Recently, and without much public notice, a consensus statement was published in the American Journal of Clinical Nutrition which I think is monumental in understanding why losing and maintaining body weight is so difficult. This 6 page analysis of what is currently known in scientific circles about energy balance discounts the dogma that nearly all diet programs are founded upon; the notion that a pound of body weight is equal to 3500 kilocalories. Hence, most if not all weight loss programs have erroneously been built around the unproven but widely accepted “fact” that reducing dietary intake by 3500 kilocalories per week will lead to a loss of a pound a week.

The American Society for Nutrition and the International Life Sciences Institute formed a taskforce in May of 2011 charged with the goal of clarifying what is known about energy balance and their findings should be enlightening:

• Energy balance is a complex system involving many individualized factors including components of intake, output and storage which interact with each other. Those who “gain weight at the sight of food” will be comforted at the recognition that resting energy expenditure (REE) varies between and within individuals and cannot be explained by body composition. The study also remarks that there is a hierarchy of macronutrient effects on the magnitude of the thermal effect of food (TEF), which means isocaloric amounts of protein has a greater effect on TEF than carbohydrate or fat. So a calorie is not always a calorie, regardless of the source.

• Another interesting conclusion is that short term weight loss is really a reflection of a temporary energy imbalance. What the panel felt was a key point was that energy balance as a concept depends on the time over which it is considered. We generally compensate for energy imbalances over the short term but over the long term our intake and our expenditure don’t vary greatly. Since dietary carbohydrate intake has an impact on renal sodium excretion, which results in changes in extracellular fluid, short term changes in macronutrient composition despite calories being held constant, are not reflective of changes in body weight. As an example, every 10 calorie reduction in energy/day will lead to an eventual loss of 1 pound when the body weight reaches a new steady state. It will take nearly a year to achieve 50% and about 3 years to achieve 95% of this weight loss.

• A caution that this paper suggests is that people tend to compensate for increased exercise with elevating food intake and reductions in physical activity at other times of the day. When people who are attempting to lose weight reach a plateau, the authors state that it is not due to metabolic slowing but to failure to comply with their diet. Often this is due to biological and psychological drives to eat which are hard to control.

These experts conclude that since it is expected to take a relatively long time for human body weight and composition changes to occur, it is important not to have unreasonable expectations about the impact of dietary or exercise changes on body weight. More research needs to be done especially to identify the mechanism(s) responsible for how and why we compensate for differences in energy intake.