Are Seed Oils Bad for Athletes? What the Research Shows and What to Watch For

You turned the dressing bottle around at the grocery store, saw soybean oil near the top of the list, and put it back. You'd decided to cut seed oils. Then the crackers went, and then the bread you always grab. It all happened quietly. A few weeks later you're playing two soccer games a week with school or work on top, and your legs feel heavier in training than they did in preseason.

So, are seed oils bad for athletes? My short answer: I haven't found a study that tested seed oils as a performance question, for eating them or for cutting them. When researchers added linoleic acid, an omega-6 fat in seed oils, to healthy people's diets, they found almost no sign of inflammation markers going up. What I specifically watch most is whether there's still enough food around an athlete's training after the switch.

What Are Seed Oils?

Seed oils are cooking oils made from seeds: soybean, canola, corn, sunflower, safflower, cottonseed, grapeseed and rice bran oil. They're mild-tasting and inexpensive, so they show up in a lot of packaged and restaurant food. Olive oil and avocado oil come from fruit, and butter, ghee and tallow come from animals, so they usually aren't counted as seed oils.

What Foods Have Seed Oils in Them?

Seed oils often show up in dressings, sauces, crackers, chips, snack bars, store-bought bread, frozen meals, protein bars and a lot of restaurant food. The ingredient label will tell you.

Look at that list again. Those are the easy foods, the ones you grab before training or toss in your bag for the bus. In my experience, when they leave the kitchen and nothing takes their place, there's less food around your training, and that's where it catches up with you.

What I usually see: the pre-training snack disappears, and by the second game of the week it shows up as flat legs and a second half that fades earlier than it should. I see this pattern over and over with players, and I haven't found a study that has tested it.

Do Seed Oils Cause Inflammation?

When researchers have tested the main omega-6 fat in seed oils in healthy people, they've found almost no sign of inflammation markers going up.

The idea goes like this. Seed oils contain an omega-6 fat called linoleic acid, and eating a lot of it supposedly revs up inflammation. In the body linoleum acid can be converted into arachidonic acid which is what acts as a starter for other inflammatory molecules that are actually causing inflammation in the body. That is the pathway and thought process behind why seed oils and the linoleic acid have a bad reputation. So far that process hasn't been shown to happen directly when seed oils are simply consumed more. Researchers can test that directly by adding it to people's diets and checking inflammation markers in the blood.

A 2012 review in the Journal of the Academy of Nutrition and Dietetics looked at 15 of those trials in healthy people and found virtually no evidence that the markers went up. A 2024 trial in the same journal gave people a lot of oil for eight weeks, either cottonseed oil or olive oil: about a third of their daily energy came from it. In my experience, that's more than most kitchens go through. Neither group's markers changed.

Keep in mind who was studied. The review was in healthy people, and the 2024 trial was in 42 inactive adults, about 53 on average, with untreated high cholesterol. It was paid for by the National Cottonseed Products Association and Cotton Incorporated, and the study says the funders had no role in the design or analysis. A blood marker is also one lab number, and doctors read it alongside a lot more. Just a few factors to keep in the back of the mind when reading those findings.

Are Seed Oils Bad for Your Heart?

Long-term studies of adults link eating more linoleic acid with a slightly lower risk of dying from heart disease, though a link like that can't prove cause.

A 2020 review in the American Journal of Clinical Nutrition combined 38 of those studies. Adults who ate more linoleic acid, or had more of it in their blood, had a slightly lower risk of dying from heart disease, cancer or any cause. Researchers tracked what people already ate, so they could only measure a link, and experts still disagree on what the trials show. Two of the authors have received research support from the California Walnut Commission.

That's an adult question that plays out over decades. For the rest of this post, let's stay with your season.

Is Your Omega-6 to Omega-3 Ratio the Thing to Fix?

In my work, omega-3 is the fat I look at most with athletes, and the ratio moves when omega-3 goes up. That higher ratio in favor of omega-3 is an indicator of decreased inflammation in the body.

In a 12-week trial at Ohio State, medical students who took fish oil saw the ratio in their blood drop, even though they were asked to keep their usual diet. They took 2.5 grams of omega-3 a day which is what contributed to that shift.

A 2026 study in Frontiers in Nutrition found that semi-pro female soccer players started with omega-3 levels below the range the researchers aim for. The players who took a DHA supplement (a type of omega-3) with whey protein for four months raised their levels. Their sprint, jump and endurance results were no different from the players who didn't take it. It was a small study of 38 players. The groups weren't picked at random, nobody got a dummy pill, and the company that supplied the DHA paid for it.

