We've heard for some time that breakfast is the most important meal of the day, and more recently, that breakfast−eaters tend to weigh less than those who skip the meal altogether. But new research from the University of Nottingham in the UK has found that what women eat for breakfast may affect how much fat they burn during exercise later on, as well as how full they feel after lunch.

The team found that when women had eaten low-glycemic breakfasts, they burned almost twice as much fat as when they ate high-glycemic breakfasts.

The research team, led by Emma J. Stevenson, set out to determine how high− vs. low−glycemic breakfasts would affect fat−burning during exercise. The glycemic index is a measure of how quickly carbohydrates are broken down and affect blood sugar level. Low−glycemic foods take longer to break down, resulting in a slower climb in blood sugar; high−glycemic foods break down quickly and lead to a faster rise in blood sugar.

The team studied eight healthy women whose mean age was 24 and who were all sedentary before the study began. Each woman ate a high−glycemic breakfast in one portion of the experiment and a low−glycemic breakfast in a second portion. Breakfasts all contained the same amounts of carbohydrates, fats, and protein − the only difference was the glycemic factor. High−glycemic breakfasts contained "cornflakes and milk, white bread and jam, and a carbonated glucose drink" and contained about 1.5 grams of fiber, Stevenson said in an interview. The low−glycemic meals contained more fiber − 3.5 grams − and were made up of "muesli and milk, yoghurt and canned peaches, and a small amount of apple juice."

After eating one of the breakfasts and waiting for three hours, the women then walked for 60 minutes. Researchers drew blood at various intervals to monitor fat metabolism. The team found that when women had eaten low−glycemic breakfasts, they showed significantly more fat oxidation than when they ate high−glycemic breakfasts — in fact, they burned almost twice as much fat as when they ate high−glycemic breakfasts.

Another interesting finding was that on days when women had eaten low−glycemic breakfasts, they reported feeling fuller after lunch than when they had eaten high−glycemic breakfasts (even when lunches were identical). This indicates that the glycemic index for foods may have an effect not only on fat−burning during exercise later on in the day, but also on satiation several hours later.

Stevenson says that her results are particularly interesting because most studies of this kind have looked at men, often endurance athletes, who may not be good indicators of the general population.

The results should come as good news to those of us who have been sedentary in the past but are interested in getting in shape.

This study was published in The Journal of Nutrition's May 2009 issue.