Do school-based obesity interventions really work?

‘Science-ish’ looks at the evidence behind taking the anti-obesity fight to the classroom


Alan Cleaver/Flickr

We’re fatter than ever and efforts to reduce our ever-expanding waistlines are failing, according to a new report by the Community Foundations of Canada.

Between 1981 and 2009, obesity roughly doubled across all age groups and tripled for youth (age 12 to 17) in Canada. This translates to a rate of obesity that’s close to 25%.

Our padded figures have left governments scrambling to address the chronic condition. Carrying extra weight increases the risk of a range of health conditions (from Type 2 diabetes to high total cholesterol and several cancers), meaning health-care costs balloon with our waistlines. (The Community Foundations of Canada put the price tag on health spending related to obesity at between $4.6 and $7.1 billion each year.)

Some jurisdictions are getting creative in response to the so-called obesity epidemic. Denmark just became the first country in the world to impose a ‘fat tax’ or surcharge on foods that contain more than 2.3% saturated fat, including much-loved greasy staples like pizza, butter, and cheese.

Here and abroad, schools have taken it upon themselves to turn out healthier students. Calgary schools have banned junk food—a practice a number of boards in this country have adopted—and two Niagara schools recently announced they are taking part in an exercise program that requires schoolchildren to exercise vigorously for 20 minutes before class.

Though the impact of the fat tax on portly Danish people will not be known anytime soon, there is a growing evidence base about obesity interventions in our schools. So, do they work?

First, let’s look at the evidence about school-based physical activity programs. Dr. Maureen Dobbins (PhD), associate professor in the school of nursing at McMaster University, has authored two systematic reviews on the subject (the newest will be published in the coming months). Overall, she found that while these programs get kids to spend more time during the day being physically active, reduced blood cholesterol, and increased VO2 max (aerobic capacity), the extra exercise did not produce a reduction in Body Mass Index. There was also little impact on the amount of exercise taken in leisure time.

Her advice? “I don’t see a reason not to keep going down this road of encouraging more activity during school time, but the research suggests it’s one part of a complicated approach to promoting physical activity in children. If we’re able to achieve more children being more physical active during the school day, it is one piece of what needs to happen.”

In Europe, studies on promoting exercise among European teenagers led to similar conclusions. A 2009 review of 20 trials on the effectiveness of interventions to promote physical activity among the EU’s teenagers found that “school-based interventions generally lead to short term improvements in physical activity levels” but these improvements in activity levels had “no conclusive transfer to leisure time physical activity.”

As for school interventions that mixed both diet and exercise, a review looked those in 2009 (along with programs that involved only increased physical activity or dietary changes). The University of Melbourne’s Dr. Elizabeth Waters (PhD), one of the researchers on the study and the lead on a soon-to-be-released updated review on the subject, spoke to Science-ish about the work, which builds on over 15 years of tracking intervention research conducted under trial conditions.

She said the latest review was actually more promising than previous studies: it showed some reduction in BMI from interventions that focus on nutrition and physical activity, particularly in a school setting. “Overall, the evidence is mounting now that (school-based) interventions are more likely to be effective,” said Dr. Waters. “The differences observed could equate to a significant population change if implemented across all schools and settings, and sustained over school generations.” However, her work also suggested that benefits while children are at schools tend to be lost or reduced during leisure time. For Dr. Waters, this means “we need to work on sustaining these benefits outside of the school environment.”

If given the chance to change policy, what would Dr. Waters do? She told Science-ish that she’d take a holistic approach and integrate healthy eating, physical activity, and body image components into the curriculum, as well as policies to increase the availability of healthy food in cafeterias and decrease the availability of unhealthy foods. She’d also build more exercise time into school hours, and create supports for parents to make healthy lifestyle choices at home.

So it seems the best quality science demonstrates what we already know: there’s no magic bullet solution for the obesity epidemic.

Science-ish is a joint project of Maclean’s, The Medical Post, and the McMaster Health Forum. Julia Belluz is the associate editor at The Medical Post. Got a tip? Seen something that’s Science-ish? Message her at or on Twitter @juliaoftoronto


Do school-based obesity interventions really work?

  1. No, obesity interventions don’t work because appetite is controlled genetically, not will power. Over weight kids are not over weight because of moral failing, it is because they feel compulsion to eat way more food than their bodies actually need. 

    There is plenty of evidence that illustrates that there is plentiful amounts of cheap food available and now people can fulfill their genetic destiny. Launching obesity interventions makes about as much sense as launching interventions to make short kids grow taller. 

    Tho I do agree that exercise before school starts is good idea – I remember listening to Jim Croce ‘Bad, Bad, Leroy Brown’ and Elton John’s “Don’t Go Breakin’ My Heart” in elementary school and doing basic calisthenics – to make people more fit and alert. 

