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.
Our metabolic functions, as controlled by the circadian clock, evolved to cycle in harmony with the Earth’s daily rhythms, to optimize processes such as energy use and storage. In doing so, we became adapted to eat during the daytime, and maladapted for eating at night. Opposing these rhythms, as many of us now do, may challenge our bodies’ normal cycles and set us up for disease. “Like many evolutionary arguments, it’s hard to prove,” says Lazar. “But otherwise it’s hard to imagine why else we would need things so tightly linked to the Earth’s rotation.”