It may be self-evident that exercise reduces obesity, but that doesn't make it true

Over at The Economist blog, it is written:

It seems self-evident to suggest that if schools that have eliminated physical education and recess reinstituted them, there would be fewer obese adolescents in America.

Evidence suggests adding phys ed isn’t the cure for fatkiditis the Economist imagines. Quoting Gina Kolata ((If my last name was “Kolata,” I don’t think I’d name my child anything that rhymes with “Pina.” Just saying.)) in the New York Times:

In the 1990’s, the National Institutes of Health sponsored two large, rigorous studies asking whether weight gain in children could be prevented by doing everything that obesity fighters say should be done in schools — greatly expand physical education, make cafeteria meals more nutritious and less fattening, teach students about proper nutrition and the need to exercise, and involve the parents. One study, an eight-year, $20 million project sponsored by the National Heart, Lung and Blood Institute, followed 1,704 third graders in 41 elementary schools in the Southwest, where students were mostly Native Americans, a group that is at high risk for obesity. The schools were randomly divided into two groups, one subject to intensive intervention, the other left alone. Researchers determined, beginning at grade five, if the children in the intervention schools were thinner than those in the schools that served as a control group.

They were not. The students could, however, recite chapter and verse on the importance of activity and proper nutrition. They also ate less fat, going from 34 percent to 27 percent fat in their total diet. Alas, said the study’s principal investigator, Benjamin Caballero, director of the Center for Human Nutrition at the Johns Hopkins Bloomberg School of Public Health, “it was not enough to change body weight.”

What I’d really like to know — but this article doesn’t say — is if the kids were healthier, as measured by blood pressure, cholesterol levels, ability to walk on a treadmill and so on. There’s an unfortunate attitude that an intervention that doesn’t lead to thinness is necessarily a failure, which leads us to ignore many important indicators of health. ((Somewhat related, from the same Times article: “Nearly 49,000 women were randomly assigned to follow a low fat diet or their regular diet for eight years while researchers kept track of their rates of breast cancer, colon cancer and heart disease. Not only did the diets have no effect on these diseases, they also had no effect on the women’s weights.”))

So why does “it seem self-evident” that we can make thinner kids by adding gym and stirring, when the evidence says otherwise? Well, part of the reason is that “self-evident,” in this case, means that the blogger is reciting conventional wisdom. And conventional wisdom is selective:

The paper appeared in The American Journal of Clinical Nutrition in 2003 to no acclaim, Dr. Caballero said. No press release, no media coverage, no invitations to speak about the results at scientific meetings. On the journal’s Web page, a search of articles that refer to the study comes up empty. It has not been cited anywhere.

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30 Responses to It may be self-evident that exercise reduces obesity, but that doesn't make it true

  1. Meowser says:

    Do none of these people remember the same gym classes (from the 1970s) that I do? I seem to remember an awful lot of standing around waiting for teams to be chosen up, waiting around for a turn at bat/kick, or waiting to run after something or away from something coming towards me. The only time we got any real “exercise” as such was when we were doing folk dancing. Which was actually my favorite thing, since I hated all the competitive games I sucked at.

    And speaking of sucking at gym, I guess all those people were good at it, because otherwise they’d know that kids are absolutely lethal to you if you suck at it. Which doesn’t exactly make kids who suck at it want to suit up for more. Same goes for the “more public parks” stuff; parks are great, but if you’ve been harassed on the playground because of your weight — and what fat kid hasn’t? — you’re not going to want to go back there unless someone makes you.

    And of course, making kids do certain activities will make them fall in love with those activities and do them for life. Except, NAWWT.

  2. Meowser says:

    Oh, and also re Gina Kolata, she was born in 1948, or about six years before the invention of the piña colada. (Also, I’m pretty sure her birth surname was Bari, as her mother, father, and sisters all had this name; Kolata was likely a surname acquired through marriage.)

  3. I think your point about measuring health vs. size is very apt. Our society is so focused on the visual as the primary indication of a person’s health, yet there are many overweight people who are far healthier (cardiovascular fitness, blood pressure, etc) than their thinner counterparts.

