For the first time in its 93-year history, the American Heart Association has released a "scientific statement" on meal timing and frequency, and how they can affect weight and cardiovascular disease. The advisory committee behind the statement — a mix of physicians and nutrition researchers — note several reasons for the review's importance now. These include rising rates of obesity, heart disease and diabetes, as well as increased professional and popular interest in meal-timing topics.

For example, is breakfast good or bad for health and weight control? Does fasting reduce body weight? Can it improve glucose control? What about calories consumed after dinner?

"Americans have an around-the-clock lifestyle, so food consumption also occurs at nearly all hours," says Marie-Pierre St-Onge, associate professor of nutritional medicine at the Columbia University Medical Center and chair of the AHA committee. "Animal studies have shown that this can have adverse effects on health. Now is the time for studies on optimal food consumption times for humans."

In general, the 27-page AHA statement concludes that breakfast remains an essential daily meal for optimal well-being. The advisory group also says it thinks that intermittent fasting holds promise for weight loss. Intentional planning of meals and snacks can maximize the benefits of healthy food consumption while minimizing pitfalls such as excessive snacking and late-night consumption.

Meal timing makes a difference, the advisory committee notes, because the body has a system of internal "clocks" that regulate all aspects of metabolism. Many of these clocks are more affected by food consumption than by daylight and nighttime. For example, experiments have shown that mice gain more weight and develop more diseases when fed around the clock than when fed only in a "window" of nine to 12 hours. This occurs even though total calorie consumption remains the same in both conditions.

On key aspects of meal timing and frequency, the committee made the following observations:

- Breakfast

Twenty to 30 percent of Americans don't eat a traditional breakfast. This proportion is still increasing, and it parallels the rise in obesity rates. In one study of 20- to 39-year-olds, those who regularly consumed a breakfast cereal were 31 percent less likely to be overweight or obese. Also, three large-group studies have shown significantly lower diabetes rates among breakfast eaters.

- Intermittent fasting

Interest in this popular weight-loss approach has mushroomed so much that it's challenging to track all the new diets. The phenomenon has grown too fast for science to keep up. Still, some early results are promising. If a fasting plan reduces overall calorie consumption, subjects should lose weight and reduce glucose concerns. Every-other-day fasting produces better results than 5:2 fasting. A big caveat: Nothing is known about long-term success and health outcomes linked to intermittent fasting.

- Meal frequency

The idea of "grazing" one's way through the day has long had advocates who claim the practice can increase energy and decrease hunger. However, the AHA council found little support for the strategy, at least in research documenting weight loss and health enhancement. There have been a number of small studies with impressively bizarre designs — 17 mini-meals a day? — but not enough to reach a strong conclusion.

The advisory committee listed eight ways physicians and nutritionists might help their patients improve food-consumption patterns. For consumers seeking direct action, the following six are most instructive.

1. Eat more earlier in the day, and less later, distributing calorie consumption over fewer hours of the day.

2. Give your body an ample overnight "fast," as that's when much important metabolic work is done.

3. Consider intermittent fasting to lower total calorie consumption and body weight.

4. Plan your meals and snacks to minimize hunger and achieve portion control.

5. Reduce consumption of high-calorie beverages.

6. Eat more slowly as a possible means to decrease calories and increase satiety.