Eat meat to support healthy levels of testosterone, the primary hormone for male health and muscle building. Testosterone is directly linked to health status in men and low levels lead to a host of problems, including decreased insulin sensitivity and diabetes risk, kidney disease, fat gain and muscle loss, anemia, and overall poor health. Additionally, low testosterone has been shown to lead to feelings of greater aggression, lower mood, and depression in men.
You might find it surprising that low testosterone can increase aggressive behavior in light of a popular misconception that low levels of this essential hormone result in calm or passive behavior. There is some evidence that anabolic steroid use of testosterone and testosterone derivatives can lead to unnaturally aggressive behavior and psychological problems. However, anabolic steroids are synthesized hormones, not native testosterone, and they are typically administered in extremely high levels that are far greater than the amount naturally occurring in males.
In fact, there is evidence that males with naturally higher levels of testosterone behave in more pro-social ways because this secures status within the human social environment, while aggression does not. Greater feelings of self confidence and better mood have been shown to result in less aggression, which is one of the reasons adequate testosterone can lead to less egocentric, less hostile behavior.
It’s true that research shows that males are generally more aggressive than females, but it appears that the hormonal process that facilitates male aggression is much more complicated than the higher level of testosterone in males. While researchers admit that there are many questions to be answered regarding the endocrine system and aggression, they have found that it is actually low serotonin levels that increase aggressive behavior in men. Serotonin plays a role in mood, emotion, sleep, and appetite, and low levels are correlated with low testosterone. This is likely one of the reasons that low testosterone fosters greater aggression
Interestingly, there is evidence that higher estrogen levels may in fact lead to greater aggressive behavior. A study from Penn State compared the effects of giving estrogen therapy to girls who suffered from delayed onset puberty with that of giving testosterone to boys who likewise were late in starting puberty. The girls demonstrated a larger increase in aggression than the boys.
The relationship between these hormones on behavior and mood is fascinating and remains somewhat unclear. We do have significant evidence that low testosterone is unhealthy for men, and including meat in the diet appears to be a strategy for men to maintain testosterone levels, in part because it allows them to avoid nutritional deficiencies that can result in lower testosterone. Here, I review the evidence linking a vegetarian diet with low testosterone and consider the nutritional implications of banishing meat for healthy testosterone levels.
1) Where’s the Evidence that a Vegetarian Diet Leads to Low Testosterone?
A Danish study compared the effect of a vegetarian diet with a mixed, meat-rich diet on testosterone and related sex hormone levels in male endurance athletes. The macronutrient makeup of the diets was similar with 58 percent of energy coming from carbohydrates, 28 percent from fat, and 15 percent from protein. There was a significant decrease in total testosterone after six weeks in the vegetarian diet group. Other sex hormone levels were comparable between the two groups. Additionally, the meat diet group had greater physical performance on an endurance test than the vegetarian group as a whole, although this was not statistically significant.
A second study of the relationship between testosterone, related sex hormones, and a vegetarian diet in men demonstrated that vegetarians had less testosterone available for androgenic actions, which refer to normal testosterone function in the body such as the anabolic response from strength training. This study tested hormone levels in men who were either omnivores or vegetarians and found that although levels of the various sex hormones varied between the vegetarian and meat-eating groups, overall, less biologically usable testosterone was evident in the vegetarians. Research suggests eating meat as a solution to enable a better hormonal environment.
Testosterone and the other sex hormones such as estrogen are synthesized in the body from cholesterol. Meat eaters may have higher testosterone because they intake more fat and cholesterol than the typical vegetarian. However, there is evidence that there is something about “the meat itself” that makes meat a better quality protein for the body to use for muscle building and optimal hormone function.
For example, another study found higher testosterone in omnivores in a comparison between vegetarians and meat eaters. Vegetarians had a 19 percent lower level of testosterone than the meat eaters. One thing for meat eaters to be aware of is that omnivores tend to intake lower levels of dietary fiber, which has negative health consequences. Indeed, in this study the meat eaters ate significantly less fiber as analyzed from a three-day diet journal. Meat eaters averaged 20 grams of fiber daily, while vegetarians ate 37 grams. The obvious solution is for meat eaters to make effort to raise fiber intake for optimal health.
2) Does Soy Play a Role in the Lower Testosterone Levels of Vegetarians?
It very well may. A new case review published in the journal Nutrition presented the result of eating a soy-based vegan diet on testosterone levels and the related symptom of erectile dysfunction. A 19-year-old type 1 diabetic healthy male had been eating a vegan diet that included a large quantity of soy. He suffered loss of libido and erectile dysfunction, and had low testosterone levels. The subject stopped the vegan diet and within one year, his testosterone levels were normal and sexual function was regained.
Researchers suggest that high isoflavonoid intake resulted in disregulation of sex hormones and low testosterone levels in this male, which provides insight into the relationship between vegetarian diets that typically contain soy and low testosterone.
3) What are other Possible Reasons for Lower Testosterone Levels in Vegetarians?