  4. Exercise reduces obesity like work reduces poverty — it’s great while it last, but having a job is no guarantee of wealth.

    My Uncle was a college basketball player — played in high school as well. But as with many athletes, once the exercise stopped, the weight gain started. I went through the same thing when I moved from Dallas to Austin — Dallas, very easy to bicycle all over the place without getting run over. Austin, not so easy, considering some of the hills around here. I gained 30 or 40 pounds after moving to Austin and getting off my 12-speed. Exercise works great, and then it stabs you in the back.

  5. Glaurung says:

    Amp, may I recommend most highly to you “Good Calories, Bad Calories” by Gary Taubes. It’s a thick tome, but in it Taubes lays out the ways in which the real scientific knowledge of how and why mammals gain or lose weight (done by anatomists and metabolic researchers doing basic science), which has been thoroughly known and established for 30 years now, has been totally and completely ignored by the doctors and public health “experts” who have the ear of the government, who write the textbooks for medical students and who set policy.

    It’s a textbook case of scientific failure: you have three or four people with big egos and fixed prejudices about fat people totally derailing the public health agenda of the entire medical establishment while advancing their own careers.

    Meanwhile the health advice given to the entire world for 30+ years has been the exact opposite of what it ought to be, given the knowledge of metabolism amassed by those ignored basic researchers. Refined and processed foods high in carbohydrates are, most likely, the chief cause of heart disease, stroke, cancer, and, as a by-product, obesity (which isn’t a disease but carries a heavy social stigma). Ergo, the best way to avoid getting those diseases, and the best way to keep from getting fat, is to avoid processed foods rich in fast-digesting carbohydrates (white flour, white rice, sugar, fruit juice, etc).

    Losing weight is more tricky, of course, since the process of becoming fat, again from that metabolic research, involves multiple factors leading to damage to the body’s ability to mobilize fat out of the fat cells to sustain itself in the hours between meals, especially overnight. It’s not an area that those basic research scientists are interested in, and the medical establishment is still stuck in its geocentric insistence that sun goes around the earth, so there’s been no testing of it, but logically a low-carb diet is probably the best candidate.

  6. Ashley says:

    @ Meowser: Gym class has changed a lot. I graduated high school in 2002 and at least once a week we’d have a “fitness day” where the normal scheduled gym activity would be replaced with running around a track or on a treadmill. At my school you could choose what you did in gym for a few weeks starting sophomore year, and one popular option was going to lift weights. A less popular option was swimming laps (which I took a couple of times cuz I heart the water). There was pretty much no standing around choosing teams, and unless you chose to take baseball or volleyball little standing around during the actual activity. Plus we had fitness testing every year. Oh, and I had one teacher who made us do tae bo or step aerobics once or thrice a week!

    Yeah, gym’s changed a lot. Still hated it, except for swimming, dance, and pickleball (life-size ping pong).

  7. DRST says:

    Ergo, the best way to avoid getting those diseases, and the best way to keep from getting fat, is to avoid processed foods rich in fast-digesting carbohydrates

    Actually the best way to avoid those diseases and avoid getting fat is to select two parents and four grandparents who are thin and don’t have any of those diseases, since there is a huge genetic component to all of them.

  8. saacnmama says:

    Youngsters in middle and high school eating 27 g of fat per day? No wonder they didn’t loose any weight! I need to stay around the low 20s, and I’m a 5’8″ adult.
    Still, I’d also like to know what influence these changes had on their other health indicators.
    I also wonder what activities they did in gym class. It doesn’t have to be war ball to be aerobic (although D. Sedaris has a funny bit on the aerobic effects of fear).

