Women in both groups lost weight after 12 weeks, but those who ate the large meal in the morning lost two and a half times as much as those eating the large dinner. The large-breakfast group also lost more body fat — especially belly fat — and saw more improvement in metabolic factors like fasting glucose levels.
“We observed that the time of the meal is more important than what you eat and how much you eat — it’s more important than anything else in regulating metabolism,” Dr. Jakubowicz said, attributing that to the body’s biological clocks.
Artificial lighting, changing eating patterns, shift work and other variables of modern life can disrupt our internal system of biological clocks, so they are often out of sync, said Courtney M. Peterson, an assistant professor in the department of nutrition sciences at the University of Alabama at Birmingham. While bright light is the dominant timing cue for the body’s master clock in the brain, the peripheral cells and tissues in the body also have biological clocks, and food intake is an important factor for setting their time zones, she said. Ideally, all of the clocks should be in sync and in the same time zone.
“If your timing to light exposure is out of sync with the timing of meals, it’s like your clocks are at different time zones and don’t know how to communicate with each other,” Dr. Peterson said. “It’s like an orchestra whose musicians are playing out of time with each other,” and the result is “cacophony, not music.”
Intermittent fasting may have other advantages as well.
“Twenty years of work on animals shows that compared to those that have constant access to food, those on intermittent fasting diets live longer, their brains function better as they get older and the nerve cells respond to the period of going without food by increasing their ability to cope with stress,” said Mark P. Mattson, chief of the National Institute on Aging’s laboratory of neurosciences. “From an evolutionary perspective, it makes sense that animals in the wild — especially predators — would have to function optimally in a fasted state when they haven’t been able to obtain food.”
Dr. Kahleova says the take-home message is like the old proverb, to eat “breakfast like a king, lunch like a prince and dinner like a pauper.”
That may be a difficult prescription to follow, since family life and social get-togethers so often revolve around sitting down to an expansive meal at the end of the day. Dr. Kahleova suggested making the evening meal smaller as often as possible.
“The message is very straightforward: Make breakfast your largest meal of the day, and eat dinner as your lightest meal of the day,” she said.