If you’ve ever tried to lose weight, you’ve probably heard about the importance of “calories in versus calories out.”
This concept is based on the idea that as long as you eat fewer calories than you burn, you’re bound to lose weight.
However, some people insist that the type of food you eat matters much more than the number of calories it contains — both in terms of weight loss and long-term health.
This article investigates whether the “calories in versus calories out” model really matters.
The “calories in versus calories out” model is based on the idea that to maintain a stable weight, the number of calories you eat needs to match the number you expend.
“Calories in” refers to the calories you get from the foods you eat, while “calories out” is the number of calories you burn.
There are three main bodily processes that burn calories:
- Basic metabolism. Your body uses most of the calories you get from food to sustain basic functions, such as your heartbeat. This is commonly referred to as your basal metabolic rate (BMR) (1).
- Digestion. Around 10–15% of the calories you eat is used to power digestion. This is known as the thermic effect of food (TEF) and varies based on the foods you eat (2, 3).
- Physical activity. The leftover calories you get from your diet are meant to fuel your physical activity, including workouts and everyday tasks like walking, reading, and washing dishes.
When the number of calories you take in from food matches the number of calories you burn to sustain your metabolism, digestion, and physical activity, your weight will remain stable.
Thus, the “calories in versus calories out” model is strictly true. You need a calorie deficit to lose weight.