Having the largest meal in the morning appears to have advantages for weight control compared with having a large meal in the evening, she said, since the digestive process and the action of insulin, the pancreatic hormone that the body uses to process the sugars in carbohydrates and store glucose, appear to be at their peak performance early in the day. As a result, “our body can use the nutrients as a source of energy the easiest,” Dr. Kahleova said.

A person eating the identical meal at different times of day might deposit more fat after an evening meal than a morning meal, she said.

Image Credit... Natalya Balnova

That’s because insulin action is more efficient in the morning, experts say. “If you give a healthy individual a big bolus of glucose in the morning, the blood glucose might stay high one or two hours before coming back to normal,” said Dr. Satchidananda Panda, a professor at the Salk Institute for Biological Studies in San Diego. “You take that same normal healthy individual and give them the same bolus of glucose late at night, and now the pancreas is sleeping — literally — and cannot produce enough insulin, and blood glucose will stay high up to three hours.” Doctors once called this “evening diabetes,” he said.

But many people snack all day long, Dr. Panda said. He asked volunteers to use a smartphone app to photograph everything they drank and ate throughout the day and found that even generally healthy people ate and snacked over a period of about 15 hours a day, stopping for an extended amount of time only when they were in bed.

In earlier experiments in mice, Dr. Panda and his colleagues found that when the animals were given unlimited access to a high-fat diet — “the equivalent of humans eating only ice cream, cheese and nachos” — they became obese in nine or 10 weeks, and developed insulin resistance or diabetes and high cholesterol a few weeks later. But when the mice had access to the high-fat diet for only eight hours a day, they did not become obese or diabetic, even though they consumed the same amount of calories as the animals who ate round the clock.

Dr. Daniela Jakubowicz, an Israeli researcher at the Wolfson Medical Center in Tel Aviv, has tested these principles in small clinical trials. For one study, she recruited dozens of obese and overweight women with metabolic problems and put them all on identical 1,400-calorie-a-day diets. The researchers told half the women to consume 700 calories at breakfast, 500 calories at lunch and 200 calories at supper, and instructed the other group to reverse the order. Regardless of when it was eaten, the large meal included foods like tuna, whole wheat bread, a tomato and mozzarella salad, skim milk and a small amount of chocolate.