If you spend any time in the men's health corner of the internet, you have been told that seed oils are destroying your testosterone. Canola, soybean, sunflower, corn, grapeseed — the "hateful eight" — are blamed for low energy, belly fat, weak erections, and hormone levels a fraction of your grandfather's. The proposed fix is usually to replace them with butter, tallow, or ghee, and often to buy something.
It is worth taking the question seriously, because the underlying biochemistry is not made up. Dietary fat composition genuinely influences steroid hormone production, inflammation, and cell membranes. The problem is the leap from "linoleic acid participates in these pathways" to "canola oil is why your testosterone is 380." That leap is not supported by the human data, and treating it as settled has a real cost: men spend months auditing their cooking oil while ignoring the drivers that actually move their labs.
There is no controlled human trial showing that seed oils lower testosterone in men. The evidence that diet composition affects testosterone at all is modest, and where it exists it points slightly in the opposite direction of the popular claim: very low-fat diets appear to reduce testosterone modestly, while polyunsaturated versus saturated fat comparisons produce small and inconsistent effects. The genuine problem with seed oils is indirect — they are the calorie-dense backbone of ultra-processed and fried food, and excess body fat is one of the most reliable ways to suppress testosterone. Fix the food, not the oil.
The Claim, Stated Fairly
The strongest version of the seed-oil argument goes like this: industrial seed oils are high in linoleic acid, an omega-6 polyunsaturated fat. Human intake of linoleic acid has risen dramatically over the past century, and body-tissue linoleic content has risen with it. Omega-6 fats are precursors to arachidonic acid and downstream inflammatory signalling molecules. Polyunsaturated fats are also more prone to oxidation, especially under repeated high heat. Inflammation and oxidative stress both suppress testosterone production. Therefore, high seed-oil intake should suppress testosterone.
Every link in that chain is at least partly real. That is what makes the claim persuasive. But a plausible chain is not evidence of an outcome — and when researchers have actually measured testosterone in men eating different fats, the effects have been small, inconsistent, and dwarfed by body composition.
What Seed Oils Actually Are
"Seed oil" is a marketing category rather than a biochemical one. What matters is fatty-acid composition, degree of processing, and how the oil is used.
| Oil | Dominant fat | Approx. linoleic acid | Notes |
|---|---|---|---|
| Soybean | Polyunsaturated | ~50–55% | The largest single source in the U.S. food supply |
| Corn | Polyunsaturated | ~55% | Common in fried and restaurant food |
| Sunflower | Varies by cultivar | ~20–65% | High-oleic versions are mostly monounsaturated |
| Canola (rapeseed) | Monounsaturated | ~19% | Also the highest common source of plant omega-3 (ALA) |
| Olive oil | Monounsaturated | ~5–10% | Extra-virgin retains polyphenols |
| Butter | Saturated | ~2% | Higher saturated fat; no polyphenols |
Two things fall out of that table. Canola, the most-maligned oil, is predominantly monounsaturated — closer to olive oil than to corn oil in fatty-acid profile. And "seed oils" as a group span such different compositions that any blanket claim about them is imprecise by construction.
Six Proposed Mechanisms — Graded
1"Omega-6 fats are inflammatory"
Linoleic acid is the precursor to arachidonic acid, which yields both pro-inflammatory and anti-inflammatory signalling molecules. The intuitive step — eat more linoleic acid, make more arachidonic acid, become more inflamed — does not hold up well in humans. Systematic reviews of controlled feeding trials have repeatedly found that increasing dietary linoleic acid does not meaningfully raise tissue arachidonic acid or circulating inflammatory markers such as CRP and IL-6. Conversion is tightly regulated and inefficient.
Verdict: Weak. This is the load-bearing claim of the seed-oil argument, and it is the one that has failed most consistently in human trials.
