You stayed up too late scrolling through your phone, answering emails or watching just one more episode. The next morning, you feel groggy and irritable. That sugary pastry or greasy breakfast sandwich suddenly looks more appealing than your usual yogurt and berries. By the afternoon, chips or candy from the break room call your name. This isn’t just about willpower. Your brain, short on rest, is nudging you toward quick, high-calorie fixes.

There is a reason why this cycle repeats itself so predictably. Research shows that insufficient sleep disrupts hunger signals, weakens self-control, impairs glucose metabolism and increases your risk of weight gain. These changes can occur rapidly, even after a single night of poor sleep, and can become more harmful over time if left unaddressed.

I am a neurologist specializing in sleep science and its impact on health.

Sleep deprivation affects millions. According to the Centers for Disease Control and Prevention, more than one-third of U.S. adults regularly get less than seven hours of sleep per night. Nearly three-quarters of adolescents fall short of the recommended 8-10 hours sleep during the school week.

While anyone can suffer from sleep loss, essential workers and first responders, including nurses, firefighters and emergency personnel, are especially vulnerable due to night shifts and rotating schedules. These patterns disrupt the body’s internal clock and are linked to increased cravings, poor eating habits and elevated risks for obesity and metabolic disease. Fortunately, even a few nights of consistent, high-quality sleep can help rebalance key systems and start to reverse some of these effects.

How sleep deficits disrupt hunger hormones

Your body regulates hunger through a hormonal feedback loop involving two key hormones.

Ghrelin, produced primarily in the stomach, signals that you are hungry, while leptin, which is produced in the fat cells, tells your brain that you are full. Even one night of restricted sleep increases the release of ghrelin and decreases leptin, which leads to greater hunger and reduced satisfaction after eating. This shift is driven by changes in how the body regulates hunger and stress. Your brain becomes less responsive to fullness signals, while at the same time ramping up stress hormones that can increase cravings and appetite.

These changes are not subtle. In controlled lab studies, healthy adults reported increased hunger and stronger cravings for calorie-dense foods after sleeping only four to five hours. The effect worsens with ongoing sleep deficits, which can lead to a chronically elevated appetite.

Why the brain shifts into reward mode

Sleep loss changes how your brain evaluates food.

Imaging studies show that after just one night of sleep deprivation, the prefrontal cortex, which is responsible for decision-making and impulse control, has reduced activity. At the same time, reward-related areas such as the amygdala and the nucleus accumbens, a part of the brain that drives motivation and reward-seeking, become more reactive to tempting food cues.

In simple terms, your brain becomes more tempted by junk food and less capable of resisting it. Participants in sleep deprivation studies not only rated high-calorie foods as more desirable but were also more likely to choose them, regardless of how hungry they actually felt.

Your metabolism slows, leading to increased fat storage

Sleep is also critical for blood sugar control.

When you’re well rested, your body efficiently uses insulin to move sugar out of your bloodstream and into your cells for energy. But even one night of partial sleep can reduce insulin sensitivity by up to 25%, leaving more sugar circulating in your blood.

If your body can’t process sugar effectively, it’s more likely to convert it into fat. This contributes to weight gain, especially around the abdomen. Over time, poor sleep is associated with higher risk for Type 2 diabetes and metabolic syndrome, a group of health issues such as high blood pressure, belly fat and high blood sugar that raise the risk for heart disease and diabetes.

On top of this, sleep loss raises cortisol, your body’s main stress hormone. Elevated cortisol encourages fat storage, especially in the abdominal region, and can further disrupt appetite regulation.

Sleep is your metabolic reset button

In a culture that glorifies hustle and late nights, sleep is often treated as optional. But your body doesn’t see it that way. Sleep is not downtime. It is active, essential repair. It is when your brain recalibrates hunger and reward signals, your hormones reset and your metabolism stabilizes.

Just one or two nights of quality sleep can begin to undo the damage from prior sleep loss and restore your body’s natural balance.

So the next time you find yourself reaching for junk food after a short night, recognize that your biology is not failing you. It is reacting to stress and fatigue. The most effective way to restore balance isn’t a crash diet or caffeine. It’s sleep.

Sleep is not a luxury. It is your most powerful tool for appetite control, energy regulation and long-term health.

Joanna Fong-Isariyawongse does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.