Experts on nutrition are slowly beginning to realize that not all calories are created equal.

Many people still believe the colloquial phrase, “a calories is a calorie,” meaning that two diets with the same number of calories can’t lead to losing a different amount of weight. “We conclude that a calorie is a calorie,” write Andrea Buchholz and Dale Schoeller of the Department of Nutritional Sciences, University of Wisconsin-Madison in the influential American Journal of Clinical Nutrition.

But those people don’t know what they are talking about, as Professor Richard Feinman of the Department of Biochemistry, State University of New York Downstate Medical Center, cogently proved in his article,“‘A calorie is a calorie’ violates the second law of thermodynamics” in the BioMed Central Nutrition Journal.

“A calorie is a calorie” sounds nice and has a certain poetic ring about it that is equivalent to “a rose is a rose is a rose,” as Gertrude Stein wrote in one of her poems. But just like roses do come in different colors, calories come in different intensities.

How our bodies react to calories is especially important to people with diabetes. Most of us have a life-long struggle with our weight. Now, a new study indicates that the strength of the calories we consume depends on when we eat them.

Six professors from universities in the U.S. and Spain teamed up to report on “Timing of food intake predicts weight loss effectiveness” in the January 29, 2013, issue of the International Journal of Obesity. While only the abstract is free online, the senior author, Frank Scheer, kindly sent me the full-text. Dr. Scheer is director of the Medical Chronobiology Program and associate neuroscientist at Brigham and Women’s Hospital and assistant professor of medicine at Harvard Medical School.

Professor Scheer and his associates have found that it’s not simply what you eat but also when you eat it that can influence how much weight we lose. “Our results indicate that late eaters displayed a slower weight-loss rate and lost significantly less weight than early eaters,” he says.  “This suggests that the timing of large meals could be an important factor in a weight loss program.”

The researchers studied 420 overweight people who followed a 20-week weight-loss treatment program in Spain. Since the study participants lived in Spain, their main meal was lunch, when they consumed about 40 percent of their total daily calories. The two groups were early-eaters, who ate lunch before 3 p.m. (that’s early in Spain) and late-eaters, who waited until after 3 p.m. for their main meal. The researchers found that late-eaters lost significantly less weight than early-eaters and lost weight at a much slower rate. The late-eaters also had a lower estimated insulin sensitivity, which is a risk factor for diabetes.

Professor Scheer and his associates also found that timing of the smaller meals had no effect on their weight loss. However, the late eaters -- the ones who lost less weight -- also consumed fewer calories during breakfast and were more likely to skip breakfast altogether.