Short answer: No, fasting does not appear to increase testosterone in lean, healthy men. In the controlled human trials that measured it, time-restricted eating (such as the 16:8 schedule) left testosterone unchanged or lowered it, even though men kept their muscle and strength. The one route by which fasting may help testosterone is indirect: if it helps a man with excess body fat lose weight, research on weight loss shows testosterone tends to rise as the weight comes off.
Key Takeaways
- A 2022 review of human trials concluded that time-restricted eating can decrease testosterone in healthy, active men without changing SHBG.[2]
- In an 8-week trial of 34 resistance-trained men, the 16:8 group lost more fat and kept its muscle and strength, but total testosterone and IGF-1 fell compared with a normal eating schedule.[1]
- A 2024 meta-analysis of Ramadan fasting (35 studies, 1,107 healthy adults) found no significant change in testosterone from before to after Ramadan.[3]
- For men with obesity, weight loss itself is linked to higher testosterone, and the more weight lost, the bigger the rise.[4]
- People who take insulin or sulfonylureas, people with a history of eating disorders, and anyone under 18 should not start fasting without medical guidance.[5][6]
What Intermittent Fasting Is (and the Versions Studied)
Intermittent fasting is an eating pattern that changes when you eat rather than what you eat. Johns Hopkins Medicine describes two common approaches: daily time-restricted eating, where all food is eaten in a 6 to 8 hour window (the popular 16:8 plan is 16 hours fasting, 8 hours eating), and the 5:2 approach, where you eat normally five days a week and limit two days to a single meal of about 500 to 600 calories.[5]
Johns Hopkins neuroscientist Mark Mattson calls the shift from burning sugar to burning stored fat “metabolic switching.” The same source warns that longer fasts of 24, 36, 48 or 72 hours are not necessarily better and may be dangerous.[5]
Almost all the testosterone data in men comes from two settings:
- Time-restricted eating (TRE) trials, mostly 16:8, in young, lean, trained men.
- Ramadan fasting studies, where people abstain from food and drink from dawn to sunset for about a month.
There is very little controlled data on testosterone in older men or in men with obesity who use fasting, which matters when you read the results below.
Does Fasting Increase Testosterone? What Human Studies Show
The clearest summary comes from a 2022 review in Nutrients by Cienfuegos, Varady and colleagues, which pulled together every human trial of intermittent fasting that measured reproductive hormones.[2] For men, it found four time-restricted eating trials. All enrolled lean or athletic men, and none included men with obesity.
Study table: time-restricted eating and testosterone in men
| Study | Who | Length | Eating pattern | Testosterone result | Body composition |
|---|---|---|---|---|---|
| Moro 2016 | 34 resistance-trained men | 8 weeks | 8-hour window plus training vs normal schedule plus training | Total testosterone fell about 21% with TRE (significant vs control) | Fat mass down about 15%; fat-free mass unchanged |
| Moro 2020 | 16 elite cyclists | 4 weeks | 8-hour window vs usual diet | Free testosterone fell about 27% with TRE vs about 8% in controls | Weight down about 2%; fat and fat-free mass unchanged |
| Moro 2021 | 20 resistance-trained men | 44 weeks | 8-hour window plus training vs normal diet plus training | Total testosterone fell about 17% with TRE | Fat mass down about 12%; fat-free mass kept |
| Stratton 2020 | 26 physically active men | 4 weeks | 8-hour window plus 25% calorie cut plus training vs calorie cut plus training | Total testosterone down about 1% in both groups | Fat mass down about 9% in both groups; fat-free mass unchanged |
Source: Table 2 of the Cienfuegos et al. 2022 review.[2]
The best known trial: 16:8 in resistance-trained men
In the 2016 trial published in the Journal of Translational Medicine, 34 resistance-trained men followed the same 8-week lifting program. One group ate three meals at 1 p.m., 4 p.m. and 8 p.m. (a 16 hour fast), and the other ate at 8 a.m., 1 p.m. and 8 p.m. Calories and macronutrients were matched (roughly 2,800 versus 3,000 kcal a day, about 22% protein in both).[1]
The fasting group lost more fat mass, kept its fat-free mass, arm and thigh muscle area, and kept bench press and leg press strength. But testosterone and IGF-1 dropped significantly in the fasting group and not in the normal-diet group. Triiodothyronine (T3, an active thyroid hormone) also decreased, while adiponectin rose.[1]
What about Ramadan fasting?
A 2024 systematic review and meta-analysis in PLOS ONE pooled 35 studies covering 1,107 healthy, non-athlete adults. It found no significant relationship between pre- and post-Ramadan testosterone, LH or FSH, and concluded that Ramadan fasting causes minimal hormonal changes in healthy people, aside from signs of circadian disruption such as lower morning cortisol.[3]
How to read the evidence honestly
- No trial showed fasting raising testosterone in lean men. Results ranged from no change to a meaningful drop.
- The drops did not cost muscle or strength in the short term, which suggests the change stayed within a normal range for these young men. The review also notes no negative effect on strength.[2]
- The samples are small (16 to 34 men per trial), mostly young, and only one male study measured SHBG.[2] The authors call for larger, longer trials that include overweight and obese men.
Why Fasting Might Lower Testosterone in Lean Men
The trials were not designed to prove a mechanism, so treat this as interpretation rather than settled fact:
- Energy availability. The reproductive axis is sensitive to how much fuel the body thinks it has. In lean men who train hard, a long daily fast may read as a mild energy shortage, even when daily calories are similar.
