like rubbish to me, to be honest. It’s kind of a rationalization to me.
Another explanation is that doctors don’t treat their thin patients as aggressively as they treat their overweight patients because they have underlying assumptions that the thinner patients are not going to be as sick. But I don’t know that this explanation can explain this very consistent, very reliable finding.

Another theory is that we’re classifying people by BMI. It was never meant as an individual categorization, but rather a population measure. And BMI is just a height/weight ratio. It doesn’t take into account lean muscle mass, or other sorts of metabolic conditions that are more nuanced. And this is an interesting one I think; I know that the obesity paradox has also been found when people didn’t use BMI, when they used waist circumference instead as a proxy for weight. Some feel this a better proxy because where you carry your weight and how metabolically active your fat is basically can have health effects.

I think the best working theory is the one that says, “Hey, fitness is a much better predicate for health and mortality than fatness.” And even the most thin-focused doctors I talked to all agree that fitness is very important. And you know, there have been quite a few studies that sort of suggest that fit but fat is much better than thin but unfit. So, I hope that there’s more work that gets done along those lines.

Fitness is finally getting its due, as it were. There has also been a lot of research that says fitness is not the way to lose weight—reduction in caloric intake is the only way to really lose weight.

Yes, absolutely. A lot of people who are fat exercise. And there’s no question that fitness is positive for people’s health. How it all interacts I just don’t think we understand very well.

And it does seem to be true that exercise alone doesn’t seem to be a good way to lose weight. And I think that part of that has to do with, you know, homeostasis. I think it works both ways. Anyone who’s tried to lose weight or gain weight knows this that it’s very hard to budge your body off of where it’s comfortable. When you talk to people who have lost a lot of weight and kept it off, when they describe their daily routines, they get to sounding like people with eating disorders because the level of focus and obsession to keep that weight off.

Did you get a sense from any of the researchers that you spoke with that they’d be willing to do more research in exploring the idea of fitness?

I know that at the Cooper Institute in Dallas that’s mainly what they study: Fitness and how it affects health. I really think one of the reasons that this research hasn’t been done is that these assumptions are so huge and overpowering. For instance, the assumption that even if it’s true, people still tend to think, 'How many fat people exercise?' Or, 'It just doesn’t make sense to me that you could be fit and fat. How could that be true?' Because we’re so steeped in that other perspective.

Yes, there’s a huge confirmation bias going on.

Yes, that’s the word.

So at this point there have been several studies that have shown this trend of overweight people with chronic diseases living longer than those with normal weight. What is scope of the illnesses that have been studied?

It’s a huge scope. Diabetes is the most recent. But the trend has been found in all sorts of variations of heart issues, so heart failure, valve disease, just sort of garden variety cardiovascular disease, it’s definitely been found in renal disease and stroke. And high blood pressure.

It’s across such wide variation now that it’s not a fluke.

You also cited a 2007 survey with 11,000 Canadians. Something that concluded that overweight people had the lowest chances of dying of any cause.

Yes according to that study people who are overweight, so with a BMI of 25 to 30, had a significantly lower risk of death. And the increased risk was for people who were underweight and BMI over 35.

And when you say underweight, how underweight?

With a BMI under 18.5.

So in the end we can conclude that exercise is sort of like drinking more water, it solves so many problems. And couple this with the recent research on mice that shows that exercise improves brain function, even when there is no enrichment in your environment! As long as those little mice are running they are better able to preserve their smarts.

Interesting. Yes, we seem to have been designed for moving.

Share this

Christie Nicholson

Contributing Writer

Christie Nicholson produces and hosts Scientific American's podcasts 60-Second Mind and 60-Second Science and is an on-air contributor for Slate, Babelgum, Scientific American, Discovery Channel and Science Channel. She has spoken at MIT/Stanford VLAB, SXSW Interactive, the National Science Foundation, the National Research Council, the Space Studies Board and Brookhaven National Laboratory. She holds degrees from the Columbia University Graduate School of Journalism and Dalhousie University in Canada. She is based in New York. Follow her on Twitter. Disclosure