A recent study conducted at the University of Worcester and published in the academic journal: Nutrition and Health, has found high protein diets decrease men’s testosterone by 37%.
For the average man, this can cause medically low testosterone (hypogonadism), increasing the risk of infertility, low sperm counts, and erectile dysfunction. Low testosterone levels are linked to a higher risk of chronic diseases such as heart disease, diabetes, and Alzheimer’s. On the other hand, healthy testosterone levels are important for strength, muscle building, and athletic performance.
The finding was part of a review compiling the results of 27 studies, with a total of 309 men. The research also found low-carbohydrate diets, especially high protein ones, increase the hormone cortisol. This is described the body’s stress hormone, and is released during the ‘fight or flight’ response. High levels of cortisol suppress the immune system, making people more susceptible to catching viral and bacterial infections such as colds, flus, and Covid-19.
High protein diets can reportedly induce a phenomenon known as ‘rabbit starvation’. This was first discovered by the Romans, when soldiers were forced to survive on large quantities of rabbits (i.e. lean meat), during the siege of Villanueva del Campo, many of which developed severe diarrhoea and died. In the body, protein breaks down into ammonia, which at high levels becomes toxic. This can lead to adverse effects including diarrhoea, nausea, and ultimately death. The researchers propose low testosterone is another symptom of rabbit starvation, also known as protein poisoning.
Joseph Whittaker the lead researcher said “Most people eat about 17% protein, and the high protein diets which caused low testosterone were all above 35%, which is very high. So for the average person, there is nothing to worry about, however for people on high protein diets, they should limit protein to no more than 25%.”
Bodybuilders, weight lifters, and those on extreme weight loss diets are most at risk of excessive protein intakes, the researchers said. Typically, this is achieved by eating lot of lean meats, white fish, and protein shakes.
