Researchers at the University of Sydney, Australia, asked the same question, then compared the effects of a high-fat breakfast with a breakfast that was mostly carbohydrates. The two breakfasts were balanced in terms of nutrients and calories.
Turns out that people in the high-fat group got hungrier earlier, reports the International Journal of Food Science and Nutrition. They started snacking between breakfast and lunch, so their total calorie counts went up. By contrast, people in the high-carbohydrate group could wait longer. As a side benefit, they were smarter and more alert during the day.