Canola oil has been shown to significantly lower testosterone levels in animal studies, but no human clinical trial has directly tested whether the same effect occurs in people. The most cited evidence comes from research on a specific strain of rats prone to high blood pressure, where canola oil cut testosterone levels by more than half compared to soy oil. That’s a striking result, but translating rodent findings to humans requires caution, and the full picture is more nuanced than the headline suggests.
What the Animal Studies Found
The strongest evidence linking canola oil to lower testosterone comes from studies on stroke-prone spontaneously hypertensive rats (SHRSP), a breed specifically developed to study cardiovascular disease. In one study published in Toxicology Reports, male rats fed a canola oil diet for 13 weeks had plasma testosterone levels of about 1,302 pg/mL, compared to 3,034 pg/mL in rats fed soybean oil. That’s a 57% reduction. Female rats showed a similar pattern: the canola group measured 62.7 pg/mL versus 128.4 pg/mL in the soy group.
The canola-fed males also showed microscopic changes in their testes, including signs of immune cell infiltration, shrinkage of the tissue where sperm develop, and atrophy of Leydig cells, the cells responsible for producing testosterone. Researchers noted increased cell debris in the reproductive tract, suggesting that reduced testosterone may have been disrupting normal sperm formation.
An earlier study found the same basic result: testosterone in both blood and testicular tissue was significantly lower in canola-fed rats. Interestingly, hydrogenated soybean oil, which shortened the rats’ lifespan at a rate comparable to canola oil, also lowered testosterone to a similar degree. This hints that the testosterone-lowering effect may not be unique to canola oil itself but could relate to broader characteristics shared by certain processed fats.
Why Rat Studies May Not Apply to You
SHRSP rats are not ordinary lab rats. They’re genetically predisposed to vascular problems, metabolic dysfunction, and early death, which makes them useful for studying cardiovascular disease but potentially poor stand-ins for healthy humans. Their extreme sensitivity to dietary fats means effects observed in these animals can be exaggerated compared to what would happen in a person with normal metabolism. No study has measured testosterone changes in healthy humans consuming typical amounts of canola oil, so the direct relevance remains unknown.
The doses used in these studies also matter. The rats were fed diets where canola oil made up a substantial portion of their total calorie intake, far more than most people consume. A tablespoon or two of canola oil in cooking is a very different exposure than a diet built around it as a primary fat source.
How Fat Quality Affects Testosterone Production
There are plausible biological reasons why certain oils could influence hormone levels. Canola oil is about 64% monounsaturated fat, 28.5% polyunsaturated fat, and roughly 7.5% saturated fat. Testosterone is synthesized from cholesterol, and the type of dietary fat you eat can influence how efficiently your body carries out that conversion.
One pathway involves oxidative stress. When polyunsaturated fats break down (through heating, processing, or normal metabolism), they can generate oxidized particles in the blood. Research published in Cell Death & Disease found that oxidized LDL particles directly impair the Leydig cells that produce testosterone. These particles disrupt the energy-producing structures inside the cells and suppress the enzymes needed to convert cholesterol into testosterone. In a human sample from the same study, men with higher levels of oxidized LDL in their blood had significantly lower testosterone, and the correlation was strong enough to be statistically meaningful.
High-fat diets in general, particularly those that cause dyslipidemia (abnormal blood fat levels), have been shown in multiple animal studies to alter the structure and function of Leydig cells and reduce the production of steroid hormones. This suggests the issue may be less about canola oil specifically and more about overall fat quality, quantity, and how much oxidative damage the fats cause in your body.
Phytosterols and Cholesterol Competition
Canola oil contains plant sterols, compounds that are structurally similar to cholesterol. These phytosterols are actually marketed as heart-healthy because they block cholesterol absorption in the gut, lowering blood cholesterol levels. But because testosterone is built from cholesterol, there’s a theoretical concern that reducing the cholesterol available to reproductive cells could limit testosterone production. This mechanism hasn’t been confirmed in human studies, but it’s one hypothesis researchers have considered when trying to explain the animal findings.
Processing and Contaminant Concerns
Most canola oil on store shelves is refined using hexane, an industrial solvent. Hexane has been identified as a potential endocrine disruptor in occupational studies. Women exposed to hexane in factory settings showed disrupted reproductive hormones, and animal experiments have confirmed that hexane and its byproducts can cause oxidative stress in reproductive organs and alter hormone balance.
However, the residual hexane left in finished canola oil is extremely small. Testing of refined canola oil found the highest detected concentration at just 0.043 mg/kg, a trace amount that’s orders of magnitude below the levels that caused harm in occupational or laboratory settings. Whether this residual amount has any meaningful hormonal effect at normal dietary intake is unclear, but it’s likely negligible.
Modern canola oil also contains very low levels of erucic acid, a fatty acid that was once a health concern in older rapeseed varieties. The European Union limits erucic acid in vegetable oils to 20 g/kg, and testing has found commercial canola oils fall well below this threshold.
What This Means in Practice
If you’re concerned about testosterone, the honest answer is that canola oil has not been proven to lower testosterone in humans. The animal data is real and worth taking seriously as a signal, but it comes from a genetically unusual rat strain eating far more canola oil than you’d use in a typical diet. The broader science on dietary fat and hormones suggests that what matters most is the overall quality of your diet, your body fat levels (excess body fat is one of the strongest predictors of low testosterone in men), and whether your fat intake is causing metabolic problems like elevated oxidized cholesterol.
If the animal findings still concern you, diversifying your cooking oils is a simple, low-cost change. Olive oil, which is also high in monounsaturated fat, has been associated with better testosterone levels in some observational research. Coconut oil and butter provide more saturated fat, which some studies have linked to higher testosterone, though they come with their own cardiovascular trade-offs. Cold-pressed or expeller-pressed canola oil avoids the hexane extraction process, though no study has compared its hormonal effects to those of the refined version.