A Primer on Body Fat Metabolism: Fuel Usage…

As a continuation from previous posts to document best practice of fat loss training and nutrition we always feel it is best to educate first so people who train with us understand the principles of fat metabolism. To understand how to burn fat it is important to understand how it is stored. Fat cells are very well suited to energy storage though their role in their body is more extensive than commonly reported. They are not inert but perform a number of vital functions- body fat in fact is not necessarily bad in fact it plays a number of roles.

After absorption in to the blood stream dietary fat is broken down and packaged in to a structure called a chylomicron. Here it is absorbed in to the lymphatic system appearing in the blood stream around three hours after consumption. Some of this will be used for energy while some will be stored. This will be dictated by energy demands influenced in part by hormonal activity- simple so far!

 Fat cells are made up of a molecule of glycerol (a molecule of carbohydrate) combined with three fatty acids storing them as a triglyceride. When stored triglycerides are broken down it releases the three fatty acids and the glycerol in to the blood stream. 

Glycerol can be converted back to glucose(carbohydrate) in the liver and hence can be re-used by the body as a carbohydrate energy source. Glycerol comes from dietary carbohydrate or in periods where this is unavailable the body will convert other fuels (pyruvate, lactate and the amino acids (proteins) leucine and alanine).

What it is important to understand is that firstly the body will always find a fuel to use if it’s primary sources are not available. Secondly, the usage of these fuels is in a state of constant flux meaning that you don’t just burn fat or carbohydrates or even proteins- they are all used concurrently in different amounts. And thirdly, energy utilization is dictated by activity, current dietry practices (short and long term) as well as in part hormonal regulation.

In the next post I will describe the types of body fat we have and why certain body fat types are vital for our survival.

Published by ianmellis

Ian Mellis MSc. CSCS is the co-founder of Results FAST (www.resultsfast.com)based in Ware, Hertfordshire. Specialising in athletic development, physique improvement and injury rehabilitation he provides personal training, strength and conditioning and nutrition coaching for motivated exercisers and those looking to make a long term change to their health, fitness and performance.

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