2"Polyunsaturated fats suppress Leydig cell steroidogenesis"
Cell and rodent studies have shown that certain polyunsaturated fatty acids can alter steroidogenic enzyme expression and testosterone output in isolated Leydig cells. Real finding, wrong scale: those experiments use concentrations and exposures that do not correspond to a man cooking with sunflower oil, and the effects have not been reproduced as clinical hypogonadism in human feeding studies.
Verdict: Mechanistically plausible in vitro, unproven in men.
3"Low-saturated-fat diets lower testosterone"
This one has the most support of any version of the argument, but it is not really about seed oils. Several small crossover studies and a 2021 systematic review found that low-fat diets were associated with modestly lower total testosterone — on the order of 10–15% — compared with higher-fat diets in the same men. The trials were small, often confounded by fiber and calorie changes, and the clinical significance of a 10% shift within the normal range is limited. Notably, the signal tracks total fat, not seed oils specifically.
Verdict: Moderate for very low-fat diets. Irrelevant as an argument against a tablespoon of canola.
4"Repeatedly heated oils oxidize and damage the testes"
This is the most legitimate concern on the list. Polyunsaturated oils held at frying temperature for hours generate aldehydes and lipid peroxidation products, and rodent studies feeding repeatedly heated oil show oxidative damage including testicular effects. That is a specific indictment of deep-fried restaurant and fast food, not of a fresh bottle used at home.
Verdict: Reasonable, but the target is fried food, not the oil aisle.
5"Soy-derived oils have estrogenic effects"
Soybean oil contains essentially no isoflavones — they are proteins-associated compounds that stay behind in the meal, not the oil. Separately, the best human evidence on soy foods themselves, including a meta-analysis of dozens of studies, shows no significant effect on testosterone or estradiol in men at normal intakes. This particular claim is a category error.
Verdict: Not supported.
6"Seed oils make you fat, and fat lowers testosterone"
The second half of this is unambiguously true and is the most important sentence in the article. Visceral fat raises aromatase activity, converting testosterone to estradiol, which feeds back to suppress LH; obesity is the single strongest modifiable predictor of low testosterone in men, and weight loss reliably raises it. Seed oils contribute by being the cheap fat that makes ultra-processed and fried food calorie-dense and easy to overeat — not through any hormone-specific mechanism. Our pieces on belly fat despite training, body composition after 40, and testosterone and weight loss cover this loop.
Verdict: Strong — but the mechanism is calories and food quality, not linoleic acid.
What the Human Evidence Shows
Being explicit about evidence quality is the only honest way to write about a contested nutrition topic.
| Claim | Evidence level | What it means for you |
|---|---|---|
| Seed oil intake lowers testosterone in men | Very weak — no controlled human trial testing this endpoint | Not a reason to overhaul your kitchen |
| Higher linoleic acid raises inflammatory markers | Weak — controlled trials mostly show no effect | The core mechanism does not replicate |
| Very low-fat diets modestly lower testosterone | Moderate — small crossover trials, systematic review | Don't fear fat; eat enough of it |
| Repeatedly heated frying oils cause oxidative damage | Moderate — strong in rodents, plausible in humans | Cut deep-fried takeout, not olive or canola at home |
| Soy foods or soybean oil alter male hormones | Weak to none — meta-analyses show no effect | Ignore this claim |
| Obesity and visceral fat lower testosterone | Strong — large cohorts plus interventional weight-loss data | This is where your effort belongs |
| Omega-3 intake supports testicular and metabolic health | Moderate — consistent but modest human data | Worth doing on its own merits |
Two additional points of context. Observational nutrition data on this topic is badly confounded: the men eating the most seed oil are, in general, the men eating the most fried and ultra-processed food, carrying the most visceral fat, sleeping the least, and drinking the most. Any correlation between seed oil intake and low testosterone is exactly what you would expect from those confounders alone. And the widely cited claim that population testosterone has declined across generations is real in several cohorts — but the leading candidate explanations are rising obesity, reduced physical activity, worse sleep, and comorbidity, all of which have moved in lockstep with seed oil consumption without implicating it.
