Where does the fat we lose go?

Beth Furness - Assistant Nutritionist | 23 Oct, 2023

Healthy Balance magazine!

Spring edition now live.
Find it in the app – tap 'More'.

Read now

Weight loss is an intriguing and multifaceted topic that raises many questions! From the process of how we shed those extra pounds, to the mystery of where the fat we lose goes. This latter question is particularly interesting, when we speak of fat 'burning off', where does it actually end up? Join me on this journey as we delve into the fascinating science of fat loss!

Why do we lose weight?

In simple terms, we lose weight when we use the fat we have stored as a source of energy. The energy stored within the fat cells is mobilised and released to be used by the body cells that need it. This causes the fat cells to shrink in size, as the energy stored within them is released and utilised – this is why we get smaller because our fat cells and tissue shrinks.

Where is the energy used?

Our bodies require energy every day to perform all our functions such as breathing, keeping our hearts beating, moving, fidgeting, digesting food, talking, thinking, blinking – you name it, it needs energy. This energy comes from a combination of the foods we eat, and the energy stores we have in our body, in the form of fat tissue or carbohydrates stored within our liver and muscles. When we create an energy (calorie) deficit, by taking in less energy from the foods we eat than our body needs or through exercise, we cause our body to call on its energy stores to make up the shortfall. This is when fat and carbohydrate stores are tapped into and weight loss occurs.

Of course on a more complex level there are a whole host of chemical reactions that occur within our body during fat loss which lead to the production of by-products such as carbon dioxide and water, and these are removed from our body through breathing and sweating for example. This is how some of the weight is removed from our body. But in the most basic sense, the fat we lose is broken down and used as energy.

Below I've included a little breakdown of all the ways our body uses energy each day as helpful content on where our fat loss goes!

Person

  1. Basal Metabolic Rate (BMR)

    The vast majority of our energy expenditure is used on simply keeping us alive. Around 60-70% of the total number of calories burned in a day are used on all the internal processes in our bodies that we don't control – the function of all our 37 trillion cells that make up our organs, including our hearts and brains. This is known as our basal metabolism. If we spent 100% of our time asleep, this would be the number of calories we'd burn.

  2. Non-exercise Activity Thermogenesis (NEAT)

    Okay, now imagine you've woken up, got out of bed, and headed to the bathroom to brush your teeth. Already, your body is burning more calories from these everyday movements. Walking around the house, moving your arm to brush your teeth or spread butter on your toast – all of this requires energy. We term this 'non-exercise activity thermogenesis', or 'NEAT' for short. Under this umbrella comes everything we do when we're awake that isn't eating or intentional exercise. Depending on how much you happen to move day to day, this type of movement makes up around 10-15% of our calorie needs.

  3. Thermic Effect of Food (TEF)

    Yes, even eating burns calories! The digestive process is complex and requires energy to work properly, plus there's evidence to suggest different foods require different amounts of calories to be processed. You might have heard that foods like celery and broccoli contain 'negative calories' – that is, the body uses more energy digesting them than they actually provide us with. Negative calorie foods don't really exist, as we'd need to use at least 100% of the calorie content of a food to digest it for this to be true. We only use around 8% of the calories in celery to digest it. The nutrient with the greatest thermic effect is protein, using up to 20-30% of the energy supplied, as it's quite a tough one for our bodies to break down and process. In total, the thermic effect of food only comprises around 10% of our total calorie burn, so you can't really rely on it as a method of weight loss.

  4. Exercise Activity Thermogenesis (EAT)

    Any remaining calorie burn comes from exercise, known as exercise activity thermogenesis, or EAT. Depending on how active you are, this can vary a fair bit, but for the average person, this usually comes in at around 10-15% of energy expenditure. Which might be surprisingly low! But if you think about how much of your day is spent exercising, this really isn't a lot. Don't get me wrong – exercise is a crucial part of a healthy lifestyle, but it goes to show how much food choices underpin weight loss success.

Nutritionist Beth Furness (ANutr), holding a BSc in Nutrition and Health, is deeply dedicated to applying evidence-based knowledge to all aspects of nutrition. Her passion lies in fostering healthy relationships with food, ensuring that everyone maintains a balanced and sustainable approach to nutrition.

This site uses cookies to personalise content and ads, provide social media features and analyse our traffic. Find out more about how we use cookies.

Choose which cookies you allow us to use. You can read more about our Cookie Policy in our Privacy Policy.

Accept cookies Reject cookies