Weight and health – show me the data!

Since I gave my talk on dieting at TEDGlobal, a few people have asked for the references. I like that spirit, so here you go. Today’s post is on weight and health. Tomorrow I’ll cover the long-term consequences of dieting, and Friday I’ll explain what happens to teenage girls who worry too much about their weight.

80614206 (1)My bar graph contained data from Figure 1 of this paper, showing that mortality is better correlated with healthy lifestyle habits than with weight. Researchers have a lot of evidence that fitness is a key to health, independent of fatness. As this commentary explains, obese people with moderate cardiovascular fitness (those who walk for 150 minutes a week, for example) are half as likely to die prematurely as normal-weight people who don’t exercise at all. A review article concluded that “active or fit women and men appeared to be protected against the hazards of overweight or obesity. This apparent protective effect was often stronger in obese individuals than in those of normal weight or who were overweight.” So if you’re obese, exercise is probably even more important to your health than it is for normal-weight or overweight people.

By the way, epidemiology suggests that the ‘normal’ weight range is set too low for optimum health. Most recently, this meta-analysis of many studies found that people in the ‘overweight’ range actually live a bit longer than people in the normal range. For more details on this research and the controversy surrounding it, check out this piece in Nature.

Of course I’m not suggesting that we should all go out and gain weight for our health. I am suggesting that focusing too much on weight loss distracts us from reliable – and easier – ways to promote health. No matter how much you weigh (and perhaps especially if you’re obese), eating a healthy diet and exercising 30 minutes a day are likely to extend your life.

8 thoughts on “Weight and health – show me the data!

  1. Ms Aamodt,

    Thank you for posting the study. I came to check the calorie intake range of the participants so that I could compare the results to those of Edward Masoro’s calorie restriction study (see Calorie Restriction: A Key to Understanding Modulating Aging), but unfortunately calories were not monitored in this USC study.

    Do you know if they are planning to do a follow up study where actual calorie count is considered? I ask because some of what they are extrapolating comes in direct conflict with the Okinowa study, the Mediteranian study, and the calorie restriction study mentioned and it seems like this new information would invite closer examination.

    • The participants in that study were a cross-section of ordinary Americans, so it’s unlikely that many of them had reduced their caloric intake by 30% as calorie-restriction diets typically require. The evidence on such diets is mixed. Calorie restriction extends lifespan in animals from worms to flies to rodents, but recent studies find little effect on longevity in monkeys, suggesting that it probably will not make people live longer either. On the other hand, there’s good evidence that such extremely low calorie intake does improve or prevent many diseases of aging in primates, including humans. Realistically speaking, though, calorie-restriction diets are extremely difficult to stick to, and I don’t think they’re going to be the solution for most people.

  2. The “normal” weight range is defined in terms of BMI. Anyone who has looked closely at the BMI charts has probably noticed that those recommendations are very wrong, at least for taller people. The NIH’s BMI chart indicates that 150 pounds should be considered a “normal” weight for a 6’2″ adult. That is an insanely low weight for a person that size. I don’t see the point in having a discussion about a normal weight range when such an obviously flawed definition of normalcy is accepted as the basis for discussion.

  3. The chart shown in the TED talk, and Figure 1 from the original article this chart was based on, imply that for people with a ‘normal’ BMI, having 0 healthy habits correlates to a lower relative risk than having 1 healthy habit. Do the researchers have any explanation for this seemingly counter intuitive result?

    • The difference is small, and I suspect that’s just statistical noise due to random events in that population of participants, so I wouldn’t take it too seriously.

  4. I loved your TED Talk!

    According to the graph, overweight subjects who practiced ANY number of healthy habits had a BETTER survival rate than normal weight subjects practicing the same number healthy habits in every instance except “0”.

    Is this accurate or is the graph skewed in some way? And/Or what is the basis for “normal weight” – Is normal weight calculated using health statistics or some other measurement such as demographic averages?

    I read your comments on how overweight + exercise is better than normal weight + no exercise. But if the overweight survival rate is better than the normal weight survivial rate would it indicate that our idea of normal weight may not be an accurate indication of what is healthy – as we’ve been lead to believe? Is that idea too radical? Or would you draw a different conclusion?

    I really enjoyed listening to you and your topic. It confirmed some things I have personally found to be true.

    Thank you.

    • You’ve identified what’s called the obesity paradox – people in the so-called overweight range are more likely to get sick but less likely to die young than people in the ‘normal’ range, especially older people, the group in which most deaths occur. You can find a nice discussion of this research, and the controversy surrounding it, in this piece in Nature.

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