Eat in Sync With Your Body Clock
Thanks to the field of chrononutrition, a growing body of evidence suggests when you eat may matter as much as what you eat when it comes to wellness
The adage "eat breakfast like a king, a prince at noon, and a peasant at dinner," was first proposed by the medieval philosopher and doctor Maimonides to support good health, and it continues to resonate more than 1,000 years later. It turns out that Maimonides' advice was scientifically sound. Thanks to the field of chrononutrition, a growing body of evidence suggests when you eat may matter as much as what you eat when it comes to wellness.
Your Body Keeps the Pace
We're governed by circadian rhythms, which are fluctuations that follow a 24-hour cycle, give or take a few minutes. Circadian rhythms ensure that our bodies are in sync with our environment, and they affect how we react to food. Light and dark exert the greatest influence on circadian rhythms, but eating, sleeping and physical activity affect them, too.
By design, we're supposed to be awake and eating when the sun is up and fasting when it's dark.
Circadian rhythms are determined by internal "clocks." The suprachiasmatic nucleus (SCN), located in the brain, is the central time keeper. The SCN is coordinated with the patterns of light and dark produced by the earth's rotation, and it oversees myriad bodily functions, including when you sleep and wake. As evening approaches, the SCN directs the body to make melatonin, a hormone that induces sleep. When morning comes around, the SCN triggers the release of another hormone called cortisol to promote alertness.
The SCN is synchronized with peripheral clocks located in nearly every tissue and organ. Peripheral clocks oversee thousands of localized tasks that help the body run efficiently, including making nutrients and other compounds available to cells at the right time.
By design, we're supposed to be awake and eating when the sun is up and fasting when it's dark, but modern life makes it possible to override our natural circadian rhythms in a way our forefathers could not. Travel between time zones, sleep deprivation and sporadic eating causes misalignment that has consequences.
Though we're able to work against our internal clocks, we may be paying with our health in the long run. "We think we're smarter than our bodies, but we're not," says Joan Salge Blake, RDN, nutrition professor at Boston University.
Chrononutrition studies the mismatch between diet and lifestyle behaviors and our deeply rooted circadian variations, and the research is telling. "Disruption of circadian clocks seems to precipitate numerous disorders, including obesity and type 2 diabetes," says endocrinologist Karl Nadolsky, DO, assistant professor of medicine at Michigan State University College of Medicine.
Late Night Eating and Diabetes Risk
If there was a most important hormone, it would be insulin. Insulin allows cells to absorb glucose and use it as a source of energy and helps maintain normal blood glucose levels.
People in the U.S. eat 30% or more of their calories at dinner, and about 60% of us also eat well past 9 PM, when our internal clocks are preparing us for sleep.
Insulin has circadian rhythmicity. Insulin levels are naturally higher in the morning, which means the body is best equipped to handle food earlier in the day. However, people living in the U.S. eat 30% or more of their calories at dinner, and about 60% of us also eat well past 9 PM, when our internal clocks are preparing us for sleep. A 2023 study in the European Journal of Nutrition found that regularly snacking after 9 PM resulted in higher levels of hemoglobin A1C, a sign of diabetes risk.
"It's better for your body to eat more of your calories earlier in the day and taper them as the day goes on to be in better alignment with your metabolism and energy needs, which may also improve the quality of your diet," Blake says.
Indeed, nighttime snacking is more likely to include high-calorie, sugary or fatty foods such as cookies, candy and snack chips than plain fruits and vegetables. After-dinner snack choices matter because as the sun goes down, rising melatonin levels reduce insulin secretion, which makes it harder to regulate your blood glucose.
Eating Earlier Aids Weight Control
Consuming the majority of your calories at breakfast and lunch could make it easier to control your weight and help to body burn fat. In a study of people ages 51 to 63, eating more earlier in the day combined with no eating after dinner enhanced the use of fat for energy compared to eating the same number of calories at night. Metabolizing more fat for energy may help limit or reduce body fat stores.
Starting to eat earlier and finishing earlier may curb hunger throughout the day so that you eat fewer calories.
