The American Heart Association recently released a statement suggesting that when and how often you eat could affect your risk for developing heart disease and stroke. Until now, the focus on diet has been primarily about how much and what you eat. This news—that the time of day you eat may also be important—could change the way people are able to manage their health.
Our bodies have natural daily patterns called circadian rhythms that occur roughly over a 24-hour cycle. Many biological processes are driven by circadian rhythms, including when you go to sleep and wake up, your body temperature, heart rate, blood pressure and the release of various hormones. A “master clock,” a tiny group of cells called the suprachiasmatic nucleus (SCN), located in the hypothalamus area of the brain manages circadian rhythms. This master clock is mostly controlled by changes in light.
Every cell in the body also has its own internal clock called a “peripheral clock.” Peripheral clocks make sure all of the cells’ functions are coordinated with the master clock. Animal studies show us the importance of keeping peripheral clocks in sync with the brain’s master clock. For example, when the peripheral clock in a mouse’s heart is disrupted, the mouse develops heart failure and dies at a much younger age than normal mice.
Unlike the master clock, peripheral clocks are more responsive to the availability of food than changes in light. As a result, eating at the “wrong” time of day could shift the rhythms of the peripheral clocks so they are out of sync with the master clock. For example, shift workers who work in the middle of the night are active when they would normally be asleep and eat at times when their body doesn’t expect food. They are at much greater risk for being overweight, becoming insulin resistant and developing cardiovascular disease because their master and peripheral clocks are likely to be out of sync.
Research in mice has shown that if they consume a high-fat meal at the end of their active period (the equivalent of a high-fat dinner for humans) they gain more weight, develop insulin resistance and have impaired cardiac function compared to mice that eat the same high-fat meal at the beginning of their active phase (breakfast).
Studies in people suggest that eating meals late in the day is linked to negative health effects, but a direct relationship has not been shown. Nevertheless, if when you eat is just as important as what you eat, it might not hurt to eat your larger meals earlier in the day if you can.
John Chatham, DPhil, FAPS, is a professor of pathology and director of the Division of Molecular and Cellular Pathology at the University of Alabama at Birmingham.