Calorie Deficit and Weight Loss

Medically reviewed by Elizabeth Barnes, RDN

A calorie deficit occurs when you consume fewer calories than you use in a day. This forces your body to burn stored fat to get the energy you need, and that leads to weight loss.

Research shows that most people need to burn 3,500 calories to lose one pound. In theory, this means you can lose 1 pound per week by cutting 500 calories per day. There are usually additional factors at play, though, including the quality of the calories you eat and how much you exercise.

This article explains what a calorie deficit is and how it works. It includes tips for reducing calorie intake safely, along with other factors to consider when you're trying to lose weight.

What Are Calories?

Calories are a unit of heat energy. In nutrition, calories are a way to describe how much energy your body can get from eating or drinking something. For example, if an apple contains 95 calories, your body will gain 95 units of energy from eating it.

Calorie content is measured by using a bomb calorimeter. This device works by burning a food sample in an oxygen-rich chamber that is surrounded by water. As the sample burns, the temperature increase of the water is measured. This measurement translates to the amount of energy—or calories—in the food sample.

Calories are also used to describe how much energy your body uses to perform a physical activity. For example, if running burns 100 calories, your body will burn about 100 units of energy running the mile. Calorie expenditure, or the amount of calories burned, is determined by measuring the amount of heat released from the body during a physical activity.

How to Calculate Calories in Food

The simplest way to calculate calories is to use a calorie-counting mobile app. If you are putting together a recipe, a recipe nutrition calculator can be helpful. Otherwise, to calculate calories in a food, you will need to find the food's weight in grams, and then multiply that by the food's calorie content per gram. Use USDA FoodData Central to find the nutritional content of most foods.

How Many Calories Do You Need?

A safe and realistic weight loss goal is to lose 1 to 2 pounds per week. Research shows that in order to lose 1 pound, you need to burn 3,500 calories. You can accomplish this by either cutting calories, increasing exercise, or, ideally, both.

For example, if you eat 250 fewer calories per day and walk for 30 minutes per day, you will lose one pound in just over a week. But if you want to lose 1 pound per week without exercise, you will need to cut about 500 calories per day.

While this formula is a good starting point, there are other factors to consider when creating an effective and sustainable calorie deficit:

Basal Metabolic Rate

Basal metabolic rate (BMR) refers to the amount of energy (in calories) your body burns in 24 hours to perform basic functions at rest, like breathing and digesting food.

One of the most common ways to estimate BMR is through the Harris-Benedict formulation, which accounts for age, sex, height in centimeters, and weight in kilograms. It looks like this:

• Females: 665.09 + 9.56 x weight (kg) + 1.84 x height (cm) - 4.67 x age = BMR

• Males: 66.47 + 13.75 x weight (kg) + 5.0 x height (cm) - 6.75 x age = BMR

Once you know your BMR, you can use it to determine the number of calories you burn each day, depending on your physical activity level:

• If you have a sedentary lifestyle, multiply your BMR by 1.2

• If you have a lightly active lifestyle, multiple your BMR by 1.375

• If you have a moderately active lifestyle, multiple your BMR by 1.55

• If you have a very active lifestyle, multiple your BMR by 1.725

• If you have an extra active lifestyle, multiple your BMR by 1.9

The final result is approximately how many calories you need to eat per day to maintain your weight. To determine how many calories you should eat to lose weight through diet alone, subtract another 500; This is about how many calories you should eat per day to lose one pound per week.

Keep in mind that BMR equations aren't perfect. They don't account for medical conditions, body composition, or other personal factors that may affect your BMR. To get the most accurate numbers, see your healthcare provider.

Takeaway

While it may seem logical to cut calories entirely, taking your calorie deficit to an extreme is both unsafe and counterproductive. In fact, cutting too many calories can cause your metabolism to temporarily slow down in an attempt to conserve energy.

