Metabolic adaptation

The role of body fat

Part of what makes fat loss difficult is metabolic adaptation. The storage of fat is absolutely crucial to our survival. Even more so for humans, because our brain uses so much energy, we require a constant supply of sugar from the bloodstream. Even a minute of energy deprivation can cause long-term damage. That's why humans are unusually fat compared to other animals. For instance, a normal monkey infant has 3% body fat, but a normal human infant has 15% (a 5-fold increase!).

Because fat is so essential is why we get fat relatively easy, especially in certain environments (eg modern society with little movement and hyper-palatable foods). But not only do we accumulate body fat easily, but your body also tries to reverse the process once you do lose fat! This is why it seems so hard to diet further once you have already lost some weight. It seems that each further pound is harder than the previous one.

Physiological adaptation

This is what is known as "metabolic" adaptation. It's a survival mechanism of your body to try to revert fat loss. The people that know about this tend to think that this occurs in a fairly straightforward physiological manner, such as increased mitochondrial efficiency and hormonal changes. This definitely happens, as it is part of the adaptation process.

However, this is a very small effect! It's most certainly below 10%, and likely much less. But there is more to metabolic adaption than this. In fact, it's not even the primary factor.

Energy demand

One factor that makes dieting more difficult over time is that your calories need to be lower and lower, resulting from the simple factor that you are now lighter. This is a big contributor to how much energy your body spends, and therefore it's an unavoidable consequence of weight loss that your maintenance calories will be lower, and thus your deficit will decrease over time.

Behavioural adaptations

But the primary factors are behavioral adaptations. This is why I don't like the term "metabolic" too much, because it implies a sort of physiological adaptation that you have no control over. In reality, the most important reason why diet becomes harder over time is that your body tries to compensate by moving less and eating more. You feel hungrier and with more cravings, and hence you tend to overeat, reducing or eliminating fat loss. You have the tendency to start snacking more, to "forget" to track foods, to increase your portions, etc. Very often, without realizing this at all!

You also tend to feel more tired and move less. The most obvious one is walking, you feel like walking less, and you do. You're not consciously thinking, "I need to walk less so I stop losing weight", but that's more or less what you're body is doing.

As part of my morning routine, I take a walk first thing in the morning. I always find it very interesting that whenever I am deep into a weight loss phase, I start coming up with excuses (usually that I should use that time instead and get work done). I often don't immediately realize where this is coming from, and I simply think that I'm lacking motivation. But of course, that "motivation" isn't random, it's being influenced by my brain due to my hypocaloric state.

This is why it's so important to track both your eating and your activity level (steps). This ensures that your body isn't subconsciously sabotaging your weight loss, which will certainly try its hardest!