Testosterone Action vs Testosterone Levels: Why SHBG Matters

Understand the science behind SHBG and its profound effects on cardiovascular health, athletic performance, and total wellness.

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By Staff Writer
Lucia Gcingca
Edited by Lucia Gcingca

Published January 22, 2024.

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Sex Hormone Binding Globulin or SHBG is essential for maximizing the availability of testosterone, the biomarker every man wants to measure. Today, science is telling us that both men and women need an optimized hormonal profile, and testosterone is widely known to be important for men.

But growing research points out the importance of testosterone for women. Blood testing is a practical way to "look under the hood" and get guidance on improving your health.

In this article, we will discover how SHBG is like a key that unlocks the door to optimizing health and performance.

What is SHBG?

Sex hormone-binding globulin (SHBG) is a glycoprotein primarily produced in the liver and most commonly found in the bloodstream. It binds to any of 17 sex hormones, including testosterone and estrogen, and transports these chemicals throughout the body.

Testosterone and sex hormones are referred to as “bound” when attached to SHBG. When these hormones are not bound to SHBG, they are referred to as “free” or “bioavailable” and can freely affect your body. The sum of bound and free testosterone is referred to as total testosterone.

» Seeking balance? Discover why testosterone to cortisol ratio matters

Why is SHBG important for your health and performance?

It is well-known that a proper balance of testosterone and other sex hormones has a crucial impact on your health. Research has unveiled that abnormalities in SHBG often precede imbalances of sex hormones. High levels of sex hormones can lead to excess growth of cells, leading to the formation of certain cancers, such as breast cancer. [1]


Low SHBG is also associated with elevated levels of triglycerides and low-density lipoprotein (LDL). [2] Because of this, low levels of SHBG are linked with multiple cardiovascular illnesses in both sexes, including: [3]

  • Heart disease
  • Type 2 diabetes
  • High blood pressure

High SHBG and low free testosterone

Excessively high SHBG is problematic, especially for males and athletes, because it decreases the amount of free testosterone. High levels of SHBG—especially when total testosterone levels are already low—are associated with: [4]

  • Infertility
  • Decreased sex drive
  • Erectile dysfunction

In both men and women, low levels of free testosterone can result in reduced muscle growth and impaired post-workout recovery. [5] Additionally, recent research suggests that high levels of SHBG bind to estrogen and reduce bone mass in both men and women- potentially leading to osteoporosis. [6]

Optimal SHBG levels help maintain proper bone health. Some experts are now suggesting routine measurement of SHBG as a useful new marker for predicting severe bone diseases. [6]

» Uncover the science behind testosterone biomarkers

How to know if you need to increase or decrease your SHBG levels

The only way is to get your blood tested using a platform like InsideTracker. Once you know your SHBG levels, you can make the proper lifestyle changes to modify your levels and optimize your health.

Below, we examine some research showing how two diets (calorie-restricted and vegetarian) and a rigorous physical exercise regimen impact your levels of SHBG and testosterone.

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Calorie connection study: How diet influences SHBG and testosterone

A sustained, reduced-calorie diet may significantly increase SHBG levels in women. Researchers assessed the long-term impacts of a diet reduced by 10% in calories in two groups, over 12 months:

  • 117 females on a reduced-calorie diet with no exercise
  • 118 females on a reduced-calorie diet with moderate aerobic exercise

A group of 87 females participating in neither the exercise regimen nor the reduced-calorie intervention served as the experimental controls.

Study focus: Sustained, reduced-calorie diet's impact on SHBG levels in women.

Research setting: Single-blind, randomized control study.

Implications of study

  • SHBG increase: Diet-only group up by 22.4%, diet + exercise group up by 25.8% compared to controls. [7]
  • Estrogen decline: Diet-only group down by 21.4%, diet + exercise group down by 25.8%. [7]
  • Testosterone drop: Diet-only group down by 10.0%, diet + exercise group down by 15.6%. [7]


Combined with aerobic exercise, a reduced-calorie diet boosts SHBG levels and decreases free sex hormones like testosterone and estradiol.

Key takeaways: A calorie-restricted diet is a useful weight-loss method to increase SHBG levels and decrease levels of certain serum sex hormones such as testosterone and estrogen.

