Why is weight loss often so difficult? Why do some people lose fat faster than others? Why is fat loss initially fast and then much slower, and what can you do about it? All things that have to do with metabolic adaptation. Dr. Eric Trexler, scientist and bodybuilder, tells all about it in an interview with YouTuber Abel Csabai. Read a summary of the most interesting Q&As below, or listen to the full podcast below.
WHAT IS METABOLIC ADAPTATION? (11:07)
Metabolic adaptation is a process that determines how efficient the body is at converting food into energy. Adaptation means that the body adapts processes in the body to better cope with a changed caloric intake, so when you suddenly eat much less or much more. The consequence of this adaptation is that energy consumption decreases or increases. All this stems from the survival principles by which our bodies function.
Please note: if you lose fat, your energy needs will go down anyway. After all, your body has less mass to maintain. But that’s not what we mean by metabolic adaptation.
WHAT ARE THE CAUSES OF METABOLIC ADAPTATION? (13:45)
A frequently mentioned cause of metabolic adaptation is savings on the resting metabolism (Resting Energy Expenditure, REE). This part of our daily energy expenditure concerns the processes necessary for the body to function, such as breathing. But while the body will indeed save on REE if it consumes fewer calories, that only takes up a small part of metabolic adaptation.
Much greater is the savings on Non-Exercise Activity Thermogenesis (NEAT). That is the energy expenditure of all physical activities except sports, sleeping and eating. Think of walking, standing up, typing, shopping, cleaning, working in the garden, spinning on the chair and so on. If you have started a calorie-restricted diet, your body will therefore automatically save on these mainly unconscious daily activities.
This saving on both NEAT and REE is mainly due to the behavior of the hormone leptin. As soon as you enter a longer-term calorie deficit, leptin levels in the blood drop. Leptin feeds back to the hypothalamus, an important structure in the brain that regulates many unconscious bodily functions, including energy expenditure, hunger pangs, and activity level. The response of the hypothalamus is, among other things, that it economises on energy consumption. This can cause your metabolism to slow down by 10-15 percent if you lower your calorie intake, or speed it up by 10-15 percent if you increase your calorie intake.
HOW IS IT POSSIBLE THAT ONE LOSES WEIGHT FASTER THAN THE OTHER? (15:20)
This is often explained by saying that one has a faster resting metabolism than the other. However, the resting metabolism in itself does not determine how quickly you lose weight. Resting metabolism is a given that we can predict quite easily on the basis of body composition, gender, age and such.
However, the adaptability of metabolism, ie metabolic adaptation, is much more difficult to predict. It can vary enormously from person to person. This makes it difficult to say in advance how low a caloric intake should go to lose fat.
On the one hand, that big difference has to do with the NEAT, which is heavily dependent on lifestyle. One has a much more active lifestyle than the other, not including sports. The higher the NEAT, the stronger the adaptive response. On the other hand, how sensitive you are to over- or under-nutrition plays a role. In some people, the body shows a very strong adaptive response, as if it wants to maintain the current body weight at all costs. This is genetically determined and cannot be changed.
Please note: metabolic adaptation does not affect the calories in, calories out. If you eat fewer calories than you expend, you will lose weight. I mainly refer to metabolic adaptation as something you should be aware of, not something you should be afraid of.
WHAT IS THE BODY FAT SET POINT ? (36:30)
According to the theory of the body fat set point, the body tries to keep weight within a genetically determined range in order to function optimally. Something that is quite plausible, but scientifically insufficiently substantiated.
It is also unclear whether you can change (decrease or increase) that possible body fat set point. If you have lost a lot of weight, the body often seems to have a tendency to get back to the old weight. This is probably because fat cells do not disappear, but only become smaller in size. Something that also seems to respond to leptin, causing your brain to send out hunger signals. On the other hand, it is plausible that your body adjusts its functioning when you stay at a certain fat percentage for a longer period of time.
In any case, it is evident that you will have to permanently adopt a different lifestyle to maintain that weight.
