So I have been away from the blog for a week due to manuscript preparation, revisions and submissions, and, a good ol’ Autumn cold. But I’m back and with a topic that is the result of a conversation over dinner.
It went something like this, “what exactly am I losing now that I have increased my training?” Me, “well you are losing fat, but it is actually quite hard to lose fat because you don’t lose fat cells. This means that it is easy to gain weight again” Friend, with very confused expression, “but, where is it going then?” Me “umm…..I think I should blog about this”.
I went to the trusty search engines and stupidly typed in “Where does fat go when you exercise?” Oh the deluge of weight loss tips, super food advice and ‘buy these fat burning tablets’. Hmm, that wasn’t what I was hoping to find. So I tried a different tactic.
What is fat?
What exactly is fat? Fat (which can consist of tri-, di- and monoglycerides) is a type of macromolecule known as a lipid, and is distinguished by a chemical structure that renders is hydrophobic. This means that it does not dissolve in water. And, because of the specific structure of fats, they store large amounts of energy.
So, fats are an energy source and are therefore important fuel for the body.
Fats are stored in specific cells known as adipocytes. Fats are made up of 3 (tri-) fatty acids. Fatty acids can be obtained from the diet, or produced by our own cells. Importantly, fatty acids can be reassembled into triglycerides, aka fat.
Ahhh, so this is where the penny drops. Fatty acids that are not used will form triglycerides and stored in fat cells.
Calorie in, calorie out.
The food we eat is digested into its macronutrients that can be used by cells as building blocks for proteins, or, for energy. Calories are the energy obtained from food. So, if you are exercising and your muscles require large amounts of quick energy, consumed calories obtained from carbohydrates in the form of glucose will be utilised first before fat cell stores. Energy will be obtained from triglycerides in between meals.
So, calories in, calories out. If you consume more calories than required, these will be converted to triglycerides and stored within fat cells. If your body never needs to use the triglycerides stored in the fat cells, the fat will remain.
So…when do we use energy from fat?
It has been demonstrated that fat cell triglyceride energy production occurs during low intensity exercise or after in the recovery phase, whereas carbohydrate triglyceride comsumption is favoured during high intensity exercise. Consumption of fat triglycerides decreases with incresing exercise intensity.
So….where does the fat go?
This is the question, isn’t it? Well as you can guess, it is removed from fat cells (which then shrink) and used for energy. The energy production also produces carbon dioxide and oxygen as a by-product, which is excreted from the lungs. So, in essence, you are breathing out the fat.
The metabolism of alcohol results in triglyceride storage in fat cells. It is also preferentially metabolised as an energy source. Therefore, a big night out will not only leave you with a hangover, but also with extra fat stores……
Arner, Peter. “Human fat cell lipolysis: biochemistry, regulation and clinical role.” Best practice & research Clinical endocrinology & metabolism 19.4 (2005): 471-482.