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What Happens to Fat When You Lose Weight?

Reviewed by Dan Brennan, MD on June 29, 2021

You definitely know what happens when you gain weight. It stubbornly clings to your hips, arms, gut, and rear. But when you decide to lose weight, what happens to it then? 

Some people say it turns to muscle. Others say it turns invisible, only to reappear months later when you stop going to the gym. Diet and exercise can seem challenging, but the way they burn fat is much easier than it may seem. 

What Is Body Fat?

Fat is created by an excess of calories. Calories are your fuel source, providing energy for your body. You get calories from the food and drinks you ingest. 

You need calories. Everything your body does requires calories. It even burns calories to help your heart beat and lungs breathe. Your body needs a certain amount of calories to support all of these functions and more. 

How many calories? The number of calories you need depends on several factors, including age, sex, weight, and height. You also need more calories if you’re physically active and fewer if you’re sedentary.

Adult women generally need between 1,600 and 2,400 calories per day, and adult men generally need between 2,000 and 3,000 calories. Taller, heavier, or more active people will be at the higher end of each range. 

Too many calories equal fat. When you eat too many calories each day, the excess calories (or energy) have to go somewhere. Your body stores these calories by turning them into body fat

Do fewer calories equal less fat? It’s not that simple. Once your body has stored away fat, it won’t burn away that fat if you only cut back on calories. You have to give your body a reason to use the stored energy. 

How Is Fat Burned?

To lose weight and burn body fat, your body needs to use the energy. This is accomplished through diet and exercise 

The diet side. Too many calories create fat in your body. The first step toward burning fat is to take in an appropriate amount of calories. This creates an even exchange: your body uses your daily calories and has none extra to store away. ‌

‌The exercise side. Now that you have your caloric intake in check, it’s time to increase the number of calories your body needs through exercise. Moving more means your body requires more energy. ‌

If you don’t increase your caloric intake, your body starts burning away at the stored energy in your fat. With enough time and dedication, the fat stores will be gone. 

Where Does the Fat Go?

What does it mean to “burn away” fat? Doesn’t science say that energy can’t be created or destroyed? 

When you lose weight, fat goes through a series of metabolic processes. It’s used to fuel all of the moving your body is doing now that you’re exercising. 

There are two byproducts left when fat is broken down for energy: water and carbon dioxide. All of the other good, energizing molecules from your fat are used up by your body. 

The water leftover from your fat comes out of your skin as sweat or is eliminated as urine. The carbon dioxide is breathed out from your lungs. 

Not only does exercise use up the leftover energy stored in your fat, but it also gets rid of the traces left behind. Since exercise makes you breathe more, the lungs make an efficient fat-burner. 

How to Burn the Fat Easier

The process for burning fat sounds simplistic. But for many people, diet and exercise are a real challenge. 

Once you do the math to determine how many calories you need, you can start working toward lifestyle changes to burn away the extra fat. 

Observe your habits. Monitor your current eating and exercise habits using a notebook or tracker app. This will provide you an awareness of your current lifestyle and can help direct you toward informed change. 

Find your favorite exercise. It doesn’t have to be running or weightlifting. You can get exercise doing many activities, including:

  • Swimming
  • Dancing
  • Recreational sports
  • Physically interactive video games
  • Playing with your children or pets

The important thing is to make it fun

Sleep. Sleep works twice as hard. It provides your body with necessary energy and burns calories. 

Eat mindfully. Make your meals something you actively do. Take your time while eating, and be mindful of the food — each bite — and the whole meal. 

Show Sources

SOURCES:

BMJ: “When somebody loses weight, where does the fat go?”

Cleveland Clinic: “Where Does Body Fat Go When You Lose Weight?”

Harvard Health Publishing: “7 habits to help you lose weight and keep it off.”

HealthySD.gov: “Learning About Calories.”

Mayo Clinic: “When you lose weight, where does the lost body fat go?”

U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015–2020 Dietary Guidelines for Americans. 8th Edition. December 2015.

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