SO ANYONE CAN (CONTINUE TO) LOSE FAT, NO MATTER HOW STRONG THE ADAPTIVE RESPONSE IS? (21:52)
Yes. Anyone can lose weight, only one person will have to lower his calorie intake faster than the other in order to continue to lose weight. At the same time, the following applies to everyone: the less (fat) mass you have, the lower you will have to go in calories. Some people then get to a point where the calorie intake has to be so low that they are not comfortable with it. Then you have to make a choice: continue or adjust your goal. Both options are defensible.
Whether or not you feel comfortable with a certain calorie intake partly depends on the hunger regulation in your body: some people experience hunger more quickly than others. This may be determined by how far you are from your body fat set point.
Your relationship with food also plays a role. If I have to go on a strict diet with only chicken and broccoli for the next few months, I don’t mind. But for other people, food is a form of entertainment, they want to be able to enjoy good food. In their case, such a strict diet is a much bigger task and therefore more difficult to maintain.
In principle, how one experiences a calorie restriction does not seem to depend on the actual level of calorie intake. Whether you have to eat a lot or little to create the energy deficit, in both cases there is a shortage and the perception is the same. In theory at least. In practice, however, I can imagine that it does make a difference whether your plate is completely filled or whether there is only a little on it.
DOES IT MAKE SENSE TO INCREASE YOUR ENERGY CONSUMPTION TO MAKE DIETING EASIER? (48:38)
That is also highly personal. For example, you can do some cardio, but some people get very hungry because of that. Another disadvantage of doing (a lot of) cardio is that the body will also respond adaptively to that. Research has shown that the body manages to limit energy consumption when you are very active. Our bodies are built to keep us from starving. (For more explanation, see this video, ed.). Finally, a large amount of cardio can simply be too much for your energy level and recovery, when you, as a bodybuilder, also have to do a lot of strength training.
I myself never do cardio to lose fat, even when preparing for a bodybuilding competition. I walk to and from work, the rest is a matter of diet and strength training.
WHAT ELSE CAN YOU DO TO LIMIT THE ADVERSE EFFECTS OF LOW CALORIE INTAKE? (54:03)
Make sure you distribute the macronutrients well. Eat enough protein but not more than necessary (~1.8 g/kg body weight/day, ed.), eat enough fat but not more than necessary (don’t go below 0.6 g/kg though) and eat the rest carbohydrates. Proteins are crucial for muscle maintenance, a minimum amount of fat is needed for your hormone levels and the absorption of vitamins, carbohydrates are your main source of energy for strength training.
There is another reason to keep carbohydrate intake as high as possible, within your caloric restriction. Leptin appears to decrease most strongly with restriction in carbohydrates with an energy restriction. Not that eating a lot of carbohydrates can prevent metabolic adaptation, but theoretically it could limit it somewhat.
WHAT DO YOU THINK OF NON-LINEAR DIET METHODS? (1:00:03)
Refeeds and diet breaks can certainly be useful to limit the adverse effects of metabolic adaptation. A refeed will have to take at least three days to bring about any recovery in metabolism and hormone levels. A diet break usually takes a minimum of one week. So, for example, maintain a calorie deficit for three weeks and eat maintenance for one week.
Another possibility is an intermittent fasting protocol where, for example, you eat (almost) no calories two days a week and use a normal calorie intake on the other days. Because there are only short low calorie phases, you could minimize metabolic adaptation. Meta-analyses have shown that such methods work, but no better than linear diets. After all, the fact remains that with alternate-day fasting you are only in a calorie deficit for a limited part of the time. On balance, you seem to lose no more or less fat than when you are continuously in an albeit smaller calorie deficit.
CAN YOU IMMEDIATELY START BULKING AGAIN AFTER A CUT? (1:07:00)
In principle yes, but you have to be careful with increasing your calorie intake. Research suggests namely that you are sensitive to the termination of a calorie-restricted diet for fat gain than normal, once again you find yourself in a calorie surplus, which is needed to bulk. Therefore, initially ensure a limited calorie surplus and at the same time provide sufficient training stimulus to be able to use that surplus for muscle growth. So increase your calorie intake step by step.
The foregoing does not mean that you should remain in a calorie deficit for a long time after your diet. So I’m not a fan of slow reverse dieting, where you increase your calorie intake in tiny steps, so that you actually remain in a calorie deficit for a long time.
See also an extensive article by Eric Trexler on metabolic adaptation at Stronger by Science.