Where Does Fat Go When We Lose Weight?

Jennifer O'Donnell-Giles | May 9, 2016

Obesity rates and the overweight population are on the rise and researchers are trying to understand why this is happening and how we can reverse this trend. Despite all the attention and research going toward lowering the rate of obesity, there’s still confusion among experts and the general public about metabolism, how your body processes food, and the biological process of weight loss.

When we lose weight, where exactly does all the fat go? It’s important that we know the answer to that question, because the answer provides the key to fighting obesity. This knowledge can help us build more tools and educational programs to better understand how our bodies work. And when we understand how fat is really stored and burned, we have more control in our weight management efforts.

Popular Myths about Fat During Weight Loss

Most people don't know what happens to fat during weight loss, but there are common misconceptions about the process. The popularity of these ideas can come from a number of places, including unqualified research on the internet, a misunderstanding of explanations given by medical professionals, or unsubstantiated word of mouth. The most common include:

  • Fat is converted to muscle.
  • Fat is converted to energy or heat.
  • Metabolites (byproducts) of fat leave the body through the excretory system.

The Real Story

When your body doesn’t use up all of the calories you’ve consumed in your diet, the extra calories get stored as fat. Excess carbohydrates and protein are converted into triglyceride, a type of fat found in your blood. Triglyceride is then stored in lipid droplets of fat cells, called adipocytes. Excess dietary fats are more easily stored and don’t require any conversion aside from lipolysis, in which lipids are broken down to release fatty acids. People who wish to lose weight are attempting to metabolize the triglycerides that are stored in their fat cells. In other words, they’re trying to use up and break down fats so that less gets stored in their bodies.

Lifting the Veil on Weight Loss

At rest, an average person who consumes a balanced and varied diet, exhales a certain amount of carbon dioxide every minute. This same person exhales double the amount when he or she is awake and performing everyday activities. Exercising releases seven times the amount of carbon dioxide! Ultimately, the lungs are the primary excretory organ of fat and losing weight requires unlocking the carbon that is stored in fat cells.

While weight loss is not a perfect science, we can all agree that it’s important to keep moving. The more active you are, the more carbon dioxide you exhale, which is how fat exits your body. However, consuming excess food easily hinders weight loss efforts, even with physical activity, because the caloric intake of food offsets the amount of carbon dioxide that gets exhaled.

So, remember to combine your exercise routine with healthy, portioned meals so you’ll have more control over your weight and your health!


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Jennifer O'Donnell-Giles

Jenn Giles, R.D., C.S.S.D. is all about health and wellness. She has over 15 years’ experience, including a dual master’s degree in Nutrition and Exercise Physiology from Columbia University. She is a Registered Dietitian (RD) and a Board Certified Specialist in Sports Dietetics (CSSD). She supplements all of this with her spin instructor certification and USATriathlon Level I Coach Certification.

Jennifer is passionate about (actually, obsessed with) the sport of triathlon. She has been personally participating in triathlons since 2000 and running road races since 1992. She is a two-time Ironman finisher and has completed countless numerous marathons. She has been a member of Power Bar Team Elite since 2006 and competed as a member of the 2006 Aquaphor/Active.com Sponsored Athlete Team. She was ranked as USAT All American Honorable mention in 2006 and 2011. Jennifer does all of this along side of her husband, Patrick, who is an equally accomplished triathlete and runner. They try as hard as they can to do all of their training and racing together.

She will tell you, however, that her most important, most rewarding and most challenging job is as a mother of four. She knows first hand the challenges of maintaining optimal fitness, overall good health and achieving goals while raising a family - of which good nutrition is the cornerstone.

Most importantly, she knows how to motivate, inspire and challenge athletes based on their own abilities, strengths and everyday lifestyles. She believes there is an athlete in everyone - no matter what their abilities are – and if those abilities are manifold, then there is an even better athlete in there!

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