When it comes to weight loss, paying attention to your internal clock could be as important as counting steps or setting the stopwatch on your fitness tracker.
Your circadian rhythm, the 24-hour clock that governs bodily rhythms — ranging from sleep-wake cycles and body temperature to hormones and digestion — also appears to have an impact on your weight.
Changing the timing of sleep, meals and workouts can wreak havoc on circadian rhythms. In contrast, sticking to a specific schedule — and timing when you consume most of your calories — can aid in weight loss.
“We can optimize our performance by trying to achieve a match between our body clocks and time of day that we perform various tasks,” explains Robert L. Matchock, PhD, associate professor of psychology at Pennsylvania State University.
BIG BREAKFAST, SMALL DINNER
Research published in the journal “Obesity” found the timing of your biggest meal was linked to the number on the scale. Study participants who consumed 700 calories at breakfast, 500 calories at lunch and 200 calories at dinner for 12 weeks lost more weight and had a greater reduction in waist circumference than those who ate 200 calories at breakfast, 500 calories at lunch and 700 calories at dinner. The researchers noted that eating a bigger breakfast also helped reduce fasting glucose, insulin and insulin resistance, which could lead to a decreased risk of Type 2 diabetes.
A 2017 study reported similar findings, noting that those who ate a heavier meal at lunch lost 25% more weight than those who ate a heavier dinner — despite similar nutrient and caloric intakes.
Kristen Knutson, PhD, associate professor of neurology at the Feinberg School of Medicine at Northwestern University, admits that the link between circadian rhythm and weight gain is not fully understood but posits, “This association may be related to eating at the ‘wrong’ time, that is, when your body is not expecting you to eat. It could also be that eating in the evening impairs sleep, which has been associated with impairments in metabolism.”
TIMING AND REGULARITY MATTER
Shifts in the circadian system may also impact glucose tolerance, impairing your ability to lower blood sugar after an evening meal and causing your body to burn just half of the calories two hours after an evening meal that it does after an identical earlier meal.
In a new study, published in The American Journal of Clinical Nutrition, researchers examined data from 110 adults and found that eating late in the day increased the risk of metabolic syndrome, noting that those with the highest BMI and body fat percentages consumed most of their calories late at night. Based on their findings, researchers suggested that eating your last meal several hours before bed gives your body time to digest, decreasing the risk of storing fat.
“Sleeping and eating at regular times each day helps to keep circadian rhythms synchronized,” Knutson says. “Avoid eating in the evening and at night, and even give yourself a time window for eating food — for example, 8 a.m. to 8 p.m.”
While honoring your circadian rhythms is important, it’s not license to overeat. Regardless of when you eat, losing weight still requires counting calories but consuming them at certain times can be helpful.
“Jumping all around the clock from one day to the next (or from weekdays to weekends) is hard on the body’s circadian rhythms,” says Knutson. “Keeping a regular schedule of sleep, meals and exercise will help to optimize health.”