You’re walking down the street early in the morning after having been up all night completing a project for your boss. The coffee shop on the corner beckons you as always. But today, this siren song is about more than just a cup of joe. Somehow, there is an irresistible urge to buy a donut or two as well.

If you’ve ever wondered why, read on.

The amount of sleep Americans say they get every night has declined from an average of approximately 8.5 hours in the 1960s to slightly less than 7 hours today. There are probably lots of reasons why, but they likely include 24/7 occupations, prolongation of the “day” with artificial lighting, the use of electronic devices at bedtime (blue-wavelength light from these devices delays sleep onset), and the widespread belief that sleep is less of a priority compared to other activities, whether they are work- or pleasure-related.

And today, not only do more of us sleep less, but we tend to weigh more, too. More than 30% of adult Americans are now obese, compared with less than 15% of adults in the 1960s. This “obesity epidemic” also has spread to children, with approximately 17% now considered obese. This is an alarming trend because obese children are likely to become obese adults.

Is there a link between the decrease in sleep duration and the rise in obesity? Compelling evidence suggests that there is. A number of large studies involving thousands of adults have generally found that short sleepers (defined as 5 hours or less per night, but sometimes 6 hours or less) were up to 45% more likely to be obese. We don’t have as much data on children, but one study found that kids who slept less than 7.5 hours per night had a three-fold greater risk of developing obesity over a 5-year period.

Studies also demonstrate that short sleepers don’t eat healthfully. Over all, their diets have less food variety, a greater percentage of calories from snacks, and higher amounts of sugar, caffeine, and alcohol. Furthermore, they tend to skip the main meals (breakfast, lunch, and dinner), and also tend to snack more. These habits promote weight gain and the eventual development of obesity.

Is there a scientific explanation for the eating behavior of short sleepers? Experimental studies indicate that sleep restriction leads to abnormalities in the processing of blood sugar (glucose) and changes in hormones that control appetite. For example, the hormone ghrelin stimulates appetite, whereas the hormone leptin reduces it. With sleep restriction, levels of ghrelin rise and those of leptin fall, thus leading to an increase in hunger and appetite. Additionally, these studies have observed that sleep-restricted individuals have a greater desire for high-calorie, high-carbohydrate foods.

So what do the data that link inadequate sleep with weight gain tell us?

The take-home message is that getting enough sleep is one way to lower your risk for weight gain and obesity. There is a tendency to put on pounds as one grows older. Inadequate sleep will only worsen this trend. If a person is already overweight or obese, weight loss will be more difficult without adequate sleep. From a societal perspective, the obesity epidemic, with its associated increases in the rates of several chronic conditions (e.g., heart disease, diabetes), places a greater burden on the health care system and contributes to rising health care costs. Adequate sleep deserves to be included with exercise and good nutrition as one of the essentials of good health.