  9. PG says:

    Glaurung,

    Taubes has no educational background in biology or medicine; he studied physics, engineering and journalism. He’s basically been touting the Atkins Diet. People in other cultures have been eating white rice for centuries without its causing “heart disease, stroke, cancer, and, as a by-product, obesity,” because in much of Asia, they need the calories from that rice to sustain them in manual labor (especially farming work). My dad lived on white rice and pickle as he was going through medical school in India, and he weighed 98 lbs at the end of it without any of the maladies you describe (nor has he developed them later in life). The problem is not with carbohydrates, but with our failure to be active enough to burn foods that were meant to provide a cheap source of energy to people whose livelihoods depended on having enough energy to produce all the food they would need plus enough extra to cover the other necessities of living.

    Of course, most Westerners aren’t going to be following buffalo through rice paddies, so a diet that supplies a great deal of easily-accessible energy that we’re not actually using may not be good for us, but that culture-specific fact does not make carbs inherently evil.

    When people force themselves to avoid carbs, they replace those carbs with fats, especially animal fats. As you acknowledge, the body has more difficult drawing energy from fat and thus fats are more difficult to use up before they are stored in the body.

  10. PG says:

    Amp,

    Do you have the title of the article that was published in the American Journal of Clinical Nutrition? I pulled up this article that seems to be based on the same study, but it has been cited many times and does not precisely fit with Kolata’s description.

  11. Glaurung @ 4:

    Most of that research ignores differences in diet and metabolism between groups of people, as well as differences in muscle types.

    If I eat a diet high in the sorts of carbohydrates that text seems to recommend, I gain weight and my cholesterol goes up and I become less healthy. If I eat a diet high in meat protein and above RDA values for fat, my weight goes down along with my cholesterol and my health goes up.

    Likewise, I am mostly made of fast-twitch muscles. I was a sprinter in track and turned in great times in 110 and 440 yard runs. I ran for crap much past a mile and can’t keep up with the slow-twitch, prolonged aerobic exercise crowd. I can beat their pants off in my body’s “preferred” zone, but they are going to beat me any time I’m dumb enough to try running a Marathon.

    There is no such thing as A Human Body, and that’s one of the things that needs to sink into the skulls of the people who make these universal assertions about exercise and obesity and so on.

  12. B. Adu says:

    PG,

    he studied physics, engineering and journalism.

    That might be why he was able to deconstruct ‘the calories in calories out’ is based on physics arguement, in his book ‘The diet delusion’.

    I have to agree with your scepticism on his love of low carb though, I wasn’t persuaded.

    The problem is not with carbohydrates, but with our failure to be active enough to burn foods

    The process is less linear than that, your energy requirements influence your hunger and vice versa, it makes no sense for the body to demand energy it doesn’t need.

    What’s also interesting though, is why so many fat people have a BMI of between 30-35, we didn’t have a conference on it.

    If free form greed is the issue, why does it lead to such a congruence of outcome?

  13. Vidya says:

    saacnmama — 27 *percent*, not *grams*.

    Btw, young people need a very high percentage of fat in their diets to ensure proper development of the brain and nervous system. Fat deprivation can cause irreversible damage.

  14. PG says:

    it makes no sense for the body to demand energy it doesn’t need.

    Who said that our interest in food in 21st century America is driven primarily by our energy needs rather than food engineering, advertising, socialization and a host of factors wholly unrelated to our body’s needs? If we only ate what our body needed, I would have had no problem choosing between a fresh peach and a piece of fudge last night.

  15. PG says:

    Vidya,

    The need for plenty of fat is correct with regard to very young children — that’s why they should get whole milk, not 2% nor skim — but I don’t think that holds equally true for older children (i.e. 8 years and older). I already had high cholesterol at age 11 and was supposed to avoid animal fats (i.e. meat and dairy fats). I suppose it may have stunted my brain’s growth, but I don’t think that’s likely.

  16. Sebastian says:

    A key problem in much discourse, but especially when discussing weight issues, is that of magnitude.

    Yes, your average person can diet and exercise and convince his body to settle in at 10-20 pounds from where it seems to want to go. They can often do this without starving themselves and without dramatic changes in lifestyle. This may or may not have an effect on health. But the magnitude of the effect is small if it exists at all.

