Eating by the Clock, the One Inside You

Food intake needs seem to have their own rhythm.

Posted Nov 17, 2020

Eating was so simple in the fairly recent past. We ate or slept through breakfast, ate lunch more or less in the middle of the day, and had dinner relatively soon after arriving home in the late afternoon or early evening. And we sometimes snacked during a television commercial a few hours later. If we ate out at a restaurant or someone’s home or at a catered social event, the timing of the meal might be altered, but we didn’t think that very important. At least not to our overall health and well-being.

But according to a relatively new field of nutritional interest, chrono nutrition, when we eat may have positive or negative effects on our health. Chrono nutrition arises out of our understanding that there is an internal clock located in the suprachiasmatic nucleus (“SCN”) in the hypothalamus that regulates many physiological activities in our body. This clock imposes a light-dark, day-night rhythm on many daily bodily functions, such as our sleep/wake cycles, the autonomic nervous, and core body temperature.

Our body contains other so-called peripheral clocks that regulate on a 24-hour (more or less) cycle the timing of digestion, the release of hormones, appetite, and physical activity. Traveling outside one’s time zone brings us face to face with the disruption in our bodily functions caused by the disconnect between what the clock in the new time zone says and our internal clock. Being wide awake at 2 a.m. in the new time zone (going west to east) or hungry at 4 a.m. (going east to west) makes us realize that our body is out of sync with the rhythms of the new time zone.

This relatively new field of chrono nutrition suggests that our internal clocks may determine many aspects of our behavior, such as what we eat and our alcohol consumption, as well as how much we smoke and exercise. According to a recent review, the authors give numerous examples of the correlation between food intake and whether our chronotype is morning (early riser) or evening (delayed sleeper). In one study they cite, those with a morning chronotype ate 0.25 more servings of fruit and 0.13 servings of vegetables each day than adults with an evening chronotype. Having an evening chronotype was also associated with a higher intake of wine, chocolate, and sugar, but a lower intake of starchy carbohydrates, protein, fiber, and folic acid, i.e., less time spent in exercising but more in smoking. Evening chronotypes also tended to watch more television, but whether this was because more interesting shows may be on schedule for later in the evening or some innate biological reason was not addressed.

But how does one know one’s chronotype? Unfortunately, it is not as easy as determining who your ancestors are by a few drops of saliva. Extensive questionnaires have been developed, but they leave unanswered whether the self-described behavior is a result of an innate tendency to wake and sleep later or family, cultural, social, and economic circumstances. “If I didn’t have to wake early to make breakfast, take kids to school or daycare, begin an early shift, start a long commute or interact with foreign offices six or 12 hours ahead of my time zone, would I sleep later?”

Age also makes a crucial difference. Adolescents tend to sleep late if they can, and older adults often wake earlier in the morning than they wish. Seasonal differences have an impact on awakening and sleeping patterns. When sunrise ranges from 5:30 to 7:30 a.m., awakening can also vary, making one a chrono-morning person in June and an evening one in late December. Some tests of chronotypes incorporate testing saliva for melatonin, but so far, the tests have not proven consistent or reliable, according to this review.

Commonsense suggests that by the time we are adults, we know what our chronotype is, even though it may be at odds with the schedule we follow. Moreover, simply because there is an association between what people eat and their chronotype, there is no evidence for causality. Someone may eat chocolate at night because it can be consumed privately when the household is asleep. Leisurely dinners that stretch into the evening may be more likely to be accompanied by wine or other alcoholic beverages than the 5 p.m. supper with children who have to be bathed and put to bed soon after the meal is completed. And people in places such as Argentina and Spain that traditionally begin eating a dinner meal when most of us would be watching the late evening news don’t seem to be any more prone to eating more chocolate and less high-fiber food than the rest of us.

But many of us are aware of daily alterations in our mental performance, appetite, mood, fatigue and energy level, focus, and sleepiness throughout the day that might be imposed by our chronotype. What we may not realize is that what we eat or avoid eating at these times can adjust these shifts in behavior to our advantage. Many years ago, I wrote a book that suggested eating or avoiding certain foods to enhance mental performance and improve mood. The dietary suggestions were based not on chronobiology per se but rather on the effects that eating protein and carbohydrate had on two brain neurotransmitters (norepinephrine and serotonin).

When protein is consumed, one of the amino acids, tyrosine, increases norepinephrine synthesis and mental performance while carbohydrate intake, by allowing an amino acid tryptophan to get into the brain, increases serotonin, and subsequently calmness and relaxation. Caffeine increases alertness, and high-fat foods tend to make people feel mentally dull if eaten in large amounts. Thus you can, to some degree, enhance productivity, decrease stress, maintain alertness, and avoid fuzzy-headed fatigue that might be associated with your own biological rhythms by diet. Food may not cause you to wake up earlier or be able to stay awake later, but it may be able to alter how you feel in-between.