Summer Weight Gain Is Surprisingly Common — But Not Inevitable

Does your beach bod seem to disappear as the summer progresses? You’re not alone. Although weight gain is seen as a winter sport, gaining weight when it’s hot out is much more common than people think. And like a thunderstorm on a sunny day at the beach, it sneaks up on parents and kids alike.

Two recent studies suggest that children lose weight during the school year and gain weight in the summer due to increased consumption of sugary drinks and decreased structure when it comes to meals, activity, and sleep. It’s possible similar variables cause summer weight gain in adults.

There’s evidence that people generally sleep less during the summer, due to increased daylight exposure and just being too hot to sleep comfortably, and sleep deprivation increases the production of cortisol — a stress hormone that drives sugar cravings, swelling, and overall weight gain.

Adults also tend to diet in preparation for the summer, which really prepares them to pack on the pounds. “Summer weight gain is often simply the biological response to pre-summer attempts at weight loss,” says health coach and fitness specialist Ragen Chastain. “That lose-gain cycle can be compressed with more extreme dieting. So that crash diet they sold you to get your summer body will actually be likely to give you your summer weight gain.”

The lose-gain cycle Chastain is referring to is often seen in crash or yo-yo diets, or regimens designed for rapid weight loss that are rarely sustainable and often backfire. When people try to lose weight a month before vacation instead of gradually throughout the year, it depletes their metabolism in several ways.

Calorie deprivation slows thermogenesis, the amount of energy the body spends digesting food, while increasing overall fatigue, which discourages exercise. Extreme dieting also leads to muscle breakdown, which means fewer calories burned both during physical activity and while resting. Likewise, depriving the body of nutrients further disrupts sleep, which takes a toll on a person’s metabolic rate, studies show.

Once summer starts and these diets end — or just get cheated on a lot — an uptick of parties, barbecues, vacations, and the all the high-calorie indulgences that come with them create a perfect storm for summer weight gain.

Although warm temperatures encourage physical activities, really hot ones have the opposite effect, and people opt for sedentary summer days blasting the A/C. The American College of Sports Medicine recommends canceling outdoor exercise when the heat index is above 90 degrees, for anyone who works out regularly. For those who are not as fit, the ACSM suggests tapping out closer to 86 degrees and calling off any sport competitions or forms of extended activity at 82 degrees. That means in places with the highest heat indexes — which accounts for humidity as well as temperature — like Texas, Louisiana, and Florida, outdoor physical activity may not be a safe option for most of the summer season.

Regardless of where they live, people are more likely to put off exercising outside in the summer than in the winter due to the weather, according to one study. Consumer trends data confirms that many people fill this time with more beer, ice cream, and hot dogs, only making weight gain more likely.

That’s not to say that winter weight gain isn’t real. Research shows that people tend to pack on the pounds between October and January because of the holiday season, as well as the cold weather, which tends to decrease physical activity and increase the urge to indulge. However, exposure to cold weather helps activate brown fat to heat the body, which in turn burns other fat, and shivering burns calories further.

Still, if people are prone to gaining weight in the summer and winter, is everyone just getting fatter year-round? Not so. Spring, it turns out, is more conducive to healthy eating, exercise, and weight loss than any other season. Research shows that people are more likely to think about weight loss during winter and summer months, but the spring months are when they actually do it. On average, people consume 86 fewer calories per day in the spring compared to the fall, are more likely to exercise outside, and engage in physical activity for longer periods of time.

The best thing parents who don’t want to gain summer weight can do is treat it like spring. Think of it as summer with a little more structure, sleep, and healthy food.