Why we don't use seed oils

What are seed oils, and how are they made?

Seed oils include soybean, corn, canola (rapeseed), sunflower, cottonseed and safflower oils. What separates them from oils like olive or avocado is not the plant so much as the extraction.

Most are extracted using high heat and chemical solvents such as hexane, then refined, bleached and deodorised. That sequence strips the oil of colour, odour and flavour — and in doing so damages the fatty acids, creating byproducts including oxidised lipids and trans fats.

Olive and avocado oil, by contrast, can be mechanically pressed and used without that treatment. The distinction matters more than the marketing term “vegetable oil” suggests.

The omega-6 to omega-3 imbalance

The most-discussed concern with seed oils is their high content of omega-6 polyunsaturated fatty acids, particularly linoleic acid. Omega-6 fats are essential — the body cannot make them — but the ratio to omega-3 is what has shifted.

Humans evolved on a dietary omega-6 to omega-3 ratio of roughly 1:1 to 4:1. Estimates put most Western diets between 15:1 and 20:1, driven in large part by seed oil consumption.

The imbalance matters because excess omega-6 without sufficient omega-3 is associated with chronic low-grade inflammation, itself a factor in cardiovascular disease and insulin resistance.

Linoleic acid, oxidation and metabolic health

Linoleic acid, the primary omega-6 in seed oils, is highly prone to oxidation. Unlike saturated fats, it degrades readily — during processing, during high-heat cooking, and inside the body.

When it oxidises it produces oxidised linoleic acid metabolites, known as OXLAMs. These compounds have been linked to oxidative stress, mitochondrial dysfunction and inflammation.

This is why the cooking method matters as much as the ingredient list. An oil that is already partly oxidised from refining, then heated again in a commercial kitchen, has been through the process twice before it reaches a plate.

Where seed oils hide in prepared food

In prepared meals, seed oils are rarely the headline ingredient. They appear in the places least likely to be read:

• Pre-cooked proteins, which often arrive at a kitchen already fried or par-cooked in a neutral oil
• Sauces, dressings and marinades, where an emulsifier is needed and cost matters
• Anything described only as “vegetable oil” on a label

If you want to check a service you already use, we wrote a two-minute audit for spotting hidden seed oils, and a wider look at which services genuinely avoid them.

What Locale cooks with instead

Locale cooks with olive oil and avocado oil only. Seed oils are excluded from the entire menu, sauces and dressings included, and they sit on the list of 60+ banned ingredients alongside refined sugars, artificial colours and preservatives.

That exclusion is one rule among several: every meal also carries 40–60g of protein and 8g or more of fiber, produce is organic, and ingredients are third-party lab tested by Light Labs for heavy metals, pesticides, phthalates and PFAS — with the results published.

Meals are delivered across the San Francisco Bay Area and Los Angeles on Mondays, in reusable glass jars that are collected and sanitised each week.