Metabolic Adaptations: Don’t Ruin Your Body

When you are on a weight loss diet, you are putting your body in a caloric deficit, which means you are consuming less calories (i.e, less energy) than what you are expending. In simple terms, weight loss boils down to being in an energy restricted state: you must eat less than what you expend. Although energy restriction will lead to weight loss, which is the goal for many people aiming for a healthy body composition, it also causes changes in circulating hormones, mitochondrial efficiency, and energy expenditure. These changes lead to a smaller energy deficit, slows the rate of weight loss, and promotes weight regain. If you want to lose weight, you must be on a calorie deficit, but you may also experience metabolic adaptations. In this blog, we will discuss metabolic adaptations when on a weight loss diet and how to optimize your diet to prevent the negative side effects of dieting.


In my body building days, I had to be in a caloric deficit state for a long period of time to reach the required body composition needed to compete. During the 4 months of contest preparation, I was consistently dropping my caloric intake week to week, ending at an extremely low caloric intake while still having a heavy training load. I did experience weight loss and was definitely seeing myself get leaner week to week, but it got increasingly more difficult to lose body fat as I got leaner. At the beginning of my 4-month preparation, all I had to do was make small changes to my diet and I would lose weight. There was one week where I ate 6 rice cakes instead of 7, and I got noticeably leaner after 2 weeks. That was not the case by the end of my preparation. Why was I experiencing this difficulty towards the end?

  • I was extremely hungry and had trouble adhering to my caloric intake target…it was low and my hunger levels were super high.

  • Metabolic adaptations were taking place, which we will describe below.


The endocrine system is a network of glands and organs that use hormones to control several functions in your body, to include your metabolism and energy levels. In an energy-restricted diet, your hormones are affected. 

  • Less T3 (thyroid gland) = lower metabolic rate

  • Less Leptin = lower satiety and lower energy expenditure

  • Increased Ghrelin = increased hunger

  • Increased Cortisol = increased muscle protein breakdown (increased muscle loss)

  • Decreased Testosterone and Insulin = less fat breakdown (adipogenesis) therefore more fat storage

If you try to maintain an unhealthy low body fat composition for long periods of time- even after active weight loss- these unfavorable changes in hormones will persist. 

Energy Expenditure

In previous blogs, we discussed Total Daily Energy Expenditure (TDEE). When you lose weight, your TDEE tends to drop significantly. This is the body’s way of wanting to return to baseline weight, where it feels healthier and happier. TDEE drops for several reasons:

  • Decreased EAT (Exercise activity thermogenesis). When you are on an extremely low calorie diet or low body fat, your body will be fatigued and not work to optimal levels in training.

  • Decreased NEAT (Non exercise activity thermogenesis). You will fidget and move less throughout the day due to fatigue, which in turn results in less calories burned. 

  • Decreased BMR (basal metabolic rate) due to less muscle mass/less active tissue in the body. This means you burn less calories per day than you would if you were at a heavier weight. 

When you get to a very low body fat percentage, the body will want to fight against the caloric deficit diet and will want to refuse to lose more weight. This is another reason why people who are at low body fat percentages tend to have difficulty losing more weight. It’s also why the body tends to gain weight very easily when you are either at a low body fat percentage or eating a very low-calorie diet.

Notice a trend here? Being in a low-calorie diet allows you to lose weight initially, but will eventually prevent further weight loss and conserve energy. So you may be thinking: “how can I lose weight without experiencing all of these negative side effects? What’s the optimal way?” Or “I’m extremely lean now, so how do I get out of this?”

We recommend the following:

  • Aim to make small changes and progressively decrease your calorie intake in small steps. If you make extremely big leaps in a calorie-deficit or if you are already on an extremely low-calorie diet, then you will experience these negative metabolic adaptations to a larger degree and eventually it will be harder for you to lose weight. 

  • A low calorie diet jeopardizes muscle mass. These large calorie-deficit diets eat away at muscle and lean body mass. Instead, aim for small decreases in calories. If you experience a plateau, adjust your intake (decrease calories in a small way) or increase expenditure (increase training in a small way) in order to create a new deficit. 

  •  If you go on a sustainable and smart calorie-restricted diet, keep protein intake high. Aim for 0.8-1 gram per lb bodyweight. This will prevent muscle loss. 

  • Consider periodic refeeds. This entails an increase in calories for a period of time (a few days to a week) in order to restore hormone function, to stimulate the metabolic rate, and to give the person a mental break from being on a calorie deficit. The caloric intake for a refeed is slightly above maintenance calories. 

  • If you are already at a very low body fat and are stuck in a very low calorie diet, but you don’t know how to get out of it without regaining a bunch of body fat, then aim for a step by step increase in your caloric intake. This is hard mentally for someone who has been on a low calorie diet for a long period of time and/or is scared to put on body fat, but the only way to restore hormone levels and get your body back to a healthy baseline is to eat more food. Instead of taking a big leap, we recommend small increases to reduce body fat accretion and rapid fat gain. 

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