- Parallel drops in other anabolic and metabolic hormones. In the 2016 trial, IGF-1 and T3 fell alongside testosterone, a pattern consistent with the body conserving energy.[1]
- Lower leptin. Leptin, a hormone made by fat tissue that signals energy stores to the brain, fell in the fasting group, although the change was not significant once fat loss was accounted for.[1]
If you already have healthy levels and want to know where you stand, our guide to normal testosterone levels explains reference ranges, and the best time to check testosterone levels covers why a morning, fasted blood draw matters.
Weight Loss and Testosterone: Where Fasting Could Help
The story changes for men carrying excess body fat. A 2013 systematic review and meta-analysis in the European Journal of Endocrinology looked at 24 studies of weight loss in men. Both low-calorie diets and bariatric surgery significantly raised total testosterone, and the rise after surgery was roughly three times larger than after dieting.[4]
The key detail: the amount of weight lost was the strongest predictor of how much testosterone went up. Bigger gains were also seen in younger men, men without diabetes and men with more severe obesity. Weight loss also lowered estradiol and raised the pituitary signals (gonadotropins) that tell the testes to make testosterone.[4]
So fasting is not a testosterone tool on its own. It is one of several ways to create a calorie deficit. If a 16:8 schedule is the method that helps an overweight man actually lose fat and keep it off, his testosterone may improve because of the weight loss, not because of the fasting window. Examine.com notes that in the 12-week TREAT trial of 116 adults with obesity, 16:8 eating did not produce significantly more weight loss than normal eating, so the window is not magic for fat loss either.[7]
For a wider view of the habits with the strongest evidence, see how to increase testosterone naturally.
How to Fast Without Undercutting Your Hormones
If you like intermittent fasting for appetite control or convenience, these steps keep it closer to the conditions in which men preserved muscle and strength:
- Start moderate. A 12 to 14 hour overnight fast is a gentle entry point. The Hopkins approach describes 16:8 as a common daily method; it does not recommend multi-day fasts.[5]
- Eat enough protein inside your window. The trained men who kept their muscle ate about 22% of calories from protein.[1] Our article on how much protein men need gives practical targets.
- Keep lifting. Resistance training was part of every trial where fat-free mass held steady.[2]
- Do not stack extremes. A long daily fast plus a steep calorie cut plus hard training is the scenario most likely to push energy availability too low.
- Give it time. Mattson’s research suggests the body takes about two to four weeks to adapt, and hunger or irritability is common early on.[5]
Side Effects and Who Should Not Fast
Examine’s review of 16:8 safety data in adults with obesity found no increase in gastrointestinal or neurological side effects or in eating disorder symptoms.[7] Johns Hopkins still advises checking with your doctor first and calling them if you develop unusual anxiety, headaches, nausea or other symptoms.[5]
Do not start intermittent fasting on your own if you:
- Take insulin or sulfonylureas. An NIDDK interview with endocrinologist Martin Grajower, MD, names hypoglycemia (low blood sugar) as the number one fasting risk for people with diabetes. Insulin and sulfonylureas need dose changes planned with a clinician, and short-acting glinides should not be taken without carbohydrates.[6]
- Take SGLT2 inhibitors or diuretics. These increase fluid loss and raise dehydration risk during longer fasts.[6]
- Have type 1 diabetes. Hopkins lists people with type 1 diabetes who take insulin among those who should not try intermittent fasting.[5]
- Have a history of eating disorders. Strict eating windows can trigger or worsen restrictive or obsessive eating.[5]
- Are under 18.[5]
If you already have symptoms that could point to low testosterone, such as low energy, reduced libido or loss of muscle, read our guide to the signs of low testosterone and get a blood test with your doctor rather than changing your diet to self-treat.
Where Ultra Bann Fits
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Frequently Asked Questions
Does fasting increase testosterone?
Not in the controlled trials so far. In lean, active men, time-restricted eating either did not change testosterone or lowered it.[2] In men with obesity, weight loss (by any method) is linked to higher testosterone, so fasting may help indirectly if it leads to fat loss.[4]
Does intermittent fasting lower testosterone?
It can in lean, trained men. Trials of 8-hour eating windows reported drops of roughly 17% to 21% in total testosterone, while muscle mass and strength were maintained.[2] A meta-analysis of Ramadan fasting in healthy non-athlete adults found no significant change.[3]
Does 16:8 fasting cause muscle loss?
In the trials that combined 16:8 eating with resistance training, men kept their fat-free mass and strength while losing fat.[1][2] Adequate protein and continued lifting appear to be the key conditions.
Is intermittent fasting good for men over 40?
There is little direct testosterone data in older men. For men who are overweight, the evidence on weight loss is encouraging, and younger and non-diabetic men saw the largest testosterone gains after weight loss in the 2013 meta-analysis.[4] Check with your doctor first, especially if you take medication for diabetes or blood pressure.
References
- Moro T, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine. 2016;14:290. PubMed
- Cienfuegos S, Corapi S, Gabel K, Ezpeleta M, Kalam F, Lin S, Pavlou V, Varady KA. Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. Nutrients. 2022;14(11):2343. PMC
- Poursalehian M, et al. Impact of Ramadan fasting on serum levels of major endocrinology hormonal and biochemical parameters in healthy non-athlete adults: A systematic review and meta-analyses. PLOS ONE. 2024;19(5). DOAJ
- Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis. European Journal of Endocrinology. 2013;168(6):829-43. PubMed
- Johns Hopkins Medicine. Intermittent Fasting: What is it, and how does it work? hopkinsmedicine.org
- National Institute of Diabetes and Digestive and Kidney Diseases. Fasting Safely with Diabetes (interview with Martin M. Grajower, MD). 2020. niddk.nih.gov
- Examine.com. 16:8 Intermittent Fasting: Research. examine.com
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease. This article is for information only and is not medical advice.
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