How Insufficient Sleep May Contribute to Weight Gain

As a new school year begins, many families find themselves waking teenagers long before they feel ready to get up.

This is not only a matter of staying up late by choice. During puberty, the body’s internal sleep clock shifts later, which can make early bedtimes harder to manage.

Health experts advise that teenagers get eight to 10 hours of sleep each night, yet about seven in 10 high school students do not meet that target.

Researchers at the University of Colorado Anschutz School of Medicine are examining what the loss of sleep may mean for health.

Their findings suggest that repeated short nights may quietly shape behaviors and body changes that increase the likelihood of unhealthy weight gain.

Sleep researchers Stacey L. Simon, Ph.D., and Seth Creasy, Ph.D., helped author a recent scientific review exploring sleep as a possible behavioral tool in obesity care. Published in 2025 and indexed in PubMed, the review combines evidence on how sleep affects eating, activity, and weight management.

Obesity is complex and cannot be traced to a single habit. Weight can be influenced by genetics, food access, family circumstances, stress, medications, physical activity, sleep, and many other factors.

Even so, sleep has drawn more attention because it may affect several of those factors at once. People who sleep poorly may wake up hungrier, crave different foods, feel too tired to exercise, and spend more time sitting.

Controlled studies in adults provide a useful clue. When sleep is intentionally shortened, participants often eat an extra 200 to 300 calories the following day, even when their bodies do not need the added food.

The reverse may also be true for people who usually sleep too little. In one study, habitual short sleepers increased their sleep to about seven and a half hours and, without being told to diet, consumed roughly 270 fewer calories per day.

Scientists are still trying to determine why. Sleep deprivation can disrupt appetite signals and may alter how full people feel after eating, which could make it easier to keep snacking after energy needs have already been met.

Tiredness may also change which foods seem most appealing. Brain research suggests that too little sleep can heighten reactions to rewarding foods, especially items high in sugar and fat that are easy to obtain and quick to eat.

Teenagers may be especially vulnerable because their sleep challenge is shaped by both biology and daily life. During adolescence, the internal body clock shifts later, so a teen may genuinely not feel sleepy at the hour needed to get enough rest before an early school day.

School schedules can worsen the mismatch. The American Academy of Pediatrics has recommended that middle and high schools begin at 8:30 a.m. or later, although many students still start earlier.

Modern teen life adds more pressure. Homework, extracurricular activities, anxiety, social demands, and phones or other electronic devices can all compete with sleep at night.

Too little sleep may also affect movement the next day. Studies have shown that adults on restricted sleep schedules can become more sedentary and spend more time sitting, even when they are awake longer.

Similar results have appeared in Simon’s research with teenagers. When adolescents who typically slept too little on school nights were allowed to stay in bed about an hour longer, they slept more and also cut down on sedentary time.

That matters because replacing late-night phone use with sleep may bring two benefits at once. It increases rest while also reducing time that might otherwise be spent sitting and possibly snacking.

Researchers are also exploring possible sex differences. Some evidence suggests that adolescent girls may have earlier internal body-clock timing than boys and may also report more insomnia, which could create a difficult mix of greater sleep need and poorer sleep.

The health concern goes beyond body weight alone. Short sleep and delayed sleep timing in adolescents have been linked to poorer insulin sensitivity, an early metabolic change that could contribute to future type 2 diabetes if it persists.

These studies do have limits. Associations do not prove that sleep loss directly causes weight gain, adult findings cannot always be applied to teenagers, and short lab studies cannot fully reflect years of real-life school, family, and social pressures.

Still, the overall pattern is hard to ignore: sleep appears closely tied to eating and movement, two major drivers of long-term health. Treating sleep as a basic health need rather than leftover time could make obesity prevention more realistic.

The main lesson is not simply to tell teenagers to go to bed earlier, since biology may make that advice ineffective. Better approaches may include steady routines, less late-night stimulation, attention to anxiety and workload, and school schedules that fit adolescent sleep patterns more closely.

Taken together, the research supports sleep as a promising addition to healthy-weight programs, though not as a cure-all. More long-term studies are needed, but helping teens sleep enough may improve several parts of health at once and make healthy choices easier during a stage when lifelong habits are forming.

If you care about weight loss, please read studies that hop extract could reduce belly fat in overweight people, and early time-restricted eating could help lose weight .

For more health information, please see recent studies that Mediterranean diet can reduce belly fat much better, and Keto diet could help control body weight and blood sugar in diabetes.