Do High Protein Diets Actually Cause Low Testosterone and Infertility?
- Low testosterone, also called low T is associated with an increased risk of type 2 diabetes, heart disease and low sperm count which is often associated with male infertility.
- A recent study claimed that plates overflowing with meat (low carb-high protein diets) can lead to a decrease in testosterone.
- This study suggests that really high protein intake relative to other macronutrients—particularly carbohydrates—has the potential to mess with testosterone levels.
Could eating high amounts of protein-rich meat lower your testosterone to the extent that it can cause infertility? A recent study from the academic journal Nutrition and Health made the claim  that plates overflowing with meat (low carb-high protein diets) can lead to a decrease in testosterone.
Testosterone (T) is the primary male sex hormone and is primarily produced in your testes. Testosterone is vital for reproductive development and function. Low testosterone, also called low T is associated with an increased risk of type 2 diabetes, heart disease and low sperm count which is often associated with male infertility.
The study’s lead researcher, nutritionist Joe Whittaker, told The Sun, “Low testosterone levels cause low sperm counts, which is the major determinant of men’s fertility. In our study, high protein diets caused low testosterone, so it is very likely they also caused low sperm counts, which would reduce men’s fertility.”
This is a big statement that can drive fear into the heart of any carnivorous male. But how accurate is it?
While there’s a lot to unpack from this article, we’re going to focus on the main claim of the article and others like it: “High protein intake causes low testosterone levels.” But first, you need to understand how this study was constructed.
Meta-Analysis Studies Aren’t as Pure
This claim is based on a meta-analysis (or a study of studies). Why is knowing that important?
In a meta-analysis, the researcher sets the parameters surrounding whether a study can be used in the analysis. The studies have to be somewhat similar for the analysis to make sense. For this particular study, researchers found 86 studies on the topic that could potentially qualify before whittling down to the 27 studies that were used for this paper.
From there, the authors used 13 studies for the resting total testosterone analysis section. And of those 13 studies, only three (with a notedly small total of 26 participants) were used for the high protein intake analysis.
Why does this matter? Because as the pool of viable studies and study participants dwindles, the resulting findings can become less applicable to the population as a whole. It is best to have a larger number of participants in order to qualify the data but sometimes that is difficult to do. When a small number of participants are studied, the results may not be as accurate or credible compared to a larger study.
This Study’s Focus Wasn’t High Protein Diets
Now, the study in question looked at the effects of low carbohydrate diets on total testosterone and cortisol in men. In other words the primary focus was on carbohydrates and how they affected cortisol and testosterone; however parameters of high protein, moderate protein and low protein levels were assessed within the carbohydrate diets.
When looking specifically at resting total testosterone, researchers reported that high protein and low carbohydrate diets—where protein represents more than 35 percent of the total diet—resulted in a significant decrease in testosterone.
Meanwhile, moderate protein and low carbohydrate diets—where protein represents less than 35 percent of the total diet—did not seem to have any significant effects on testosterone levels.
Researchers concluded: “[High protein, low carbohydrate] diets caused a large decrease in resting [total testosterone], suggesting individuals consuming such diets may need to be cautious about adverse endocrine effects.” Okay, this seems reasonable, but you also need to…
Understand the Nutritional Breakdown
Now we have to dive into the actual nutritional breakdown of the diets that were used for the analysis. The average carb intake was just south of 16 percent (with two of the studies below 10 percent). The studies also had an average fat and protein intake of 37 percent and 48 percent, respectively.
Also, this study was not talking about absolute amounts of protein, but amounts relative to the rest of your macronutrients, especially when relative carbohydrate amounts were very low.
Which raises an important question often forgotten when looking at research: “How does this finding apply to the real world?”
Let’s break that down for you. If the average macronutrient intake of the diets analyzed were applied to a 3,000 calorie-per-day diet—not unheard of for an active 200-pound (roughly 91kg) man—48 percent of total energy from protein would be 1,440 calories coming from 360 grams of protein. That would be almost four grams of protein per kilogram of body weight.
That’s simply too much protein.
For reference, the International Society of Sports Nutrition suggests a protein intake of 1.6 g/kg to 2.4g/kg for active individuals looking to maintain or build muscle mass. Even if the threshold used in the study (35 percent), it would still result in a protein intake of approximately 2.9g/kg.
Ultimately, it’s not high protein diets that are being examined in this research paper; it’s very high protein diets.
- Meta-analysis studies can be slightly skewed due to which studies are being included or excluded
- This study’s focus was not on high protein diets, but rather on carbohydrate levels
- The amount of protein that was consumed in diets that had adverse affects was too high by any standards
You Need to Understand Your Testosterone
The term “total testosterone” here has been used interchangeably with “testosterone.” That’s mostly correct. Still, some nuances that should be addressed and while finding total testosterone levels is important, it’s only the beginning.
To understand if testosterone is being used optimally, we have to look at other hormones related to testosterone’s effectiveness. Those include free testosterone, bound testosterone, and sex-hormone binding globulin (SHBG). This study didn’t examine those hormones; only total testosterone which is the combination of free and bound testosterone.
Free testosterone interacts with cells of the body to produce androgenic outcomes. These are things like regulating bone and muscle mass, your sexual and reproductive function, your metabolism, and more. Bound testosterone is combined with another hormone called sex hormone-binding globulin (SHBG). Bound testosterone is often less effective, if at all, at causing the same androgenic outcomes. Each of these hormones are in constant flux as they respond to internal signals and external stressors, including food.
This gets complicated quickly, but the point is this: just because total testosterone is going up, that does not mean that benefits are being realized. And vice versa. There are many details to examine before blanket statements like “eating massive amounts of meat is going to make you sterile” can be made.
Still, Your Diet Will Affect Your Testosterone
While the application of these findings seems to have missed the mark, it’s not completely useless. This study suggests that really high protein intake relative to other macronutrients—particularly carbohydrates—has the potential to mess with testosterone levels.
If your diet calls for an extremely high amount of protein relative to the other macronutrients, like the carnivore diet, and you start feeling crummy, your nutrient intake may be a factor.
The Bottom Line
You are not a walking meta-analysis boiled down to one simple hormone measured in response to one simple variable. There are many things that are going to play into the inner workings of your internal environment and how your body functions in response to that internal environment. Staying within reasonable limits will yield healthy sustainable success in realizing your health and performance goals.