madman
Super Moderator
Abstract
Elevations in the circulating concentration of androgens are thought to have a positive effect on the anabolic processes leading to improved athletic performance. Anabolic-androgenic steroids have often been used by competitive athletes to augment this effect. Although there has been a concerted effort on examining how manipulating training variables (e.g., intensity and volume of training) can influence the androgen response to exercise, there has been much less effort directed at understanding how changes in both macronutrient and micronutrient intake can impact the androgen response. Thus, the focus of this review is to examine the effect that manipulating energy and nutrient intake has on circulating concentrations of testosterone and what the potential mechanism is governing these changes.
1. Introduction
Testosterone, together with its potent metabolite, dihydrotestosterone (DHT), are the principal androgens in the circulation of mature male mammals, including humans. They are important hormones for various biological processes and are vital for the development and maintenance of secondary male characteristics. They are also crucial for reproductive functions, body composition, and muscle and bone health [1,2].
As the primary anabolic steroid, testosterone promotes an increase in protein production as well as stimulates both anabolic and anti-catabolic functions in skeletal muscle and neuronal tissue leading to increased muscle strength, power, endurance, and hypertrophy in a dose-dependent manner [3]. Testosterone is also responsible for the mass, density, and strength of bone. As for its androgenic effects, testosterone mediates the development of male primary and secondary male characteristics such as sexual organ growth, deepening of the voice, and growth of facial and body hair [4].
Structurally, testosterone has a characteristic four-ring C18 steroid structure and is synthesized from cholesterol through an enzymatic multistep process primarily within the Leydig cells (~95%), which are located in the interstitium of the testes. The adrenal glands also produce small amounts (~5%) of androgens [5]. In women, testosterone is produced in much smaller amounts, primarily from the adrenal glands and the ovaries [2,6]. There are two metabolic pathways, the progesterone (delta-4) and dehydroepiandrosterone (DHEA) (delta-5) pathways [6]. Once synthesized, testosterone is secreted into the bloodstream and delivered to target tissues [7]. In the blood, most testosterone is transported bound to several proteins, mainly serum albumin and sex hormone-binding globulin (SHBG). A small amount is transported unbound, referred to as free testosterone (FT) [8]. FT is the active form of testosterone while protein-bound testosterone is inactive [9]. When testosterone reaches its target tissues it diffuses through the cells’ fatty membrane, where it can interact with its receptor stimulating its biological effects or it can be reduced into DHT by the cytoplasmic enzyme 5α-reductase, which is highly expressed in male reproductive organs, skin, and the brain [8].
The classical biological effects of androgens are primarily mediated by FT binding to the androgen receptor (AR). DHT binds to the same AR even more strongly than testosterone, so that its androgenic potency is about five times more potent than testosterone [10]. The AR complex undergoes a structural change that allows it to move into the cell nucleus and bind directly to specific nucleotide sequences of DNA, resulting in the transcription of certain genes. The AR complex itself serves as a transcription factor [7,11]. Testosterone can also be converted to estradiol (E2) by the aromatase enzyme and then activate certain estrogen receptors. Bone, adipose tissue, and the brain are tissues in humans where the primary effect of testosterone is via aromatization to E2 [4,12]. The enzyme aromatase is a member of the cytochrome P450 enzyme superfamily that catalyzes the conversion of androstenedione and testosterone to the aromatic estrogenic steroids estrone and estradiol, respectively [9]. These are the last key steps in the catalyzation of androgens into estrogens, hence inhibition of aromatase activity can elevate androgen concentrations. There are numerous natural substances that have been scientifically tested or suggested to inhibit aromatase activity, alongside pharmaceutical compounds whose non-medical use is considered illegal [2,6].
