Few environmental factors are as reliable as the 24-hour day, and an evolutionary argument can be made for why the diurnal rhythms of the Earth’s rotation are so coupled with human metabolism. Our behavior, our physiology, and our biochemistry reflect the daily cycles of the planet, and people who fall out of sync with these cycles are more likely to suffer from diabetes, obesity, and heart disease. Gastrointestinal disorders, depression, and other ailments are also more common among people who don’t have normal sleep habits. But according to new research, it’s not just disrupted sleep that can lead to these myriad physiological symptoms; it’s also the altered patterns of food consumption that go along with keeping such strange hours.
Shift workers who punch in in the evening have offered epidemiologists a glimpse into the importance of keeping normal sleep-wake patterns—that is, with activity coinciding with daylight. It’s been shown repeatedly that these employees are prone to developing metabolic disorders, and one review of the research concluded that night-shift workers are 40 percent more likely to develop cardiovascular disease.1
The mechanisms for these associations have been less clear, but a wealth of animal studies and emerging research on humans implicate the timing of eating as an important factor in maintaining energy balance and good health. In rodents, “simply restricting feeding to incorrect times has adverse consequences,” says Joe Bass of Northwestern University. Mouse studies have shown that a high-fat diet, freely available around-the-clock, will make the animals obese and unhealthy. But if mice are fed only at night—when these nocturnal animals are normally active—the untoward metabolic effects are drastically reduced, despite consuming the same number of calories.