Most people want to lose weight, and while the details of each individual method vary, for the most part it involves cutting calories and increasing exercise. Less carbs, more time on the treadmill = weight loss. Simple. But what is going on inside your body? What makes your system burn fat instead of muscle? Are you sure you are burning fat and not muscle? Why can such a simple formula be quite difficult to put into practice? Why do we get so hungry, why is it easy to lose fat at first and then it gets harder and harder? What happens inside our body when we diet?
When you reduce caloric intake and increase caloric expenditure, your blood glucose and insulin levels drop. Glucose is the energy source into which food is broken down, and insulin is what the body uses to drive that energy into fat, muscle cells, and the liver. Therefore, less food equals less energy and consequently a drop in the amount of insulin needed to process it. This drop makes your body turn to fat for energy, which is great! Catecholamines are released, which further triggers your body’s use of fatty fats, causing the amount of acid in your blood to increase, which leads to increased fat burning in the muscles and liver, as looking for a source of energy to replace glucose.
So, in effect, glucose and insulin drop, causing your body to recruit fatty acids from your fat stores, which are then used by your liver and muscles for fuel. You become mildly resistant to insulin, as your body no longer wants to store glucose but rather use it, with the side effect of helping you burn even more fat. These are all good things, but they are not everything.
Your fat acts as its own endocrine system, releasing hormones like leptin, ghrelin, and others. By reducing the number of fat cells doing this, you reduce the amount of hormones that are released, alerting your brain to the decrease in fat. So your brain assumes you’re not eating enough, which slows down the metabolism of your liver, muscles, and fat cells. Your drop in insulin causes fat mobilization, but it also causes testosterone to better bind to sex hormone-binding globulin, which reduces the amount of free testosterone in your system, while increasing cortisol. This causes protein/muscle breakdown through your liver, as well as decreased protein synthesis as your body places a lower priority on building muscle. You basically start to lose muscle.
So the consequence of dieting is that muscle breakdown outpaces muscle building and hormone levels drop, so your metabolism slows down. This causes you to burn less fat, your muscle development slows or stops, and damages your immune and reproductive systems (they’re not considered important when you’re starving yourself). What’s more insidious is that all this slowing down means your body will go into overdrive when you start getting enough food. And that acceleration will translate into the recovery of all your fat.
Therefore, dieting is a complex process that becomes more difficult as you progress. Losing weight at first is easy, but within a few days your metabolism slows, your immune and reproductive systems fail, you start to break down muscle, and all your losses will be made up when you start eating normally again. How do you avoid this bounce when you reach your desired weight? One word: exercise. But that is material for another article.
