Study participants shed a substantial amount of weight, helped curb their percentage of body fat, and increased their testosterone levels. “The low-calorie keto diet represents a therapeutic nutritional intervention to treat obesity with a great effect on weight loss and, consequently, on testosterone levels,” says one of the authors of the study, Angelo Cignarelli, MD, PhD, of the section of internal medicine, endocrinology, andrology, and metabolic diseases at the University of Bari Aldo Moro in Italy. RELATED: A Detailed Guide on Low Testosterone
Keto Diet May Offer Weight Loss and Low T Benefits
On average, the men in the study were 41 years old and had a body mass index (BMI) of 36.4, indicating obesity. They started the study with average total testosterone levels of 2.5 nanograms per milliliter (ng/mL), on the low end of what’s considered normal for an adult male, and they had levels of so-called sex hormone binding globulin (SHBG) — a protein that carries testosterone through the blood — that were in a normal range at 24.2 nanomoles per liter (nmol/L). All of the men followed a keto diet and consume no more than 800 calories a day for four weeks. By the end of the study period, the men lost an average of 9.3 kilograms (20.5 pounds), reducing their BMI by an average of 3.1 points. While the men still had obesity based on their BMI at the end of the study period, they lost an average of 6.5 kilograms (14.3 pounds) in fat mass. They also experienced average increases 0.89 ng/mL in total testosterone levels and 10.94 nmol/L in SHBG after four weeks on the low-calorie ketogenic diet.
Could a Keto Diet May Help Treat Hypogonadism?
Four in five men in the study started out with testosterone levels low enough to be diagnosed with hypogonadism, Dr. Cignarelli adds. Obesity can be one of many different potential causes of hypogonadism, a condition that can lead to symptoms such as low sex drive, fatigue, depression, and erectile dysfunction in men, according to the Mayo Clinic. While it’s possible a keto diet might help treat hypogonadism, the study wasn’t designed to prove this, and more research is needed to determine whether this approach might work, Cignarelli says. Any benefits would also need to be balanced against potential side effects of a keto diet, which can include the potential for lost muscle mass or vitamin and mineral deficits, Cignarelli notes. The study didn’t assess whether men had sexual dysfunction or whether they experienced any increase in sexual desire or improved sexual function when they followed a keto diet and their testosterone levels increased. It also didn’t examine whether men had other symptoms of hypogonadism. Testosterone therapy can help improve symptoms of hypogonadism — including sexual dysfunction, depression, difficulty with concentration, decreased muscle mass, and increased body fat, according to the Mayo Clinic. But testosterone won’t have this effect for healthy men who don’t have a hypogonadism diagnosis, and shouldn’t be prescribed without this diagnosis, according to the Mayo Clinic. In guidelines released in January 2020, the American College of Physicians recommended that men with age-related low testosterone, often called “low T,” only be prescribed testosterone therapy if they have sexual dysfunction. For other symptoms of low testosterone, it’s not clear that taking testosterone will help, according to these guidelines. RELATED: Testosterone and Women’s Health
Previous Studies on Keto Suggest a Temporary Weight Loss Benefit
The main goal of a ketogenic diet is to deprive the body of carbohydrates, which then forces the body to burn fat for energy. Restricting carbohydrates leads to fat getting broken down in the liver, a process that produces ketones to use for fuel when sugar, a byproduct of carbs, isn’t as readily available to sue for energy. When the body is in this metabolic state, it’s called ketosis. In a classic keto diet, about 70 percent to 80 percent of daily calories come from fats, 10 to 20 percent come from protein, and only about 5 to 10 percent come from carbohydrates, according to the Harvard T.H. Chan School of Public Health. Potential benefits of a ketogenic diet can include fewer food cravings, reduced appetite, and loss of fat instead of lean muscle mass as people shed excess pounds, according to Harvard. Risks of keto may include headaches, constipation or diarrhea, hunger, fatigue, and irritability, as well as nutrient deficiencies. A low-calorie keto diet like the one used in the study has previously been associated with short-term weight loss and blood sugar reductions, less is known about the impact on testosterone and sex hormones, says Cignarelli. Research on the weight loss effects of keto in the long term are also lacking. One meta-analysis of ketogenic diet trials published in July 2020 in Nutrients, for example, found that a ketogenic diet helped people with obesity lose significantly more weight than a low-fat diet. This study also reported significant reductions in blood sugar compared to a low-fat diet, in patients with and without type 2 diabetes. And a previous meta-analysis, published in December 2015 in the British Journal of Nutrition, examined long-term data on more than 1,000 people who were randomly assigned to follow either low-calorie or low-carbohydrate diets. This study found significantly greater weight loss in people who drastically reduced carbohydrates. A study published in October 2018 in Nutrients found men and women with obesity who started a ketogenic diet experienced significant weight loss and reductions in body fat and reported reduced food and alcohol cravings, increased physical activity, and less daytime sleepiness. In this study, the women, but not the men, also reported improved sexual function. RELATED: What Are the Benefits and Risks of the Keto Diet?
Limitations of the New Study on Keto, Weight, and Low T
The biggest drawback of the new study is that it has too few participants to draw broad conclusions about how a keto diet might work for all men with obesity, or for all men with low testosterone levels, says Richard Kravitz, MD, MSPH, a professor and co-vice chair for research in the department of internal medicine at the University of California Davis Medical Group in Sacramento. Although men did experience an increase in testosterone levels after four weeks on a keto diet, the magnitude of this change may not be large enough to be clinically meaningful, Dr. Kravitz says. Beyond this, the study didn’t explore whether the keto diet resulted in any improvements of symptoms often associated with low testosterone such as low sex drive or poor sleep, Kravitz adds. And if men are worried that low testosterone might be wreaking havoc with the sleep or their sex life, that doesn’t mean they should simply start a very low-calorie keto diet on their own. “Very low-calorie diets can be dangerous and need to be conducted under medical supervision,” Kravitz warns. “Ketogenic diets are probably safe for most people but … I would not assume that a very low-calorie ketogenic diet is safe.” RELATED: 10 Steps Beginners Should Take Before Trying a Keto Diet
When It Comes to Keto, Shorter Is Better
The best way to try a keto diet is for a very short period of time, as the men in the study did, says Uberto Pagotto, PhD, MD, a professor of endocrinology and metabolism at the University of Bologna in Italy. Dr. Pagotto was not involved in the new study. The study results suggest that the rapid, significant weight loss associated with the low-calorie keto diet may have a strong impact on testosterone levels. But there’s a catch: Men who already have testosterone levels in a normal, healthy range, may not necessarily experience a surge in this hormone when they go on a low-calorie keto diet, Pagotto says. What the study does suggest, however, is that men with a specific type of low testosterone known as functional hypogonadism — the kind that’s not caused by irreversible damage in the brain or testes, but instead by obesity and other potentially reversible health conditions — might indeed benefit from a stint on a low calorie keto diet, Pagotto notes. In some cases it can be hard to pinpoint the exact cause of low testosterone, Pagotto says. “The real advance of this study is the following: The keto diet may be a very efficient test to help to identify functional hypogonadism,” Pagotto says.
