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.

13 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.

  5. Hi Sandra,

    I’ve probably seen hundreds of TED Talks but yours was by far the best. So, just one question that I’m struggling with after listening to your talk a few times and reading the research paper you cited: I can understand how more fruits/vegetables, exercising regularly, and not smoking are all considered healthy habits – but what does ‘alcohol in moderation’ actually mean? I know it means < 2 for men – but does it also mean that men *should* drink 1 or 2 drinks/day vs. 0 or that 0 is better than 1? I ask because I've always heard people mention that longevity studies for some reason have consistently showed those that live longest usually had a habit of drinking 1 or 2 glasses per day but I've always wondered if that's causality or correlation (e.g. those that drink more have the means to do so therefore get better medical care; or those that drink more are generally more relaxed people / less stress, etc.). I don't smoke, I exercise, and I eat mostly vegetables – but I don't drink and I'm wondering whether it would be a good idea to have a glass of wine every night…


    • The epidemiology does show that people who have one or two drinks a day are healthier than people who don’t drink at all, but the differences are relatively small and the causal relationship is unclear. Having one drink a day is associated with the lowest mortality. People who never drink have the same mortality risk as people who have three drinks a day. As you suggest, that doesn’t imply a direct effect of alcohol on health. For instance, people who drink wine are healthier than those who drink beer – probably because wine drinkers have more money, which is definitely associated with better health. In the study I cited, there was little difference in longevity between people with three versus four health habits, so it sounds like you’re doing great! I don’t think you need to take up drinking for your health, though it would be fine to have a glass of wine with dinner if you would enjoy that.

  6. Hi Sandra
    I recently watched your Ted Talk and really liked your message about “only eating when you’re hungry”. However you didn’t really talk much about why we eat when we’re not hungry or why we continue to eat after we’re satiated. I have had these 2 habits for most of my life. I call them a habit because I often find myself snacking or overeating without being aware of it (especially in social situations when I’m talking and not paying attention). Or how do you explain our need to eat when viewing a food advertisement even though we’re not necessarily hungry?
    You also talked about how you personally trained yourself over the period of about a year to eat only when hungry and ultimately reduced your cravings for snack foods. But you also said “willpower” does not usually work consistently for most people. How do you suggest ending these “bad habits” without willpower?
    And what is your view on why we eat “comfort foods” like chocolate? We enjoy it for the taste or the pleasure areas in the brain it seems to satisfy. e.g. most people eat chocolate for the “sweet rush” it brings, not because they’re hungry. And yet experts agree that eating these types of foods in moderation is ok but how does one define moderation?

    • About half of our behavior is controlled by habits, which are most likely to develop around things we do at a specific time every day, like eating. It’s not realistic to imagine that you’ll never eat from habit, but you can use willpower and mindfulness in a temporary intervention to build habits that are better aligned with your goals and to train yourself to notice when you’re full. The advantage of using willpower in these ways is that once you’ve finished learning the new behaviors, then willpower is no longer necessary to keep them going. In contrast, diets depend on maintaining willpower consistently for years, which is difficult or impossible for most of us. Dieting also teaches us to ignore hunger, which increases our vulnerability to external cues like food marketing when we’re not hungry.

      The issue of comfort foods is more complicated. Eating them in moderation isn’t a big problem, and research shows that they actually do provide comfort in times of stress. But there are two common pitfalls. The first is that if you’re repeatedly rewarded for comfort eating, then it can become habitual, and you may start to do it even when you’re not stressed. The second is that people who feel guilty about comfort eating may get into a vicious cycle where they try to eat for comfort, end up feeling guilty instead, and then eat more to chase after the comfort they were originally seeking. The problem isn’t so much that they’re eating for comfort as that they’re bad at it because their guilt gets in the way.

      If you’re eating for pleasure, you’ll notice that the first few bites taste the best, and after that the experience becomes less and less appealing. Many mindful eaters eventually find that a little chocolate goes a long way, if you take the time and attention to savor it. Because habitual actions are usually accompanied by mind wandering, not attention, we actually get less pleasure (or pain) from them. That’s why I recommend automating the aspects of good health that you don’t enjoy as a daily habit and keeping treats unpredictable, so we can fully enjoy them.

  7. Pingback: The Science Behind Why Diets Don't Work | The DiehaRD Foodie

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