Snacking on treats high in saturated fat this winter could trick your body into storing more fat, a recent study has found.
Scientists at the University of California, San Francisco (UCSF) found that dietary fats can influence how our bodies measure the passing of the seasons.
“We found that the types of food that you eat help to tell the time of year to your biological clock,” lead author Dr Dan Levine – a postdoctoral scholar of neurology at UCSF – told BBC Science Focus.
They found that if we eat more saturated fat – found in red meat, butter, cake, pies and other buttery baked goods – a protein called PER2 tells the body that it’s summer and that we should store more energy to prepare for the cold winter months.
But if we eat more unsaturated fat – the type found in nuts, seeds, oily fish and vegetable oils – PER2 makes the body believe it’s winter, and that we should burn the energy we eat.
At least, these are the results of an experiment on mice, which the UCSF team exposed to periods of light and dark, to simulate the changing seasons.
The rodents experienced 12 hours of light per day when the scientists wanted to mimic spring and autumn, 20 hours of light for summer and only four hours of light for winter.
As the nights got longer in fake winter, mice who were eating a balanced diet exhibited normal winter behaviour for the nocturnal rodents – they began to run on their wheels as soon as it got dark.
But mice who were fed a high-fat diet took a little while to wake up, and started running much later than the fake sunset – suggesting their internal clocks were slightly out of sync with the light cycles.
Then, the scientists compared the effects of different types of dietary fat. They found that mice who ate a diet high in saturated fat didn’t wake up and start running on their wheels until many hours into the night.
So, their internal clocks seemed even further out of sync with the light patterns when they ate more saturated fat in fake winter.
Levine said that, while the study was done on mice, the interaction between these fats and the body’s internal clock via the protein PER2 was shared across species.
“We think that many of the lessons we have learned from our studies on mice will be generally applicable to humans,” he said. “It will be exciting to see what differences, if any, exist between the species.”
How our bodies may be wired for winter
For wild animals and hunter-gatherer humans, adapting to the seasons is crucial for survival – particularly to endure a long, cold winter where food resources may be scarce.
“In the wild, seasonal water, light and temperature patterns completely change the landscape and force organisms throughout the food chain to adapt,” explained Levine.
“One of these adaptations is that plants produce more unsaturated fat to survive the cold, which causes herbivores – and carnivores – to consume and store more unsaturated fat.”
So, our bodies might be programmed to expect more unsaturated fats as the days get shorter.
But this natural dietary switch is a process that many of us miss out on because we have access to the same foods all year round.
We can eat our saturated-fat favourites regardless of the season – but eating too much of it in autumn and winter could confuse our biological clocks into thinking it’s summer.
“In modern society, food is readily available, including saturated fats,” senior author Prof Louis Ptacek, neurologist at UCSF, told BBC Science Focus. “We also tend to eat at ‘unnatural’ times of day, and we can do this because of electric lights. In general, it’s healthier to eat on a schedule that’s locked to the circadian daytime.”
Levine added that it may also be beneficial to eat foods according to the season – and perhaps alter our fat sources over the course of the year. But, he said, further studies were needed to confirm that this approach would be beneficial.
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