Many of us succumb to a yearly cycle of gaining weight during the cold, short days of winter only to start working towards our “summer bod” come the warmer, energizing springtime. So, is this phenomenon due to natural instincts or just another modern excuse for overindulgence?

It’s true that putting on an extra layer of fat during the winter gave our ancestors an evolutionary advantage by offering insurance against food scarcity during winter. Being underweight was a real threat to our survival because it led to a quicker death during times of famine. Being overweight, however, has not posed a health risk until recently; in fact, obesity was practically unheard of just a century ago. Now, 69% of adults in the U.S. are overweight or obese.

When we were hunting and foraging our own food, gaining some weight was not a result of severe overindulgence and lack of movement. Similarly, the subsequent loss, did not require calculated effort like caloric deficits and intense workout plans. According to the “thrifty gene hypothesis,” the humans that survived (and therefore evolved into the human race today), were those that had the best metabolic flexibility. They were able to store calories in the form of body fat quickly when food was available as well as burn calories efficiently (i.e., slowly) when food was scarce. This allowed for maintenance of an energy-intensive lifestyle dependent on weather and food availability.

The same metabolic flexibility that allowed our ancestors to gain and lose weight quickly according to survival needs is now, with unlimited access to food, making many of us overweight year-round. Most of us no longer experience famines that cause a slow depletion of fat stores. And, with largely sedentary lifestyles (and indoor heating), extra pounds put on in the winter now largely “outweigh” any potential benefits to our survival. In fact, there’s really no evolutionary advantage to storing extra weight in the winter for most of us in modern society. While people with high BMIs have shown to have less susceptibility to hypothermia since fat insulates the core, muscle tissue generates heat, which also offers protection from the cold. So, in theory, you could build muscle mass before the winter instead of just gaining body fat and receive similar heat-promoting benefits to keep you warm during your outdoor adventures.

When eating processed food, our body does not know when it has had enough—so you can end up consuming way more calories in treats and cocktails than our ancestors would have in whole foods they foraged and hunted themselves during the fall and winter months. The artificial flavors and never-ending novelty override our natural instincts to stop eating when full. Unless you’re eating whole foods mindfully and exclusively, it’s easy to put on a lot of extra unneeded weight during the fall and winter months.

Many of us vow to start a diet on New Year’s Day—right in the heart of winter. This poses many challenges, since the cold weather urges us to eat more and store body fat. Spring, however, is the ultimate time to kick your eating and exercise habits into gear. The days are longer and full of pristine weather. Moreover, our bodies are physiologically primed to shed some pounds to prepare for the warm summer months ahead (which historically meant more food abundance and therefore less need to store body fat for potential famine). Spring also brings a freshness that has evoked feelings of motivation and rebirth across centuries and cultures.

So, now’s the time! Your brain and body are ready to make big changes to support your goals. There’s no need to wait until January or your birthday to set resolutions. Instead, harness the energy of spring to get moving and eating whole, fresh foods. By summer, you’ll be feeling great in your body and ready for some wild adventures.