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  • Writer's pictureJulian Molteno


“Mm, but she blinded me with science

She blinded me with science 

And failed me in biology, yeh yeh”

As any one of my Personal Training clients could tell you, I am not exactly sciencey, although I did actually pass biology — albeit by the skin of my teeth! If you want to know how many calories are in a carrot, or how many carbs there are in a tomato, I’m not your guy. I have never been good at those sort of stats — I’m much more about the broader principles involved in building muscle or losing fat — rather than the biological details. Every now and again however, it is helpful to know exactly how, biologically, we build muscle and lose (or gain!) fat. When I tell people to stop eating carbs if they want to lose weight, I find it does help with their motivation to understand how the process works. In this post I’ll try to explain (to myself as well!) how fat loss and fat gain works at a cellular level. So here we go . . . The number of fat cells in our bodies can not change, the cells just get bigger or smaller. Carbohydrates are broken down into glucose, the product of which, is glycerol. Fatty acids travel in and out of our fat cells and are used as fuel in this process. If 3 fatty acids are joined by glycerol (carbohydrate) in the fat cell, they become a triglyceride. Triglycerides are too big to exit the fat cell and are stored as human fat.  

Therefore: The more carbohydrates you eat, the more opportunities you create for triglycerides (human fat) to form. Your body is either in a: Carb/glucose/fat-storing environment Or, a: Carb-free/fatty acid/fat-burning environment How exactly do we move from a carb/glucose/fat-storing environment, to a carb-free/fatty acid/fat-burning state? To put it into more simply, we need to understand the difference between: The fed vs fasted state We transition between three metabolic states: Post Prandial State Lasts for four hours and starts as we begin to eat. We digest,absorb, store and utilise the fuel we have eaten. Post Absorptive State Lasts for six hours as we start to breakdown carbohydrate stores and begin to mobilise fat for fuel from your adipose tissue (fat). The Fasted State Takes ten hours post meal to be in a true fasted state, burning fat as your energy source. Assuming the typical person has their evening meal at 8pm, they are only in a fasted state from 6am until breakfast when we break-the-fast. In reality this translates into a 2 to 3 hour fasted period, during most of which, we are asleep and not actively burning calories. In summary . . . Post Prandial Fat burning is suppressed in favour of carb burning Post Absorptive Carbs (glycogen) stored in your liver and fats (lipid) cleared from your blood stream are used for energy Fasted Only now (8-10 hours later) are you truly using fat as fuel 

If you eat carbohydrates, you are in a Fasted State for only a few (relatively unproductive) hours a day, not long enough really to make any fat-burning difference. However, we can lengthen this fasted state by not eating until much later in the day. If we eat at about 2pm we will have been in a fasted state for around 8 hours — a third of the day — this is known as Intermittent Fasting. The plus-side to Intermittent Fasting, for carb-lovers, is that when you do (eventually!) eat, you can eat carbs. The down-side is that you have to not eat for a long stretch of the day. A further issue with Intermittent Fasting and its long periods of not eating, is that protein cannot be stored in the body. You need to eat protein regularly throughout the day to ensure you have an adequate supply available for muscle-building. Bodybuilders eat protein every 3 hours, so limiting your protein intake for 8 hours (actually longer because it takes 10 hours to reach the fasted state) every day, is not conducive to muscle-building. Some people don’t have much of an appetite, especially in the morning, so the wait until afternoon to eat is not too onerous. If you have a good appetite and the thought of not eating all morning is unacceptable to you, then the solution is to adopt a low, or no, carb diet. Instead of waiting for 10 hours or so to achieve a fasted state, not putting any carbs into your system in the first place will get you there much more quickly, or even keep you in a permanently fasted state. Low carb dieting is a vast subject and I’ll spout off about that another time. Hopefully this post has been of help in understanding the biological processes involved when using carbs or fats as an energy source. Understanding how our bodies respond to the foods we put into them can help us make more informed choices of how we want to eat.  

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