Meal timing affects multiple systems in the body that are closely connected with metabolism, appetite, and overall energy balance. Eating late can impact these systems in ways that contribute to weight gain.
1. Late-Night Eating Impacts Sleep
Eating close to bedtime may cause gastrointestinal (GI) discomfort, heartburn, and acid reflux, leading to sleep disruption. Indeed, eating a meal within three hours of bedtime may increase nighttime awakenings by up to 60 percent, according to research in young adults.
This sleep disruption can fuel weight gain by interfering with appetite-regulating hormones, leading to increased hunger and cravings the next day.
Late-night eating can also interfere with sleep. “Your body has a natural daily clock, called your circadian rhythm, and eating late goes against this rhythm,” says Dr. Corrado. This can affect the hormones involved in sleep and metabolism. Even if you fall asleep without trouble and don’t notice obvious symptoms, your sleep may be lighter or more fragmented, meaning your body isn’t fully resting or recovering overnight.
2. Late-Night Food Choices Tend to Be Poor
Research shows that people tend to satisfy late-night cravings with foods higher in fat, sugar, salt, and calories, rather than nutrient-dense options like fruits, vegetables, lean protein, and low-fat dairy. This isn’t poor willpower — our circadian rhythm naturally increases hunger and appetite in the evening, making us especially drawn to calorie-dense foods.
This may once have been an evolutionary advantage, as high-calorie, high-fat foods may have helped sustain our ancestors through periods of food scarcity, researchers note. Today, however, regularly consuming these extra calories (whether in the form of a meal or snack) right before sleep can contribute to weight gain over time.
3. Late-Night Eating May Increase Overall Calorie Intake
Research reveals that adults who eat a meal or snack after 8 p.m. consume an average of 300 more calories per day than those who stop eating earlier. Moreover, these extra calories typically come from salty snacks and sweets.
“If late-night eating is in addition to normal levels of food intake during the day, this can lead to a surplus of calories, resulting in weight gain,” says Jeff Stanley, MD, a board-certified internal medicine physician, and the medical director of Virta Health, a virtual clinic specializing in weight loss and metabolic health.
4. Late-Night Eating Affects Blood Sugar Control
Eating close to bedtime can disrupt overnight blood sugar control. One study found that eating dinner at 10 p.m. instead of 6 p.m. caused an 18 percent higher peak blood glucose that persisted for four hours. Late dinner participants also had elevated glucose and insulin (the hormone responsible for regulating blood sugar) levels the following morning after breakfast meals than earlier eaters.
These blood sugar spikes matter because elevated glucose triggers the release of insulin. Higher insulin levels also promote fat storage. Over time, repeated late-night eating with these blood sugar fluctuations may contribute to obesity and metabolic disease.
“Late-night eating, particularly with foods high in sugar or processed carbohydrates, increases insulin levels,” says Dr. Stanley. “One of the functions of insulin is fat storage, so elevated levels can lead to insulin resistance and obesity,” he adds.
5. Late-Night Eating Affects Metabolism
Research shows that eating late at night disrupts multiple metabolic processes in ways that may promote weight gain.
In one study of 16 participants, eating dinner later altered appetite-regulating hormones in ways that increased hunger throughout the day. At the same time, late eaters burned approximately 5 percent fewer calories daily compared with early eaters.
The study also found that late eating changed the expression of genes involved in fat metabolism, shifting the body from fat burning to fat storage mode. Together, these metabolic changes may lead to weight gain.
“Studies show that late-night meals can make you feel hungrier, slow down how many calories your body burns, and throw off your metabolism, or how your body uses food for energy,” Corrado explains. In fact, your body burns fewer calories digesting the same meal late at night than it does earlier in the day, she says.
