For the last several years there has been a lot of intense discussion, controversy and disagreement amongst bodybuilders, trainers, nutritionists and coaches within the fitness industry regarding whether avid exercisers looking to decrease body fat, while gaining/maintaining muscle,should utilize a zero-carb approach to dieting for the best results (also known as a “keto diet”).

As a professional natural bodybuilder myself who has prepared for about twenty competitions, as well as one that has coached hundreds of clients, at all levels, whose main goal was to strip off fat without losing muscle (which in effect can make one look worse rather than better) I have a very definite opinion on this matter…based both on experience and science.

Drum roll please………zero carb diets are not the best way to go, especially long term, if one’s goal is to lose body fat and keep (or gain) their muscle!

And why do I say this? It’s just simple (ok, not that simple) physiology really…hormones, signaling molecules, and how they are affected when zero carbs are ingested! That said; let’s get a little more specific about why zero-carb fat-loss diets are not the Holy Grail, but will likely lead you to fail.

Reason #1: Without any carbs there will be no insulin!

Insulin is a protein-peptide hormone that is released by the pancreas in response to the ingestion of food, with the greatest release occurring by way of the consumption of carbohydrates. Insulin promotes a dramatic muscle-building effect through its ability to drive amino acids, glucose, creatine, etc. directly into muscle cells and by inhibiting muscle degradation. The powerful anti-catabolic (prevents muscle loss) properties of insulin are most important first thing in the morning and right after a good workout, when an optimum hormonal environment is necessary to build/maintain muscle tissue. If you do not elevate your insulin levels at these two critical times you will fail to optimally transport vital nutrients into starving muscle cells, and will perhaps even rob them of amino acids already stored. Result? Muscle loss (and a negative impact on your body fat percentage).

Reason # 2: Without any insulin you will secret more cortisol!

Cortisol is a natural hormone of the adrenal glands and is the primary glucocorticoid. It is released in greater amounts in times of stress (yes, training is considered by the body to be a stress), and possesses many qualities essential to life. However, in too large amounts, cortisol is the enemy of anyone looking for a fit, toned, muscular physique (yeah, this sucker wears both a white and black hat)! Excess cortisol can directly result in a loss of lean mass by reducing the utilization of amino acids for protein formation in muscles cells. Cortisol can also lead to a redistribution (and increase) of body fat causing a larger amount of storage to occur in the abdominal region. In addition, too much of this devilish little hormone can cause both sodium retention and potassium excretion. Less muscle…more bloat…and a bigger waistline? No thank you!

Reason # 3: With more cortisol there will be decreased thyroid function!

It has been known for quite some time that one of the downfalls of a lengthy zero-carb diet is the negative effect it can have on thyroid activity. One of the possible mechanisms behind this, once again, is increased cortisol secretion. Not only does excess cortisol directly inhibit TSH, or thyroid stimulating hormone, but it may also suppress 5′ deiodinase, an enzyme that converts the less active thyroid hormone T4 into the far more powerful T3! The result is a decreased metabolic rate, which of course can make it harder to burn fat. This is why so many zero-carb dieters reach a plateau in progress rather quickly!

Reason # 4: More cortisol = less GH!

I find this effect particularly interesting because strong proponents of the zero-carb diet often claim that one of its benefits is increased GH output, leading to higher levels of the anabolic (muscle building) hormone, IGF-1. However, you should be aware of another nasty tidbit about cortisol…it increases the output of the GH antagonist, somatostatin! So, there goes that theory right out the window! Less GH (which helps burn fat) = less IGF-1 (which helps build/maintain muscle), which in turn = decreased muscle retention and slower losses in body fat while dieting.

Next month I will continue my discussion about why zero-carbohydrate diets are not optimal when it comes to fat loss and the fitness-oriented individual.



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About Eric Broser

Eric Broser has been involved in the fitness industry for over twenty years as a personal trainer, natural pro bodybuilder, supplement company representative, model, author, magazine columnist, and gym owner. He is the developer of both the P/RR/S and FD/FS training systems, which are practiced by trainees all over the world.