Everything You Need To Know About TDEE - Part 2: Science and Sensibility

June 12, 2023

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Whether you are here because you read Part I of TDEE and are in dire curiosity to know the answers to my teaser questions in Part I, or you landed here via a random Google search, you are still going to get an easy recap of Part I, Netflix style.

In Part I we learned about the fundamentals of TDEE – the what, why, and how, the various components of TDEE namely BMR/REE, EAT, NEAT, and TEF, calorie calculators and methods to calculate your TDEE using the Harris-Benedict equation, and the relevance of TDEE in a CICO diet – how you can use TDEE as a starting point to understand your daily caloric needs but not as a sole tool for overall health management inclusive of weight management.

In this article, let us dive a little deeper into the nuances of TDEE with respect to changes in the seasons.

A Little Magic Called Thermogenesis

Like any other biological parameter, TDEE is influenced by a vast number of factors. The human body, as a whole and in parts, is a dynamic, complex intertwined web of processes that influence each other and the overall existence of the being, which will always continue to fascinate mankind. Without a doubt, an individual’s metabolic rate is also influenced by a variety of factors ranging from what you eat, to the intensity of UV radiation from the sun. A key physiological process that is tied to the metabolic rate is thermogenesis. In literal terms, thermogenesis is ‘heat production’. Physiologically, thermogenesis translates to ‘the heat produced in direct response to a meal, which is then utilized in the digestion, absorption, assimilation of nutrients and disposal of waste’. This utilization of heat is termed the ‘Thermic Effect of Food (TEF)’. [1], [2] If that was a little too over your head, just remember the layman’s version – when you eat, your body generates heat as it breaks down what you eat.

TDEE x Heat Waves

Now, let us look at what happens to your appetite when the temperature soars outside. Our bodies are not exposed to high temperatures on an everyday basis, which means we are not attuned to thrive in hot weather without significant changes happening to some physiological and biological processes to help our body get acclimatized. Once the body’s natural adaptive mechanisms kick in, it gets acclimatized to the heat. The first thing your body does is prioritize cooling the body in whatever way it can. This is why you get thirsty a lot more often in summer than in winter; which is also why you experience reduced appetite because less appetite = reduced consumption of food = reduced thermic effect of food. Your body needs less energy to maintain homeostasis in summer and so your TDEE is lowered by way of a natural caloric deficit. [3]

In addition, your hormones also experience a natural shift due to the shift in seasons, thus impacting physiological processes. Specifically, it has been noted that Ghrelin – the hunger hormone – and Leptin, the hormone that triggers satiety,fluctuate with the seasons. [4] While a lot of research is still emerging in this area, there are enough studies that indicate warmer seasons cause an increase in leptin in combination with a decrease in ghrelin leading to a reduced appetite. [5], [6]

TDEE x Sweater Weather

On the contrary, during colder seasons, the lower temperatures in the external environment mean your body needs to expend more energy to try and keep you warm and stay in homeostasis. In other words, your body wants to increase the level of thermogenesis, and in order to do that, your appetite is stimulated to increase the consumption of food, leading to an increased thermic effect of food. Naturally, this translates to an increase in TDEE. Ghrelin and Leptin also shift with the drop in temperature. Colder seasons lead to an increase in ghrelin and a drop in leptin leading to an increased appetite. [7]

In summary, TDEE is never constant and keeps fluctuating with the change in seasons.

So what?

With all these science-y pieces of information, two questions loom over our heads: If TDEE is going to stay inconsistent through the year, what is the point of even taking it into account? Also, if I were to use TDEE as a measure of calorie intake, how do I leverage that against the fluctuations in TDEE that arise from seasonal shifts?

As mentioned in Part 1, TDEE is not all that useless. TDEE is a great starting point to understand your metabolic requirements, as long as you have factored in your activity levels as accurately as possible. Yes, it is not a super accurate measure, but hey – we’re not all Sheldon, so we can do with what the Harris-Benedict equation outputs. Or the Katch-McArdle if you get your TDEE worked out by a professional. One can also be wise and use the TDEE to plan your meals in such a way that you get a variety of nutrients from whole foods across the day, as well as get enough calories in a meal. As seasons shift, shift your eating patterns accordingly so you meet your natural TDEE. Eat to satiety, and eat in such a way that works in tandem with the body’s need to stay in homeostasis. For example, in summer, spruce up your plate with foods that can cool down your body – think cucumbers, melons, avocados, fish, lean cuts of chicken, coconut water, etc. This helps your body to balance into homeostasis a little easier without having to experience a massive drop in appetite. Similarly, during colder seasons, add warming spices like cinnamon, ginger, nutmeg, and cumin to your dishes so your body grows warm to combat the external cold. Add a few extra reps to your workout to increase blood circulation, which will allow your body to stay warm as well.

As Thomas Huxley would say, “Science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.” So, use your TDEE measures wisely, with an extra ounce of common sense, for a healthy you.