What Is a Calorie Deficit?

​What Is a Calorie Deficit?

Calories are a measure of the amount of energy in food. All of the cells in your body require energy in order to work properly, just like a car needs fuel. They get that energy from the foods that you eat. Your body breaks down that food during digestion, releasing the energy that it contains. Those food calories – now converted to energy – power everything that you do: breathing, thinking, walking, sleeping, digesting, you name it.

But your body may not need to use all that energy right after you eat. It stores those extra calories – mostly as fat but also as carbohydrates – for later use. When you go to the gym, study hard for a test, or find yourself involved in any other energy-demanding activity, those stores provide the energy you need to power through.

If your activities burn fewer calories than you consume, those stores of extra calories will grow, and you will gain weight.

But the opposite is also true: You will lose weight if you burn more calories than you consume. That’s because doing so creates a calorie deficit. It forces your body to burn through the stores of fat that you have built up. This leads to weight loss. In fact, you won’t lose weight without a calorie deficit.

What Should Your Calorie Deficit Be?

A good rule of thumb for healthy weight loss is a deficit of about 500 calories per day. That should put you on course to lose about 1 pound per week. This is based on a starting point of at least 1,200 to 1,500 calories a day for women, and 1,500 to 1,800 calories a day for men. It can be unhealthy to take in less than that per day. Talk to your doctor about the minimum calories you need.

Keep in mind that you may not need a calorie deficit at all. You only need it if you want to lose weight for health or other reasons. Always talk to your doctor before you start a weight loss plan, especially if you have health problems.

How to Reach a Calorie Deficit to Lose Weight

Reaching a calorie deficit sounds simple: Eat fewer calories than your body needs. But to do that, you must first find out what those needs amount to: How many calories do you burn each day? Once you have established that, you take that total number of calories and subtract from it the number of calories necessary to achieve the calorie deficit you desire.

An example: Let’s say you find that you need roughly 2,000 calories a day, and you want to lose about 1 pound per week. You could do this by eating about 500 fewer calories every day. Your goal, then, is to eat 1,500 calories daily. That creates a 500-calorie deficit.

There’s another way. Instead of eating fewer calories on a daily basis, you instead increase the amount of exercise you do so that you burn 500 more calories every day. The result: You need 2,500 calories daily, but you keep consuming 2,000 calories. You have created that same 500-calorie deficit.

You also can mix and match: Increase the amount of exercise you do daily to burn, say, 200 more calories while cutting 300 calories from your daily diet. Your calorie deficit: 500.

These basic examples simply explain how it’s done. The best way to create – and maintain – your calorie deficit is the way that works for you.

Keep in mind that your calorie needs depend on several things: your age, sex, height, weight, and exercise habits. This calculator can help you figure out your daily calorie requirements. 

Other things that determine your calorie needs:

Your metabolic rate. This is how quickly or slowly you burn calories at rest. It varies widely from person to person.

Some health conditions. Hypothyroidism, in which your thyroid gland is underactive, slows metabolism. So does Cushing’s syndrome, a condition that’s caused by having too much of the hormone cortisol.

Remember, creating too much of a calorie deficit is a bad idea.

It can cause several side effects, including:

Constipation
Dehydration
Fatigue
Headaches
Nausea

It may also leave you feeling "hangry": angry because you’re hungry.

Along with those side effects, an oversized calorie deficit will be harder for your body to adjust to and harder for you to maintain. You’ll likely be more successful over the long haul with a significant but sustainable calorie deficit.

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