Seasonal Shifts and Your Metabolism: Why TDEE Isn’t One-Size-Fits-All

Explore how changing weather affects your calorie needs—and how to adapt for optimal health.

Whether you’re here because you caught Part I of the TDEE series or you stumbled upon this by chance, you’re in the right place. Get ready for a quick recap before diving into some fresh insights!

In Part I, we explored the fundamentals of Total Daily Energy Expenditure (TDEE)—what it is, why it matters, and how to calculate it. We broke down its key components like BMR/REE (Basal Metabolic Rate/Resting Energy Expenditure), EAT (Exercise Activity Thermogenesis), NEAT (Non-Exercise Activity Thermogenesis), and TEF (Thermic Effect of Food). We also touched on how TDEE is a useful starting point for understanding your daily calorie needs in a CICO (Calories In, Calories Out) diet, though it’s not the end-all for overall health management.

In this follow-up, we’re going deeper, looking at how TDEE fluctuates with changes in the seasons.

Thermogenesis: The Body’s Heat-Generating Magic

TDEE isn’t a static number—it’s influenced by a host of factors. One of the key processes that impacts your metabolic rate is thermogenesis, which refers to the production of heat in the body. Simply put, thermogenesis is what happens when your body generates heat in response to the food you eat. This is also known as the Thermic Effect of Food (TEF), and it’s all about using that heat to digest, absorb, and metabolize nutrients​. So, every time you eat, your body gets a bit warmer as it breaks down your meal.

Hot Weather and TDEE

What happens to your appetite and energy needs when the temperature outside spikes? When the weather turns hot, your body shifts into cooling mode. It adapts to the heat by focusing on ways to cool down, which explains why you tend to feel thirstier in the summer and less hungry overall. Reduced appetite means you’re eating less, and as a result, the thermic effect of food is lower. In turn, your body’s energy needs drop, leading to a naturally lower TDEE during the hotter months​.

In addition to this, seasonal shifts can alter hormone levels. Studies have shown that during warmer weather, levels of leptin (the satiety hormone) rise while ghrelin (the hunger hormone) decreases, which suppresses appetite​​. This natural response helps the body maintain a lower caloric intake during the summer.

Cold Weather and TDEE

On the flip side, colder temperatures mean your body has to expend more energy to keep warm. It kicks up thermogenesis to maintain homeostasis, increasing your appetite and driving up the thermic effect of food. Simply put, you eat more to stay warm, which raises your TDEE​. Your hormones adjust too, with higher ghrelin levels and lower leptin levels, making you feel hungrier during the chilly months​. So, your body’s energy needs are higher when it’s cold outside.

The Takeaway: What to Do with a Fluctuating TDEE?

With all these seasonal changes, you might wonder—what’s the point of calculating TDEE if it’s always in flux? And how do you adjust your diet to match these shifts?

The key is to use TDEE as a baseline for understanding your energy requirements, rather than as a fixed number. While it might not be super precise, it gives you a good starting point, whether you’re using a basic Harris-Benedict equation or a more tailored calculation like the Katch-McArdle formula. Think of TDEE as a basic guide for planning balanced meals that fit your needs​.

As the seasons change, adapt your diet and exercise habits to match. In the summer, focus on cooling foods like cucumbers, melons, lean proteins, and hydrating options like coconut water. This can help you maintain balance without forcing your body through drastic shifts in appetite. During winter, add warming spices like cinnamon, ginger, and cumin to your warm and soothing soups and broths, and maybe throw in a few extra sets during workouts to boost circulation and keep warm.

As Thomas Huxley put it, “Science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.” With a little common sense and a clear understanding of how TDEE works, you can use these seasonal shifts to your advantage and maintain a healthier lifestyle all year round.