Starting to eat earlier and finishing earlier may curb hunger throughout the day so that you eat fewer calories. When people participating in a study published in Cell Metabolism had an early breakfast and an early dinner, they reported less hunger than those who ate a late breakfast and a late dinner. It's possible that eating earlier influences the levels of hormones that regulate hunger and satiety. The later-eaters had lower levels of leptin and more ghrelin in their blood. "Ghrelin is our 'hunger hormone,' while leptin is a hormone that reduces appetite," Nardolsky explains.
There's more research supporting eating earlier for weight control. One study found that taking in more of your total daily calories after waking up and fewer of them close to bedtime was associated with less risk for being overweight, but the relationship was stronger in so-called early birds – people who go to bed earlier and wake earlier.
How Sleep Affects Hunger
As anyone who has ever worked night shift, stayed up all night caring for a loved one, or sleeps fitfully for any reason, knows, inadequate sleep can lead to daytime fatigue and a lack of enthusiasm for eating a balanced diet. It can also make you hungrier.
Just a couple nights of sleep deprivation are all it takes to disrupt the regulation of leptin and ghrelin. A review that analyzed the results of seven studies found that inadequate sleep resulted in greater hunger and a bigger appetite for salty and sugary foods. It's no surprise, then, that chronic fatigue is associated with an increased risk of having obesity, which could be related to higher-calorie food choices during the day.
Sleep deprivation can also increase insulin resistance which may ultimately result in type 2 diabetes. "Sleep quality is very important for appetite, metabolism, nutrition, exercise and energy balance," Nadolsky says.
Fast Longer for Less Cardiovascular Disease
Meal timing may affect the risk for stroke and other cardiovascular disease. In a Nature Communications study, dining after 9 PM was associated with a 28% increase in risk of cerebrovascular disease such as stroke as compared to eating the evening meal before 8 PM, especially in women. The authors noted that people who ate later dinners also drank more alcohol, went to bed later, and had more erratic eating patterns.
Choose satisfying nutritious foods for snacks rather than treats (like cookies or candy) most of the time and limit the size of after-dinner noshes.
In other research, men who consumed at least 40% of their daily calories after 7 PM experienced greater damage to their arteries that typically precedes the onset of cardiovascular disease. Eating fewer calories at night is also associated with lower levels of artery-clogging cholesterol.
Stay In Sync for Better Health
Chronobiology is a burgeoning field, and researchers don't yet have all the answers about how eating relates to our internal clocks. Until they do, stick with these tips to stay aligned with your internal time to better support your health.
Eat satisfying meals throughout the day. "Avoid banking and consuming the majority of your calories for later in the day and evening," Blake suggests. "This bottom-heavy eating pattern may cause you to skip breakfast because you're not hungry when you wake up, which perpetuates this bottom-heavy eating pattern."
It's a good idea to eat within two hours of waking up because your body expects food in the morning. If you're not hungry for breakfast, you may be eating too much at night. Include adequate amounts of protein and fiber in every meal to keep yourself fuller for longer, particularly at dinner. A satisfying dinner helps reduce nighttime snacking.
Get enough sleep. "Sleep is the unsung hero of health and needs to be optimized," Nadolsky says. Regular sleep is necessary for the proper functioning of your internal clocks. It can be harder to fall asleep and stay asleep as you age but try to go to bed at the same time every night and wake at the same time each morning, even on the weekends. Avoid naps as they may interfere with nighttime sleep. If you are chronically sleep deprived, speak with your doctor about solutions.
Snack smarter. Choose satisfying nutritious foods for snacks rather than treats (like cookies or candy) most of the time and limit the size of after-dinner noshes. Avoiding nighttime snacks altogether may improve sleep.
Limit or avoid alcohol. Alcohol is a relaxant, but it prevents you from getting the deep sleep you need, possibly by disrupting the circadian rhythms of melatonin and cortisol, the hormones that rule your sleep/wake cycle.
Ward is the author or co-author of eight nutrition, food, and health books. Her most recent book is The Menopause Diet Plan, A Natural Guide to Hormones, Health, and Happiness (co-author). Ward lives in the Boston, MA, area. Read More
