Does Intermittent Fasting Increase Testosterone?

Most people try intermittent fasting, or IF (restricting your calorie intake to a specific window of hours each day) with one of two goals in mind: weight loss or better health. 

The evidence is mixed on intermittent fasting for weight loss: A study in the New England Journal of Medicine suggests IF is no better than daily calorie restriction for dropping pounds, though some prior research suggests it can melt fat.^{1 2}

But the data is pretty solid on intermittent fasting to improve overall health: Some research suggests IF may help people manage type 2 diabetes, lower blood pressure, curb inflammation, and reduce oxidative stress.^{3 4 5 6}

Several studies have also examined whether intermittent fasting could help increase testosterone levels. As of now, the research is ongoing as to whether intermittent fasting boosts or lowers testosterone, but here’s what we know so far.

About the Expert

Vince Kreipke, Ph.D., is the owner and founder of Kreipke Research and Consulting, which focuses on helping people optimize their lifestyles through dietary and lifestyle modification. His Ph.D. is in exercise physiology with a focus on sports nutrition.

Joshua Calvert, M.D., is a urologist who specializes in testosterone management and male infertility.

What Is Intermittent Fasting?

Intermittent fasting (IF)—or time-restricted eating—is the practice of splitting your day (or week) into feeding and fasting windows. During a fasting window, you don’t eat or drink anything that contains calories (although some experts debate whether coffee can actually break your fast). During a feeding window, you eat all of your meals for the day. 

There are a few common types of IF:

• 16:8 method: 16 hours of fasting, 8 hours of feeding
• 5:2 method: 5 days of normal eating and 2 days of fasting, defined as eating 600 calories per day for men⁷
• Alternate-day fasting method, or AD: fast day consists of consuming about 500 calories per day, feast days are a normal diet⁸
• 24-hour fast: fast for up to 24 hours once or twice a week (there is also a 48-hour fast)⁹
• Circadian fasting: fast when the sun is down, shifting as daylight hours change

Does Intermittent Fasting Increase Testosterone?

Intermittent fasting does not increase testosterone levels, and actually may decrease them.

A review of research on fasting and testosterone found a decline ranging from 1 percent to 21 percent after 4 to 44 weeks.¹⁰ However, it’s still unclear whether this decline impacts male health, if at all.

All four trials observed in the review used eight-hour, time-restricted eating (TRE) schedules and most combined intermittent fasting with resistance training (three times per week). Study participants were physically active, lean, young men. 

The findings revealed that TRE, both alone and combined with resistance training, consistently reduced total testosterone levels and free testosterone. The reductions in total and free testosterone didn’t appear to be related to how long people followed an intermittent fasting schedule: Shorter trials produced similar drops in testosterone as the longer ones did. 

Why might intermittent fasting influence testosterone levels? One theory has to do with calories. 

“Some studies have shown that IF can lead to caloric restriction. When you cut calories, your body may respond to getting fewer nutrients by slowing down hormone production,” says Vince Kreipke, Ph.D., who specializes in exercise physiology and sports nutrition. 

“Researchers are still working on developing theories as to these responses when caloric needs are met,” he adds.

Research limitations on intermittent fasting and testosterone

There are some major caveats to this research on intermittent fasting and testosterone: 

• There isn’t much data on the impact of fasting on sex hormones.
• Sample sizes in each of the four clinical trials in the review were small (ranging from 16 to 34 men), so the findings are hard to generalize.
• Some trials did not include a control group.
• The trials were short in duration, so researchers aren’t sure what the effects of intermittent fasting are on testosterone over time. 

Plus, there’s more to the review’s results than meets the eye, says Kreipke. 

“The most recent report shows that intermittent fasting seems to decrease testosterone levels in lean, physically active individuals. But if you read further, the authors note: ‘Interestingly, the decreases in the anabolic hormone, testosterone, did not lead to any deleterious body composition changes or compromises in muscular strength.’ They’re suggesting that while participants did see a decrease in testosterone, they did not see the negative effects one would associate with it (i.e., reduced physical performance and lean mass) and did see benefits associated with intermittent fasting (fat loss), which is often what men worry about.” 

