Fat loss, in theory, seems simple enough. Eat less food, burn more calories than you eat, and supposedly we can watch the fat fall off. While this isn’t incorrect, it doesn’t necessarily always work as simply as that. Many people set themselves incredibly low, difficult to maintain, caloric intake limits and they still struggle to reach their fat loss goals. However, there is a reason behind the struggle. This is due to the fact that setting a strictly low caloric intake, in some cases, does not provide your body with enough energy to live, resulting in a decrease in your metabolism. You might have heard of this before, commonly known as “Starvation Mode”.
Starvation mode is how your body reacts to a caloric intake that is too low to match how much energy your body needs for normal metabolic function, and life itself. Your metabolism is reduced and generally can match your limited energy intake. As a result your body will likely favour the most efficient energy source available to sustain life – muscle and liver glycogen. Glycogen is what sugar or carbohydrates convert to inside the body, and is the main fuel source our body uses during activity. Glycogen is stored in the muscle and liver, and as a result, low calorie diets will draw energy from the muscle and decrease your lean mass – but not necessarily your fat mass. While the body is favouring glycogen and muscle, it will hold its fat mass as a reserve fuel source in case you run out of glycogen since the body thinks it is starving. As a result, your weight may decrease quite rapidly and then plateau, but this weight loss is likely not fat.
We were first introduced to this concept in what was known as the Minnesota experiment by Ancel Keys in 1944 and 1945. What can you take from this? Starving yourself isn’t going to help you achieve your fat loss goals. For you to effectively burn fat mass, you need to provide your body with enough energy to let it go. This may sound contradictory, but to make sure you’re losing fat rather than muscle, you may need to eat more food.
So how do you know if you’re not eating enough food to lose fat? One of the most obvious signs that you may be under-eating is a reduction in lean mass, with no change in fat mass. The DEXA will clearly show this pattern or result (and in some cases even an increase in fat). Your weight (on the scales) might also decline rapidly, for example 2-3kgs in 1-2 weeks. Fat is a slow source of energy and is not rapidly utilised. This weight may also return fairly quickly as well. On top of a fast reduction in weight, you may find that your physical appearance is not changing to match this reduction you are seeing on the scales and you may also feel lethargic or weaker during your training.
The most effective way to determine whether or not you may not be eating enough food is to assess your DEXA scan results and observe the changes in fat and muscle. Using these results, you can then determine whether or not you may need to increase your calories. The most effective guide in whether or not this is the case is what is known as your “Resting Metabolic Rate”, or RMR. Your RMR is calculated using the Cunningham Equation, which takes into consideration your Fat Free Mass from your DEXA scan. This then provides you with the total caloric energy you utilise each day for normal body homeostasis – to sustain life at rest. By using RMR, you can then be set an appropriate calorie intake to provide you with enough energy throughout the day while still maintaining an overall calorie deficit.
If you feel as though your caloric intake is too low, gradually increase it over a period of a few weeks to ensure the body can appropriately digest and store this energy, and return to normal metabolic function. Shocking the body with a large increase in energy may result in further fat mass increases.
While you might hear numbers like 1200 calories for women, or 1500 calories for men are the optimal levels for fat loss, this isn’t always the case. A DEXA scan will provide you with the information you require to make sure you get this right.
Jonathon Fermanis AEP ESSA
Exercise Physiologist
