Why Slow Cutting Burns Your Muscle

“Lose weight SLOWLY!”

“Diet on as MANY calories as possible!”

“If you decrease calories too fast, you WILL lose muscle!”

Really? Is there real science behind any of these claims or are they just bro-science wisdom?

To answer this question, let’s have a look at real data from real research. This data comes from probably the best and absolutely unique weight loss study; the Minnesota experiment.

The reason why I consider this study to be the best is because it studied very drastic weight loss conditions for a prolong period of time on normal weight people.

[ You may be wondering what the problem with current research is. Most drastic weight loss studies involved overweight or obese individuals. Therefore the findings from these studies aren’t necessarily applicable to normal weight people undergoing drastic weight loss diets such as for a bodybuilding competition for example. ]

In the Minnesota experiment, 32 normal weight young men were put on a radical weight loss diet for half a year with the aim to lose 1 kg (2.2 lbs) per week. That’s a lot; 24 kg (~ 53 lbs) in six months!

Each participant was weighed once a week and if he hadn’t lost 1 kg during the week passed, his calories were subsequently decreased. A pretty sadistic weight loss protocol if you were to ask me. This is also the reason, why the study is so unique. Nowadays, it would be impossible to get the ethical approval for such a study!

Over the course of the study the weight loss progress of the subjects were precisely recorded; how much weight they lost, how much of it was fat and how much was muscle.

The amount of muscle mass loss in relation to the total weight loss can be expressed as energy-partitioning p-ratio [p-ratio = burned energy from protein/ total energy burned] (1, 2). If a person burned mostly fat during weight loss and only a low amount of muscle protein, then the ratio is low. In contrast, if the person lost lots of muscle, then the ratio is high.

In the figure below I plotted the data from the Minnesota experiment. We can instantly see that the participants who started at a higher body fat percentage lost less muscle mass (smaller p-ratio) than the participants who started the severe weight loss diet at a lower body fat percentage.

To make it clearer, for participants who had about 20 % body fat at the beginning of the study about 20-30% of the burned energy came from protein, whereas for those who started at about 10 % body fat, 40-60 % of burned energy originated from protein.

A big part of the lost protein came most likely from muscle protein; however; also other sources, like organs for example, were used to cover the energy needs during the weight loss diet. ]

To be honest, this finding is basically common sense:

 If you have more fat, you can lose more fat when dieting.  

In my opinion, for long, drastic weight loss diets, like bodybuilding show preps, it makes more sense to start with a higher energy deficit and decrease it over time to maintain as much muscle mass as possible.

This is exactly the opposite to what most bodybuilders do during show prep; after they lose lots of weight and get to a low body fat percentage, they decrease the calories even further.

A research study conducted on a bodybuilder during the contest prep showed how inefficient the typical bodybuilding cutting strategy can be (3). The poor guy started at 14 % body fat and dropped his energy intake over time ending up with an energy deficit of just over 1000 kcal per day during the last two weeks before the show. Of the 11.7 kg he lost during 14 weeks of show prep, 43% came from fat free mass and ‘only’ 57% from fat. This means that about half of the weight he lost WAS NOT FAT!

So this brings us to the important question, what should you do to prevent unnecessary muscle loss at low body fat percentage?

One important thing we shouldn’t forget is that there is an ongoing balance between muscle protein synthesis and breakdown in the human body. It’s not like your body decides on the day when you start your cut that it is going to stop building muscle and switches to using them as a fuel. Muscle protein breakdown and muscle protein synthesis occurs at the same time. In the fed state, muscle protein synthesis dominates over muscle protein breakdown, thus is it the time when we build muscle. In the fasted state, muscle protein breakdown is higher than the muscle protein synthesis, therefore we lose muscle.

“Skeletal muscle protein turnover illustrates the balance between protein synthesis (shaded bars) and protein breakdown (open bars) during different physiological conditions, including the anabolic period after a meal or the catabolic period during an overnight fast.” Figure source (4)

“Skeletal muscle protein turnover illustrates the balance between protein synthesis (shaded bars) and protein breakdown (open bars) during different physiological conditions, including the anabolic period after a meal or the catabolic period during an overnight fast.” Figure source (4)


Thus, an important take-home message is: fast less and eat more.

I know, this almost comes across as sarcastic advice coming from someone currently on a weight loss diet. Nevertheless, it is not as useless as you think. There are some things you can do to reduce muscle loss whilst in an energy deficit:

1.      Don’t fast for a long time. Intermittent fasting is probably not the best strategy for muscle retention in an energy deficit at low body fat percentage.

2.      Considering that the longest fasting period for most people is the overnight fast, it makes sense to get some protein in before bed to counteract muscle protein breakdown at least in the few hours after falling asleep. This strategy is supported research as well (5). An additional bonus is that protein before bed increases the resting energy expenditure the next morning, thus making it beneficial for weight loss (6).

3.      Of course, the ideal scenario would be not to wait until the next morning, but to just consume more protein at night to prevent your body from breaking down more muscle. If you don’t want to compromise your sleep quality to pour down a protein shake in the middle of the night, you may want to consider a rather unconventional tool: a gastric tube! There is a cool research study on this topic (7). Participants received a constant protein supply via a gastric tube throughout the night, which resulted in an increased rate of muscle protein synthesis.

Does this sound too extreme to you? Your Bro-friend would probably say: No Pain, No Gain. Incidentally, this quote may be even more applicable to nutrition than to training.


If you want to know how I cut and what my cutting macros are, watch this video:


Now, as we’re approaching the end of this post, I will answer a few questions some of you may have in mind or may have asked me already.


If I am one of the nut cases that decides to have protein shakes throughout the night, how much protein should I aim to get?

Most likely 16 g protein per serving is enough, at least for isolated, well digestible protein source like a protein shake. This amount of protein contains enough leucine to maximally stimulate the muscle protein synthesis. If you have protein as a part of a meal, issues with protein digestion and absorption may arise, which in turn may increase the protein requirements per meal. If you want to know more, read this.


Should I take BCAA before bed?

The answer is: BCAAs are better than nothing. If you are lost somewhere in the wildness and have nothing but BCAA with you, take it. However, if you can choose between a protein source that contains amino acids, including all the essential amino acids, then choose that over BCAA.

There are two reasons, why BCAA is not as good as protein:

First, you need all amino acids to build muscle, not only the three that BCAA supplements contain (leucine, isoleucine and valine). BCAA intake without other amino acids doesn’t give enough building blocks for building muscle, especially in a fasted state.

Secondly, it can happen that a part of the BCAAs doesn’t even get to the desired destination: your muscle. Free amino acids (not as part of a protein that needs to be broken down first) are a very easy energy source for your gut cells (8). BCAAs are basically ready to be eaten. Yumyumyum… your gut cells will thank you.


Take-home messages:

1.      When you have more fat to lose, you will lose less muscle in a drastic energy deficit. If you are already at a low body fat percentage and drop your calories too much, you will most likely lose more muscle than necessary.

2.      When you get to low body fat percentages, your goal is to reduce the time during which you muscle protein is broken down as much as possible. This means: reduce your fasting times and have some protein before sleep.


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 If you are confused and don't know what is the best way to lose weight and gain muscle? Then consider booking a consultation with me.