Higher Body Fat Linked To Low Sperm Count, Testosterone. Here's Why

• Researchers say body fat measurements are a better predictor of male reproductive health than body mass index readings.
• They report that men with higher body fat percentages have lower sperm counts than men with lower body fat measurements.
• Men can potentially improve their reproductive health by maintaining a healthy body weight, eating a well-balanced diet, and minimizing stress.

Body fat percentage can be a better predictor of male reproductive health than body mass index (BMI), according to a new study.

Researchers report that higher body fat percentages are associated with lower sperm counts and changes in male reproductive hormones, including testosterone.

They said those associations persist even among males with normal BMI but higher body fat percentage.

The researchers noted that males with a high body fat percentage generally had lower sperm counts than males with a normal body fat percentage. They added that the males with high body fat percentages also tended to have lower semen volume and sperm concentration.

They concluded that body fat percentage was a better predictor of reduced sperm count than BMI or waist-to-height ratio. The researchers also reported that even males with a normal BMI but a relatively high body fat percentage had lower sperm counts and poorly formed sperm.

The researchers published their findings in the journal Human Reproduction on July 29.

“[Our research] suggests that measuring body fat percentage may identify men at risk of impaired reproductive health who would not be identified based on BMI alone,” said Nis Brix, MD, an associate professor in the Department of Public Health at Aarhus University in Denmark and first author of the study, in a statement.

The researchers are also involved in another study, the BIOSFER project, which is examining the biological and social determinants of low fertility. They’re collecting information on reproductive health, including semen samples, in 1,250 Danish males and 1,250 Norwegian males as part of this larger research project.

Philip Werthman, MD, a urologist, men’s health specialist, and director of the Center for Male Reproductive Medicine and Vasectomy Reversal in Los Angeles, said male fertility has become an increasingly important topic. Wethman wasn’t involved with the study.

“The decline in male fertility is real and significant,” he told Healthline. “[It’s] not a subtle shift. It’s a major public health signal.”

Higher body fat associated with 23% lower sperm count

The researchers noted that previous studies have shown that obesity and other weight management issues are associated with impaired reproductive health in men, including worse semen quality and reduced fertility.

However, the researchers noted that BMI is only an indirect measure of fatty tissues and does not distinguish between fat mass and lean body mass, which can include muscle mass. As a result, the researchers said that males with the same BMI can have markedly different body fat levels.

For their study, the researchers studied 1,058 Danish men who had just turned 18 years and 9 months of age.

They measured the participant’s body fat percentage using a bioimpedance analyzer, which sends a weak electric current through the body with the voltage being measured to estimate body fat, body water, and muscle mass. 

Body fat percentage was divided into four categories: low (less than 8% fat), normal (8-19%), high (20-24%), and very high (25% or more).

In addition, the researchers measured the participants BMI and waist-to-height ratio. The men also provided semen and blood samples, measured the size of their testicles, and completed a questionnaire on health behavior.

The researchers reported that, compared to men with a normal body fat percentage, their analysis indicated that men with a high body fat percentage had, on average, a 23% lower sperm count.

The researchers said men with very high body fat percentages had a 15% lower sperm count than men with a normal body fat percentage.

The researchers reported that men in the higher body fat categories also had lower sex hormone-binding globulin (SHBG) and testosterone levels, as well as altered balances of male reproductive hormones.

“For men, maintaining a healthy body composition, not just a healthy body weight for height, may be important for fertility,” Brix said. “For doctors, assessing body fat percentage in selected patients could help identify men at risk of reduced fertility who might otherwise be overlooked based on BMI alone.”

“More broadly, the results highlight the importance of preventing excess body fat through healthy lifestyle initiatives, which may benefit both reproductive health and overall health,” Brix added.

Werthman said that obesity can be a major contributing factor in male infertility.

“Obesity alone plays a major role as excess fat tissue converts testosterone into estrogen and directly impairs sperm production,” he explained. “It is important we recognize that modern life is actively working against male reproductive health.”

Werthman added it’s important for men to obtain a semen analysis if there are any signs of fertility issues.

“You cannot optimize what you haven’t measured,” he said. “It’s inexpensive, non-invasive, and provides critical insight into count, motility, and morphology.”

S. Adam Ramin, MD, a urologist, urologic oncologist, and medical director of Urology Cancer Specialists in Los Angeles, wasn’t involved in the study but said the findings provide valuable information.

“It presents good reasons as to why a decrease in sperm count occurs as body fat increases,” he said.

Ramin noted that reproductive health issues may also indicate other health problems. “A low sperm count may be a signal of something more serious happening inside the body,” he told Healthline.

What to know about male infertility

It’s estimated that infertility affects about 15% of couples in the United States. The male partner is solely responsible for about 20% of these cases and contributes to another 30% to 40%.

However, a 2025 study concluded that sperm concentration remains stable among men in the United States with no known fertility challenges. That’s in contrast to earlier studies that have indicated that sperm counts have decreased significantly among men worldwide.

Male infertility is usually linked to sexual function as well as semen quality. These conditions can include:

• decreased sperm count, motility, or quality
• decreased libido, or sex drive
• erectile dysfunction
• low levels of hormones such as testosterone and prolactin

The risk factors for male infertility, especially low sperm count, include:

• obesity
• injury or surgery to the testicles
• sexually transmitted infections (STIs)
• exposure to pesticides, herbicides, or industrial chemicals
• exposure to radiation
• excessive drug use or alcohol consumption
• anabolic steroid use

Infertility can’t always be treated, but there are ways for men to improve their reproductive health. Among the strategies:

• exercising regularly
• trying antioxidant supplements, in particular vitamin C
• minimizing stress
• eating a well-balanced diet
• maintaining a healthy body weight
• getting consistent, quality sleep
• quitting smoking
• limiting alcohol consumption

Ramin adds that testicles need unobstructed blood flow to function properly, so wearing loose-fitting pants can help circulation to that part of the body.

He also noted that testicles tend to be about 2 degrees cooler than the rest of the body, so sitting for extended lengths of time in warm water, such as in a jacuzzi, may affect sperm quality.