    And Denmark’s fat tax is probably a terrible idea that will lead to even more obesity.

    JAMA ~ A Twin Study Of Human Obesity:

    Height, weight, and body mass index (BMI) were assessed in a sample of 1974 monozygotic and 2097 dizygotic male twin pairs. Concordance rates for different degrees of overweight were twice as high for monozygotic twins as for dizygotic twins. Classic twin methods estimated a high heritability for height, weight, and BMI, both at age 20 years (.80,.78, and.77, respectively) and at a 25-year follow-up (.80,.81, and.84, respectively). 

    Height, weight, and BMI were highly correlated across time, and a path analysis suggested that the major part of that covariation was genetic. These results are similar to those of other twin studies of these measures and suggest that human fatness is under substantial genetic control.

    LA Times ~ A Reversal On Carbs:

    Most people can count calories. Many have a clue about where fat lurks in their diets. However, fewer give carbohydrates much thought, or know why they should. But a growing number of top nutritional scientists blame excessive carbohydrates — not fat — for America’s ills. They say cutting carbohydrates is the key to reversing obesity, heart disease, Type 2 diabetes and hypertension.

    “Fat is not the problem,” says Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health. “If Americans could eliminate sugary beverages, potatoes, white bread, pasta, white rice and sugary snacks, we would wipe out almost all the problems we have with weight and diabetes and other metabolic diseases.”

    It’s a confusing message. For years we’ve been fed the line that eating fat would make us fat and lead to chronic illnesses.

    • If I were Dr. Willlet, I would make it much easier and just warn people to stop eating foods that offer no nutrtional value.   That would encompass his whole list, with the exception of potatoes….why can’t a person have a potato?  The second thing I would encourage people to do is make sure you are eating enough protein and three servings of fat because that is what keeps you from feeling hungry.  The third thing is to eat an unlimited amount of raw veggies (though start out slow so you don’t get a tummy ache).  Finally, eat to satiation.  You don’t have to feel stuffed – you just have to feel satisfied.
      It takes about 2 weeks to get over the craving for sugar & unhealthy food but you feel alot better.
      My final comment is about the removal of junk food at school – yes, they removed the pop but they left the juices.  I am sorry but juice is full of sugar (even if it is natural), has no fibre and is fattening.  Drink water and EAT the fruit.  For some reason nutritional studies have shown that sweet drinks cause weight gain v. eating the same calories.

  2. Jane Galt interviews Paul Campos ~ America’s Moral Panic Over Obesity: 

    Q: Let’s start with the first. If there’s one thing that everyone in America knows, it’s that being fat is really unhealthy. Why do you call it a fake problem?

    A: The correlations between higher weight and greater health risk are weak except at statistical extremes. The extent to which those correlations are causal is poorly established. There is literally not a shred of evidence that turning fat people into thin people improves their health. And the reason there’s no evidence is that there’s no way to do it. 

    So saying “let’s improve health by turning fat people into thin people” is every bit as irrational as saying “let’s improve health by turning men into women or old people into young people”. Actually it’s a lot crazier, because there actually are significant health differences between men and women and the old and the young — much more so than between the fat and the thin.

    Q: Over the last five years or so, I’ve noticed that public health efforts about obesity are not just amping up the volume, but exploring increasingly coercive methods to induce weight loss: taxes on junk food, lawsuits against fast food companies (which are basically a tax on junk food), and so forth. Does that match your analysis?

    A: It’s the classic pattern of moral panics. As public concern about the damage being done to the fabric of society by the folk devils increases, increasingly intense demands are made on public officials to “do something” about the crisis, usually by eliminating the folk devils. That of course is the strategy for this crisis.

    If fat people are the problem, then the solution is to get rid of them, by making them thin people. The most amazing aspect of this whole thing, for me, has always been the imperviousness of policy makers, and even more so people who consider themselves serious academics and scientists, to the overwhelming evidence that there’s no way to do this. 

    I mean, there’s no better established empirical proposition in medical science that we don’t know how to make people thinner. But apparently this proposition is too disturbing to consider, even though it’s about as well established as that cigarettes cause lung cancer.

    So all these proposals about improving public health by making people thinner are completely crazy. They are as non-sensical as anything being proposed by public officials in our culture right now, which is saying something.

