Weight loss is a captivating and complex topic that sparks numerous questions. From the process of shedding those extra pounds to the enigma of what happens to the fat we lose. This latter puzzle becomes even more intriguing when we talk about fat 'burning off.' But where does it actually disappear to? Come along as we embark on an enthralling exploration of the science behind fat loss!
In straightforward terms, we lose weight when we tap into the fat we've stashed away as an energy source. The energy tucked inside those fat cells gets unleashed and put to work by the body's cells in need. This process leads to a reduction in the size of fat cells and, in turn, our body size shrinks.
Our bodies demand a daily supply of energy to carry out a myriad of functions: breathing, maintaining our heartbeat, moving, digesting food, thinking, chatting, blinking – you name it, it requires energy. This energy comes from both the foods we eat and the energy stores within our bodies, including fat tissue and carbohydrates stored in the liver and muscles. When we create an energy deficit by consuming fewer calories than our body requires, it triggers a call to our energy reserves to make up the difference. That's when we tap into our fat and carbohydrate stores, leading to weight and fat loss.
So, what's the deal? Contrary to popular belief, we don't sweat or excrete the lost fat. Instead, it's a simple energy transfer. The stored energy in the form of fat cells is transformed into another type of energy – whether it's energy for movement or digestion, depending on what our body needs.
Here's a breakdown of the various ways our bodies use energy each day:
The lion's share of our energy expenditure goes toward sustaining basic bodily functions – things we don't consciously control. It encompasses all the processes within our 37 trillion cells that make up our organs, including our hearts and brains. This is known as our basal metabolism, and it accounts for approximately 60-70% of our daily calorie burn. Imagine if we were asleep all day; this would be the number of calories we'd burn.
From the moment you get out of bed, your body starts burning extra calories as you move around – brushing your teeth, walking around the house, even spreading butter on your toast. This type of movement is classified as 'non-exercise activity thermogenesis' (NEAT) and contributes to around 10-15% of our daily calorie needs. It's all the stuff you do when you're not eating or intentionally exercising.
Did you know that even eating burns calories? Digestion is a complex process that demands energy to work effectively, and different foods require varying amounts of energy for processing. While you might have heard of foods like celery having 'negative calories,' where the body expends more energy digesting them than they provide, this is a bit of a myth. We only use about 8% of the calories in celery to digest it. Protein has the highest thermic effect, using up to 20-30% of the energy it supplies, as it's quite challenging for our bodies to break down. In total, the thermic effect of food makes up only about 10% of our total calorie burn, so it's not a substantial weight loss method.
The remaining calorie burn arises from exercise, labeled as exercise activity thermogenesis (EAT). Depending on your activity level, this can vary significantly, but for the average person, it usually contributes to around 10-15% of energy expenditure. Surprisingly, it might seem low, but when you consider how much of your day is spent exercising, it makes sense. Exercise is undoubtedly crucial for a healthy lifestyle, but it highlights the pivotal role of food choices in achieving successful weight loss.
Nutritionist Emma White (ANutr), MSc Human Nutrition is passionate about how food science applies to the human body, and how the nutrients in what we eat affect us and ultimately have an impact on our health.