You might think your holiday snacking habits are all about willpower, but your body may be responding to deeper seasonal cues.
A study from the University of California, San Francisco (UCSF), published in Science Translational Medicine, found that certain fats, especially the saturated and hydrogenated types found in processed snacks, may “trick” the body into thinking it’s summertime, a season when mammals naturally stock up on calories. The result? A biological push to store fat, even when food is abundant year-round.
Researchers studying mice discovered that the type of fat in the diet can influence a protein called PER2, which helps regulate metabolism and the body’s internal clock. When the mice ate more saturated fat, PER2 sent a signal to conserve energy and store fat, mimicking the way animals bulk up before winter.
In contrast, unsaturated fats, the kind found in nuts, seeds and other plant foods, sent a different message, helping the body adjust to shorter days and encouraging fat burning instead of storage.
“It makes a lot of sense that both nutrition and the length of the day would guide seasonal behavior,” said Louis Ptacek, MD, a senior author of the study and professor of neurology at UCSF.
The research team, which simulated seasonal light cycles and fat intake in mice, found that diets high in hydrogenated fat disrupted the animals’ ability to adapt to shorter winter days. Those mice became sluggish and shifted their activity later into the night, a sign their biological clocks were out of sync.
“These types of fats seem to prevent mice from being able to sense the early nights of winter,” said Dan Levine, PhD, a postdoctoral scholar in Ptacek’s lab. “It begs the question of whether the same thing is happening for people snacking on processed food.”
While the study was done in animals, the findings add to growing evidence that fat type, not just calorie count, affects how the body regulates metabolism. The researchers suggest that too much saturated fat, combined with artificial light and constant food availability, may confuse our natural rhythms and increase the risk of obesity and metabolic disease.
Levine advises resisting the urge to graze on fatty snacks, especially in winter.
“That one holiday cookie could turn into two cookies the next day, because you've now tricked your circadian clock into thinking it's summer,” he said.
This study was supported by multiple public and private research organizations, including the National Institutes of Health and the Novo Nordisk Foundation.