Why diets don’t work: the talk

Sandra Aamodt giving TEDGlobal talkWelcome, TED viewers! My talk from TEDGlobal in June 2013 was posted today. For those who came here looking for the details, I’ve got you covered. Start with the three posts explaining the science behind the talk: Weight and health – show me the data!, Long-term effects of dieting, and Early dieting predicts weight gain. Then move on the my favorite post on the site, How obesity is like nearsightedness, which explains how genes and environment interact to control body weight.

These ideas didn’t originate with me, of course. This research represents decades of work by many scientists, much of it old enough to be found in physiology textbooks. But since most people don’t read textbooks, here are some good places to look for more information.

The Health at Every Size community site has many resources for people interested in focusing on healthy behaviors without dieting, including the Fat Friendly Health Professionals list.

Much of the work on fitness versus fatness comes from Steven Blair of the University of South Carolina. Here’s an interview containing his recommendations for a healthy life. Just 30 minutes a day of moderate exercise is enough to provide most of the benefits.

The Fat Nutritionist has a good recent round-up of the science on why people have a strong tendency to regain the weight lost by dieting.

Arya Sharma is an obesity specialist who takes a realistic view of the difficulties associated with weight loss. Most relevant to my talk, see his blog posts Will losing weight make you fat? and Will losing weight make you sick? [links to his site are failing intermittently, but they’re correct]

Here’s a nice summary of the original study by Rudy Leibel, Jules Hirsch and colleagues showing that weight loss reduces metabolism.

If I’ve missed anything that you wanted to know about, tell me in the comments, and I’ll update the post later on.

Exercise can save you from needing a bunch of pills

Why do exercising people in photos always look so happy?

Why do exercising people in photos always look so happy?

In classic #slatepitch fashion, Emily Oster argues that calls for people to exercise to improve their health ignore the problem that most of us find exercise unpleasant. As an economist, she feels that public policy should factor in the costs of exercise, not just in gym memberships but in time that we could spend on more enjoyable activities.

She’s responding to media coverage of a recent meta-analysis showing that exercise and drug treatments are equally effective for preventing diabetes or heart attacks. Exercise was more effective than drugs for stroke patients, but less effective for patients with heart failure.

The Slate headline is golden clickbait (“Taking a Pill While Watching TV Just as Good as Exercise, Study Finds”). I fell for it, even though I’d already seen the study. But it’s wrong in one important way: no single pill can substitute for the broad benefits of exercise. Instead we’re talking about different medications to prevent or treat heart attacks, diabetes, high blood pressure, depression, and so on. Most of the seniors I know are taking handfuls of pills every day. Not to mention that exercise lowers the risk of getting some diseases of aging that can’t be cured, like Alzheimer’s disease. There’s no pill for that.

Is it OK to be fat? Wrong question.

Two recent meta-analyses have reignited the public debate about whether it’s possible to be both fat and healthy. Neither publication changes the scientific picture much – and their findings are surprisingly similar, considering that the authors of the two papers drew opposite conclusions. The media coverage is what I found interesting, as it illustrates the deep cultural biases in the way we talk about these issues.

Let’s start with the facts. Cardiovascular fitness is well known to predict people’s risk of dying within a certain number of years of follow-up. “Risk of death” is the common shorthand for that lengthy concept, and I’ll use the term here (though it sounds weird to me because we’re all going to die eventually).

The first paper combined the results of ten studies that looked at whether obesity predicts some additional risk of death beyond the known risk associated with low fitness. All the studies used objective measures of weight, height, and fitness, rather than unreliable self-report. Participants were followed for 7.7 to 16 years afterward. The authors of the meta-analysis concluded that the risk of death depended only on fitness, not on fatness.

The second paper combined the results of eight studies of a related question, whether obesity predicts any additional risk of death beyond the known risks of poor metabolic health. That’s a fancy way of describing the set of risk factors that your doctor might monitor at check-ups: blood pressure, HDL (good) cholesterol, triglycerides, waist circumference, and fasting glucose. Those authors concluded that among people with good metabolic health, obesity was still associated with an increased risk of death, though only in studies with at least a ten-year follow-up.

(Dr. Arya Sharma points out that the definition of metabolic health in this paper was lenient. His work has shown no increased risk over 16 years for obese people who are metabolically healthy under a more stringent set of requirements.)

