OMAD does not increase testosterone. The available evidence points in the opposite direction: intermittent fasting protocols, including tight eating windows like one meal a day, consistently reduce both total and free testosterone levels. This effect has been observed in men across studies lasting 4 to 44 weeks, and shorter trials produced similar drops to longer ones.
What the Research Actually Shows
A 2022 review of human trials on intermittent fasting and reproductive hormones found that time-restricted eating, both alone and combined with resistance training, consistently reduced total testosterone and free testosterone in lean, physically active young men. Free testosterone, the portion your body can readily use, dropped even in a 4-week trial using an 8-hour eating window. OMAD compresses that window even further, making it reasonable to expect at least the same degree of suppression.
Multiple studies by the same research group found significant testosterone reductions in men following a 16:8 fasting protocol. These weren’t sedentary or overweight participants. They were young, active men, exactly the population most likely to try OMAD for performance or body composition reasons. The review’s conclusion was blunt: it is possible that intermittent fasting decreases androgen markers in both men and women.
Why Fasting Lowers Testosterone
Your body produces testosterone through a chain of hormonal signals. The hypothalamus releases a signaling hormone that tells the pituitary gland to release luteinizing hormone (LH), which then tells the testes to produce testosterone. Fasting disrupts this chain at the top. Animal research shows that after extended fasting, the hypothalamus reduces its signaling output. Serum LH and testosterone both drop significantly. The testes themselves still work fine when stimulated directly, meaning the problem isn’t with the testosterone-producing cells. It’s that the brain stops asking them to work as hard.
This makes biological sense. When your body perceives a caloric deficit or prolonged periods without food, it downregulates reproductive function. From an evolutionary standpoint, reproduction is expensive, and the body deprioritizes it when energy is scarce. The longer and more severe the fasting window, the stronger this signal becomes.
Free Testosterone and SHBG
Total testosterone is only part of the picture. What matters for muscle growth, energy, and libido is free testosterone, the fraction not bound to carrier proteins in the blood. One of those carriers is sex hormone-binding globulin (SHBG). When SHBG rises, it grabs more testosterone and makes it unavailable.
In women, intermittent fasting tends to increase SHBG levels, which effectively lowers the amount of usable testosterone even further. In men, the pattern is slightly different but no more encouraging. After 4 weeks of 8-hour time-restricted eating, SHBG stayed the same in male participants, yet free testosterone still dropped. Researchers noted this was surprising because less free testosterone usually means more of it is being bound up. The fact that SHBG didn’t rise suggests the body was simply producing less testosterone overall rather than just trapping more of it.
The Growth Hormone Misconception
One reason the idea persists that OMAD boosts testosterone is the well-documented rise in growth hormone during fasting. Growth hormone does increase substantially when you go long periods without eating. But growth hormone and testosterone are regulated by completely separate systems. A spike in growth hormone does not trigger a corresponding rise in testosterone. The research makes this clear: even as growth hormone climbs during fasting, testosterone moves in the opposite direction.
Does the Effect Wear Off Over Time?
You might wonder whether the testosterone drop is temporary, something your body adjusts to after a few weeks of OMAD. The data doesn’t support that hope. The review of human trials found that testosterone reductions did not appear to be related to the duration of the intervention. Men in 4-week studies saw similar changes as men in trials lasting up to 44 weeks. There’s no evidence of the body recalibrating and restoring testosterone to baseline while fasting continues.
That said, most studies on this topic have been relatively short, and no trial has specifically tracked OMAD (as opposed to 16:8 or other protocols) over a year or more. The long-term trajectory beyond 44 weeks remains genuinely unknown.
Effects in Women
For women, the testosterone question carries different implications. Women with polycystic ovary syndrome (PCOS) often have elevated testosterone, and lowering it can be beneficial. Time-restricted eating in women with PCOS and obesity decreased both total testosterone and the free androgen index while increasing SHBG. One study found these changes alongside just 2% body weight loss after 5 weeks of 8-hour eating windows. A longer study using the 5:2 approach (fasting two days per week) showed similar SHBG increases with 7% weight loss over 24 months.
For women managing PCOS-related symptoms, intermittent fasting’s testosterone-lowering effect could actually be a feature rather than a drawback. For women without PCOS, the clinical significance of modest androgen reductions is less clear.
What This Means for Your Goals
If you’re considering OMAD specifically to raise testosterone, the evidence says it will do the opposite. This matters most if you’re training for muscle growth or strength, since testosterone is a key driver of muscle protein synthesis. Several of the studies showing testosterone drops involved men who were also doing resistance training, meaning the fasting effect persisted even alongside a stimulus that normally supports testosterone production.
The testosterone reductions observed in these studies don’t necessarily mean you’ll lose muscle or feel terrible on OMAD. Testosterone is one of many factors in body composition and performance, and people on time-restricted eating protocols still build muscle successfully. But the specific claim that OMAD boosts testosterone is not supported by any published human trial. Every study measuring testosterone during intermittent fasting in men has found either a decrease or no change. None have found an increase.
If maintaining testosterone is a priority, eating adequate calories spread across multiple meals, getting enough dietary fat, sleeping well, and managing stress are all strategies with stronger evidence behind them. Compressing your entire caloric intake into a single meal works against the hormonal signaling your body needs to keep testosterone production running at full capacity.