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The Body’s Fat Thermostat — Part 2 — The Science

Eating Less Lowers Fat Burning

Dr. Jason Fung
8 min readJan 25, 2024

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My last article, The Body’s Fat Thermostat — Part 1, discussed the concept of homeostasis and how body fat is regulated like a thermostat rather than simply the end product of Calories In — Calories Out. The level set by the thermostat is determined by multiple hormones (like most everything else in our body), rather than the number of calories we eat. It is true, however, that the types of food and the amount of food will influence those hormones, but different foods, even with the same calories, have different hormonal effects. This is why calorie counting is such an unsuccessful weight loss strategy.

Is there scientific evidence to show the existence of this Body Set Weight (BSW)? Totally. Virtually every study done over the last 50 years shows this. It’s rather stunning that so very few people discuss the mechanisms of this fat thermostat because it has massive implications for weight loss. Massive.

How the Body Fat Thermostat Works

The Body Set Weight (BSW) is like a thermostat. Our body sets a certain level of body fat and then defends it according to the energy balance equation Body Fat = Calories In — Calories Out, which is always true.

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Dr. Jason Fung

Nephrologist. New York Times best selling author. Interest in type 2 diabetes reversal and intermittent fasting. Founder www.TheFastingMethod.com.