Metabolic adaptation

In this article we will tackle an issue that every dieter encounters, especially if they’ve had success. We will answer two questions

1. Why are diets successful early on?

2. Why do diets slow down the longer we stick to them?

In order to discuss today’s topic we have to be familiar with the text about calories because the information and terms from that piece are essential for today’s discussion.

Let’s set up a very simplified diet, say a person maintains their weight at 2000 calories (TDEE). This person decides to go on a diet whereby they will eat 1500 calories per day. Say this person weighs 70 kg. On a weekly basis, this person achieves a caloric deficit of 3500 calories which will be enough to drop around 450 grams of fat (this is a very simplified model, but it’s a decent estimate). The largest component of your total daily energy expenditure is BEE which depends on a person’s height, weight, muscle mass, gender and genetics. Most diets are based on the exclusion of carbs, especially sweets, pasta and dough-based products. In the first 3 weeks of this restriction will lead to a drop of 3 or kilos of weight. That drop will be mostly water and maybe a kilo or so of fat. The reason why you will mostly drop water is due to a simple fact that carbohydrates retain water in your body. There is also a solid chance that the diet doesn’t include enough protein and if the person isn’t physically active, that drop will also be made up of muscle mass loss.

A month into the diet, the person from the example has 65 kg, even less muscle mass than at the beginning which will result in a decrease in BEE and with that decrease comes a lowered TDEE. Say that the total energy expenditure has now dropped to 1600 calories a day and the person is still consuming 1500, that deficit is now a lot less significant. The results will start to slow down which leads to frustration and the person eats a chocolate bar (worth 300 calories) to reward themselves for the good effort and results and we are back in a calorie surplus. What does a calories surplus do? It leads to an increase in weight.

Obviously, this example is extremely simplified, but it explains reasonably well why diets yield great results early on. The reality is even worse because most diets are too restrictive both in terms of caloric intake and food selection which leads to extreme results fast. However, those results are not sustainable and neither is that lifestyle. As mentioned in the example above, this restriction often comes at the cost of carb intake which will lead to “emptying” and the drop in weight won’t be real because the weight will come back as soon as you start eating carbs again.

The fact that you will be a smaller human being after a while on the diet makes it easier for your organism to keep you alive which will reduce BEE, but that’s not the only type of energy expenditure that goes down. NEAT type of activity will go down as well. You will simply choose the elevator over stairs every time and you will stop fidgeting or making hand gestures whilst you speak. If NEAT goes down so does the total energy expenditure which means that you need an even bigger deficit.

What else goes into your TDEE? The thermic effect of food. It’s based on the total caloric intake. What’s happening to your calories? They are decreased leading to an even smaller expenditure. The only element of TDEE we haven’t talked about is physical activity. This is important for people who train, your gym performance or whatever it is that you train will be weaker due to a lack of energy. If your output is weaker so will be the energy you need to produce that output meaning that your total expenditure goes down, forcing you into a state where you need an even lower calorie deficit. This happens due to the fact that you cannot produce the same force as you could when you were 5 or 6 kilos heavier and on top of that fatigue catches up with you faster.

Just as the sum of 4 types of energy expenditure gives total energy expenditure, the sum of decreases in those 4 types of energy expenditure gives metabolic adaptation.

The sole piece of advice I will leave you with is that you should not fall for the trap of the “magic diet”. Namely, if a diet is giving “unbelievable” results, it is simply the natural course of events of extreme restrictions.