The relationship between supplements destroying gains and testosterone levels is more complex than most fitness influencers admit. Several commonly marketed products genuinely do interfere with testosterone synthesis and anabolic signaling This article covers the ones I see causing the most damage in my clinical practice and the science backs every single point.
The truth is, the supplement industry makes a lot of money. Over $50 billion every year. Most of this money comes from selling people products that do not really work or can even be bad for their body. If you have been working out hard paying attention to what you eat and you still do not feel right. You are tired all the time. It takes you a long time to recover. You are not building muscle like you want to or you think your testosterone levels are not what they should be. The problem might be the supplements you are taking.
This is not something to worry about. The supplement industry is worth a lot of money. The research is clear. Some of the popular supplements that people take to build muscle and work out contain things that can interfere with the testosterone that your body naturally makes. The supplement industry makes a lot of money. Some of these supplements can also make your body produce too much cortisol or act like estrogen. Let us look at these supplements one by one and see what the supplement industry is really selling us. The supplement industry has a lot of products that can be bad for us. We need to know what we are taking.
SUPPLEMENT
Soy Protein Isolate
People often forget about this one thing. Soy protein is not expensive. You can find it almost anywhere. It is also marketed a lot as a way to build muscle, like whey. The thing is, soy has a lot of phytoestrogens. These are like plant compounds, also called isoflavones , specifically genistein and daidzein. They act like estrogen in the body.
If you eat soy in large amounts it is probably okay.. If you use soy protein isolate as your main protein supplement you are getting a lot of these isoflavones every day. Some studies have found that eating a lot of soy can lower the testosterone in your body and raise the estradiol. This is not good for men because it affects the muscles, your sex drive and your energy. Soy protein can really work against soy protein when it comes to building muscle and feeling good.
Better alternative: You should try using whey protein isolate or casein protein or grass-fed beef protein. These things are really good for building muscle. They help your body make muscle without messing with your hormones. Whey protein isolate and casein protein and grass-fed beef protein are all choices because they support muscle synthesis.Â
Fertility and Sterility, 94(3): 997–1007 ·
PubMed ID: 19524224
Analyzed 15 placebo-controlled treatment groups. Found no significant effect of soy protein or isoflavone intake on total testosterone, free testosterone, SHBG, or free androgen index in men.
pubmed.ncbi.nlm.nih.gov/19524224Â
Reed KE et al., 2021
Reproductive Toxicology, 100: 60–67 · ScienceDirect
Updated and expanded meta-analysis of 41 studies (n=1,753 men). Regardless of dose or study duration, neither soy protein nor isoflavones affected total testosterone, free testosterone, estradiol, or SHBG. Sub-analysis by isoflavone dose also showed no effect.
sciencedirect.com
Chronic High-Dose Caffeine & Pre-Workouts
I think pre-workout supplements are really overrated when it comes to fitness. A lot of these supplements have a lot of caffeine in them. We are talking about 300 to 400 milligrams per serving. That is like drinking three or four espressos before you even start lifting weights.
At first the caffeine in these supplements can actually help you perform better.. If you take these supplements every day the caffeine can cause some problems. It can raise the level of cortisol in your body. Cortisol is a hormone that your body produces when you are stressed.
The thing about cortisol is that it can actually lower the level of testosterone in your body. So if you have a lot of cortisol you will probably have testosterone. It is pretty simple. Some pre-workout supplements can also raise your insulin levels because they have a lot of sugar in them. This can make it even harder for your body to produce the amount of hormones.
If you take these supplements at night they can also keep you awake and make it hard for you to sleep. When you do not sleep well it can cause more problems with your hormones. So if you put all of these things together you can see why some people might have testosterone levels.
Better alternative: Time your caffeine intake strategically. Have it before your workout, not throughout the day. Take a break from it for 2 weeks every 2 months. You can also try supplements. Some options are ashwagandha and rhodiola. They help with stress resilience.
International Journal of Sport Nutrition and Exercise Metabolism ·
PubMed ID: 22349085
Double-blind crossover study in 16 professional rugby players. 4 mg/kg caffeine increased testosterone response to exercise compared to placebo — but cortisol response also rose significantly in parallel, raising the testosterone-to-cortisol ratio concern under chronic use.
pubmed.ncbi.nlm.nih.gov/22349085Â
Fernandez-Elias VE et al., 2015
European Journal of Applied Physiology · PubMed ID: 24867603
High-dose caffeine (6 mg/kg) significantly elevated both testosterone and cortisol post-resistance exercise in men. At moderate/high doses, caffeine also attenuated insulin responses. The simultaneous cortisol spike at high doses undermines the net anabolic benefit over time.
pubmed.ncbi.nlm.nih.gov/24867603
Certain Testosterone Boosters (Proprietary Blends)
The irony hurts. Products that claim to increase testosterone levels naturally often cause more harm than good. Many testosterone booster supplements have blends that hide low doses of ingredients. Or even ingredients that lower testosterone. Behind fancy labels.