    • Let’s just not talk about “fat” and “thin” – let’s talk about – “healthy” and “unhealthy” – let’s talk about “nutritional value” vs. “no nutritional value”.  It is that easy.  TonyAdams, how can you defend junk food??  It is “junk”?  It has no nutritional value. If we taxed junk food, we could subsidize healthy food, like fruits & vegetables.  I used to eat in the hospital cafe…I ate a salad & fruit plate and paid “thru the nose”; my buddy ate poutine & paid almost nothing.  My 50 yr old buddy has since had a heart attack; been diagnosed with type II diabetes & had breast cancer.  The hospital finally grew a conscience and quit serving unhealthy food – why should the taxpayer shell out $100K+ for open heart surgery and then we serve them poutine post-op????
      TonyAdams, go ahead – pretend that it is all genetic and that we have no control over what we eat and we are fighting a losing battle to stay healthy but the truth is we are the ONLY ones that have control over what we eat and how heallthy we stay.

      • I am not defending junk food, calm down. I have been in hospital a few times myself and complained about lack of fresh food and how moronic it was to give sick people shockingly processed food. 

        I am interested in food/genes because of me, my father and uncle. Males on paternal side of family are either underweight or obese. I am tall and thin – like Obama or Dion – and my father and uncle same height but both morbidly obese and my grand father was tall thin but his brother was obese. No males that I know of are average. 

        I am 40 yrs old and weigh 170 lbs and was 160 lbs when I was 15 yrs old. For the past 20 yrs I have been eating pretty much whatever I want to try and gain weight while my father and uncle are both embarrassed by their weight and eat much better than I do and exercise regularly. 

        Father and uncle are both morbidly obese but are healthy because they have been eating well for past 30 yrs.

      • I read Galt’s blog a few years ago and ordered Kolata’s book for my father. He recognized himself in book – my morbidly obese father can eat 3, 500 calories in day and start to panic at night if he doesn’t plan next morning’s breakfast – he thinks he’s going to starve. I struggle to eat 3,000 calories a day – I feel ill if I eat too much but want to gain a bit of weight.  

        Jane Galt ~ June 2007:

        I just finished Gina Kolata’s “Rethinking Thin”, which is pretty scathing on the subject of weight loss. She heavily endorses the theory that people have a natural set point for weight, around which they vary by no more than 10-20 pounds. Try to go beyond that, and natural defense mechanisms kick in that push you back into your range; either you lose your appetite, or you become ravenously hungry and obsessed with food.

        The idea seems to be that the natural tendency of most people is to be somewhat overweight–say, 10-30 pounds over what society sees as normal. Obese people, however, have something wrong with the mechanism their body uses to perceive how fat they are, so the chemical signals to eat keep coming. Basically, any time that they are losing weight, their body thinks they are starving.

        Normal people think of obese people dieting down to something near normal as being essentially the same activity as it is for them to diet off those ten unwanted pounds, when in fact they are fundamentally different. Normal people are dieting down to the bottom of their set range, where it might be a little tempting to have more dessert. Obese people, on the other hand, are dieting down to a point where their body thinks they are starving, and floods them with chemical signals to EAT! 

        Obese people who have lost a lot of weight act like normal people do when they are severely food deprived–tellingly illustrated by an anecdote from a World War II prisoner of war, who reports that the GI’s in German prison camps sat around, not talking about tail, but swapping recipes. Imagine a force powerful enough to make 19 year old males stop thinking about sex, and start thinking about ways to bring out the parsley flavour in your cheese croquettes, and you have some inkling of what the obese go through.

        • I don’t know that I believe that as a rule  the morbidly obese can be considered a healthy group – studies tell us that belly fat causes all kinds of medical problems.  Everyone could probably point out one or two life long smokers who have no health issues either but it does not mean that you can conclude that smoking isn’t harmful to your health.
          If I am correct in my interpretation of what you are describing, you are saying that obese people have issues with their “satiety centre”.   It does not signal them to say they are full and so they constantly feel hungry.  As a psychiatric nurse, I am familiar with this phenomenon.  There are some  anti-psychotic medications that have this as a side-effect…certain people feel constantly hungry when they take them and massive weight gain often occurs.  One psychiatrist told me this does not happen in China though because the patients there strictly adhere to what the physicians tell them about not over eating.  We have found as well that IF patients adhere to a proper diet, they don’t gain a lot of weight OR if they do alot of strenuous exercise – like kick boxing – they can keep the weight off.
          I would be interested to hear about your Grandparents and great Grandparents.  Were they morbidly obese as well?
          As for what you described with the WWII GI’s, you only have to go to any Weight Watchers meeting to see that played out everyday.  As soon as people are deprived of dessert, they become obsessed about it….or maybe go to an AA meeting, they all discuss their drinking days.
          I am not talking about deprivation, I am talking about good food choices – everyday and moving around everyday…..not a diet but a life change.  Eat to satiation – just make sure you eat healthy food and if you are worried that you will be starving maybe you need to see a counsellor about behavioral therapy.

