To explain the theory of fat availability, we have to start with a little bit of basic physiology. Specifically, we have to look at how our body fat actually works.
The main purpose of our body fat is to serve as an ‘energy reservoir’ for our bodies. In times of caloric excess (overeating) our body fat expands to store energy by one of two processes:
1. Hypertrophy (fat cells get bigger in size)
2. Hyperplasia (fat cells multiply in number)
They expand to store energy in the form of triglycerides, to be used later as energy to supply our metabolic demands when energy from food is limited (caloric restriction or dieting). In other words, our body fat has the unique ability to rapidly expand or contract depending on nutritional status (Energy Surplus or Energy Deficit).
Free fatty acids (FFAs for short) are what is released from adipose (fat) tissue when we need energy. Notice, this is happening throughout the day even if you’re not dieting; however, it’s elevated when we are fasting, exercising or in a caloric deficit (dieting). This is a very good thing since most of us who are dieting and exercising are doing so because we want to decrease the amount of our body fat!
When “fat” is released from your body fat stores, it can end up in a few different places.
1. It can go to the liver and get stored there
2. It gets burned for fuel by other organs (heart, liver, kidneys etc).
3. It simply gets recycled back into your body fat cells to be re-stored. (Thompson BR Mol Cell Endocrinol. 2010; Ahmadian M Int J Biochem Cell Biol 2010)
The simple reality is that all 3 of these processes are happening throughout the day, every day. The major difference when gaining or losing weight will be the percentage of fat being recycled back into fat tissue versus the amount being burned by other organs.
The movement of fat in and out of your fat cells is an extremely important process that needs to be tightly regulated. The FFAs that are not burned as fuel must quickly be taken up by the liver or recycled and stored back in your fat tissue.
Excess circulating fat that is not either burned or stored can cause an inflammatory response, which when chronically elevated, can lead to a whole host of health issues and metabolic disease states (Sun K J clin invest 2011). This is how excess fat and an inability to effectively burn/store the fat contributes to metabolic disorders like adult onset diabetes and heart disease.
And it gets worse!
Should this extra fat remain circulating for too long, it can also cause ‘ectopic’ fat storage, which is basically fat being stored in places it shouldn’t be stored (like your heart and liver). I'm sure you can imagine how this can lead to severe health consequences in the long-term.
As you can see it is extremely important for your body to regulate the amount of fat entering your blood stream.
Basic gist: you cannot have every single one of your fat cells empty out all at once into your blood - the results would be catastrophic!
Each of your fat cells is able to release fats into your blood stream at a predetermined rate, and the ‘rate’ at which an adipocyte can do this is relatively fixed for your own protection. It can increase to match the needs created by dieting and exercise, but even during exercise, higher energy needs simply cannot be met by fat (which is why we rely primarily on carbohydrate during high intensity exercise).
The amount of energy your fat can provide when you are dieting is dependent on how much body fat you have. The more body fat you have, the larger the calorie deficit you are able to ‘fill’ with the energy stored in your fat.
The word ‘fill’ is actually a good way of describing what your body fat does when you’re dieting. When you diet, you create an energy deficit (essentially a gap between the amount of energy you take in, and the amount of energy you’re expending on a daily basis). In an ideal world, this gap is filled exclusively by the energy that is stored in your body fat.
However, as you lose body fat, the amount of fat that can be released also decreases. This means most people do dieting wrong, and specifically, they do it backwards. The more body fat you have, the lower you can go with your calories and longer you can go eating low calories without experiencing any ill effects. But, towards the end of a diet, when body fat levels get lower and lower, the calorie deficit needs to be shorter and smaller.
When you are carrying large amounts of excess body fat, you can eat less for longer because your body has plenty of fat to burn as a fuel to ‘fill in’ your calorie deficit. One way to imagine it is like having a full ‘tank’ of reserve energy. As your body fat levels decrease you can no longer handle as large a deficit for as long a period of time. This makes sense that the less fat you have to lose, the slower it comes off. Think of it as having less “taps” to pull from, where each “tap” has a maximum outflow of fats that can be released in any given time period.
At the extreme low end, when your body fat cannot ‘keep up’ with the energy deficit you've imposed on your body, the energy MUST come from SOMEWHERE. This is when you are at risk of losing lean body mass during dieting (commonly referred to as ‘starvation mode’). This happens at extremely low levels of body fat, under 6% in men and 12% in women (Friedl K.E. J Appl Phsiol, 1994).
When a large energy deficit is maintained while there is limited body fat available, metabolic disturbances such as altered Testosterone, Thyroid and Cortisol levels begin to take place and negatively affect both your muscle mass, and overall muscle strength. (Nindl B.C. Med Sci Sports Exerc, 2007; Freidl K.E. J Appl Physiol 2000).
As body fat levels decrease so does your ability to handle a large energy deficit. Most trainers or weight loss coaches are not paying attention to (or are completely unaware of) the Theory of Fat Availability when they design a diet. They end up telling their clients to continually decrease the amount of calories they consume as they get leaner; this leads to a whole host of problems, including feeling sluggish, depressed, moody, a loss of muscle mass, water retention and bloating, metabolic alterations and a general feeling of ‘not wanting to diet or exercise anymore’. This is something that a lot of trainers do and I have to hold up my hands to say that when I first started doing PT it is something I recommended but since researching this, I have stopped.
The Theory of Fat Availability:
• There is a fixed rate of fat that can be released from a fat cell.
• The more fat you have, the more fat can be used as a fuel when dieting.
• The less fat you have, the less fat can be used as a fuel when dieting.
• Towards the end of a weight loss diet, when body fat is extremely low you may not have enough fat to handle a large caloric deficit anymore.
Next week I will be adding a new article to discuss Metabolic rates and then I will be sharing some tips to help you lose weight while actually eating more, following the above principle!