Medically reviewed on January 4, 2024 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.
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When losing weight, there’s one word you hear most: calories. Calories from the food and drinks you consume give you the energy you need to shuffle your kids out the door, complete your pilates workout, and fuel your daily activities.
Eating too many calories, however, can lead to weight gain. The body is unable to use all the excess calories for immediate energy needs, and the surplus is stored as excess fat. Adopting a healthy lifestyle with physical activity and creating a calorie deficit—that is, eating fewer calories than your body requires (such can be the case with a low-carb, high-protein diet)—can help facilitate body fat loss for some people.
But where does fat go when you lose weight? It all starts in the mitochondria.
After consuming food, the stomach and small intestine break it down and convert it into glucose (sugar), amino acids (the building blocks of protein), or fatty acids (which make up fat). The small intestine then absorbs these particles and passes them into the bloodstream, where nutrients can travel to various parts of the body and be used as fuel.
Eating a surplus of calories, especially those containing fats, can lead to weight gain. These particles are broken down into fatty acids and glycerol, and they still make their way into the bloodstream. However, the body does not need them—it’s had its fill.[1,2]
In that case, adipose tissue, or fat tissue, absorbs the excess glycerol and fatty acids. Here, they become triglycerides, a type of excess fat that’s stored within fat tissue as the body’s energy reserve.[1,2]
If a calorie deficit occurs, the body uses the stored fat cells for energy.
Losing fat involves a process called lipid metabolism, a term that refers to how the body breaks down and uses fats in the body. During this process, triglycerides are fragmented into their principal components: fatty acid and glycerol.
Various physiological processes further break down each component until the molecules are small enough to pass into the mitochondria of the body’s many cells, where energy production occurs, thus fueling the body.
There are two byproducts after this progression: water and carbon dioxide. The body dispels water through the skin via sweat, and the kidneys via urination. Carbon dioxide leaves the body through the lungs when you breathe out.
Consuming fewer calories isn’t the only way to burn fat. You can also implement healthy lifestyle changes, such as regular exercise, to facilitate fat loss. Understanding the difference between fat loss vs. weight loss is crucial to achieve a healthy weight.
Let’s say you’re running a 5K. Your quadriceps help to lift your knees, your calf muscles contract to propel you forward, and your abdominals help to stabilize the spine and pelvis. To complete each of these actions, your muscles require energy. First, your body uses stored sugar, a readily available energy source. After about 30 to 60 minutes, fat burning begins.
Weight lifting and resistance training can also facilitate healthy weight loss by increasing your muscle mass and basal metabolic rate—the amount of calories (energy) your body uses at rest.
Where you’ll lose weight is largely determined by genetics,each person’s unique body composition, and weight distribution. There’s no one-size-fits-all answer when losing weight.
Namely, genetics can determine where in your body fat is stored. If you have family members with larger hips and thighs, you may also have a higher chance of carrying adipose tissue in these areas. In the same vein, studies suggest that looking at your family tree may also help inform weight loss. Asking your parents about what types of weight loss strategies work best for their body composition might also help you, too.[4,5]
That said, your sex may be able to give you a few hints as to where you might first see smaller measurements. Research found that men and people assigned male at birth (AMAB) most commonly experience fat loss in the trunk area, while women and people assigned female at birth (AFAB) may lose more weight around their hips.
As you lose weight, cells utilize fat reserves to fuel the body’s various functions, such as breathing, digesting food, or walking to your mailbox. The body then expels the byproducts, water and carbon dioxide.
While it’s not possible to determine exactly where you’ll first observe fat loss in your body, you can gain a few clues by looking at your family history and personal history with weight loss. If you’re unsure where to start, Everlywell is here to guide you through various stages of weight loss.
Our fast and easy telehealth visits assign you to a qualified healthcare provider who can discuss your weight loss journey and provide valuable insights. When you enroll in the online weight management program, you’ll also have access to glucagon-like peptide 1 (GLP-1) prescriptions (pending qualification), as well as at-home lab tests, supplements, and lifestyle recommendations to support your journey.
Enroll today for a healthier tomorrow.
Jordan Stachel, M.S., RDN, CPT is most fulfilled when guiding others towards making stepwise, sustainable changes that add up to big results over time. Jordan works with a wide variety of individuals, ranging in age from children to the elderly, with an assortment of concerns and clinical conditions, and has written for publications such as Innerbody. She helps individuals optimize overall health and/or manage disease states using personalized medical nutrition therapy techniques.