If a man swapped every seed oil in his kitchen for butter tomorrow and changed nothing else, the best prediction from existing evidence is that his testosterone would not change measurably. If he instead cut fried takeout and ultra-processed food and lost 20 pounds of fat — which incidentally reduces seed oil intake substantially — his testosterone would very likely rise.
The Verdict
Seed oils are not a hormonal poison, and they are not health food either. A defensible position looks like this:
- There is no good evidence that seed oils specifically lower testosterone in men.
- The inflammation mechanism, which the entire claim rests on, has largely failed in controlled human trials.
- Deep-fried food cooked in repeatedly heated oil is genuinely worth avoiding — for oxidation, and for the calories.
- Ultra-processed food built around cheap industrial oil is worth reducing, primarily because of what it does to your body composition.
- Extra-virgin olive oil is the best-evidenced cooking fat for cardiometabolic health, and cardiometabolic health is a strong driver of testosterone.
- Eating enough total fat matters more than which fat, within reason. Very low-fat dieting is the version of this that has real hormonal evidence behind it.
If you find seed-oil avoidance a useful heuristic for eating less junk food, it will probably help you — just be clear about why it is helping. If you have swapped your oils, eat the same fried and processed food, and still feel terrible, the oil was never the problem.
What Actually Lowers Your Testosterone
Ranked roughly by effect size and how much control you have over each.
1Excess body fat, especially visceral
The most reliable modifiable driver. Aromatase in fat tissue converts testosterone to estradiol; estradiol suppresses LH; less LH means less testosterone. Men who lose meaningful weight typically see substantial increases in total testosterone. Start with why you can't lose weight and medical weight loss for men.
2Poor and short sleep
Most of your daily testosterone is produced during sleep. One week of restricted sleep can lower daytime testosterone in healthy young men by a double-digit percentage. Undiagnosed sleep apnea is common in exactly the demographic worried about seed oils — see testosterone and sleep apnea and tired after eight hours of sleep.
3Alcohol
Directly suppresses testicular steroidogenesis, degrades sleep architecture, adds empty calories, and damages the gut barrier. Cutting from daily to occasional is one of the fastest changes men notice — see does alcohol lower testosterone.
4Chronic stress and inflammation
Sustained cortisol elevation and chronic low-grade inflammation suppress the HPT axis at multiple levels. See high cortisol in men and the gut–testosterone connection for the inflammatory pathway that actually has human evidence behind it.
5Inactivity — and, at the other extreme, chronic overtraining
Resistance training and adequate protein support lean mass and insulin sensitivity. Very high endurance volume without recovery does the reverse. Exercise and testosterone goes deeper, and losing muscle even while lifting covers the pattern when training isn't working.
6Medical causes you cannot out-diet
Primary testicular failure, pituitary problems, prior anabolic steroid use, opioids, certain medications, thyroid disease, and age-related decline all cause low testosterone regardless of your cooking oil. This is why the sequence is always: get a panel, then decide. See normal testosterone but symptoms and the symptoms checklist.
A Sane Approach to Cooking Fat
Default to extra-virgin olive oil
It has the best cardiometabolic evidence base of any cooking fat, it carries polyphenols, and it is stable enough for normal home cooking including most sautéing and roasting. Make it your everyday oil and the question mostly resolves itself.
Eat omega-3s deliberately
Fatty fish two to three times a week, or a supplement if you don't eat fish. Omega-3 intake supports metabolic health and, in some trials, sperm parameters. The ratio arguments online overcomplicate a simple action: add omega-3, rather than obsessing over subtracting omega-6.
Cut deep-fried food, and mean it
This is where the oxidation concern is real, and it is also where the calories are. Reducing restaurant fried food does more for your hormones than any oil swap, partly for the oxidation and mostly for the body composition.
Don't fear saturated fat, and don't chase it either
Butter and tallow are not toxic, but replacing olive oil with tallow for hormonal reasons has no evidence behind it and worsens your lipid profile in most people. Cardiovascular risk matters independently — see TRT and blood pressure for how these overlap on therapy.
