Exercise and the Control of Body Weight

There is perhaps no better starting point than weight control. The ideal BMI is generally agreed to be in the range 18.5-25. Alas, an epidemic of obesity that started around 1980 has now swept the Western world. It has led to a secondary epidemic of diabetes and other conditions. All physicians therefore need to make weight control a priority issue. The core advice was neatly encapsulated by Orson Welles: “My doctor told me to stop having intimate dinners for four. Unless there are three other people.”

Integral to this is the encouragement for all patients to engage in regular physical activity. For health, an appropriate goal is 30 min of exercise, of at least moderate intensity, such as brisk walking, on most days of the week. Increasing the intensity to vigorous (such as jogging or fast walking) or duration (to 1 h) is better. People should be encouraged to engage in whatever form of exercise they enjoy and are therefore most likely to do on a regular basis (hiking, cycling, swimming, soccer, etc.). Where weight loss is a goal of exercise, then the laws of physics are crystal clear: more exercise burns more calories.

The optimal amount of exercise has been much debated. Our best evidence comes from a pooled analysis of cohort studies [8]. The researchers used the 2008 Physical Activity Guidelines for Americans as their reference point. This calls for 75 min/week of vigorous exercise or 150 min/week of moderate intensity exercise. Compared to people who have no exercise the mortality risk was reduced by 20% for those who exercise but at a level below the reference level, and by 31%, 37%, and 39% at 1-2, 2-3, and 3-5 times the reference level, respectively. Based on this evidence, everyone should be strongly encouraged to exercise at least to the reference level but preferably at double that level.

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