If you’ve spent any time read up on diets, meal plans, fat loss, and muscle gain, you’ve likely come across two terms:

  • Calorie deficit
  • Calorie surplus

But what do these terms mean? More importantly, do they matter in a practical sense? And if so, how should we go about them?

Let’s discuss.

What’s Total Daily Energy Expenditure (TDEE) And What Does It Mean?

Before discussing calorie deficit and surplus, we first need to know how the body burns calories. That way, we can better understand the role of exercise and nutrition in weight manipulation.

Your TDEE represents the number of calories you burn every day. It includes your (1):

  • BMR, which stands for basal metabolic rate – the number of calories your body burns at rest even if you don’t move a muscle all day.
  • NEAT, which stands for non-exercise activity thermogenesis – the number of calories you burn from daily movement and includes everything aside from dedicated exercise time.
  • EAT, which stands for exercise activity thermogenesis – the number of calories you burn while exercising.
  • TEF, which is the thermic effect of food – the number of calories your body burns to break down foods and absorb their nutrients.

What Is a Calorie Deficit?

Okay, say that your total daily energy expenditure is 3,000 calories (on average). A calorie deficit would mean consuming fewer calories than that. It might be 2,800 or 1,500 calories per day. So long as you eat fewer calories than you burn, you’re in a calorie deficit.

So, what does it mean to be in a calorie deficit?

Since you’re consuming less energy than your body needs, you force it to break down muscle and fat tissue to get the remaining energy it needs to function and stay healthy (2). In other words, you lose weight.

Depending on your calorie deficit, you could lose weight slowly or quite rapidly. Both approaches have their advantages but losing weight more slowly is the sustainable way to go about it (3).

By maintaining a moderate deficit, eating plenty of protein, and exercising regularly, you get to lose mostly fat and maintain your muscle mass (4, 5).

What Is a Calorie Surplus?

If a calorie deficit means consuming fewer calories than you burn, a calorie surplus means eating more than you need. For example, with a TDEE of 3,000 calories, a surplus would be anything over that number.

Now, because your body is intelligent and future-oriented, the excess calories get stored for later use (6). This mostly means gaining fat, but your body also stores some of that energy in the form of lean tissue (anything that isn’t fat). 

Like the calorie deficit, depending on how big of a surplus you maintain, you could gain weight slowly or rapidly.
When used correctly and in combination with an adequate protein intake and a good training program, a calorie surplus allows you to build muscle and only gain small amounts of fat (7, 8, 9).

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