Dietary recommendations typically focus on the quality and quantity of food rather than on when it is consumed. But emerging evidence helps illustrate the relationship between meal timing and its physiological effects. A study published in April 2015 in the Proceedings of the National Academy of Sciences demonstrated the intersection of the circadian system (internal body clock), the behavioral cycle (including the sleep/wake and fasting/feeding cycles) and the impact of these patterns on glucose tolerance levels.
The study, which followed 14 healthy participants, found that after consuming identical meals, glucose levels were 17 percent higher (meaning lower glucose tolerance) in the evening than in the morning, independent of when a participant had slept or eaten. Additionally, simulated night work (sleeping during the day, having breakfast at 8 p.m., etc.) was associated with lower glucose tolerance throughout multiple days. Low glucose tolerance over time typically results in Type 2 diabetes.
This has crucial implications for both shift workers and people who work a 9-to-5 schedule. It has long been reported that shift workers (those who work outside a typical 9-to-5 schedule, often at night) are at an increased risk for certain ailments; this study indicates shift work as a risk factor for Type 2 diabetes.
Past research also has found that women involved in shift work have an increased risk of cancer and diabetes. Even for those who work regular hours, consuming carbohydrates in the morning may be less detrimental to glucose levels than when eating them at night. But why? There are two theories about what is behind glucose tolerance changes: a reduction in the function of beta cells (responsible for producing insulin to manage blood sugar levels), and a decreased insulin sensitivity.
The misalignment of one's internal clock could be due to light exposure. Light works as a major cue to reset the brain's clock. When mealtimes do not match sleep-wake cycles, a disconnect emerges. Scientist Satchin Panda of the Salk Institute explains, "When the clocks of our body are out of sync … then our body stores extra fat as energy. And over a long period of time, that can lead to Type 2 diabetes, obesity and increased risk for heart disease."
More research is needed to analyze these mechanisms and see if mealtimes can change circadian alignment for the better. Similarly, developing eating time strategies that can improve glycemic control could be helpful for both 9-to-5 and night-shift workers. Economic, social, biological and nutritional habits are equally important in determining an individual's overall health.
The exciting news is that, unlike our genetics that can predispose us to certain chronic illnesses, we have the ability to choose what we eat and when we eat it. These choices allow us to play a role in preventing illness and managing our health.