Let’s get this out of the way.
If you’re a man over 35 considering intermittent fasting, you’ve probably already searched “does fasting lower testosterone.” And what you found was either terrifying clickbait or so vague it was useless.
I get it. Testosterone matters. It affects your energy, your mood, your body composition, your drive — pretty much everything that makes you feel like yourself. The last thing you want is a fat-loss strategy that quietly tanks the one hormone holding your life together.
So here’s the straight dope — what the research actually says, what it doesn’t say, and what I’ve seen over years of coaching men through intermittent fasting.
What the Studies Show (It’s More Complicated Than the Headlines)
A 2022 review published in Nutrients looked at the available human trials on intermittent fasting and reproductive hormones. Here’s what they found:
In lean, young men doing time-restricted eating (like the 16:8 or 17/7 protocol): Total testosterone decreased modestly. But — and this is important — muscle mass and muscular strength were NOT negatively affected.
In overweight men: IF often improved testosterone levels, because losing body fat reduces the conversion of testosterone to estrogen. Belly fat is one of the biggest drivers of low testosterone in men over 40. Lose the fat, and testosterone tends to recover.
In extreme fasting (3+ days of zero food): Testosterone dropped significantly — around 35%. But nobody’s recommending that. That’s a completely different conversation from skipping breakfast and eating lunch at noon.
A 2024 trial of 10 men doing intermittent fasting found that total testosterone, DHEA, and sex hormone-binding globulin (SHBG) did not change significantly.
The honest summary: the research is mixed, the sample sizes are small, and the effects depend heavily on whether you’re eating enough during your eating window.
What’s Really Going On
Here’s what most articles won’t tell you, because it requires nuance instead of a scary headline.
Testosterone responds to signals. The main ones: body fat percentage, sleep quality, resistance training, stress levels, and caloric adequacy.
Intermittent fasting doesn’t directly attack testosterone. What CAN happen:
1. If you under-eat. Chronic caloric restriction — not just skipping breakfast, but consistently eating far too few calories — sends a starvation signal that down-regulates testosterone production. This isn’t a fasting problem. It’s an eating problem. During your eating window, eat real food. Enough of it. Protein, healthy fats, quality carbs.
2. If you stop lifting. Some men start IF and drop their resistance training because they’re worried about fasting and working out. That’s backwards. Resistance training is one of the strongest natural testosterone signals. Keep lifting. You can train fasted — I do it regularly.
3. If your sleep falls apart. Poor sleep is the single fastest way to crash testosterone. Some men find that eating too close to bedtime disrupts sleep. IF can actually help here — stopping eating by 7 PM means your body isn’t digesting when it should be recovering.
4. If you carry excess belly fat. This is the big one. Visceral fat contains an enzyme called aromatase that converts testosterone to estrogen. More belly fat = more conversion = lower testosterone. IF is one of the most effective ways to reduce visceral fat. Losing the belly may be the single best thing you do for your testosterone.
What I’ve Seen Coaching Real Men
I’m not a doctor. I’m not an endocrinologist. But I’ve coached hundreds of men through this program, and here’s what I see consistently:
Men who follow the 17/7 Protocol — eat within a 7-hour window, fast for 17, move in the fasted state, eat real food — report feeling more energetic, not less. More focused. More driven. They’re not describing testosterone crashes. They’re describing men who are sleeping better, carrying less belly fat, and feeling in control of their bodies for the first time in years.
Again — I’m sharing what I observe, not prescribing. If you have concerns about your hormone levels, get your bloodwork done. That’s what responsible men do. A testosterone panel before and after 28 days of IF will tell you more than any article on the internet, including this one.
The Practical Takeaway
If you’re a man over 35 worried about IF and testosterone, here’s what I’d tell you the same way I’d tell a friend:
Don’t starve yourself. Fasting is about timing, not deprivation. During your eating window, eat enough. Protein at every meal. Healthy fats. Don’t skip meals within your window just because you “aren’t that hungry.”
Keep lifting. Or start. Resistance training 3-4 times a week is non-negotiable for testosterone, whether you’re fasting or not. You can absolutely lift in a fasted state — your body will use stored fuel. I do fasted workouts regularly.
Prioritize sleep. Stop eating by 7 PM. Get to bed at a reasonable hour. Sleep is when your body produces most of its testosterone. IF makes this easier, not harder.
Lose the belly. This is the biggest lever most men over 40 have. Reduce visceral fat and you reduce the enzymatic conversion of testosterone to estrogen. IF is one of the most practical ways to do that.
Get your levels checked. Baseline bloodwork before you start. Check again at 30, 60, 90 days. Know your numbers. Don’t guess.
The Bottom Line
The fear that intermittent fasting destroys testosterone is mostly noise. The research shows small, inconsistent effects in lean young men — and potentially positive effects in overweight men who lose body fat.
The real testosterone killers for men over 35? Belly fat. Poor sleep. No resistance training. Chronic stress. Processed food. Those are the battles worth fighting.
IF is a tool that helps you win most of those battles. Not because it’s magic — because it simplifies your relationship with food so you can focus on what actually matters.
You can do this. It’s not a big deal.
Stay strong, keep busy and active.
To Your Success,
Bob
References:
- Cienfuegos, S., et al. (2022). Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. Nutrients, 14(11), 2343.
- Shkorfu, S., et al. (2025). Intermittent Fasting and Hormonal Regulation: Pathways to Improved Metabolic Health. Food Science & Nutrition.
- Kalsekar, A., et al. (2024). Effects of Fasting on Metabolic Hormones and Functions: A Narrative Review. PMC.