MEN who eat too much meat are raising the risk of becoming infertile, a study has claimed.
Experts warned that those who plan to have a baby should make sure they are eating limited levels of chicken, beef and lamb.
The research, conducted at the University of Worcester, found high protein diets decrease men’s testosterone by 37 per cent.
For the average man, this would cause medically low testosterone (hypogonadism), the experts said.
Lead researcher Joe Whittaker, a nutritionist, told UK Times: “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.”
Low testosterone is also linked to chronic diseases such as heart disease, diabetes, and Alzheimer’s.
The paper, published in the academic journal Nutrition and Health, described the effects as “protein poisoning”, which is when the breakdown of protein into ammonia becomes toxic.
It suggested the body may become too occupied in fixing protein poisoning that it suppresses the production of testosterone.
Mr Whittaker said: “It would take one to two weeks to see the first signs of protein poisoning such as nausea, diarrhoea, and low testosterone (including the related symptoms e.g. low sex drive).”
How much meat is ‘too much’?
For the study, Mr Whittaker and colleagues compiled the results of 27 studies, involving 309 men.
It found that high protein diets, which tended to be low in carbohydrates as a compromise, consistently affected testosterone and raised cortisol.
A diet high in protein was one in which 35 per cent of calories came from protein, such as meat, fish, eggs, dairy, beans and pulses.
For a man eating 2,500 calories per day, this would mean they were eating around 865 calories in protein.
It’s the equivalent of three eggs for breakfast (240kcal), a chicken breast for lunch (212kcal), and 250g of beef mince at dinner (420kcal), for example.
Mr Whittaker guessed some one per cent of men eat this much protein – and said it would “be mostly men trying to put on muscle, and those that rely on a lot of protein shakes”.
“Bodybuilders and weightlifters (even the amateurs in regular gyms) are notoriously dedicated to diets, and may achieve this [35 per cent] at times,” he said.
“Anecdotally, I have heard numerous men complain of mild symptoms of protein poisoning such as stomach ache and diarrhoea, when trying to bulk up.
“Anything above 35 per cent protein for more than two weeks is dangerous territory.
“It could be safe for some people, but it is not well studied, and what little research exists on it, strongly suggests it will do harm.”
Mr Whittaker recommended sticking to below a 30 per cent protein limit, or 15 to 25 per cent if looking to start a family.
He added: “Reduce alcohol, quit smoking, take regular exercise, lose weight if needed, and eat a diet rich in whole, unprocessed, nutritious foods such as meat, fish, eggs, fruit, vegetables, nuts and legumes.
“Avoid processed and/or sugary foods like the plague.”
Eating protein is vital and has a number of benefits, including to repair muscle and keep you feeling fuller for longer.
That’s why it’s favoured so much by the bodybuilding community, as well as those trying to lose weight.
Many celebrities such as Kim Kardashian, LeBron James, and Meagan Fox have promoted them.
And they are the basis of Atkins and the more modern keto diet.
The British Nutrition Foundation says it recommends protein amounts per day based on how much we need per kilogram (kg) of our bodyweight.
“For adults this is 0.75g per kg of bodyweight. Current recommendations are 56g/day for men and 45g/day for women (based on bodyweights of 75kg for men and 60kg for women).
“On average in the UK men are eating about 85g and women about 67g of protein a day.
“So, on average we are eating more than the requirements. It is likely that most of us are getting enough protein.”
The takeaway is moderation is key.