Manipulation of testosterone concentrations without the use of anabolic steroids has been a highly investigated topic because of the known effect testosterone has on enhancing athletic performance [2,6]. While the use of androgens in competitive athletics is illegal, it has not stopped the search for “natural” ways to increase testosterone concentrations. In this review, we will examine the specific effect of various macronutrients and micronutrients on enhancing circulating testosterone concentrations at rest and during exercise. In addition, we will also discuss the role of low energy availability, a growing condition in the athletic population, and its effect on testosterone concentrations. While other reviews have previously discussed the effect of nutrition on testosterone status [13–16], most of these papers have examined the role of single nutrient (macro/micro) or food/food groups. To the best of our knowledge, this review is the first to focus on the nutrient influence on circulating testosterone concentrations. Its purpose is to provide an evidence-based assessment of how specific nutrients found in the diet or specific dietary manipulation can enhance the androgen response, with the assumption being that elevation in circulating androgens will enhance the anabolic response and potentially improve exercise performance.
1.1. Natural Product Extracts and Aromatase Inhibition
1.2. Flavonoids
1.3. Other Nutrients
2. Macronutrient Effects on Changes in Testosterone Concentrations
2.1. Low Energy Availability and Calorie Intake
2.2. High-Fat Diets and Dietary Fats
2.3. Dietary Protein and Protein Supplements
3. Micronutrient Effects on Testosterone Concentrations
3.1. Vitamin D
3.2. Zinc
3.3. Magnesium
4. Summary
In summary, this article discussed several nutrients that have been proposed to have anti-aromatase activity. Although evidence has been presented supporting the benefits of certain nutrients, the evidence supporting most of the nutrients suggested influencing anti-aromatase activity remains largely inconclusive. Much of this issue is related to the small sample sizes found in many of these papers, and the limitations that are associated with examining trained and athletic populations. More effort appears to have been focused on the effects of energy intake and manipulating macronutrient composition, specifically protein and fat composition on changes in circulating levels of testosterone at rest and in response to various exercise stresses. Evidence is consistent in demonstrating that low energy intake negatively impacts testosterone concentrations that may affect human performance. In addition, certain vitamins and minerals have important roles in testosterone synthesis. The importance of supplementing these vitamins and minerals appears to become efficacious when the body becomes deficient in these specific micronutrients. However, evidence supporting any benefits of supplementing with these micronutrients to augment testosterone concentrations is lacking.
Elevations in the circulating concentration of androgens are thought to have a positive effect on the anabolic processes leading to improved athletic performance. Anabolic-androgenic steroids have often been used by competitive athletes to augment this effect. Although there has been a concerted effort on examining how manipulating training variables (e.g., intensity and volume of training) can influence the androgen response to exercise, there has been much less effort directed at understanding how changes in both macronutrient and micronutrient intake can impact the androgen response. Thus, the focus of this review is to examine the effect that manipulating energy and nutrient intake has on circulating concentrations of testosterone and what the potential mechanism is governing these changes.
1. Introduction
Testosterone, together with its potent metabolite, dihydrotestosterone (DHT), are the principal androgens in the circulation of mature male mammals, including humans. They are important hormones for various biological processes and are vital for the development and maintenance of secondary male characteristics. They are also crucial for reproductive functions, body composition, and muscle and bone health [1,2].
As the primary anabolic steroid, testosterone promotes an increase in protein production as well as stimulates both anabolic and anti-catabolic functions in skeletal muscle and neuronal tissue leading to increased muscle strength, power, endurance, and hypertrophy in a dose-dependent manner [3]. Testosterone is also responsible for the mass, density, and strength of bone. As for its androgenic effects, testosterone mediates the development of male primary and secondary male characteristics such as sexual organ growth, deepening of the voice, and growth of facial and body hair [4].
Structurally, testosterone has a characteristic four-ring C18 steroid structure and is synthesized from cholesterol through an enzymatic multistep process primarily within the Leydig cells (~95%), which are located in the interstitium of the testes. The adrenal glands also produce small amounts (~5%) of androgens [5]. In women, testosterone is produced in much smaller amounts, primarily from the adrenal glands and the ovaries [2,6]. There are two metabolic pathways, the progesterone (delta-4) and dehydroepiandrosterone (DHEA) (delta-5) pathways [6]. Once synthesized, testosterone is secreted into the bloodstream and delivered to target tissues [7]. In the blood, most testosterone is transported bound to several proteins, mainly serum albumin and sex hormone-binding globulin (SHBG). A small amount is transported unbound, referred to as free testosterone (FT) [8]. FT is the active form of testosterone while protein-bound testosterone is inactive [9]. When testosterone reaches its target tissues it diffuses through the cells’ fatty membrane, where it can interact with its receptor stimulating its biological effects or it can be reduced into DHT by the cytoplasmic enzyme 5α-reductase, which is highly expressed in male reproductive organs, skin, and the brain [8].
