Can High Protein Diets Reduce Testosterone?

What Does This Study Mean For You?

Author: Dr. Stephen Chaney

Protein is in the news. Recent studies have shown that our need for protein increases as we age. And the latest USDA Dietary Guidelines are telling us that all of us should substantially increase our protein intake.

When you add protein to the diet, you need to remove something. So, many of these diets are lower in carbohydrate. And many people are choosing the high protein versions of low carb diets for “health” reasons. For example:

High protein, low carb diets have become popular for weight loss.

And in our society, high protein diets are considered a good thing. We associate protein consumption with strength, energy, and virility. So, many athletes also include high protein, low carb diets as part of their training regimen.

Are high protein, low carb diets the best choice? Perhaps not, if the latest study is correct. This study (J Whittaker and M Harris, Nutrition And Health, 1-12, March 2022) claims that high protein, low carb diets decrease testosterone levels.

So, you are probably wondering, “Is this claim accurate?” To answer this question, I will evaluate the study and put it into perspective for you.

How Was This Study Done?

This study was a meta-analysis of 27 studies with a total of 309 participants looking at the effect of low carb diets on cortisol and testosterone levels. The participants were young (average age = 27.3), healthy, non-obese (BMI = 24.8), active males.

The selection criteria for studies included in the meta-analysis were:

Measurements of resting and post-exercise cortisol and testosterone levels. For simplicity, I will focus only on the testosterone results for this discussion.

Young, healthy male participants to minimize variation in steroid hormone metabolism due to age, sex, or disease.

Comparison of a low carb, high protein (average = 18% carb, 49% protein) and high carb, moderate protein diets (average = 58% carbohydrate, 23% protein).

Elimination of studies containing confounding variables that might affect steroid hormone metabolism such as:

- Weight change of more than 6 pounds

- Use of hormones, phytoestrogens, or medications.

In analyzing the data, they also compared:

Duration of <3 weeks or longer because it takes about 3 weeks for the body to fully adapt to ketone body utilization.

Moderate protein (average intake = 23.1% of calories) versus high protein (average intake = 48.8% of calories) intake. [Note: For comparison, the average protein intake for adults in this country is ~16%, with some experts recommending 17-21% to prevent weight loss as we age.]

This study looked at the effect of low carb, high protein diets on both resting and post-exercise testosterone levels.

Moderate protein (23% of calories), high carb diets had no consistent effect on either resting or post-exercise testosterone levels.

However, high protein, low carb diets reduced both resting and post-exercise testosterone levels.

The effect on resting testosterone was highly significant. High-protein, low carb diets caused a 37% decrease in resting testosterone levels.

The effect on post-exercise testosterone was smaller, but still significant.

In the words of the authors, “High-protein, low carb diets greatly decreased resting and post-exercise total testosterone…Individuals consuming such diets may need to be cautious about adverse endocrine effects.”

Is There A Good Metabolic Rationale For These Results?

As a biochemist, I always like to look at whether there is a metabolic rationale for the results. And there is a good metabolic rationale for the effect of high protein diets on testosterone levels:

When protein is metabolized ammonia is released, and excess ammonia is toxic.

To combat ammonia toxicity the body has a metabolic pathway called the urea cycle. It removes ammonia from the bloodstream and converts it to urea, which is excreted in the urine.

The ability of the urea cycle to remove ammonia from the bloodstream is limited. High protein intakes can overwhelm the ability of the urea cycle to remove ammonia. This typically occurs when protein intake exceeds 35% of calories.

In situations like this, the body produces cortisol, and cortisol upregulates the urea cycle so it can handle the excess ammonia.

For reasons that aren’t entirely clear, cortisol and testosterone are regulated oppositely. Whenever cortisol goes up, testosterone goes down.

To be clear, I am not saying this is what is happening. I am merely saying this is a plausible mechanism for explaining the fall in testosterone levels on a high protein diet, and many popular low carb diets are also high protein diets.

It could equally well represent a side effect of long-term ketosis. Ketosis was meant as a survival mechanism for short-term starvation. We have no idea what the potential effects of long-term ketosis might be.

