A recent study from UC San Francisco suggests that consuming snacks high in saturated fat, particularly during winter, may prompt the body to crave more calorie-dense foods. The research indicates that saturated fats can signal the body to store energy, mimicking natural seasonal patterns seen in mammals.
Traditionally, scientists believed that mammals determined how much to eat based on day length. For example, black bears eat heavily during longer days and fast during hibernation. However, this new study points to the balance of saturated and unsaturated fats in the diet as another important factor.
Researchers found that saturated fat influences a protein called PER2, which regulates both fat metabolism and circadian rhythms. Depending on intake levels of saturated fat, PER2 can signal the body either to burn or store fat.
As plants produce more saturated fats in summer, these compounds indicate abundance to mammals. In response, PER2 promotes energy storage for use during food-scarce winters. In autumn, when plants increase production of unsaturated fats for cold adaptation, eating these fats signals an end to abundance and prepares the body to use stored energy.
“It makes a lot of sense that both nutrition and the length of the day would guide seasonal behavior,” said Louis Ptacek, M.D., professor of Neurology and a senior author of the study. “If it’s fall and there are still plenty of nuts and berries to eat, the bear might as well keep eating rather than settle in for winter sleep, even while it senses that the days are getting shorter.”
The mouse-based study is reportedly the first to examine how nutrition helps mammals adapt seasonally. Published on October 23 in Science and partially funded by the National Institutes of Health (NIH), its findings could inform new treatments for obesity and type 2 diabetes.
Ptacek and co-senior author Ying-Hui Fu have previously shown that PER2 is involved in regulating daily sleep-wake cycles as well as fat metabolism. This led them to investigate how dietary fat combined with light exposure affects seasonal adaptation.
In their experiments simulating seasonal light cycles—ranging from equal periods of light/darkness to extended daylight or darkness—mice fed normal diets adjusted easily by changing activity patterns according to nightfall. However, mice on high-fat diets delayed their activity after darkness began.
Further tests compared diets rich in unsaturated versus hydrogenated (saturated) fats typical of processed foods. Mice consuming more hydrogenated fats had trouble adjusting their activity schedules under simulated winter conditions.
“These types of fats seem to prevent mice from being able to sense the early nights of winter,” said postdoctoral scholar Dan Levine. “It begs the question of whether the same thing is happening for people snacking on processed food.”
Modern factors such as year-round electric lighting and constant access to food may further disrupt natural rhythms tied to seasons. Levine noted that humans evolved mechanisms encouraging overeating during times when food was plentiful—a trait now maladaptive given continuous availability.
Disrupted biological rhythms have been associated with various health issues including sleep disorders, obesity, diabetes, and mental health problems; similar effects may result from disturbed seasonal cues. Researchers suggest correcting these imbalances could benefit overall health and help those affected by shift work or jet lag.
Levine advised caution with fatty snacks during 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.