To me, the similarities between the two papers far exceed their differences. The first paper just missed finding a statistically significant effect on relative risk for obese people who are fit (average 1.13, 95% confidence interval 1.00-1.27). The second paper’s results barely achieved significance for obese people who are metabolically healthy (average 1.24, 95% confidence interval 1.02-1.55). As each paper reports on tens of thousands of participants, the problem is not a lack of statistical power but that the effect is weak, if it exists at all. At worst, the second paper suggests that the healthy obese have a 24% greater risk than healthy normal-weight people.

Compare that to the much larger risk increase for unfit or metabolically unhealthy people at any weight, reported in both papers. The relative risks ranged from 2.42 to 3.55, or roughly a threefold higher risk than healthy normal-weight people. So if obesity does present an independent risk, it’s about one-tenth as large as the risk associated with poor fitness or poor metabolic health.

What would a sensible society do with that information? Perhaps encourage everyone to concentrate on the risk factors that have a huge effect and are relatively controllable, by exercising and eating their veggies. Or worry about the many people who face a high risk of death because of unhealthy lifestyles but aren’t concerned because they’re thin.

What do we do instead? Ignore the first study and use the second to argue about whether it’s (sometimes) OK to be fat, with headlines like “Healthy Obesity is a Myth, Report Says” and “Overweight And Healthy: A Combo That Looks Too Good To Be True.” Sigh.

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.

Running from Alzheimer’s disease

Seniors_Walking_The_Beach_4146426The last time Sam Wang and I wrote about the value of exercise for the aging brain, we got a comment that made us laugh out loud. A video gamer dismissed us as “jocks” who didn’t understand the lifestyles of nerds. To the contrary, we’re both nerds in good standing who have never been described as jocks by anyone who’d met us. I don’t like to exercise all that much, but I keep encouraging everyone to do it anyway. And I take my own advice.

The reason that I do is because those of us who exercise have better brain function than sedentary people from preschool through old age. Exercising regularly from middle age reduces the risk of developing Alzheimer’s disease in your 70s by a factor of three. Starting to exercise as late as your 60s can still reduce the risk by as much as half. Now a new study reports that exercise reduces the buildup of an Alzheimer’s disease-associated protein called amyloid in the brain, particularly in people with a genetic susceptibility to the disease.

Among the genes identified as risk or protective factors, one has a stronger effect than all the rest put together. People with two copies of the risky allele of the ApoE gene, ApoE4, get Alzheimer’s fifteen years earlier than people with the protective allele, on average. The risky allele also speeds the cognitive decline associated with ordinary aging. Even cognitively normal people with the ApoE4 allele have more amyloid in their brains than people without the allele, as shown by PET imaging with a radioactive tracer. In long-term studies, people with a lot of amyloid revealed by this type of imaging are more likely to develop Alzheimer’s later on.

Previous studies have suggested that exercise has extra cognitive benefits for people with the ApoE4 genotype, and the new study provides a clue to why that might happen. Participants who met the American Heart Association recommendation of 30 minutes of moderate exercise on five days per week were considered to be exercisers, while people who did less (many did nothing) were categorized as sedentary.

downloadAs expected, people with at least one copy of ApoE4 had more brain amyloid than people without the allele, and exercisers had less amyloid than non-exercisers. The effects of exercise on amyloid were especially strong for people with the ApoE4 genotype, suggesting that they are particularly vulnerable to the bad effects of a sedentary lifestyle on the brain. As the figure shows, people with ApoE4 who exercised had less brain amyloid than people without the risky allele who were sedentary. This study shows that regular exercise eliminates the excess risk of brain amyloid accumulation associated with the ApoE4 genotype — and suggests that it may greatly reduce the risk of Alzheimer’s disease in people with this genetic susceptibility.

There’s one important caveat to the exercise recommendation: people with the ApoE4 gene variant have an increased risk of brain damage following head injury, so they should avoid playing contact sports. A disease called chronic traumatic encephalopathy or CTE has symptoms resembling those of Alzheimer’s disease, Parkinson’s disease, or Lou Gehrig’s disease. (Researchers now suspect that the famous baseball player had CTE, misdiagnosed as the disease that was named after him.) Professional soccer players in Italy are more likely to be diagnosed with Lou Gehrig’s disease than the general population. Professional football players in the US have a higher than average incidence of depression and memory problems, which may be due to CTE, as reported in an extensive series in The New York Times(Teenagers have a particularly high risk of brain damage from contact sports.)

Given these concerns, those of us who manage to exercise despite our lack of enthusiasm might be better off than the real jocks in some ways. But there’s no question that both groups can look forward to a sharper old age than most sedentary people.