Although your body isn’t an actual watch, it does have an internal clock that runs approximately every 24 hours. This “circadian rhythm” keeps your body functioning on a schedule. It helps your body adjust to environmental changes, sleep, and behaviors like eating.
It’s clear that what foods you eat can affect your body. But when you eat can also have an effect. The timing of your meals and snacks can affect:
- metabolic regulation
- body-weight regulation
- management of obesity-related diseases
- sleep cycle
Read on to learn about what science says about your circadian rhythm and eating habits, and how they impact each other.
Trying to figure out the best time to eat can be confusing, and researchers are looking to see if there are answers. One study showed that late lunch eaters (after 3:00 p.m.) lose less weight than early-eaters. It also found no difference in weight loss for the timing of breakfast and dinner meals. Restricting when you eat to 6 a.m. to 7 p.m. can reduce overall calorie intake by 244, according to another study. This is most likely due to the fact that you eat fewer calories due to less time spent eating. A longer overnight fast can also help with increasing fat loss as your body has time to reach a state of ketosis, which indicates that the body is using fat for energy.
What about breakfast?
Research shows mixed results as to whether breakfast intake contributes to weight loss. One study found that people who ate breakfast saw reduce dietary fat intake and impulsive snacking. Another study found that people who ate more calories at breakfast didn’t necessarily eat less during the day. Breakfast patterns have a smaller role in daily intake than post-breakfast meals.
After reviewing studies regarding breakfast’s impact on weight, the United States Department of Agriculture recommends that people eat a nutrient-rich breakfast to help manage weight and improve overall nutrient intake.
The connection between the body’s natural biorhythms and weight gain is more than just what you eat. Restricting what you eat to a certain time every day sets your body on a schedule. Research shows that trying to delay this window can take multiple days before your body adapts. This may explain why splitting up three meals into six can be an adjustment for someone going on a diet.
Regular meal times also play a long-term role in body weight. Your body generally gets hungry every three to five hours, but it’s also used to your regular schedule. Try to eat at the same time every day. You can keep healthy, high-satiety snacks like vegetables and cheese around to eat between meals to curb your appetite.
In some cases of meal timing, switching when you eat bigger meals can make a difference. One study saw that obese women who ate more for breakfast than dinner lost more weight and had an improved metabolism.
Sleep loss disrupts your body’s internal clock and metabolism and can affect hormonal balance. Research suggests that this disruption can confuse your body’s signals for tiredness and hunger and increase your cravings for sugar and starchy foods.
One study found that mice who were exposed to light at night gained 50 percent more weight than mice who had truly dark nights.
One 2009 study found that people who ate and slept out of their circadian rhythm had symptoms of metabolic syndrome. Metabolic syndrome is the name for a combination of disorders that increase your risk for heart disease, stroke, and diabetes.
Why do we tend to snack at night?
We often think of diet as the quality of the food we eat, but it really also includes when you eat. Research suggests that messing with sleep and the body’s internal clock can cause you to eat at the wrong times and gain weight.
The “night owls” who got less sleep overall had:
- more fast food
- more soda
- fewer fruits and vegetables
- larger portions of food later in the day
Overall, they ate about the same amount of calories per day as people who slept normally, but calories consumed after 8:00 p.m. are more strongly associated with weight gain.
The 16/8 fast
If you exercise regularly and want to maintain lean mass, you may be interested in intermittent fasting (IF). IF is different from eating on a regular schedule, as you restrict your energy intake to certain time periods of the day. This study saw a decrease in fat mass and weight for people who practiced 16-hour fasting with an eight-hour eating window along with resistance training.
Research shows that IF can:
- have similar effects as intensive exercise
- reduce resting heart rate
- reduce blood pressure
- help with weight loss
- decrease risk of coronary artery disease
- suppress appetite
One study also suggests that IF works as an alternative to calorie restriction for weight loss in people with type 2 diabetes. Another study in mice found that IF had more benefits than permanent calorie restriction.
How to fast
One popular method of IF is the 16/8 fast, meaning you fast for 16 hours every day and restrict eating to an eight-hour window. For example, if your last meal was at 11 p.m., you wouldn’t eat until 3 p.m. the next day. But this method of weight loss on its own may not be as effective without exercise.
You may need to fast for three to four weeks before you see measurable results.
Potential side effects
Fasting can lead to vitamin deficiency and muscle loss if you’re not careful about what you eat. But you can also address these concerns with proper nutrition and strength training.
In general, intermittent fasting may not be right for your lifestyle. You may also find it hard to not eat for a lengthy amount of time or to avoid eating during social situations.
Calorie restriction is believed to be the most effective method of weight loss, but when you eat may affect how your weight loss journey goes. The recommended route to managing your food intake is to have an eating schedule that suits your lifestyle. You may find a food journal helpful to avoiding mindless eating.