Eat enough total fat
Roughly 25–35% of calories from fat is a reasonable range. Aggressive low-fat dieting is the one dietary pattern with genuine evidence of lowering testosterone, and it is the opposite of what most seed-oil-avoidant men are worried about.
Skip the supplement stack
There is no supplement that offsets a bad diet, and the products marketed alongside seed-oil fear are almost uniformly unevidenced. The same skepticism applies to most natural testosterone boosters.
Labs Worth Running
If you are asking this question because you feel bad, the answer will come from a blood draw rather than from nutrition debates.
| Marker | What it tells you |
|---|---|
| Total and free testosterone (morning, fasted) | The baseline; free testosterone is the biologically active fraction |
| LH and FSH | Separates central suppression from testicular failure |
| SHBG | Frequently low in insulin resistance; changes how total testosterone reads |
| Estradiol (sensitive assay) | Reflects aromatase activity and visceral fat load |
| Fasting glucose, insulin, HbA1c | Insulin resistance — the strongest modifiable metabolic driver |
| Lipid panel and triglycerides | Where your actual fat-quality question gets answered |
| hs-CRP | Systemic inflammation, measured rather than assumed |
| Ferritin, vitamin D, TSH | Common alternative explanations for identical symptoms |
For interpretation, see free vs total testosterone and our biomarker guide. If your numbers come back low and you are symptomatic, should I start TRT and questions to ask your doctor are the right next steps.
Frequently Asked Questions
So should I avoid seed oils or not?
You don't need to avoid them for hormonal reasons. If avoiding them helps you eat less fried and ultra-processed food, the net effect will be positive — but you would get the same benefit, with less effort, by targeting fried and packaged food directly and cooking with olive oil.
Is canola oil really as bad as people say?
No. Canola is predominantly monounsaturated, contains meaningful plant omega-3, and performs well in cardiometabolic trials. It became a symbol of industrial food rather than an evidence-based villain.
What about the omega-6 to omega-3 ratio?
The ratio framing has fallen out of favor because absolute omega-3 intake predicts outcomes better than the ratio does, and because lowering omega-6 does not produce the inflammatory improvements the theory predicts. Add omega-3s; don't audit your ratio.
Will eating more butter raise my testosterone?
There is no good evidence that it will. Total dietary fat adequacy may matter modestly; the specific swap from unsaturated to saturated fat has not been shown to raise testosterone, and it typically raises LDL cholesterol.
Are seed oils bad for fertility?
Repeatedly heated frying oils cause oxidative stress in animal models, and oxidative stress is genuinely relevant to sperm quality. Fresh seed oils in normal home cooking have not been shown to impair human fertility. If fertility is your concern, TRT and fertility covers the factors that matter far more.
Why has average testosterone declined if not seed oils?
The decline appears real in several cohorts, but the strongest candidate explanations are rising obesity, falling physical activity, worse sleep, more chronic disease and medication use, and possibly environmental exposures. Seed oil consumption rose alongside all of those, which makes it a correlate rather than a demonstrated cause.
Does any of this change once I'm on TRT?
Diet stops being your lever for the testosterone number itself, but it still governs estradiol conversion, blood pressure, lipids, hematocrit, and body composition — all of which determine how well therapy goes. See what to expect in your first month and estradiol on TRT.
The Bottom Line
Seed oils are a proxy war. The real fight is over ultra-processed food, fried food, excess calories, alcohol, sleep, and visceral fat — and those are the things with strong human evidence for suppressing testosterone. Cook with extra-virgin olive oil, eat fish, cut the drive-through, lift, sleep, and drink less. That advice happens to reduce your seed oil intake substantially, which is probably why the swap seems to work for the men it works for.
And if you have done all of that and still feel flat, stop debating nutrition and get a morning panel. One blood draw tells you whether you are having a lifestyle conversation or a medical one.
This article is for education and is not a substitute for individualized medical advice. Testosterone therapy requires a diagnosis of hypogonadism confirmed by laboratory testing and ongoing monitoring by a licensed clinician.