Anyone who has tried to lose weight before I’m sure is familiar with the magic number of 3,500. That is the number of calories believed to be equivalent to one pound of body weight. Simply lower your caloric intake by 500 calories per day, and you’ll lose one pound per week. If only it were this easy. For people who like dealing with numbers, equations like this make sense, but for those of us who have tried to make this equation a reality, it can lead to frustration when the scale doesn’t change at the end of the week or as quickly as we’d like despite our hard efforts.
Unfortunately, our bodies aren’t machines and don’t always react to changes in intake or expenditure as we’d like them to. A recent commentary in the Journal of the American Medical Association by Katan and Ludwig brings this equation to light with regards to public-health initiatives to influence the obesity epidemic (1).
Traditional thinking suggests that when energy intake exceeds energy expenditure, weight gain results; and when energy intake is less than energy expenditure, it leads to weight loss. In the short term this may be true, but it may not be as simple as a 500-calorie deficit per day. Katan and Ludwig point out that if someone were to consume a 60-calorie cookie every day for the rest of their lives, in theory, it should produce a one-half-pound weight gain in a month, six pounds in one year and 27 pounds in a decade; but this doesn’t happen. Overfeeding studies suggest that this additional 60 calories will result in about a six-pound weight gain, which will level off after a few years. These additional calories will go into repairing, replacing, and carrying the extra body tissue (1). The same thing happens with weight loss. The initial decrease in intake and expenditure will result in weight loss, but our bodies become very efficient and go into a conservation mode where these deficits will eventually stabilize. It will take an even greater reduction in calorie intake and expenditure to accomplish a new low. Although little changes can make a difference, when dealing with the obesity epidemic, it would take drastic reductions that would be unrealistic on a personal level, so public health initiatives will need to focus on food supply, manufacturing policies and environment to encourage change (1). 
Reference:
- Katan MB, Ludwig DS. Extra calories cause weight gain--but how much? JAMA. 2010 Jan 6;303(1):65-6.
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