However, suppose you are looking to increase free testosterone and estradiol for performance or health-related reasons. In that case, a calorie-restricted diet is a poor weight-loss choice and may harm your health.

» Want to crack the code on hormones? Learn how to interpret your estradiol results

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Overtraining, SHBG, and total testosterone: A study

In a 2011 Finnish study, researchers assessed the impacts of overtraining on levels of SHBG and total testosterone (TT).

Study Overview

Participants: 57 males, average age of 20, during 8 weeks of basic military training in harsh winter conditions.

Physical regimen: Started at 2 hours/day in week one, increased to 7 hours/day by week 8.

Conditions: Cold winter temperatures averaging -13.6° C(7.52°F).

Research protocol

Testing Points: Blood samples before weeks 1, 4, and 7.

Physiological stressors: Subjects faced demanding physical training, outdoor eating, and overnight forest exercises.

Results: TT levels remained the same as baseline after the 4th and 7th weeks. In comparison, SHBG levels remained the same after week 4 and increased after week 7.[8]

Implications of study

  • Decrease in free testosterone: Increased SHBG and stable TT resulted in lower free serum testosterone levels.
  • Performance impact: Linked to lower muscle recovery and ultimately poorer physical performance.


Overtraining, especially in extreme conditions, can alter hormonal dynamics, impacting free testosterone levels and, consequently, physical performance.

Key takeaway: People participating in physically demanding activities (i.e., athletes, military personnel) and those at risk for diseases associated with high SHBG, such as osteoporosis, should carefully monitor their biomarkers to prevent overtraining.

» Are your testosterone levels low? Find out how you may be overtraining

The Impact of Vegetarian Diet on SHBG

In a 2009 research study, scientists assessed the impact of a vegetarian-based protein diet on serum levels of SHBG in middle-aged women.

Study Overview

Participants: 21 omnivores vs. 19 vegetarians (vegans, lacto-vegetarians, lacto-ovo-vegetarians) in a one-year comprehensive cross-sectional study.

Exercise regimen: Both groups exercised 0-3 hours per week.

Protein consumption: Comparable quantities per kilogram of body weight, with vegetarians favoring plant-based and omnivores leaning towards animal-based protein.

Research protocol

Assessment frequency: Every three months, researchers evaluated serum sex hormones and SHBG levels.

Results: Total testosterone levels were similar in vegetarians and omnivores (1.79 nmol/L vs. 1.76 nmol/L). [8] While in SHBG levels, vegetarians exhibited a 50% higher level than omnivores (46 nmol/l vs. 69 nmol/l). [9]

Implications of study

  • Vegetarian advantage: Increase in SHBG without affecting total testosterone.
  • Free testosterone decrease: Suggesting a potential decrease in free testosterone levels.
  • Conclusion: Opting for a vegetarian-based protein diet appears to elevate SHBG levels without altering total testosterone, possibly leading to a decline in free testosterone.

Key takeaways: A diet high in vegetable-based protein increases SHBG without decreasing total testosterone. However, women concerned with having low levels of free sex hormones should consider consuming more animal-based proteins.

Using SHBG to optimize your health

Sex Hormone-Binding Globulin (SHBG) is an overlooked biomarker that has a deep impact on your health and athletic performance. With InsideTracker, you can manage your health through comprehensive biomarker analyses, tailored action plans, and unique resources to improve your health.

Do you need to start consuming a vegetarian diet to increase your SHBG and lower your risk of cardiovascular diseases? Or do you need to increase your calorie intake to unchain testosterone and fuel muscle growth after your exhausting exercise regimen? The only way to know is to discover your SHBG levels today with InsideTracker and modify your lifestyle to take control of your health.

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[1] https://pubmed.ncbi.nlm.nih.gov/18509001

[2] https://pubmed.ncbi.nlm.nih.gov/19653170

[3] https://pubmed.ncbi.nlm.nih.gov/20554712

[4] https://pubmed.ncbi.nlm.nih.gov/11942957

[5] https://pubmed.ncbi.nlm.nih.gov/2917954

[6] https://pubmed.ncbi.nlm.nih.gov/20452803

[7] https://pubmed.ncbi.nlm.nih.gov/22614972

[8] https://pubmed.ncbi.nlm.nih.gov/20543745

[9] https://pubmed.ncbi.nlm.nih.gov/19678968