What Is a Calorie Deficit?

Medically Reviewed by Poonam Sachdev on July 15, 2024
Written by Matt McMillen, Paul Frysh
9 min read

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.

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 those assigned female at birth, and 1,500 to 1,800 calories a day for men and those assigned male at birth. 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.

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.

There’s no single best approach to cutting calories. In general, as long as you cut the calories and maintain a minimum amount, you will lose weight.

One proven method is to replace all sugar-sweetened beverages with water, which has no calories. That means soda, sports drinks, energy drinks, sweetened waters and iced teas, and other high-calorie beverages. And don’t forget: Fruit juice contains abundant calories. A 6-ounce serving has 60 to 120 calories.

Water not only keeps you hydrated. It may help you adapt to a lower-calorie diet. And keep in mind: When you feel hungry, it may actually be a sign you're thirsty, so reach for a glass of water rather than a caloric snack.

The DASH and Mediterranean diets also show some success. These focus on eating:

  • Fresh fruits and vegetables
  • Lean proteins
  • Whole grains
  • Nuts
  • Seeds

These types of foods help you feel full longer, so you may be less likely to snack between meals. Just be sure to count your calories. Smaller portions can help, too, along with careful planning of your meals.

A registered dietitian can help you figure out healthy ways to manage your portions and lower your daily calories.

Other tips for maintaining a calorie deficit:

Curb your simple carbs. White bread, white rice, regular pasta, and other low-fiber, high-carb foods won’t help you feel as full as high-fiber complex carbs like brown rice and other whole grains as well as whole fruits and vegetables.

Go light at restaurants. Avoid large portions and high-fat menu offerings. Start with a small salad or a light soup to fill you up, so you don’t overdo it. Have fresh fruit or sorbet for dessert.

Read food labels. Important info, like calorie counts and sugar content, can help guide your choices. Take time to compare. For example, some yogurts contain more sugar than others, even if they have less fat.

Limit prepackaged meals. These often contain more fat, sugar, and salt than you want. Cooking meals made from whole foods puts you in greater control.

What are the best calorie-deficit breakfast options?

For your first meal of the day, focus on fiber and animal or plant protein, which both promote fullness. That may help you avoid snacking throughout the day. Here are a few examples:

  • Plain Greek yogurt, with added berries, nuts, or seeds
  • A two- or three-egg or egg white omelet with mixed vegetables and quarter-cup of feta cheese or shredded low fat-cheese
  • A smoothie heavy on the protein, with a half-cup of Greek yogurt or a scoop of protein powder, a cup of frozen fruit, a cup of leafy green veggies like spinach or kale, and low fat-milk or an unsweetened milk alternative

Research shows that diet changes alone raise your calorie deficit more easily than exercise alone. Still, you often get the best weight loss results if you combine diet changes with moderate to vigorous exercise.

Shoot for 30 minutes or more on most days of the week, though 45 minutes or more may be better for keeping the weight off. You don’t have to do it all at once. You can do shorter bouts throughout the day. Think 10-minute spurts.

For a brief moderate workout, take a walk around the block or do a bit of gardening or lawn mowing in the afternoon. Bike riding and swimming are also great options. More vigorous exercise includes running, heavy yard work, and aerobic dancing, like Zumba.

Strength training also can help with weight loss. Make a plan to lift weights at least twice a week. You can use dumbbells, barbells, kettlebells, resistance bands, exercise machines, and even your own body weight (think pushups and planks).

Be sure to talk to your doctor before you start a new exercise program, particularly if you’re over 50, overweight, pregnant, or have other health conditions or are on certain medications, such as those that treat diabetes.

And remember: Regular exercise goes a long way in protecting your health even if you don’t lose weight. It stops your body from packing on the pounds. And if you have lost weight, it helps you maintain your weight loss.
 

Certain eating disorders, like binge eating disorder, can prevent you from achieving a calorie deficit to help with your efforts at healthy weight loss. Such disorders lead to or are caused by complex relations to food and eating, and treating them requires more than just addressing the way you eat. Different approaches work for different people. A therapist may be able to help you change thought patterns about food and exercise. Methods include:

  • Cognitive behavioral therapy
  • Motivational interviewing
  • Acceptance and commitment therapy

Smartphone apps can help you watch your food intake and remind you to exercise, among other things.

While a calorie deficit can help you achieve your weight loss goals, it can be harmful if you don’t do it in a healthy way. The risks include:

Too little nutrition. If you cut too many calories or if you don’t eat the right foods, your body won’t get all the nutrients it needs. For example, if you don’t eat enough calcium-rich food, you put your bone health at risk.

Low energy. As you cut calories, your body tries to conserve its energy stores by slowing your metabolism. This can make you feel cold and sluggish. It also can lead to constipation.

Brain drain. Just like the rest of your body, your brain needs calories for energy. Cutting too many calories may impact your brain function.

Gallstones. Severely restricting calories can lead to rapid weight loss, a risk factor for painful gallstones.

Disordered eating. Dieting can make you focus too much on food and bring other negative feelings, which may lead to problematic eating and, potentially, an eating disorder.

Can you build muscle in a calorie deficit?

Yes. But keep in mind that you build muscle with strength training exercises. Such workouts require energy, which means calories, so you may need to maintain only a small deficit. That will allow you to burn fat while still building muscle. Also, your calorie needs will be greater on the days you work out, so you’ll have to plan for that. Finally, make sure you don’t skimp on muscle-building protein when you cut calories. Instead, reduce the calories you get from carbs and fats.

Maintaining a calorie deficit will lead to weight loss. But don’t go overboard. You will struggle to keep up with an oversized calorie deficit, and you will put your health at risk. Instead, aim for a reasonable deficit that allows you lose weight slowly but steadily.

How do I calculate my calorie deficit?

It’s based on things like your age, sex, activity level, and more. Try this calculator: https://reference.medscape.com/calculator/846/mifflin-st-jeor-equation

Is 1,200 calories a day a deficit?

Any amount of calories less than what your body needs daily to maintain your current weight is a deficit. So, if you normally eat 1,500 calories a day, for example, then 1,200 would be a deficit.

What calorie deficit do I need to lose 2 pounds a week?

You should eat about 1,000 fewer calories per day. That’s a safe amount of calorie restriction, but a smaller calorie restriction, such as 500 calories, may be easier to maintain over the long term.

How many calories should I eat a day to lose weight?

It depends on how many calories you eat every day to maintain your current weight. For example, if you normally eat 2,500 calories daily, then eating fewer calories will lead to weight loss. Reduce your calories to 2,000 per day, and you should lose about a pound each week.