Mayor Bloomberg was in the news recently when his attempt to ban large sugary drinks got shot down in the courts. He feels obliged to do something to tackle the epidemic of obesity. He wants New Yorkers to go on a soda diet.

Bloomberg buys in to the notion that obesity is caused primarily by eating too much. Yet, that is not true. If it were, diets would work. Yet they do not work, and avoiding sugary drinks is not going to reduce obesity. The basic problem is not consuming too many calories. We are overweight because we move too little (1).

From a common sense perspective, it is certainly true that people today eat more than they need and that consuming too much high-fat or high-sugar foods can aggravate problems of overweight and obesity in a sedentary population. Yet, if one wants to understand how we got to the modern epidemic of obesity it is important to grasp that the real problem is not eating too much but moving too little.

How we got here

My introduction to this problem came from studying energy balance in non human animals. In a state of nature, young mammals are perfectly protected from overweight due to their high level of physical activity. The same was true of children except for populations where kids spent a lot of their leisure time sitting around watching electronic screens.

Even adults are well protected against obesity provided that they are physically active and do a lot of moving around in the normal course of their day (“non exercise” activity).

For highly active individuals, overweight is not a problem, however much they eat. In experiments where volunteers upped their food intake by 50%, there was no increase in body weight among physically active individuals. Of course the inactive individuals put on plenty of weight (2).

When one looks at pictures of people in subsistence societies, virtually everyone looks lean and fit. A common misperception is that foragers and farmers were lean because they found it difficult to get enough to eat. Yet, the truth is that relative to their body weight, they ate far more than urban people do.

So the basic problem is that urbanites sit around in offices and at home and do not get enough exercise to regulate their body weight at a healthy level. That, rather than overeating is the root cause of the modern epidemic of obesity and associated metabolic disorders.

Once a person becomes obese, cutting down on calorie intake is not an effective or healthy way of losing weight. It is not effective because the body reacts by getting more efficient at storing energy as fat. It is not healthy because the extreme calorie restriction necessary to reduce weight causes malnutrition and other health problems.

Physical activity of any kind is capable of raising metabolism at rest and also the warmth we experience after a meal (thermic effect of food) that can be enhanced by taking a walk after dinner. A lot of food energy is thus spent in producing heat instead of getting stored as fat. This means that physically active people expend much more energy than that required to do the work of movement.

These bodily mechanisms lead to the odd paradox of the skinny peoples of the world

eating more than the obese people. Among hunter-gatherers, such as the Ache of Paraguay, the average man, at 150 lbs weighs substantially less than the average American man but consumes 3,300 calories (i.e. kilocalories) compared to just 2,700 for the average American male (3).

How do the Ache manage to eat so much without getting overweight? The answer is that they are very active compared to us, using three times as much energy in physical activity as we do (about 1,800 calories compared to 600 for us). When humans lead an active life, we are good at regulating our weight, regardless of how much we eat.

What is the solution

So going on a soda diet with Mayor Bloomberg is not going to help much because it does not address the root cause of obesity – a sedentary lifestyle.

If overeating is not the real problem, why are we so obsessed with food and calorie counting? My impression is that so many people are dieting to reduce weight that there is a near-pornographic obsession with food and a moralistic belief that if we could only resist the temptation of attractive foods all would be well.

The real answer is leading a more active lifestyle. If we wanted to get up to the activity levels of the Ache, based on the numbers above, we would need to add at least two hours of moderate physical activity per day – or four times what the American Medical Association and others recommend.

That goal is attainable but only if people cultivate physical activities they enjoy and can spend time doing regardless of age or strength whether it is angling or acting, zoos or zither.

1. O’Keefe, J. H., Vogel, R., Lavie, C. J., & Cordain, L (2010). Achieving hunter-gatherer fitness in the 21st Century. The American Journal of Medicine, 123, 1082-1086.

2. Levine, J. A., Eberhard, N. L., and Jensen, M. D. (1999). Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science, 283, 212-214.

3. Cordain, L., Gotshall, R.W., Eaton, S.B. and Eaton, S.B. (1998). Physical

activity, energy expenditure and fitness: an evolutionary perspective.

International Journal of Sports Medicine, 19, 328 – 335.

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