So I start with food. Salmon, sardines or trout twice a week is an easy way to add omega-3.

What Happens to Seed Oils When They're Heated?

Heat breaks oil down, and reusing the same oil breaks it down more, but the research on what that means for people is thin.

In a 2022 lab study, sunflower oils and ghee all reached the point where they should be thrown out after a second round of frying chicken and potatoes. That's lab chemistry, the weakest kind of evidence for what happens in people, and nobody measured what a person takes in from the oil.

A small 1999 study tested old fryer fat in people. Ten men ate test meals, and four hours after a meal made with old fast-food fryer fat, their blood vessels didn't widen as well on one test. Fresh fat didn't cause that dip, and their other blood vessel and blood tests didn't change. The old fat was about half saturated, so the results can't be pinned on seed oils. A 2022 review that pooled 90 studies also found that a single high-fat meal can briefly lower that same measure.

On the road, fried food can still fits into a good week when timed appropriately and eaten in moderation. I'm not saying you can never have a donut or enjoy Wingstop ever again! Before games though, I steer players toward grilled, baked or roasted options because they sit easier and as that previous study showed, blood flow won't be impacted. And one rule holds every time: no new foods on game day.

Will Cutting Seed Oils Make You Faster?

I haven't found a study that tested whether cutting seed oils changes performance, either way. The closest is the soccer study above, and it tested omega-3. So the check I'd start with is simple: is there still enough food around your training week?

Is It Okay to Cut Out Seed Oils?

Cutting seed oils is your call or your family's, and the research I've read gives me no reason to talk you out of it. A 2024 review of 44 studies found that parents limiting certain foods at home wasn't linked to kids' diets getting worse. Those studies were mostly in younger kids and mostly one-time snapshots, so they say less about a 19-year-old doing their own shopping.

It also helps to know where a real concern starts. ARFID (avoidant/restrictive food intake disorder) is a recognized eating disorder, and doctors don't diagnose it when someone eats less because food isn't available or because of their culture's food traditions. In my practice, if a player's list of off-limits foods keeps growing and eating starts to feel stressful, that's worth bringing up with a doctor.

How Do You Know If You're Not Eating Enough After Cutting Seed Oils?

These are the signs I see most when an athlete's food changes:

- Hungry again soon after meals
- Fading late in second halves, especially in two-game weeks
- Snacking at night when you never used to
- Heavier legs in training than in preseason

If any of these sound like you, think back to which easy foods stopped showing up after the switch.

What Should You Eat After Cutting Seed Oils?

Fill the gap with easy carbs and protein before and after training. These are my go-to options with players. Pick one gap and fill it for seven days.

- Before training: a bagel with peanut butter and honey, or fruit with yogurt.
- After training: chocolate milk and a sandwich, or leftovers with rice or potatoes.
- On the road: rice bowls, pasta, sandwiches, fruit and milk.
- Cooking at home: I suggest olive oil for dressings and lower-heat cooking, and avocado oil for high heat.

If you're avoiding seed oils, check the labels on bread, bagels and peanut butter. Oats, rice, potatoes, fruit and milk rarely contain them.

You're already doing the hard part. Check what's in your bag and fridge this week, and put one easy food back.

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Frequently Asked Questions

What are seed oils?

Seed oils are cooking oils made from seeds, most often soybean, canola, corn, sunflower, safflower, cottonseed, grapeseed and rice bran oil. They show up in a lot of packaged and restaurant food, like dressings, crackers, store-bought bread and snack bars.

Are seed oils bad for athletes?

I haven't found a study that tested seed oils as a performance question, for eating them or for cutting them. When researchers tested the inflammation claim in healthy people, they found almost no sign of inflammation markers going up. With athletes, what I watch most is whether cutting them left less food around training.

Do seed oils cause inflammation?

A review of 15 trials in healthy people found almost no evidence that adding linoleic acid, an omega-6 fat in seed oils, raised inflammation markers. That 2012 review was published in the Journal of the Academy of Nutrition and Dietetics. A 2024 eight-week trial in 42 inactive adults with untreated high cholesterol found no change in markers on either cottonseed oil or olive oil; it was funded by cotton industry groups that had no role in the analysis. Neither study was about athletes.

Are seed oils toxic when you cook with them?

The research on heated oil is mostly lab chemistry, and it doesn't show what heated oil does in people. In a 2022 lab study, every fat tested, ghee included, was ready to throw out after a second round of frying. A small 1999 study in 10 men found one blood vessel measure dipped four hours after a meal made with old fast-food fryer fat. Fresh fat didn't cause the dip, and their other tests didn't change. That old fat was about half saturated, and a review that pooled 90 studies found a single high-fat meal can briefly lower that measure.

