Research Identifies the Healthiest Time of Day to Eat

Calories consumed should be less than calories burned. That’s the mantra for most weight-loss diets. Why, then, does this approach so often fail?

Lately, we’ve been told that the time of day when we consume our calories also matters. In fact, this makes a lot of sense. The human body does not behave like a blast furnace, burning up anything we toss in, no matter the time of day. Not surprisingly, biorhythms also play an important role in how the body handles food. The question then becomes: When is the best time to eat?

One popular diet emphasizes eating during a restricted period of the day. This diet, called the 16:8 diet, requires that you skip breakfast and consume all your calories between noon and 8 p.m. A recent study investigated the effectiveness of the diet.

The study followed 116 adults (men and women, 18 to 64 years old) who were overweight or obese. A control group ate three structured meals per day. The time-restricted eating group ate all they wished from 12 p.m. until 8 p.m. The primary outcome measured was weight loss. In addition, the study monitored a variety of metabolic biomarkers such as fat and lean mass, fasting insulin, fasting glucose, and total and resting energy expenditure. The study determined that consuming all of one’s daily calories between noon and 8 p.m. produced a very modest (1.17 percent) weight loss that was not significantly different from the results of the control group.

The study concluded that “time-restricted eating is not more effective in weight loss than eating throughout the day.” Unfortunately, their conclusion went beyond their data. The study only examined a single eating period from noon until 8 p.m. What happens if a majority of your daily calories are consumed during a different time frame? The influence of biorhythms cannot be ignored. Studies have shown that disruptions in biorhythms can induce obesity and, conversely, obesity can disrupt normal biorhythms.

What would happen if you could only eat between the hours of 9 a.m. and 4 p.m.? Would you gain less weight and be healthier overall even if you ate a high-fat diet? The answer seems to be yes, based on how the body is influenced by our daily rhythms of eating and sleeping. (I discussed this idea more fully in my TED talk.)

Many studies have shown the negative consequences of ignoring the role of our biorhythms: Nightshift work, including the odd patterns of sleeping and waking that this lifestyle involves, can have many negative health consequences, including insomnia, high blood pressure, obesity, high triglyceride levels, and diabetes—collectively known as the metabolic syndrome.

In a recent series of studies, mice were given free access to a nutritionally balanced diet or a diet that was high (61 percent of calories) in fat. Some mice were allowed total access to the food at all times; others were only allowed access for an eight-hour window during the early phase of their normal active period. Mice given total all-day access to a high-fat diet (the standard American diet) developed obesity, diabetes, metabolic syndrome, and poor sleep-wake rhythms. A high-fat diet also led to the degeneration of the olfactory system, and as a consequence, food would lose much of its sensory allure.

Now for the good news: The mice that had time-restricted access to the high-fat diet were significantly healthier than the mice given all-day access to the same diet. These lucky mice lost body fat and had normal glucose tolerance, reduced serum cholesterol, improved motor function, and normal sleep cycles. Most surprising, the daily caloric intake of all groups did not differ, regardless of their diet or feeding schedule.

In the human test, overweight and obese women were divided into a breakfast group (700 kcal breakfast, 500 kcal lunch, 200 kcal dinner) or a dinner group (200 kcal breakfast, 500 kcal lunch, 700 kcal dinner) for 12 weeks. The breakfast group showed greater weight loss and waist circumference reduction. Fasting glucose and insulin decreased significantly in the breakfast group. Average triglyceride levels decreased by 33.6 percent in the breakfast group and increased significantly in the dinner group.

Therefore, it truly does matter when you eat. The take-home message from both animal and human studies is to eat a big breakfast, eat a small dinner, and never have late-night snacks. Skipping breakfast and then overeating in the evening play a significant role in weight gain and obesity. Furthermore, people who skip breakfast report not feeling as satisfied by their food and being hungry between meals. If this sounds like you, then it may be time to change your mealtimes.

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This is your new mantra: Eat breakfast like a king, lunch like a prince, and dinner like a pauper.

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