How those hoping to lose weight often wind up being their own worst enemies

People hoping to lose weight with exercise often wind up being their own worst enemies, according to the latest, large-scale study of workouts, weight loss and their frustrating interaction. The study, which carefully tracked how much people ate and moved after starting to exercise, found that many of them failed to lose or even gained weight while exercising, because they also reflexively changed their lives in other, subtle ways. But a few people in the study did drop pounds, and their success could have lessons for the rest of us.

In a just and cogent universe, of course, exercise would make us thin. Physical activity consumes calories, and if we burn calories without replacing them or reducing our overall energy expenditure, we enter negative energy balance. In that condition, we utilise our internal energy stores, which most of us would call our flab, and shed weight.

But human metabolisms are not always just and cogent, and multiple past studies have shown that most men and women who begin new exercise routines drop only about 30 per cent or 40 per cent as much weight as would be expected, given how many additional calories they are expending with exercise.

Why exercise underwhelms for weight reduction remains an open question, though. Scientists studying the issue agree that most of us compensate for the calories lost to exercise by eating more, moving less, or both. Our resting metabolic rates may also decline if we start to lose pounds. All of this shifts us back toward positive energy balance, otherwise known as weight gain.

It has not been clear, however, whether we tend primarily to overeat or under-move as compensation, and the issue matters. To avoid compensating, we need to know how we are doing it.

So, for the new study, which was published last month in the American Journal of Clinical Nutrition, researchers with the Pennington Biomedical Research Center in Baton Rouge, La, and other institutions decided to exhort a large group of inactive people into exercising and closely track how their waistlines and daily habits changed.

They began by recruiting 171 sedentary, overweight men and women ages 18 to 65, measured their weight, resting metabolic rates, typical levels of hunger, aerobic fitness and, using complex, liquid energy tracers, daily food intake and energy expenditure. With standardised psychological questionnaires, they also explored whether the volunteers felt that virtuous, healthy actions now justified less-desirable ones later.

They then randomly assigned some to continue their normal lives as a control, while others began supervised exercise programs. In one, people exercised three times a week on treadmills or exercise bikes until they had burned eight calories for every kilogram of their body weight, or about 700 calories a week for most of them. The other program upped the exercise to 20 calories for every kilogram of body weight, or about 1,760 calories a week. 

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