Running on empty. Nutrition professionals , researchers debate the pros and cons of fasting

Intermittent fasting is where one does not eat at certain times of the day or specific days of the week. This rather stark approach to weight control appears to be supported by science, not to mention various religious and cultural practices around the globe. It seems to yield the benefits of calorie restriction, which may ultimately reduce the risk of some diseases and even extend life. Some fasters, in fact, ultimately switch from regular, periods of hunger to permanent deprivation. They limit calories all the time.

Adds Mark P. Mattson, chief of the laboratory of neurosciences at the National Institute on Aging: "In normal health subjects, moderate fasting - maybe one day a week or cutting back on calories a couple of days a week - will have health benefits for most anybody." Mattson is among the leading research-ers on the effects of calorie restriction.

Not all nutrition professionals see the merits of fasting. Some think of it as a recipe for disaster, setting up a person for binge eating and metabolic confusion. During fasting, almost every system in the body is "turned down". The body changes how it uses fuel. Certain hormone levels fall. Growth stops. Reproduction becomes impossible.

Put simply, intermittent fasting appears to offer the same advantages as long-term calorie restriction - defined as eating at regular times but consuming 25 percent to 30 percent fewer calories than what is recommended for that person based on age, size and gender. People who eat this way tend to do so by filling up on nutrient-dense but low-calorie foods. They get all the protein, fiber, vitamins and minerals the body absolutely needs - and very little else. Occasionally going without food or reducing calories daily makes the body more sensitive to insulin, which helps maintain normal blood sugar levels. And animal studies suggest calorie restriction may reduce the risk of cancer by slowing the growth of abnormal cells.