Part 3: Theory of Weight Loss 

Before deciding on your calorie intake you need to do some research. Stopping eating is one way to lose weight but you run a substantial risk of causing yourself irreversible damage if you try it so I wouldn’t recommend it. Measuring how much energy a person uses is actually rather difficult but the figures of 2000 calories a day for a woman and 2500 calories a day for a man aren’t far out for the vast majority of people. These figures expect you to be doing a moderate amount of exercise each day so if you sit around in an office all day and then slump in front of the TV in the evening they are a bit on the high side. The figures also don’t take into account your existing weight which has a moderate effect on your calorie requirements.

The Theory

Believe it or not exercise is not a very good way to lose excess weight. The number of calories the average person can burn exercising is not going to compensate for even moderate over indulgence. A much better way to lose excess weight is to simply not eat the excess in the first place. The total calories you need in a day can be split into three different groups:

• Basal Metabolic Rate (BMR) or Resting Metabolic Rate (RMR). These two measures are subtly different and the later is probably more realistic but they measure the amount of energy you require just to live.

• Thermic Effect of Food (TEF). Broadly this is the energy required to process the food that you have eaten. Some foods require virtually no energy to process others require substantial energy to process. An urban legend has grown up around this measure that states that celery and grapefruit have net negative energy balances in humans – there is no strong evidence for this either way. With an average diet TEF is usually about 10% of the total energy intake.

• Physical Activity (PA). This is the amount of energy required to make up for the energy expended due to exercise.

This gives us a simple equation that can be used to discover how many calories a person needs to maintain their weight:

TEE = BMR + TEF + PA

where TEE is Total Energy Expenditure. If you are consistently eating above your TEE then you will put on weight if you consistently eat less than your TEE you will lose weight – it really is that simple.

A lot of people find that they struggle to lose weight on a calorie restricted diet. At first glance this would seem to be impossible as the mathematics show that you will lose weight if you eat less. The problem is that the human body will attempt to resist losing weight and it does this in two ways. Firstly, and most importantly, it tries to lower your BMR by minimizing the amount of energy your body uses. There are various ways your body can do this but if you consistently eat well below your TEE your body will start to remove muscle mass to lower your BMR. Secondly, in an effort to reduce your PA your body makes you feel lethargic, by doing less exercise it can conserve calories.

Your body will, if given the chance, minimize you calorie requirements to the point where you are eating virtually nothing but still not losing weight. You may consider this an annoying trait but don’t forget that humans evolved to survive in an environment where food wasn’t guaranteed so being able to cut back when needed was a good thing. The trick to dieting, if trick is the right word, is to make sure your body doesn’t think that it is in survival mode which is a two step process – eat and exercise.

By eating every few hours, which seems counter intuitive, your body believes that food is in ready supply so it doesn’t panic and go into power saving mode. Exercise ensures that your body thinks that it needs to do remain active so it holds off on making you feel lethargic even though you aren’t eating enough to maintain your weight. In fact if you weren’t exercising before starting your diet then exercise is a double win as you will be increasing your calorie requirements as you build muscle.