Square One

Richard Lehman’s Journal Blog on BMJ points attention to this wonderful JAMA article on nutrition this week. In Richard’s words, “this one-and-a half-page commentary article contains more sense than most large books on Clinical Nutrition.”

Here is an excerpt:

Body weight remains stable as long as the number of calories consumed equals the number expended through physical activities and metabolic processes. When energy intake increases above expenditure, the excess is used to build new tissue, and weight gain results. However, weight gain does not continue indefinitely. Carefully controlled overfeeding experiments show that calorie expenditure increases progressively because of the energetic costs of maintaining the newly created tissue.

A person who consumes an extra cookie every day will initially experience weight gain, but over time an increasing proportion of the cookie’s calories will go into repairing, replacing, and carrying the extra body tissue. After a few years of daily cookie eating, weight gain will level off at approximately 2.7 kg. Thus, a one-time step-up in caloric intake will cause body weight to increase asymptotically to a new, stable level.

The converse occurs when an individual reduces food intake. As body size diminishes, so does the amount of fuel needed to maintain and move it, and weight settles at a new steady level. In addition, weight loss produces changes in hormones, the autonomic nervous system, and the intrinsic efficiency of muscle that serve to conserve energy. Therefore, additional weight loss can only be achieved by a more severe diet or a more arduous physical activity routine. Most individuals do the opposite: after having achieved some weight loss, they resume their original diet and exercise habits. Consequently, weight gain recurs rapidly.

The body indeed does have a remarkable ability to keep itself “stable”; a huge evolutionary advantage for any species that is so endowed! The full article is here.