Be careful, with products that have amounts of Tribulus Terrestris. There is no proof that it boosts testosterone. Also watch out for DHEA. It can turn into estrogen, not testosterone in men. Some products have blends that contain compounds that act like estrogen.
In 2024 a lab test found that many popular natural testosterone supplements had banned substances or additives that disrupt hormones.
Better alternative: Focus on getting Vitamin D3, zinc and magnesium glycinate to support testosterone.
- Get enough Vitamin D3
- Take zinc supplements
- Take magnesium glycinate
- Sleep well
These things have evidence that they can help support testosterone levels.
Vilar Neto JO et al., 2025
Nutrients, 17(7): 1275 · PMC11990417 · PMID: 40219032
PRISMA-compliant systematic review of all clinical trials on Tribulus Terrestre’s supplementation, testosterone levels, and erectile dysfunction in men. Concluded that evidence for T-boosting is not supported by clinical trials and that marketed claims substantially outpace the research.
ncbi.nlm.nih.gov/pmc/PMC11990417Â
Khaleghi S et al., 2017
Andrologia · PubMed ID: 27337519
30 men with idiopathic infertility received 750 mg/day Tribulus terrestris for 3 months. No statistically significant difference found in total testosterone, free testosterone, LH, or any semen parameters before and after treatment.
pubmed.ncbi.nlm.nih.gov/27337519
Flaxseed Oil & High-Dose Omega-6 Supplements
Flaxseed oil is said to be good for your heart. It can help with inflammation. When you use it in large amounts it is okay.. Flaxseed has a lot of lignans, which are changed in your stomach into enterolactone and enterodiol. These two things can really affect the androgens in your body.
This means that if you eat a lot of flaxseed it can lower the amount of testosterone and DHT in your body. Testosterone and DHT are important for strength and muscle hardness. Some people even use flaxseed to treat conditions like PCOS and prostate issues because it can lower the androgen levels in their body. This shows how strong the effect of flaxseed can be.
It is also important to know that some supplements have a lot of omega-6 fatty acids, like acid, which is found in cheap vegetable oils. These fatty acids can cause inflammation in your body. They can also affect the way your testicles make steroids.
Better alternative: Use good quality fish oil that’s rich in EPA and DHA. This fish oil should not be dominated by omega-6. Focus on using olive oil, eggs and animal fats as your sources of dietary fat. These fats help support making cholesterol, which’s important, for producing testosterone.
Use fish oil and these fats to help your body work well.
Hutchins AM et al., 2001
Nutrition and Cancer · PubMed ID: 11445478
Short-term flaxseed supplementation significantly increased urinary lignan output (7–28 fold above baseline), confirming robust lignan conversion to enterolactone and enterodiol by gut bacteria. No significant change in total testosterone or SHBG was observed at moderate doses over 6 weeks.
pubmed.ncbi.nlm.nih.gov/11445478Â
Kurzer MS & Xu X, 2009
PCOS Case Report · PubMed ID: 19789727
Clinically significant reduction in serum androgens documented following 4-month daily flaxseed supplementation. Free testosterone dropped from 4.7 to 0.5 ng/dl and % free testosterone fell from 3.1% to 1.1% — a reduction large enough to have therapeutic use in androgen-excess conditions.
pubmed.ncbi.nlm.nih.gov/19789727
Mass Gainers With High Sugar Loads
Mass gainer supplements are sold as the way to get bigger.. What they do not tell you is that a lot of them have 100 to 150 grams of bad carbohydrates in each serving. These are mostly maltodextrin and fructose. This causes a jump in insulin levels then a crash and over time it makes your body not respond to insulin as well.
Here is what happens with your hormones when you take these supplements: you have insulin levels all the time, which makes an enzyme called aromatase more active. This enzyme turns testosterone into estrogen. So you end up with testosterone and more estrogen which makes your body store more fat. When you have more fat it makes even more aromatase. It is a cycle.
Also having a lot of fat on your body is one of the main things that stops your body from making testosterone. So a lot of mass gainer supplements can make guys fatter and weaker and mess up their hormones. Mass gainer supplements can really hurt your body and your hormones.
Better alternative: To get bigger you need to eat calories than your body uses. So try to get calories from food like vegetables and meat. If you want something to drink you can use a good quality protein powder like whey or casein and mix it with oats, a banana and some nut butter. This way you can choose what goes into your drink. Make sure it is good for you.
Birzniece V et al., 2025
Journal of Clinical Endocrinology & Metabolism, 110(10): e3410 · PMC12448628
Adipose tissue aromatase (ARO) was significantly elevated in obese men and correlated positively with insulin resistance and blood glucose levels. Elevated aromatase directly converts testosterone to estradiol locally — creating a testosterone-suppressing loop driven by excess body fat and metabolic dysfunction.
Grossmann M, 2014
Journal of Endocrinology, 220(3): R37–R55 · joe.bioscientifica.com
Comprehensive review documenting the bidirectional relationship between low testosterone and insulin resistance — mediated by visceral fat accumulation. Low T increases fat gain, more fat increases aromatase activity and estrogen, higher estrogen further suppresses LH and T production. A self-perpetuating hormonal cycle.
