High-Protein Diet Low Testosterone

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.


Protein is an integral part of our diets and essential for building muscle; however, too much may have detrimental side effects, including reduced testosterone levels that could have serious negative repercussions in terms of fatigue and erectile dysfunction.

Although 'high-protein diets' do not have an exact definition, studies show that diets containing more than 3.4 g/kg/day of protein reduce testosterone levels. 

The Importance of Protein

Protein is an essential macronutrient (a nutrient that provides energy). As one of three calorie-supplying nutrients - alongside carbohydrates and fat - protein helps build and repair body tissues, transport oxygen into cells and make enzymes and hormones.

Protein also plays a key role in keeping bones, muscles and skin healthy while making hormones like insulin that regulate blood glucose more manageable.

Finally, proteins make up part of red blood cell proteins which carry oxygen throughout your body and even reach into the brain.

Proteins contain 20 amino acids that can be combined in millions of ways to form different protein "languages", each serving specific functions in the body.

Just as alphabet letters can be combined to form words, the sequence of amino acids in a protein determines its shape and function.

An essential part of being healthy, protein is an integral component. Our bodies rely on protein to build and maintain muscle, transport oxygen throughout our bodies, produce digestive enzymes that aid digestion. Protein produces hormones and maintain fluid and acid-base balance within cells - as well as prevent sudden shifts in water concentration between blood and cells.

Protein can be found in various food products, from animal sources such as meat and milk to plant sources like beans, peas, lentils, nuts seeds soy quinoa and some whole grains.

Combining proteins from multiple sources ensures our bodies receive all essential amino acids needed for health.

The Importance of Testosterone

Testosterone is the primary sex hormone and anabolic steroid in men and one of the key steroids for women, acting both reproductively and anabolically.

During fetal development it stimulates internal and external reproductive organ development for males; promotes growth of body hair and muscle mass among children. Testosterone increases penis size in adults as well as aggression and sexual drive in males. Furthermore it signals to your body to produce new blood cells while keeping muscles and bones strong - particularly during puberty!

Dihydrotestosterone (DHT) is then converted to more potent forms in target tissues cells' cytoplasm and converted further by aromatase enzyme into more feminizing forms of androgens such as 5a-DHT (5a-DHT). Testosterone and its metabolites then enter blood circulation before being secreted through urine into the environment for disposal.

Testing for testosterone in the body is generally easy and convenient, thanks to microtainer tests - an accurate way to monitor hormones commonly tested by healthcare providers at their office.

It should be noted, however, that traditional methods used for measuring bioavailable (free) testosterone may yield inaccurate results as much of it binds with other proteins such as SHBG.

Laboratories can improve accuracy by employing ammonium sulfate to selectively precipitate SHBG-bound forms of the hormone and make measurements more precise by employing ammonium sulfate on samples sent directly from healthcare providers' offices.

Lower Testosterone Levels

Gym enthusiasts who consume protein shakes to build muscle may unknowingly be decreasing their testosterone levels.

Protein is an indispensable macronutrient that plays an essential role in building muscle mass and strength, while also being essential for human bodily regulation and function.

According to recent studies, high-protein diets can bring testosterone levels down by one-third and lead to erectile dysfunction and lower sperm counts for men.

An eight week study published in Nutrition and Health followed 309 men over an eight week period who consumed either a low-carbohydrate, high-protein diet or conventional high-carbohydrate diet. Resting testicular testosterone (TT) levels of each participant were then recorded.

At the conclusion of the study, participants who had high-protein diets experienced a 37% reduction in testosterone levels - an indication of medically significant hypogonadism.

They also experienced symptoms related to low testosterone such as fatigue, erectile dysfunction, depression and muscle weakness.

Researchers speculate that increased protein consumption leads to higher SHBG levels, which "steal" free-floating testosterone away from the body.

Furthermore, consuming excess protein increases cortisol production and therefore suppresses testosterone production as well as inhibit muscle growth.

Reasons behind this decline could include protein-rich diets increasing insulinlike growth factor-1 (IGF-1).

IGF-1 is an essential hormone for muscle development and increasing it leads to an increase in cortisol, known as the stress hormone and having adverse effects on testosterone levels.

Researchers also note how IGF-1 raises leads to cortisol being produced, leading to its production increasing significantly and thus leading to further problems for testosterone levels.

Importantly, this study only measures short-term participant results without taking into account other variables like sleep patterns, stress levels, exercise intensity or diet factors such as protein.

Study participants consumed a high-protein diet consisting of meat, fish and protein shakes for eight weeks in this research project.

Researchers concluded that diets consisting of more than 35% protein can significantly decrease testosterone levels by an average of 37%. Authors note this is an extraordinary decrease for an average person.

Furthermore, "high protein" remains vaguely defined so interpretation of its meaning has led to widespread media coverage leading to consumer confusion.

Whilst these findings are alarming, it is recommends eating a balanced diet to optimize health - including plenty of fiber - as this will help balance hormones by decreasing cortisol levels and flushing away excess estrogen, thus decreasing testosterone.

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Increased Risk of Cardiovascular Disease

Protein is an essential macronutrient essential to the proper structure, function and regulation of many body tissues and organs.

It makes up approximately 15% of your total body weight and plays a crucial role in muscle gain; however, eating too much protein could actually lower testosterone levels instead.

Testosterone plays an integral part in controlling cardiovascular disease risk factors; low testosterone may increase heart attacks and stroke risk among males as outlined in this paper.

Attaining optimal health requires knowing how much protein to consume daily for maximum muscle growth, with the recommended daily allowance being approximately 0.75 grams per kilogram of bodyweight for the average person up to 2.0 grams per kilo for athletes.

But, some individuals consume significantly more protein than necessary in an attempt to build larger muscles more quickly, although too much protein consumption can actually decrease testosterone and cause various health issues.


Testosterone is one of the body's most critical hormones. It plays an indispensable role in everything from developing reproductive tissues and organs to secondary sexual characteristics, fat distribution, muscle growth and red blood cell production as well as producing estradiol for sexual functions. Without enough testosterone in our systems, things quickly go amiss.

Low testosterone levels have been linked with various health problems, including erectile dysfunction and increased risks of cardiovascular disease, diabetes and Alzheimer's. However, maintaining healthy testosterone levels is achievable with the proper diet and lifestyle choices.

New research suggests that high protein diets (defined as diets containing more than 35% total calories from protein) may reduce a man's natural testosterone production by as much as 37%, which could have serious repercussions for muscle growth, fertility, and the prevention of chronic diseases like heart disease and diabetes.

Study results revealed that eating high protein diets reduced testosterone levels by decreasing free-floating testosterone levels, possibly as a result of excess protein increasing levels of sex hormone binding globulin protein which binds with over 60% of free floating testosterone in the body and renders it inactive.

Researchers found that adding carbohydrates to a high-protein diet helped significantly to offset its effect on testosterone. When proteins and carbohydrates are eaten together, they create a negative feedback loop which regulates levels of free-floating testosterone and other hormones in your system. 

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