What Does This Study Mean For You?

In previous articles in “Health Tips From the Professor” I have expressed skepticism about studies that have excellent experimental design but do not have a plausible metabolic rationale.

This week’s study is the opposite. It has an excellent metabolic rationale, but the study is weak. Specifically, the meta-analysis only included 309 subjects, and several of the individual studies included in the meta-analysis were weak.

The authors considered this as a hypothesis-generating study. The authors went on to say this study shows where we should focus our attention in future studies, namely on the possible health consequences of high protein, low carb diets.

I agree. I am not ready to tell you unequivocally that high protein, low carb diets will lower your testosterone levels.

However, if you are consuming a high protein, low carb diet for either weight loss or because you are a body builder or weightlifter, this study is a potential red flag. It is not a definitive study, but the results are metabolically plausible. They might just be true.

You should also keep in mind that all the “benefits” of high protein, low carb diets are based on short-term studies. There are no long-term studies on the benefits and risks of high protein, low carb diets. There is also no historical precedent for life-long adherence to a high protein, low carb diet.

We are omnivores. Our ancestors ate whatever nature provided. There were times when our paleolithic ancestors ate high protein, low carb meals, but it is unlikely any of them had the luxury of eating that way for a lifetime. That is a 21^st century luxury.

If you plan to consume a high protein, low carb diet for an extended period, you are part of an uncontrolled experiment with an uncertain outcome.

In case you were wondering whether this applies to any high protein (>35% of calories from protein), diet which exceeds the ability of the urea cyclic to remove a toxic byproduct of protein metabolism, the answer is “We don’t know”. However, the typical American diet is around 55% carbohydrate and 20-35% fat. It would be extremely difficult to exceed 35% protein without significantly reducing carbohydrate intake.

The Bottom Line

A recent study looked at the effect of high protein, low carb diets on testosterone levels. It found:

Moderate protein, high carb diets, like the typical American diet, had no consistent effect on either resting or post-exercise testosterone levels.

However, high protein, low carb diets reduced both resting and post-exercise testosterone levels.

The effect on resting testosterone was highly significant. High-protein, low carb diets caused a 37% decrease in resting testosterone levels.

The effect on post-exercise testosterone was smaller, but still significant.

I am not ready to tell you unequivocally that high protein, low carb diets will lower your testosterone levels.

If you plan to consume a high protein, low carb diet for an extended period, you are part of an uncontrolled experiment with an uncertain outcome.

For more details, read the article above.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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My posts and “Health Tips From the Professor” articles carefully avoid claims about any brand of supplement or manufacturer of supplements. However, I am often asked by representatives of supplement companies if they can share them with their customers.

My answer is, “Yes, as long as you share only the article without any additions or alterations. In particular, you should avoid adding any mention of your company or your company’s products. If you were to do that, you could be making what the FTC and FDA consider a “misleading health claim” that could result in legal action against you and the company you represent.

For more detail about FTC regulations for health claims, see this link.

https://www.ftc.gov/business-guidance/resources/health-products-compliance-guidance

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About The Author

Dr. Chaney has a BS in Chemistry from Duke University and a PhD in Biochemistry from UCLA. He is Professor Emeritus from the University of North Carolina where he taught biochemistry and nutrition to medical and dental students for 40 years. Dr. Chaney won numerous teaching awards at UNC, including the Academy of Educators “Excellence in Teaching Lifetime Achievement Award”. Dr Chaney also ran an active cancer research program at UNC and published over 100 scientific articles and reviews in peer-reviewed scientific journals. In addition, he authored two chapters on nutrition in one of the leading biochemistry textbooks for medical students.

Since retiring from the University of North Carolina, he has been writing a weekly health blog called “Health Tips From the Professor”. He has also written two best-selling books, “Slaying the Food Myths” and “Slaying the Supplement Myths”. And most recently he has created an online lifestyle change course, “Create Your Personal Health Zone”. For more information visit https://chaneyhealth.com.

For the past 53 years Dr. Chaney and his wife Suzanne have been helping people improve their health holistically through a combination of good diet, exercise, weight control and appropriate supplementation.