    But that observation is not extendable to the magnitude of change that we are talking about for obesity. In the case of obesity, we are talking about losing 100 or more pounds. That isn’t just repeating the above process linearly 5-10 times until you get to the weight you want. After you get to the second iteration, much less the third or fourth, your body can really start to fight back. It changes your metabolism, it changes your hunger set point, it does all sorts of things.

    We don’t know what to do about that. It might be good to do something about it, but we don’t know how. And pretending that we know how (and especially pretending that it is all about chaining 5-10 iterations of losing the first 10-20 pounds) isn’t helping anyone.

    And I write all this as a person who seems to have a metabolic set point that puts me at fairly thin.

  17. Vidya says:

    I already had high cholesterol at age 11 and was supposed to avoid animal fats (i.e. meat and dairy fats).

    Oh, I agree — children of any age should be eating little to (ideally) zero animal-sourced fats. But plenty of vegetable fats (esp. non-hydrogenated ones) are quite nourishing. (I’m vegan, so I just assumed–incorrectly, of course–that ‘fat’ would necessarily be interpreted as vegetable fat).

  18. PG says:

    In the case of obesity, we are talking about losing 100 or more pounds.

    Uh, if you are using coarse BMI for this, that’s not true for everyone. Someone who is 5’3 and 170 lbs. is deemed “obese” by the public health folks, but can become “normal” by losing 30 lbs. The move from BMI of 30 to BMI of less than 25 requires different levels of weight loss depending on height, because it’s a crude measure of height relative to weight. Someone who is 6’3 and 240 lbs. is “obese,” but let him lose 45 lbs. and at 195lbs. he is “normal.”

    It’s only if you are pretty far into coarse BMI obesity — e.g. you’re 6’3 and 280 lbs. with a coarse BMI of 35 — that you’d need to lose anywhere near 100 lbs. to get to “normal.” Even from there, there’s a lot less weight to lose if you’re just shooting for “overweight but not obese.”

    I find all use of coarse BMI fundamentally silly when discussing individual rather than public health anyway, but let’s get the math right.

    Also, as the Economist article points out, the focus is less on getting people who are already obese to become thinner, and more on ensuring that people who aren’t obese now don’t become so in the future — babies generally aren’t born obese, it’s something that happens later in life due to a confluence of genetic and environmental factors. We can’t do anything about genes, but we can change the world in which we live.

  19. PG says:

    Vidya,

    But plenty of vegetable fats (esp. non-hydrogenated ones) are quite nourishing. (I’m vegan, so I just assumed–incorrectly, of course–that ‘fat’ would necessarily be interpreted as vegetable fat).

    Oh, sorry, that was my misunderstanding. Non-hydrogenated vegetable fats are usually considered OK for health, though, aren’t they? Vegans can be “overweight,” in a coarse BMI sense of just what the number of pounds relative to height is, but I have never met a vegan who had to go on statins and insulin. The derogatory social perception of the obese is of people eating steaks and doughnuts, not so much raw olive oil and almond butter.

  20. Adrian says:

    Some things are good for health, for people of any weight. Moderate exercise, eating lots of vegetables and relatively little sugar, not smoking, getting enough sleep. (Sometimes an individual can’t manage all that, and it’s unfortunate.) Often, improving health doesn’t show up as a change in weight. That’s a real problem for fat people whose doctors or families or just the fat hating world convince them to try something difficult in the hope that it will make them thin and healthy. They try for 3 months and give up when they don’t see a change in weight. People say “I’m just worried about your health,” but they don’t stop worrying (or nagging) when a fat exerciser makes high blood pressure or insulin resistance go away … and still stays just as fat.

    I remember reading about exercise having beneficial effects on blood pressure and blood sugar, (as well as other useful measures of fitness such as strength, balance, stamina), even where there is no weight loss. Unfortunately, most of what I can find advocates weight loss very, very, strongly. These studies of exercise improving insulin sensitivity are small, which doesn’t seem unreasonable to me. A lot of the studies about how weight loss protects from this or that disease seem to have been quite small, too.
    http://articles.mercola.com/sites/articles/archive/2003/04/05/exercise-diabetes-part-two.aspx
    http://linkinghub.elsevier.com/retrieve/pii/S0167494300000765
    A more significant problem is that both studies were looking at adults with diabetes. I don’t know if it’s only a benefit for adults who already have diabetes, or pre-diabetes, or if it would also be valuable for healthy children. It seems like it would be worth studying, though.