        • Gina Kolata ~ Rethinking Thin:

          Every time the result was the same.  The weight, so painstakingly lost, came right back.  But since this was a research study, the scientists looked at more than just weight loss . . . they measured metabolic changes and psychiatric conditions and body temperature and pulse.  And that led them to a surprising conclusion:  fat people who lose large amounts of weight may look like someone who was never fat, but they are very different.  In fact, by every measurement they seemed like people who were starving.

          On every count, the weird, bizarre, almost depraved behavior that Ancel Keys reported when he studied young men who were deliberately starved in his experiment during World War II was just like what Hirsch observed among the formerly obese subjects at Rockefeller University Hospital.  Something ws driving these people to regain their weight, and it was not a deep-seated desire to be fat.

          Their metabolisms, for example, had changed so that they hung onto, clung to, every calorie that was consumed, making it harder for them to stay thin.  Before the study began, the fat people had a normal metabolism–the number of calories burned per square inch of body surface was the same as for people who had never been fat.  That changed substantially after they lost weight, with fat people burning 24% fewer calories per square meter of surace area than were used by people who were naturally thin.

          The Rockefeller subjects also had a psychiatric condition that had been termed “semi-starvation neurosis”.  Hirsch’s patients dreamed about food; they fantasized about food, or breaking their diets.  They secreted food in their rooms.  They daydreamed about food.  And they binged . . . eventually more than fifty people went through the months-long process of living in the hospital and losing weight, and every one of them had the physical and psychiatric symptoms of starvation.

  3. Just a note to the Macleans people about how DISQUS sucks.

    Last Friday, TonyAdams wrote that “people should be responsible for their own pathologies” and that keeping Insite open would delay heroin addicts from making the hard decisions necessary to get themselves straight. 

    Here, when Junior can’t lay off the Twinkies it is all genetics.

    How do I know which Tony is which?

    • You are so right, StewartSmith!  TonyAdams doesn’t accept the genetic component of addictions unless it is an addiction to food.   Very astute of you to point that out.

    • “Here, when Junior can’t lay off the Twinkies it is all genetics.”

      You don’t know anything about obesity if you think too many Twinkies is the issue. As explained above, genes control weight but humans control what they eat.

      People are responsible for their pathologies and that’s why I don’t want government interference in either drug addict or obese people’s behaviours. Insite enables peoples bad behaviour – it is same thing as Government providing comfortable area for overweight people to eat their Twinkies.  

      It is not up to Government/taxpayers to make sure that drug addicts are comfortable or try to control what overweight people are eating. 

      Megan McArdle ~ Fat Politics:

      How does the idea that weight is somehow a reliable proxy for discipline and self control survive contact with the existence of people like Michael Huckabee, Oprah Winfrey, and yes, Chris Christie?  Do we think that Oprah became the most successful television personality of all time by being lazy and out of control?  She’s lost loads of weight what, a half dozen times?  Yet despite her personal trainers, her private chef, and what is by all accounts a work ethic that would be the envy of an entire busload of Puritan slave-drivers all hopped up on IV Adderall, the weight always comes back.

      Gina Kolata’s Rethinking Thin makes a pretty compelling case that almost everyone’s weight fluctuates within a band of 20-30 pounds.  Some peoples’ band is higher than others, (and perhaps, slowly increasing over time). When you get nearer to the bottom of your body’s weight tolerance, your hunger increases; drop below it, and your body reacts as if you’re starving, slowing your metabolism and focusing more and more of your mental attention on food.

      Slate ~ Leave Fat Kids Alone:

      Let’s get one thing straight: I wasn’t a fat kid; I was husky. At least that’s what it said on the labels of my pants. Maybe not the navy sweats I wore to school three times a week, but the other pants—the slacks, the dungarees, the husky dungarees.

      • The problem with leaving the obesity epidemic alone is that the cost to the healthcare system is astronomical.

  4. I would like to recommend the free NAAFA Child Advocacy ToolkitSM (CATK) and other written guidelines/resources to assist you looking at programs. 
    A Yale Rudd Center report reviewed existing research on weight stigma in children and adolescents, with attention to the nature and extent of weight bias toward obese youths and to the primary sources of stigma in their lives, including peers, educators, and parents. As a result of weight bias and discrimination, obese children suffer psychological, social, and health-related consequences. Substantial change is needed to combat this bias.
    Rebecca Puhl of the Rudd Center further brings to light the stigmatization of large children in the following article.
    The NAAFA Child Advocacy Toolkit shows how Health At Every Size® takes the focus off weight and directs it to healthful eating and enjoyable movement. It addresses the bullying, building positive self-image and eliminating stigmatization of large children. Additionally, the CATK lists resources available to parents and educators or caregivers for educational materials, curriculum and programming that is beneficial for all children. It can be found at: