Eating Late Is Really Bad for You

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You may have read that light coming into your eyes sets the body’s clock, technically known as our circadian rhythm. Fewer people know that when you eat, food shifts the clocks in tissues in your liver, muscles, and fat. Human beings evolved to eat only during daylight, which lasted 12 hours much of the year in the African savanna. That meant we didn’t eat for 12 hours a day. Sticking as nearly as possible to that plan may help you stay healthier as well as thinner.

It’s a surprisingly bad idea to skip breakfast, eat lunch or dinner late, eat a big bedtime snack, or eat in the middle of the night.

Weight Gain

Carrying enough fat to qualify as having obesity is not a matter of shame—but it does up health risks we've all heard about, including diabetes, dementia, and heart disease. Choosing when you eat is one of the tools you can put to work. Start by eating breakfast.

In a study with 776 participants, people who skipped breakfast were 80 percent more likely to have obesity. People who ate lunch after 12:30 (or dinner after 9:00 pm) were 60 percent more likely to have those extra pounds. That was true for both men and women at different ages and regardless of other factors that affect weight including your diet and exercise habits.

Similarly, a study of more than 3,600 Japanese nurses concluded that skipping breakfast helped push up their weight, regardless of how many calories they ate.

Pushing your calories early in the day, including a high-energy breakfast, is one remedy to manage blood sugar after meals in people with type 2 diabetes, again supporting the idea that timing affects how the body manages energy.

Odd hours seem to contribute to compulsive eating. When you eat late at night, you tend to eat more overall. Perhaps driven by hormone surges, we crave sweeter, starchier, saltier food at night, research suggests. In one study, night eaters ate about 300 more calories each day. Three years later, people who didn’t eat near bedtime had gained only 4 pounds, while night-eaters had put on 14.

An important exception may be the elderly, who may need late-night snacks if they don’t eat enough during three meals.

Acid Reflux

As many as 20 percent of Americans may suffer from gastroesophageal reflux disease (GERD), when stomach acid flows back into the throat, triggering heartburn, postnasal drip, hoarseness, chronic throat clearing, coughing, asthma, and even cancer. Common anti-reflux meds don’t seem to protect you against cancer—though the latest evidence suggests they don’t increase your risk, as some suspected.

Eating late in the day aggravates reflux, writes Jamie A. Koufman, who specializes in voice disorders and acid reflux. “Many of my patients find that eating earlier alleviates their allergies, sinusitis, asthma, sleep apnea and diabetes symptoms,” he says. Give your stomach at least three hours to digest before lying down to sleep, advises Jonathan Aviv, an ear-nose-and-throat specialist in acid reflux.

Breast Cancer

Eating breakfast late may increase your breast cancer risk—by about 17 percent for every hour you delay, according to a study of nearly 1,200 women with breast cancer in Spain, compared to more than 1,300 women who didn’t develop breast cancer.

If you eat late at night, other research suggests, you may up the chance of breast cancer recurrence.

While researchers work out the details of how our body clocks affect appetite, digestion, and their downstream effects, one point is clear: Early is better.