The authors of that study did point out that the effects of this decrease in testosterone could, however, negatively affect libido and metabolic health. It’s an example of an issue that’s not clear-cut and comes with both risks and benefits.
The research was also on lean, healthy, active men. There may be different considerations for testosterone in men who are overweight and lose weight from intermittent fasting. Weight loss will improve insulin sensitivity and reduce systemic inflammation, which may then indirectly—and modestly—increase testosterone levels, says urologist Joshua Calvert, M.D.¹¹

Intermittent fasting and testosterone in overweight men

Research on the effects of intermittent fasting on testosterone in overweight men is limited. In one 2024 trial of 10 men, total testosterone did not change in men on an intermittent fasting diet, and neither did dehydroepiandrosterone (DHEA, a hormone that aids in the production of testosterone) or sex hormone-binding globulin (SHBG, a protein that binds to sex hormones like testosterone that indicates how much active T is in your bloodstream).

Over the 12 months of the trial, both TRE (8- to 10-hour daily feeding window) and calorie restriction groups lost weight (about 5 percent of total body weight).¹² 

This study’s longer duration and focus on a different study population (obese males) may explain why the findings differ compared to the 2022 research, the authors point out.

What About Intermittent Fasting for Men Who Are on TRT?

If you are currently considering testosterone replacement therapy (TRT) or are on it now, there are some things to think about before combining it with intermittent fasting, Calvert says:

• If you are overweight: Intermittent fasting and TRT can improve body composition and insulin sensitivity. Theoretically, there is a synergy between the two for overweight men (meaning the interaction between them can improve the benefits compared to using one alone). But it’s not a magic combination and not a “must” for healthy testosterone levels. 
• If you are normal weight/not insulin resistant: Adding intermittent fasting to TRT probably has minimal benefits for men with a BMI under 26.

What’s more, sometimes IF can add more stress to your endocrine system. “TRT increases protein synthesis and metabolic demands. If your IF window results in insufficient protein, a calorie deficit, or electrolyte imbalance, you might feel worse—fatigue, mood swings, muscle loss, or poor recovery,” says Calvert. 
You can get results from TRT without fasting, says Calvert. But if you do combine the two, he recommends prioritizing protein, not fasting on injection day, and tracking your symptoms. Back off IF if you develop fatigue, poor sleep, or low libido.

Combining TRT and Intermittent Fasting

Hone Patient Story

Greg combined TRT with intermittent fasting to lose more than 90 pounds. He used the 20-4 method, eating a high-protein diet for four hours a day and keeping caloric intake under 2500 calories.

“I’ve found that intermittent fasting is just as effective at maintaining ketosis, without being as restrictive: when the kids want pizza, I opt for a single slice and a side salad instead of scarfing down a whole pie by myself,” Greg says.

READ GREG’S STORY

Overall, Low Testosterone Levels Are Increasingly Common

Research published in 2021 indicates that testosterone levels among adolescents and young men declined between 1999 and 2016.¹³ Additionally, testosterone levels decline with age—risk of low testosterone rises by 17 percent with each decade of aging.¹⁴

If, like many men, you have fatigue, low sex drive, and general malaise, you may be searching for a testosterone enhancement protocol.

Several solutions are available to help you increase testosterone levels, including TRT, medications like sermorelin, supplements, as well as lifestyle changes like weight loss and limiting alcohol. 

If you suspect that your testosterone is low, talk to your healthcare provider about getting your testosterone levels tested and their individualized recommendations for treatment.  

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About the author

Janet Ungless has developed a comprehensive expertise in health and wellbeing as a writer and editor.

About the reviewer

Natalie Kunsman, M.D., is a board certified physician specializing in functional, anti-aging, and regenerative medicine. She is a fellow of the American Academy of Anti-Aging medicine and the American Academy of Family Physicians.