Researchers from the University of Michigan published an article in the September 2005 issue of the Journal of Clinical Endocrinology & Metabolism showing that dietary carbohydrate restriction combined with increased protein intake increases muscle protein synthesis.

In brief, the study involved eight young (average age: 29) healthy subjects (four men; four women) who were admitted to the hospital and fed a diet of 60% carbohydrate, 30% fat, and 10% protein for two days. The subjects then switched to a carb-restricted, high-protein, high-fat study diet (5% carbohydrate, 60% fat, and 35% protein) for seven days.

All parameters were measured just prior to switching to the study diet, two days later, and at the end of the one week study. The entire study was conducted in a hospital, which means that the data is much, much more reliable than that obtained by dietary recall.

The data from this study provided some surprises (to these researchers, anyway).

One of the long held beliefs of scientists in research settings has been that low-carbohydrate diets cause muscle loss. That seems absurd to anyone who has ever been on a low-carb diet, but nevertheless that’s what most of the ivory tower folks believe.


Because a fair amount of research has shown that when subjects go on low-carb diets they go into negative nitrogen balance, an indicator of protein deficiency. Why? Both carbohydrate and fat are made of oxygen, carbon, and hydrogen. Protein, however, is made of those same three elements plus nitrogen and sulfur. When protein is broken down, nitrogen–which is gotten rid of through the kidneys–appears in the urine.

Basically if more nitrogen appears in the urine than has been consumed from dietary protein, the subject is said to be in negative nitrogen balance, and is thought to be breaking down protein instead of building it into muscle and other protein tissues.

It is well known that subjects following low-carbohydrate diets reduce their serum insulin levels substantially. In this study, for example, the subjects reduced their average 24 hour insulin concentrations by half within 2 days after switching to the low-carb diet. Insulin is an anabolic hormone, i.e., it causes growth.

So when insulin levels are low, there is less stimulus for growth, and it seems reasonable that muscle should break down, which has been shown in a number of studies.

Researchers observing this muscle breakdown have thought along these lines: low-carb diets cause a lowering of insulin levels, insulin is an anabolic hormone so lowered levels should decrease growth and bring about a decreased nitrogen balance, we usually find a decreased nitrogen balance in people on low-carb diets, so, Voila, low-carb diets cause muscle loss.

Problem is, as this study shows, it just ain’t that simple.

Researchers in this study used much more sophisticated techniques than simply looking at the nitrogen balance, which at best is a sort of blunt instrument methodology. Muscle breakdown, called proteolysis, was measured as the rate of appearance of the amino acid leucine into the plasma. Protein synthesis was determined by the measurement of the incorporation of labeled leucine into muscle tissue obtained by muscle biopsy.

The data showed that during the low-carb, high-protein diet protein was being both broken down and synthesized at the same time. The researchers posited that the increased protein in the diet led to the increased muscle synthesis, while the lowered insulin caused an increased protein breakdown.

The major finding of the present study was that muscle protein synthesis increased despite strict carbohydrate restriction and a marked reduction in the daily exposure to insulin. This increase in protein synthesis was accompanied by an increase in whole-body proteolysis.

The authors of the study take the position that there is, along with the muscle synthesis driven by the increased dietary protein, a breakdown of muscle at the same time caused by the reduced insulin levels, so that the sum of the two determines whether one is in overall muscle-building mode or muscle-wasting mode. (Interestingly, they didn’t measure the sum in this study–they only showed that both mechanisms were at work simultaneously).

I disagree with them.

A bit of physiology never mentioned in this study is the notion of ketosis. I’m quite sure that subjects restricted to the minimal amounts of carbohydrate used in this study went into ketosis in a hurry and stayed there for the duration of the study.

As shown in a July 2005 study in the Journal of Biological Chemistry ketone bodies themselves assist in the breakdown of protein, but in a good way. As cells age they begin to accumulate debris (much of it made of protein) that junks up the cells. As this cellular debris accrues it can impair the function of the cell. In fact, one of the components of aging is this trash pile of cellular junk, and many anti-aging therapies revolve around clearing the cells of it.

The body has ways of clearing the debris that involve transporting the stuff to areas of the cell called lysosomes where it can be chemically degraded into its component amino acids, which are then used by the cell or transported to the blood. Ketones accelerate this process substantially, which makes perfect sense when you think about it.

Ketones are a part of the “starvation response.” If we don’t eat, the liver starts producing ketone bodies to provide energy for the tissues such as the brain that normally use glucose. The switch from glucose to ketone bodies spares the muscle tissue because during starvation our bodies breakdown muscle to make blood sugar.

The name of the game survival-wise becomes conserving muscle tissue as long as possible. In an effort not to have to resort to muscle breakdown nature has designed us so that ketone bodies not only act as a blood sugar substitute but actually increase as well the degradation of junk proteins to provide the amino acids needed for both muscle maintenance and blood sugar conversion. Nifty, eh?

I’m convinced that the increased proteolysis seen in low-carb diets comes not from muscle breakdown, but from the increased junk protein degradation stimulated by the increased levels of ketone bodies. If I’m right, then low-carb diets do a couple of good things: they build muscle and they dejunk the cells.

What a deal!


  1. You are right!
    After more than 40 years of both anaerobic and aerobic training which has been nutritionally fuelled in different ways over this period of time I’ve now arrived at the definite conclusion that low-carb foods build muscle, for the life of me if I continue to try and diminish muscle mass then I will have to do two things; the first is the unthinkable… stop training and the second is the impossible…stop eating! The body will do what the body will, sorry this may seem a little enigmatic but it’s in the genes. Simplistic to say I know especially after all the research and study that we subject ourselves and others to, at times it results in conflicting and contradicting statements, nothing hard nor fast, this does not stop most folks from commenting that I look in my twenties when in actual fact I am in my forties. Although never the intention, it’s proof enough for me.
    Yes, again you are right but you are not what you eat – you are what you are. There’s the deal, take it or leave it but life is great!
    Best Regards
    Hi Mike–
    Glad to hear that the low-carb diet lead to increased muscle mass in your case. In my experience, it does in almost everyone’s.

  2. Dr Eades,
    Incredibly interesting topic for me, because, as someone in my forties but about to embark on a new career of fitness instructor, muscle growth and being in great shape is imperative (though it probably should be for everyone, at least generally).
    Have you found that actual evidence (not hypotheses) to be that people gain more muscle mass on a low carb, hi-pro diet? Personally, it would suit me fine for that to be the case, as I tend toward proteins and fats more anyway. Still, I want to garner as much info as I can that’s legit, not slanted according to wishes.
    Many thanks for your book (I have Protein Power) and website!
    Hi Bert–
    Yes, I have found that people gain more muscle mass on low-carb diets. You have to have protein to gain muscle, and low-carb diets typically contain a lot more protein than low-calorie diets.
    If you want to get another opinion, look at Fred Hahn’s site and contact him through the comment section of his blog.

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