While we’re all in favor of committing to a healthy living plan that feels right to you in January, you might want to think twice if your overall goal is weight loss. Turns out we’re biologically programmed to hold onto a bit more weight in these shorter, colder days, meaning winter is the worst time to try to shed excess pounds.
“People typically don’t need to intentionally gain weight in winter, but a small, unintentional increase is not inherently harmful,” explains Kathleen Benson, CSSD, CPT, RDN at VNutrition, who notes that gaining as much as two to five percent of body weight is totally normal. “In some cases, allowing the body to settle at a slightly higher weight during colder months can be protective (especially if it reflects adequate fueling), reduced stress around food, and better energy availability.”
Why Do We Gain Weight in Winter?
When it comes to winter weight gain in particular, there are a few different factors at play. First off, colder temperatures make the body seek more energy to thermoregulate — energy that comes in the form of fat and glucose. Carbs, in particular, help our bodies produce more tryptophan, a mood-boosting chemical that helps shore up our serotonin levels when sun is lacking.
It should come as no surprise, then, that as the weather gets colder, we crave carby comfort foods like baked mac and cheese and a hearty lasagna soup. And the fact that these dishes also contain a heaping helping of fat should come as no surprise.
“Fat is essentially an insurance against failing to find enough food,” Professor Andrew Higginson, an evolutionary biologist and senior lecturer in the Centre for Research in Animal Behaviour at the University of Exeter, told the Telegraph1. “Building up fat stores in autumn when lots of fruit and nuts are available is a deeply evolved strategy for surviving winter.”
Plus, it’s worth mentioning that colder months may naturally mean that we’re less active and energetic — and certainly less motivated to go on long walks or spend all day outdoors burning calories.
Choosing the Right Fats for Sustainable Weight Control in Winter
All that said, not all forms of fat are created alike. Research out of UC San Francisco published in Science in October found that unsaturated fat, like the kind found in nuts and seeds, and hydrogenated fat, which is common in processed food, had very different effects on the behavior of a protein called PER22. PER2 controls fat metabolism and circadian rhythms, so the type of fat you’re eating can make a noticeable difference.
The researchers simulated a seasonal cycle by exposing mice to seasonally appropriate lengths of sunlight, examining their behavior when fed diets high in each of the two fats. Eating more unsaturated fat in autumn and winter is evolutionarily natural, as plants produce more of this type of fat to help protect them against colder temperatures.
The result? Mice reacted well to this higher-fat diet made up of unsaturated fats, which led PER2 to perform as designed: preparing the body to tap into its fat stores and leading the nocturnal mice to wake and run on their exercise wheels as soon as it got dark. The diet rich in hydrogenated fats had the opposite effect, making the mice lethargic and unable to wake up and start running for several hours.
“These types of fats seem to prevent mice from being able to sense the early nights of winter,” said postdoctoral scholar Dan Levine, PhD. “It begs the question of whether the same thing is happening for people snacking on processed food.”
Sustainable Winter Eating is All About Small Tweaks
While winter may incite cravings for all things heavy and rich, it’s still important to strike a balance.
“In winter, people often benefit from warmer, more grounding meals that include sufficient protein for muscle and immune support, carbohydrates for energy and mood regulation, and fats for satiety and nutrient absorption,” says Benson. And while some days, that might mean a plate of cheesy, après-ski raclette, other days, it might mean enriching your homemade lentil dal with coconut milk or adding an extra spoonful of peanut butter to your morning oatmeal.
For Benson, it’s less important to focus on macronutrient rules in winter than ensuring you’re eating “consistently and enough.” Above all, if you’re hungrier than you were a few months ago, don’t ignore it: Lean in.
“Health is better supported by consistency, nourishment, and flexibility across the year rather than seasonal extremes of indulgence followed by restriction,” Benson explains. “Bodies are allowed to ebb and flow, and honoring that is often the most sustainable approach to both physical and mental health.”
Sources:
- https://www.telegraph.co.uk/health-fitness/diet/weight-loss/why-its-more-difficult-to-lose-weight-in-winter/
- https://www.ucsf.edu/news/2025/10/430946/fatty-snacks-winter-may-trick-body-packing-pounds