What is the best cooking oil for athletes?

Pick by the job. I suggest olive oil for dressings and lower-heat cooking, and avocado oil for high heat. I don't rank one fat as healthier than another, and you or your household make the call.

Can a sports dietitian help me cut seed oils without losing fuel?

Yes. As a sports dietitian for soccer players and athletes in every sport, most of my work here is rebuilding the easy foods that left, around your actual game schedule. Rise Nutrition works virtually, and on the free 15-minute Discovery Call we compare what you ate before the switch with what you eat now.

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If your food changed this season and your legs have felt heavier ever since, the free 15-minute Discovery Call allows us to see what left your kitchen and if working together can help get things rolling again for you. Book Your Discovery Call

Jay Short, MS, RD, CSSD is a Registered Dietitian and Board Certified Specialist in Sports Dietetics, and co-owner of Rise Nutrition, specializing in sports dietetics for competitive athletes. He works with US Soccer (all 27 teams), the Columbus Blue Jackets (NHL), and athletes across MLS, collegiate, and club programs.

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References

1. Johnson GH, Fritsche K. Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials. [https://pubmed.ncbi.nlm.nih.gov/22889633/](https://pubmed.ncbi.nlm.nih.gov/22889633/)
2. Prater MC, Scheurell AR, Paton CM, Cooper JA. No Observed Difference in Inflammatory and Coagulation Markers Following Diets Rich in n-6 Polyunsaturated Fat vs Monounsaturated Fat in Adults With Untreated Hypercholesterolemia: A Randomized Trial. [https://pubmed.ncbi.nlm.nih.gov/37619782/](https://pubmed.ncbi.nlm.nih.gov/37619782/) *Funded by the National Cottonseed Products Association and Cotton Incorporated; the funders had no role in the design, implementation, analysis or interpretation.*
3. Li J, Guasch-Ferré M, Li Y, Hu FB. Dietary intake and biomarkers of linoleic acid and mortality: systematic review and meta-analysis of prospective cohort studies. [https://pubmed.ncbi.nlm.nih.gov/32020162/](https://pubmed.ncbi.nlm.nih.gov/32020162/) *Two authors reported research support from the California Walnut Commission.*
4. Kiecolt-Glaser JK, Belury MA, Andridge R, Malarkey WB, Glaser R. Omega-3 Supplementation Lowers Inflammation and Anxiety in Medical Students: A Randomized Controlled Trial. [https://pubmed.ncbi.nlm.nih.gov/21784145/](https://pubmed.ncbi.nlm.nih.gov/21784145/)
5. Nolte S, Klügel S, Maier C, Hacker S, Krüger K. Four months of DHA and whey protein supplementation in semi-professional female soccer players: a prospective non-randomized controlled study of omega-3 status, hematological outcomes, and physical performance. [https://doi.org/10.3389/fnut.2026.1886305](https://doi.org/10.3389/fnut.2026.1886305) *Funded by FrieslandCampina, which supplied the product.*
6. Mohammadian Fazli M, Zanganeh H, Hassanzadazar H. Effect of heating on disposal point of main edible oils available in Iran market. [https://pubmed.ncbi.nlm.nih.gov/36514749/](https://pubmed.ncbi.nlm.nih.gov/36514749/)
7. Williams MJA, Sutherland WHF, McCormick MP, De Jong SA, Walker RJ, Wilkins GT. Impaired Endothelial Function Following a Meal Rich in Used Cooking Fat. [https://doi.org/10.1016/S0735-1097(98)00681-0](https://doi.org/10.1016/S0735-1097%2898%2900681-0)
8. Fewkes JJ, Kellow NJ, Cowan SF, Williamson G, Dordevic AL. A single, high-fat meal adversely affects postprandial endothelial function: a systematic review and meta-analysis. [https://pmc.ncbi.nlm.nih.gov/articles/PMC9437993/](https://pmc.ncbi.nlm.nih.gov/articles/PMC9437993/)
9. Werner LM, Mallan KM. Associations between restrictive feeding practices and children's dietary intake: Systematic review and meta-analyses. [https://pubmed.ncbi.nlm.nih.gov/38795944/](https://pubmed.ncbi.nlm.nih.gov/38795944/)
10. Sader M, Harris HA, Waiter GD, Jackson MC, Voortman T, Jansen PW, Williams JHG. Prevalence and Characterization of Avoidant Restrictive Food Intake Disorder in a Pediatric Population. [https://pubmed.ncbi.nlm.nih.gov/39555048/](https://pubmed.ncbi.nlm.nih.gov/39555048/)

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