Dietary and nutrition recommendations typically focus on the quality and quantity of the food rather
than on when it is consumed.  New evidence has emerged to help shed light on the relationship between mealtime and its physiological effects.  This week, a study that will be published in the Journal of Proceedings of the National Academy of Sciences sought to demonstrate 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. 

Conducted at Bingham Young Hospital in Boston, subjects were monitored during “normal” days in which they ate breakfast at 8:00 AM and dinner at 8:00 PM and then flipped sleep and meal schedules: breakfast was eaten at 8:00 PM and dinner at 8:00 AM, and wakefulness through the night (1).

“The team found that glucose levels after identical meals were 17 percent higher (i.e., lower glucose tolerance) in the evening than in the morning, independent of when a participant had slept or had their meals. They also found that simulated night work (sleeping during the day, having breakfast at 8 p.m., etc.), lowered glucose tolerance throughout multiple days” (2). Remember, low glucose tolerance over time typically results in type 2 diabetes.

This has crucial implications for both shift workers and people who work a regular 9-5 schedule.  It has long been reported that shift workers (those that work outside of a typical 9-5 schedule, usually
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 published by the Yale School of Medicine also found that women involved in shift work have an increased risk of cancer and diabetes (3). Even for those that work regular hours, the data suggests that consuming carbohydrates in the morning will be less detrimental
to glucose levels than when eating them at night.  

There are two possible mechanisms theorized to be the cause of the glucose tolerance changes: [1] a reduction in the function of beta cells (responsible for producing insulin to manage blood sugar levels) and [2] it may also decrease insulin sensitivity.

Another study found the association between circadian rhythm (the internal clock) and metabolism.  One study found that for dieters, consumption of the main meal is more likely to lead to weight loss
than if the main meal is eaten at night. Researchers in Spain recruited hundreds of middle-age participants who were overweight and put them in a diet for five months.  The subjects who had eaten their main meal of the day before 3 PM lost 5 more pounds than those who at their main meal later
in the day.  All of the dieters ate a similar number of calories and had comparable physical activity levels. (4)

The misalignment of our internal clock is perceived to be due to light exposure.  Light works as a main cue to reset the brain clock.  When our meal times do not match our sleep-wake cycles, there is a disconnect between the different clocks that are present in all of our cells.  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” (4).

More research is needed to analyze these mechanisms and to see if meal times can change circadian alignment for the better. Similarly, it would be helpful to develop eating time strategies that can improve glycemic control in day-active and night-active workers.  This research demonstrates the intersection
between economic, social, biological, and nutritional habits; each component is 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 prevention of illness and management of our health.

Happy Eating!

Samantha Mogil, Nutrition Intern