  21. Vidya says:

    Vegans can be “overweight,” in a coarse BMI sense of just what the number of pounds relative to height is, but I have never met a vegan who had to go on statins and insulin.

    Yes, certainly vegans can be ‘overweight’ — I myself technically occupy the lower end of that newly formed category above morbidly obese — ‘super obese’ — as my BMI is well over 50. And I’ve been vegan since many folks here were still in short-pants. :-p
    I, too, have never met a vegan taking statins or insulin — but, of course, both of those are drugs developed through animal testing (in some cases, insulin actually *is* an animal product), so most vegans wouldn’t take them anyways. A vegan diet is generally quite good at stabilizing blood sugar issues, and may lower cholesterol (although most cholesterol is produced by the liver, not a result of dietary intake). Also, on the whole vegans tend to be informed about natural healthcare alternatives; I take chromium to address my genetic insulin resistance.

  22. B. Adu says:

    Who said that our interest in food in 21st century America is driven primarily by our energy needs rather than food engineering, advertising, socialization and a host of factors wholly unrelated to our body’s needs?

    I think until eating becomes optional to life, as opposed to a necessity, we can still say that it is driven primarily by the desire to remain alive, that goes even for Americans.

  23. B. Adu @ 22:

    But that doesn’t preclude our appetites being “engineered” by the companies that sell food.

    Yes, obviously, if we consistently consume less food energy than we expend as body energy, a person might eventually die if the deficit was large enough and they did that for long enough.

    But once we eat more than what’s required for maintenance, we’re good. And companies want us to eat more than we require so they make more $$$’s.

  24. drydock says:

    Gina Kolata is the sister of the late environmentalist, Judi Bari, who was car bombed in Oakland CA about 20 years ago.

  25. PG says:

    Vidya @21,

    both of those are drugs developed through animal testing (in some cases, insulin actually *is* an animal product), so most vegans wouldn’t take them anyways.

    That’s very interesting — I didn’t know that some vegans refused to take medications that were developed through animal testing. Wouldn’t that be practically all medications (including immunizations)? Is this a stance taken solely for the individual, or do you know if parents apply it to children as well?

    Most cholesterol in the body (about 3/4) is produced by the liver, but the other 25% or so comes from food intake. Some people can bring their cholesterol to a healthy level simply by removing saturated and trans fats and cholesterol from their diet. I have a genetic component to my high cholesterol, but for example, when I was an adolescent and my parents freaked out because my cholesterol was over 250, putting me on a no-cholesterol, low-saturated-fat (trans fats weren’t as common then) diet brought my cholesterol just under 200. I am genetically prone to high cholesterol, but I can keep it to a healthier level through a particular diet and cardio-targeting exercise than it would be otherwise. Not letting the perfect be the enemy of the good, and all that.

  26. Vidya says:

    That’s very interesting — I didn’t know that some vegans refused to take medications that were developed through animal testing. Wouldn’t that be practically all medications (including immunizations)? Is this a stance taken solely for the individual, or do you know if parents apply it to children as well?

    It does in my case, though also because, as an adherent of homeopathy, I don’t believe allopathic medications are safe or curative. Of course, millions of people oppose vaccinations for a variety of reasons, and I’m not sure what percentage would identify veganism/vegetarianism as the primary reason; again, there is surely substantial overlap between vegan-rooted objections and awareness of vaccines’ dangers and ineffectiveness, so it might be hard to sort out figures. Most adult vegans raise their kids as vegans, too, so I would expect most apply their ethics and alternative treatments to their children as well, at least until the latter are old enough to make informed decisions; I certainly would.

  27. B. Adu says:

    FCH,

    Without food, we die, full stop.

    I’m not trying to be tiresome about this, but when we remember this, things start to make a lot more sense.