Related: Unexplained Weight Gain and Fatigue: Underlying Conditions

Thermic Effect of Food

Another important factor to consider is the thermic effect of food, or the amount of energy that is required to metabolize (digest, absorb, and utilize) the nutrients in food for energy.

Different foods have different thermic effects. When you eat foods with a high thermic effect, your body uses more energy to metabolize those foods—and burns more calories in the process.

Protein has the highest thermic effect, followed by carbohydrates and fibers. Fats sit at the lowest end of the spectrum. So, eating more protein-rich foods and fewer fats is a far more effective strategy than the reverse for creating a calorie deficit.

Foods with a high thermic effect include:

• Proteins, such as lean meats, fish, eggs, and dairy products

• Fibrous vegetables, such as broccoli, spinach, and kale

• Whole grains, including brown rice, oats, and quinoa

• Spicy foods, such as chili peppers, which contain the high thermic compound capsaicin

• Green tea, which contains the high thermic compound catechins

Does all this mean that eating excessive proteins will automatically result in weight loss? Not exactly. No matter what you eat, you still need to maintain a calorie deficit to lose weight.

However, if you have calories in your "budget" to spend, the most beneficial way to spend them is on foods with a higher thermic effect.

Active Energy Expenditure

Total energy expenditure refers to the total amount of calories your body burns during the day. It includes basal metabolic rate, the thermic effect of food, and active energy expenditure, or calories burned during physical activity.

The number of calories you need to eat per day depends on your age, sex, and active energy expenditure. If you have a high physical activity level, your body needs more food energy to keep you powered.

Take, for example, a 30-year-old active female and a 30-year-old active male. According to dietary guidelines, the active female should consume 2,400 calories per day to maintain their weight, while the active male should consume 3,000 calories per day to maintain theirs.

In order for these individuals to burn one pound per week through diet alone, the active female should reduce their calorie intake to 1,900 calories per day, while the active male should reduce theirs to 2,500 calories per day.

The amount of calories needed for sedentary individuals to maintain or lose weight is markedly less. A 30-year-old sedentary female should consume 1,800 calories per day to maintain their weight, and 1,300 calories per day to lose one pound per week. Likewise, a 30-year-old sedentary male should consume 2,400 calories per day to maintain their weight, or 1,900 calories per day to lose one pound per week.

No matter your physical activity level, you will still need to burn 3,500 calories through diet and/or exercise in order to lose one pound. But your total daily calorie intake will vary depending on your physical activity level.

Will Eating Less Burn Belly Fat?

Eating less calories will burn belly fat, as well as fat in other areas of your body. However, research also shows that high intensity exercise is critical for burning body fat and keeping it off.

Body Composition

Body composition refers to the proportion of body weight that is comprised of fat, muscle, organs, bones, and other non-fat body tissues. Learning your body composition can help you make an informed decision about the amount of calories to cut from your diet.

A body composition with more than 30% body fat (for females) or more than 25% body fat (for males) is considered obesity. If you have obesity, you have more body fat to burn and can begin with a more aggressive calorie deficit. However, as you get leaner, you will need to reduce your calorie deficit to prevent muscle loss.

A low-calorie diet (LCD) involves consuming 1,000 to 1,500 calories per day. This equates to a deficit of approximately 1,000 calories per day. An LCD is considered aggressive, and usually only recommended for people with obesity, and under the supervision of a healthcare provider.

A very low calorie diet (VLCD) involves consuming 800 or fewer calories per day. This level of calorie deficit is only recommended in limited circumstances, usually in people with severe obesity, or people with certain obesity-related medical conditions. It, too, must only be done under close medical supervision.

Takeaway

If you are just starting your weight loss journey and are not sure how many calories to eat per day, you may find it helpful to use a calorie counting app. You can also reach out to a registered dietician to help you safely cut calories and steadily lose weight.