The classical biological effects of androgens are primarily mediated by FT binding to the androgen receptor (AR). DHT binds to the same AR even more strongly than testosterone, so that its androgenic potency is about five times more potent than testosterone [10]. The AR complex undergoes a structural change that allows it to move into the cell nucleus and bind directly to specific nucleotide sequences of DNA, resulting in the transcription of certain genes. The AR complex itself serves as a transcription factor [7,11]. Testosterone can also be converted to estradiol (E2) by the aromatase enzyme and then activate certain estrogen receptors. Bone, adipose tissue, and the brain are tissues in humans where the primary effect of testosterone is via aromatization to E2 [4,12]. The enzyme aromatase is a member of the cytochrome P450 enzyme superfamily that catalyzes the conversion of androstenedione and testosterone to the aromatic estrogenic steroids estrone and estradiol, respectively [9]. These are the last key steps in the catalyzation of androgens into estrogens, hence inhibition of aromatase activity can elevate androgen concentrations. There are numerous natural substances that have been scientifically tested or suggested to inhibit aromatase activity, alongside pharmaceutical compounds whose non-medical use is considered illegal [2,6].
Manipulation of testosterone concentrations without the use of anabolic steroids has been a highly investigated topic because of the known effect testosterone has on enhancing athletic performance [2,6]. While the use of androgens in competitive athletics is illegal, it has not stopped the search for “natural” ways to increase testosterone concentrations. In this review, we will examine the specific effect of various macronutrients and micronutrients on enhancing circulating testosterone concentrations at rest and during exercise. In addition, we will also discuss the role of low energy availability, a growing condition in the athletic population, and its effect on testosterone concentrations. While other reviews have previously discussed the effect of nutrition on testosterone status [13–16], most of these papers have examined the role of single nutrient (macro/micro) or food/food groups. To the best of our knowledge, this review is the first to focus on the nutrient influence on circulating testosterone concentrations. Its purpose is to provide an evidence-based assessment of how specific nutrients found in the diet or specific dietary manipulation can enhance the androgen response, with the assumption being that elevation in circulating androgens will enhance the anabolic response and potentially improve exercise performance.
1.1. Natural Product Extracts and Aromatase Inhibition
1.2. Flavonoids
1.3. Other Nutrients
2. Macronutrient Effects on Changes in Testosterone Concentrations
2.1. Low Energy Availability and Calorie Intake
2.2. High-Fat Diets and Dietary Fats
2.3. Dietary Protein and Protein Supplements
3. Micronutrient Effects on Testosterone Concentrations
3.1. Vitamin D
3.2. Zinc
3.3. Magnesium
4. Summary
In summary, this article discussed several nutrients that have been proposed to have anti-aromatase activity. Although evidence has been presented supporting the benefits of certain nutrients, the evidence supporting most of the nutrients suggested influencing anti-aromatase activity remains largely inconclusive. Much of this issue is related to the small sample sizes found in many of these papers, and the limitations that are associated with examining trained and athletic populations. More effort appears to have been focused on the effects of energy intake and manipulating macronutrient composition, specifically protein and fat composition on changes in circulating levels of testosterone at rest and in response to various exercise stresses. Evidence is consistent in demonstrating that low energy intake negatively impacts testosterone concentrations that may affect human performance. In addition, certain vitamins and minerals have important roles in testosterone synthesis. The importance of supplementing these vitamins and minerals appears to become efficacious when the body becomes deficient in these specific micronutrients. However, evidence supporting any benefits of supplementing with these micronutrients to augment testosterone concentrations is lacking.
