The Mayo Clinic Diet blog

Is a calorie always a calorie?

By Donald Hensrud, M.D. November 10, 2012

It's been said for years that body weight ultimately depends on the balance between calories eaten and calories burned. Recently, this premise has been questioned as other factors have emerged that may affect weight.

For example, studies have shown that people who sleep less than 6 hours or more than 8 hours are at increased risk of weight gain. Factors affecting our weight may start even before we are born. Small babies that are born to expectant mothers who don't get adequate nutrition are at increased risk of weight gain later in life.

On the calorie intake side, a recent study reported that sugar intake increased the risk of obesity more in people who had a genetic predisposition to obesity. Another study reported that a low-fat diet lowered resting metabolic rate more than a low-carbohydrate diet. In this case, it's not clear differences in dietary fat vs. carbohydrate transmit into changes in weight. A long-term study showed that after 2 years there wasn't much difference in weight loss between a low-fat and a low-carbohydrate diet.

How do these factors affect weight independent from calories? It's possible they may affect metabolic processes or hormones in the body. Despite these associations with weight, it's important to keep the big picture in mind and not get too caught up with specific factors and details.

For example, there is some controversy over whether high-fructose corn syrup can somehow increase weight more than what is expected from its calorie content. However, the calorie content and the amount of high fructose corn syrup people eat have a much, much greater influence on weight than any other potential effect may have.

If people can change these factors, such as getting the right amount of sleep, it might help to better manage weight. However, the big picture is still that eating a healthy diet, which limits calories appropriately, along with increased physical activity is the most effective overall way to manage weight — and improve health long-term.

Nov. 10, 2012