Chronobiology is the study of how our bodies’ natural cycles—mental, physical, and emotional—are affected by the rhythms of the sun, moon, and seasons. Recent breakthroughs in this field have upended a key piece of nutrition dogma: the concept that a calorie is a calorie. As it turns out, it’s not just what we eat but when we eat. Because of our circadian rhythms—circadian coming from the Latin words for about and day—morning calories don’t appear to count as much as evening calories.

Have you heard the expression Breakfast Like a King, Lunch Like a Prince, Dine Like a Pauper? It speaks directly to the relationship between chronobiology and how we should eat.

Researchers randomized women into two groups given the same number of calories. One group was given a 700-calorie breakfast, a 500-calorie lunch, and a 200-calorie dinner, and the other was given the opposite—200 for breakfast, 500 for lunch, and 700 for dinner. Since they were eating the same calories overall, the two groups lost the same amount of weight, right? No. In addition to slimming nearly an extra two inches off their waistlines, the breakfast-heavy king-prince-pauper group lost 19 pounds compared to only 8 lost by the pauper-prince-king group despite eating the same number of calories. Eleven additional pounds lost eating the same number of calories. That’s the power of chronobiology.

Why do calories eaten in the morning seem to be less fattening than calories eaten in the evening? One reason is that more calories are burned off in the morning due to diet-induced thermogenesis, the amount of energy the body takes to digest and process a meal. So, a calorie is not just a calorie. It depends on when it’s eaten.

The information on this page has been compiled from Dr. Greger’s research. Sources for each video listed can be found by going to the video’s page and clicking on the Sources Cited tab. References may also be found at the back of his books.

Image Credit: Unsplash. This image has been modified.