Of great concern for athletes and recreational trainees is the fact that there is significant evidence that long-term vegetarian diets can lead to nutrient deficiencies, which are directly related to testosterone production and male health. Vegetarians tend to be low in the following nutrients: zinc, vitamin B12, vitamin D, omega-3 fatty acids, and iron, not to mention protein intake.
Vegetarian athletes are at increased risk for deficiencies in these areas because strength training and sports performance can significantly deplete some of these nutrients. Vegetarians do tend to have higher levels of vitamin C, E, beta carotene, and omega-6 fatty acids. Be aware that in addition to health issues from low zinc, vitamin D, calcium, and iron, vegetarians who have an imbalance of omega-6 to omega-3 fatty acids can be at risk for cardiovascular complications and an imbalance of anabolic and catabolic hormone levels. Ideally, you want a fairly even ratio of omega-6 to omega-3 fatty acids in the diet.
Omega-3s Fatty Acids
Optimal intake of omega-3s is related to healthy testosterone levels. For example, a new study performed on boars found that giving them an omega-3 supplement resulted in higher testosterone than those fed animal fat. Researchers concluded that omega-3s can improve fertility and anabolic hormone production in these animals, evidence that does have positive implications for humans.
Of related interest is the fact that omega-3s have been proven to lower cortisol levels and enhance protein synthesis follow resistance training. Cortisol is a stress hormone that causes muscle degradation. One way that testosterone is measured in the body is with a testosterone to cortisol ratio. If your omega-3 levels are down from avoiding meat, your cortisol will rise, having a negative effect on your testosterone to cortisol ratio and anabolic processes in the body.
Low iron is probably one of the best known deficiencies of vegetarian and vegan diets and it can lead to poor health and low energy levels. Iron is an essential nutrient because it is a central part of hemoglobin and oxygen exchange in the blood. Iron and testosterone levels in men appear to be closely related. In a study of diabetic men with low testosterone, 24 percent had anemia, which is linked to reduced iron availability in the body. Lower testosterone levels were found to be independently associated with lower hemoglobin and iron levels. Be aware that low testosterone and low iron are also related to development of chronic kidney disease and chronic inflammation.
A second study provides support that low testosterone and low iron are interrelated. Data from participants with low testosterone, all of whom had chronic kidney disease, were 5.3 times more likely to be anemic than those with sufficient testosterone levels. Researchers have not clarified the biological mechanisms relating testosterone and iron, but it is clear that low levels are detrimental to male health.
Zinc is a critical hormone for robust testosterone levels, and vegetarian diets can lead to low zinc intake. For example, in a study of 88 men aged 40 to 60 years, those with normal testosterone levels had a significantly higher zinc level compared to those with low testosterone levels. Low zinc levels were directly correlated with low testosterone levels, and this has been suggested as a factor in male menopause.
A second study found that zinc supplementation for four weeks led to higher testosterone levels after exhaustive high-intensity exercise than taking either a placebo or a selenium supplement. Researchers note that zinc enhances various mechanisms including elevating the conversion rate of androstenedione to testosterone, and that paired with high-intensity exercise, the body produces testosterone at an even higher rate.
Be aware that zinc is one of the most common mineral deficiencies and being vegetarian puts you at greater risk because many foods with the highest zinc content are animal derived such as oysters, veal liver, beef, and lamb. Zinc can be gotten from non-meat foods and seeds—sesame, pumpkin and watermelon seeds are particularly high in zinc.
The American population has been shown to be chronically deficient in vitamin D, and this mineral is critical for many biological processes including the production of testosterone. Vitamin D is produced in the body after sun exposure and can be consumed in the diet, but the best food sources of vitamin D are meat and fish products, meaning that vegetarians are at greater risk for vitamin D deficiency.
A new study on the relationship between testosterone and vitamin D found that taking a vitamin D supplement raised testosterone levels in previously deficient men, aged 20-49. Supplementing with 3,332 IUs of vitamin D daily for one year resulted in significant increases in total, free, and bioactive testosterone. There was no change in testosterone levels in a placebo group. Be aware that optimal vitamin D is crucial for muscle strength, power, and force development, possibly because of its relationship with testosterone production!
4) Are there Other Nutritional Negatives to A Vegetarian Diet For an Athlete?
Yes! There is significant evidence that muscle creatine stores are lower in vegetarians than non-vegetarians, which has implications for strength and muscle mass development as well as anaerobic power output. Creatine is the first energy source called on by the body, meaning it plays an essential role in energy metabolism. Creatine has also been shown to support brain function and supplementing with it can not only offset the effects of sleep deprivation, but improve skill execution, while allowing you to train harder and longer.
Meat and fish are the best sources of creatine, with large amounts being found in beef, salmon and tuna. Of course, you can take a creatine supplement if you’re a vegetarian, but with all this evidence, it might be easier to simply eat meat. Be aware that when choosing meat, opt for organic, local, and free range as much as possible. The growth hormones and antibiotics in nonorganic meat will mess with your hormones and likely negate a lot of the valuable data presented here.