Research has shown that dietary fat dictates seasonal eating patterns

New research from the University of California, San Francisco shows that our natural eating patterns are more closely linked to seasonal rhythms than previously thought.

Next time you’re tempted to search your pantry for snacks high in saturated fat – especially in the winter – you might want to consider that you may end up with an increased need for high-calorie snacks.

This is because from our bodies’ perspective, saturated fats – including the hydrogenated fats found in many snacks – signal the arrival of summer, when food is naturally plentiful and animals bulk up ahead of the lean winter months.

Scientists think mammals figure out how much to eat based on the length of the day. Black bears, for example, gorge on berries and nuts during the lengthening days of spring and summer, but rapidly during their long winter hibernation.

A new study from the University of California, San Francisco shows that it may have as much or more to do with the balance of saturated and unsaturated fats in their diet.

Scientists have found that saturated fat affects the behavior of a protein called PER2, which regulates fat metabolism and circadian rhythms. Depending on the amount of saturated fat you consume, this protein can either tell your body to burn fat or store it.

As summer approaches, plants begin to produce more saturated fats. In mammals that eat these plants, saturated fat signals a season of abundance, and PER2 encourages the body to store energy to use in winter when food is scarce.

As fall approaches, plants produce more unsaturated fats, which helps them function better in cool conditions. By eating more of this type of fat – instead of saturated fat – mammals receive signals that summer is coming to an end. As food stores dwindle, PER2 prepares the body to use fat stores.

“It makes sense that both nutrition and day length influence seasonal behavior,” said Louis Ptacek, M.D., professor of neurology and lead author of the study, noting the example of hibernating bears. “If it’s fall and there are still plenty of nuts and berries to eat, the bear might as well continue eating rather than hibernate even if it feels like the days are getting shorter.”

The study in mice is the first to examine the role of nutrition in mammals’ adaptation to the seasons. The findings will be published on October 23 and could inspire new approaches to treating obesity and type 2 diabetes. The research was supported in part by the National Institutes of Health.

Fat matters

Ptacek and co-author Dr. Ying-Hui Fu have been studying PER2 since discovering in 2001 that the gene and its protein control our 24-hour sleep-wake cycles. About a decade later, it was discovered that PER2 also plays a role in fat metabolism, leading researchers to suspect that our biological clocks do more than just keep time.

The team decided to investigate the combined effects of fat and light on mice. The researchers simulated the seasonal cycle by exposing mice to 12 hours of light and darkness each day to approximate the autumn and summer equinoxes; they then moved to 20 hours of light to simulate summer and 20 hours of darkness for winter.

Mice that ate a diet not high in fat and calories adapted easily to seasonal changes. As the nights grew longer, they began running on wheels as soon as darkness fell, which is normal behavior for nocturnal mice.

In contrast, mice that were on a high-fat diet were unable to wake up and run until several hours after dark.

The team then compared the effects of foods high in unsaturated fats, such as those found in seeds and nuts, with foods containing hydrogenated fats, such as those found in processed foods.

Mice that ate more hydrogenated fat did not adapt well to the prolonged darkness of winter and did not wake up and start running on wheels until many hours after nightfall.

“These types of fats appear to prevent mice from sensing the early nights of winter,” said postdoctoral fellow Dan Levine, who brought his interest in seasonal cycling to Ptacek’s lab.

“The question arises as to whether the same thing happens to people who snack on processed foods.”

Electric light and constant calories

Hydrogenated fats aren’t the only aspects of modern life that can disrupt seasonal rhythms. Electric lighting provides light throughout the day, and grocery stores provide plentiful food year-round.

Because we evolved to eat a lot in the summer and store it to survive the winter, “Eating large amounts of food becomes maladaptive when there is no escape from temptation,” Levine said.

Disruptions to biological rhythms have been linked to sleep disorders, obesity, diabetes and mental health problems, and researchers said the same is likely true for abnormal seasonal rhythms. Correcting these imbalances can improve sleep and energy levels, prevent chronic disease, and help shift workers and those suffering from jet lag.

Levine recommended resisting the urge to graze on fatty delicacies, especially in winter.

“That one Christmas cookie may turn into two cookies the next day because you tricked your circadian clock into thinking it’s summer,” he said.