"Dieting" for too long causes your metabolism to drop correct?
Well in most cases, yes, but there is an exception, so continue reading to find out more.
The majority of studies have shown that chronic dieting (eating less calories than your body needs on a regular basis) leads to a drop in metabolism.
This is why the vast majority of contestants on the TV show The Biggest Loser end up regaining all the weight back (see link below).
This happens for the following reason:
When your body feels that it is not getting enough calories (dieting), it goes into "starvation mode". This is a natural self defence mechanism which the human body developed over thousands of years to deal with periods when food is not available.
During starvation mode, the body does its best to preserve energy: lowers metabolism, increases fat preservation, lowers fertility, and lowers immune system.
Because of that, it is extremely difficult to lose fat when the body is in "starvation mode": the body is actively trying to save energy, this means that it wants to hold onto the fat it has.
If you exercise during that period, you make matters worse: you're telling the body that even though food is not available, I'm going to also stress you out. The body goes even deeper into starvation mode, trying to save every bit of energy it can.
However, a recent study (link below) has shown that there is a way to go on a very low calorie diet but still protect your metabolism from dropping.
In this study, the subjects who went on a very low calorie diet but also maintained "nutritional ketosis" actually maintained their metabolism and ended up losing more fat than those who just went on a very low calorie diet.
(Note: nutritional ketosis should not be confused with ketoacidosis, a common confusion among doctors and healthcare practitioners. The 2 are completely different and have completely different consequences).
Anyway: what is nutritional ketosis? It's a condition when the body is primarily burning fat for fuel.
When the body burns fat for fuel, it protects muscles from being broken down and used up for fuel (a common problem with dieting).
How can you get into nutritional ketosis? By limiting carbohydrates.
When you eat carbs, your insulin goes up, which switches off "fat burning" in the body. When you run out of glucose in the blood (because you're on a diet), your body goes after your muscles for fuel, resulting in higher cortisol and lower metabolism.
But when you limit carbs and focus on eating more fat (and moderate protein), your body switches to fatty acids for fuel. And when the fat from your food is completely used up, your body will stay in fat burning mode and use your own fat for fuel.