WEIGHT CONTROL: HOW CALORIC IMBALANCE INCREASES BODY FAT

Caloric balance simply means:

kilocalories in = kilocalories out.

Estimating "calories in" is easier than estimating "calories out." Since exact estimates of caloric expenditure outside of a research lab are impossible, discussions of weight-control focus on calories eaten. However, individuals eating many calories are not necessarily overweight, because physical activity can mitigate the effects of their caloric imbalance. As an example, consider lumberjacks who use manual labor (not power saws) to cut trees, eat 4500-8000 calories per day, and are very muscular, with low percentages of body fat. They do not gain body fat because their voluntary caloric expenditure allows their net caloric balance to be zero (6000 calories in minus 6000 calories out = zero change in body fat).

A relatively small positive caloric imbalance (i.e., calories in > calories out) each day translates to excess fat. A positive caloric imbalance of only 10 kilocalories each day for 365 days equates to the caloric equivalent of 1 pound of fat at the end of 1 year:

10 positive calories over caloric balance x 365 days per year = 3650 positive calories per year

1 pound of fat = about 3500 kilocalories

1 pound of fat per year x 20 years (from age of 20 to 40 years) = 20 pounds of fat gained in 20 years, which is what many middle-aged Americans gain!

Simply put, a positive caloric imbalance is the result of eating too much and/or moving around (exercising) too little.

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