Helping your patients stay fit might have more to do with when they eat than what they eat, a recent study indicates.

Diet-induced obesity has been exclusively attributed to increased caloric intake from fat, according to the study authors (Cell Metab. 2012;15:848-860). However, they learned that when mice on a high-fat diet were allowed to eat for only eight hours per day, they ate just as much as mice that were allowed to eat around the clock (outside their normal feeding cycle). Yet the time-restricted mice showed improvements in their metabolic and physiological rhythms. For example, compared with the around-the-clock mice, the time-restricted mice gained less weight, suffered less liver damage, had less hyperinsulinemia and lower levels of inflammation and experienced improved motor coordination. 

Metabolic cycles that are tied to the circadian rhythms of various organs can be made less efficient when food is consumed throughout the day and night, having a negative impact on such processes as cholesterol breakdown and insulin production. A time-restricted eating regimen appears to be a useful nonpharmacologic strategy against obesity and associated diseases.

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Another study focusing on fat intake revealed that cholesterol levels rose when people switched to a low-carbohydrate diet. Ingegerd Johansson and colleagues reported in Nutrition Journal (2012;11:40) that among 140,000 adults in northern Sweden, fat intake decreased between 1986 and 1992, and then began to rise again beginning in 2002 (among women) and 2004 (among men). These increases coincided with the introduction of positive media support for a low-carbohydrate/high-fat diet.

BMI increased continuously for both sexes, but serum cholesterol levels decreased during the 1986-2004 period, remained unchanged until 2007, and then began to rise. The increase in serum cholesterol occurred with the increase in fat intake, particularly with intake of saturated fat and fats used for cooking and as bread spreads.

Johansson commented in a separate statement, that although low-carbohydrate/high-fat diets may help with short-term weight loss, the group’s findings show that long-term weight loss is not maintained and that this diet increases blood cholesterol, which has a major impact on cardiovascular disease risk.