Calorie Deficit and Your Diet

Now that you understand the importance of calories for your metabolism, energy expenditure, and overall weight loss goals, here's how to put those principles into practice:

Reduce Calorie Intake

To reduce your calorie intake, start by thinking about the foods you typically eat and see how you can swap those foods out for lower-calorie options. For example:

In addition to making healthier food choices, it's also best to minimize snacking. On one hand, having a snack can help curb your appetite to prevent overeating at your next meal. On the other, it can lead to excess calorie intake and weight gain.

If you must have a snack between meals, opt for high-thermic, high-fiber fruits and vegetables that will help you feel full without packing on the calories.

Related: The Health Benefits of Dietary Fiber

Eat More Protein

Research shows eating enough protein helps preserve lean muscle mass during weight loss (so the pounds you lose are less likely to be muscle), and keeps you feeling full for longer.

Try to get 10% to 35% of your calories from protein. Make sure you’re eating protein-rich food with each meal and snack. Aim for a mix of animal and plant-based protein foods, like:

• Lean meats, such as chicken and turkey

• Fish and seafood

• Nuts and seeds

• Beans and legumes

• Low-fat dairy products

Discuss your protein intake with a healthcare provider if you have liver or kidney disease, as eating higher levels of protein may not be appropriate for you.

Related: Increasing Plant-Based Protein by Just 3% May Help You Age Healthier. Here's How to Do It

Eat More Fiber

Fiber is a part of plant foods that humans can’t fully digest. Instead, fiber slows digestion to keep you feeling fuller for longer, while also promoting bowel regularity.

High-fiber foods include:

• Beans, lentils, and other legumes

• Guava, raspberries, kiwi, and other fruits

• Artichoke, sweet potato, broccoli, and other vegetables

• Unsweetened wheat cereals, brown rice, oat bran, and other whole grains

• Pumpkin seeds, almonds, and other nuts and seeds

An adequate intake of fiber is 14 grams for every 1,000 calories consumed daily. Eating more high-fiber foods helps you stay full longer, so you’ll be less likely to need to reach for additional snacks.

Calorie Deficit and Physical Activity

Moving your body more and working out are excellent ways to increase your calorie deficit. Try to work in more movement and exercises by:

• Joining group fitness classes

• Taking at least 10,000 steps per day

• Doing strength and cardio workouts a few times a week

• Trying different types of workouts to find one you like

• Asking a friend to be an accountability partner

• Meeting friends for a walk rather than a meal

• Parking farther away from your destination

• Taking the stairs instead of the elevator when possible

Takeaway

Adults should get at least 150 minutes of moderate-intensity exercise, or 75 minutes of vigorous exercise per week. Examples of moderate-intensity exercises include brisk walking, tennis, and dancing.

Related: What Is Aerobic Exercise?

Limitations of Calorie Deficit for Weight Loss

As many as 90% of people who lose a considerable amount of weight eventually gain it back. The reason for this is complex, involving a combination of psychological, biological, and environmental factors.

Gaining a significant amount of weight changes your biology in ways that can undermine weight loss. Once you put the weight on, your body adapts to the changes by slowing your metabolism and sending increased hunger signals to encourage you to keep the weight on.

This is your body's way of adopting the new weight as its new normal. But it's this same self-preservation that makes it more difficult to lose weight than it is to gain it.

Fortunately, these biological changes work both ways. Studies show that people with obesity who lose as little as 10 pounds usually enjoy significant reductions in blood pressure, blood sugar levels, and overall inflammation.

Takeaway

Rather than basing your success on how you look, it may help to focus on how you feel. That way, you will feel rewarded every time you make a healthy choice, instead of every few weeks or months when you see a change in the mirror.

Summary

A calorie deficit is when you eat fewer calories than you use in a day. If you’re eating more calories than you use, the excess is stored as fat. So, to lose weight you need to bring in fewer calories than you burn.

A calorie deficit of 500 calories per day is usually recommended to create an average weight loss of one pound per week. Exercising more and tracking your calories may help you create a calorie deficit. Eating more protein and adding fiber to your diet may help you feel fuller longer, making a calorie deficit easier to achieve.

Read the original article on Verywell Health.