    As for the food companies, I share you cynicism about them, their imperative is maximum profits, brought about by (most of them) whatever the heck they can get away with.

    Having said that, within the context of the capitalist system it is to a great degree their ingenuity that makes us forget that eating is not an optional hobby. I don’t doubt they wish to use that same ingenuity to enrich themselves further, in a sense, it symbiotic.

    Their keeness to overfeed us, is to some extent their keeness to feed us in the first place.

    But that doesn’t preclude our appetites being “engineered” by the companies that sell food.

    Yes they try, but it doesn’t mean they succeed. For example weight watchers, they’ve endeavoured to make us thin. Exactly.

    The fact that they wish to stuff as much food into us as possible, doesn’t mean that they don’t run into the same body defences as the weight loss diet industry.

  28. B. Adu @ 27:

    Without food, we die, full stop.

    I’m not trying to be tiresome about this, but when we remember this, things start to make a lot more sense.

    Every false dichotomy deserves it’s time in the sun.

    No, without “sufficient food for maintenance” we die. Not “without food”. Trust me on this one — I know just how little I can eat and not actually die.

    As for the food companies, I share you cynicism about them, their imperative is maximum profits, brought about by (most of them) whatever the heck they can get away with.

    I’m not the least bit cynical about food companies — despite my strong Socialist leanings, I’m very much a Capitalist. Food companies aren’t charities — they have a profit motive. Their behavior is not at all a mystery to me. I don’t go “Gee, why isn’t Coke sold in the old 6 1/2 ounce bottles anymore?” because I know that bigger and bigger “single serving” bottles are required to keep Coke executives and stockholders happy.

    But that doesn’t preclude our appetites being “engineered” by the companies that sell food.

    Yes they try, but it doesn’t mean they succeed. For example weight watchers, they’ve endeavoured to make us thin. Exactly.

    The fact that they wish to stuff as much food into us as possible, doesn’t mean that they don’t run into the same body defences as the weight loss diet industry.

    I don’t know enough about Weight Watchers to comment — if I started a Weight Watchers diet, my friends would do an intervention and take me out for a bacon cheeseburger, fries and a Coke.

    But the problem, as some article posted here recently pointed out, “food” triggers parts of the reward centers of the brain. I’ve yet to find a food that triggers the reward centers more in ever smaller amounts. And as I understand it, that’s why Weight Watchers fails — if it tastes good enough to get you away from the supposedly “bad food”, it’s going to taste good enough to be eaten a LOT. (And again, I know nothing about Weight Watchers — my diet issue is that I starvation diet naturally because I have a crappy relationship with fat and my body.)

  29. Aaron V. says:

    @ FurryCatHerder re #4 (looks down at his belly) – Pretty much. I have to learn how to eat like a desk jockey who tries to make it to the gym, not a large-school high school football player or a Division III track and field thrower.

    I don’t see how Phys. Ed. classes will do anything but make adults feel good and employ a bunch of teachers who can’t teach anything else. Letting kids run around is the answer, not put them in stultifying death marches around a track on a “fitness day”.

    Vidya – for your own sake, please consider allopathic or osteopathic medicine. Homeopathy is a surviving quackery of the 19th century – at best, homeopathic substances are expensive placebos, at worst, they keep you from getting effective treatment for medical conditions.

  30. Aaron V @ 29:

    I don’t see how Phys. Ed. classes will do anything but make adults feel good and employ a bunch of teachers who can’t teach anything else. Letting kids run around is the answer, not put them in stultifying death marches around a track on a “fitness day”.

    “No structure” is as much not the answer as “too much structure”. I enjoyed track, once my coach learned that I was a sprinter, not a distance runner. I also enjoyed gymnastics, until I broke my nose and bled all over the floor. For PE class, I craved structure.

    What’s wrong is assuming that all kids want to run track or do gymnastics, or anything else that’s highly structured. Give them a couple of assorted balls, a wide open space, and let them make up their own games. Worked fine for me and the other kids in the neighborhood when we were away from school.

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