Do you ever feel mentally exhausted during the day, even if you’ve had enough sleep? Do you get cranky or unable to function before lunch or mid-afternoon? Or maybe you’re having a hard time learning how to use a new electronic device and just chalking it up to “getting old.”

These are just a few of the symptoms of eating unhealthy seed oils (also known as vegetable oils), according to Catherine Shanahan, MD, best known as Dr. Cate and author of The Fatburn Fix and Deep Nutrition (drcate.com). Other side effects of such fats can include weight gain, anxiety, mood problems, migraines, and other types of headaches.

Seed oils are the most common fats found in packaged foods and on restaurant menus, and they make up the largest share of fat in the typical American diet. But this certainly doesn’t make them healthy. “Vegetable oils are the defining feature of junk food,” says Dr. Cate.

While many people eliminate gluten, sugar, or other problematic ingredients from their diets to improve their health, they’re missing a basic step. “Cutting out vegetable oils is the most powerful dietary change you can make,” says Dr. Cate. “If you don’t first cut out all eight vegetable oils, it’s like taking an aspirin for a headache before deciding to stop hitting yourself on the head with a hammer.”

Did you know … Although seed oils are rich in PUFAs, whole seeds also contain other fats, fiber, and important vitamins, minerals, and antioxidants. Whole (or ground) seeds are nutritious foods.

8 Harmful Seed Oils

These are the most widely used unhealthy fats, says Dr. Cate:

• Canola oil
• Corn oil
• Cottonseed oil
• Grapeseed oil
• Rice bran oil
• Safflower oil
• Soy oil
• Sunflower oil

Although they’re usually refined, even unrefined and cold-pressed versions of these oils pose the same health risks, because the oils are naturally rich in polyunsaturated fats (PUFAs). The molecular structure of PUFAs makes them very unstable in the human body, where they generate a tremendous amount of free radicals—chaotic reactions that damage cells.

Free radicals are a normal byproduct of metabolism that our bodies are equipped to handle, but only up to a point. Seed oils produce an onslaught that far exceeds our innate capacity. “Free radicals are bad for us in the same way that radiation is bad for us,” says Dr. Cate. When you eat a lot of PUFA-rich seed oils, she adds, “it’s like you have dirty bombs inside your cells.”

PUFAs are inflammatory and damage the lining of blood vessels, affecting overall circulation and blood flow to the brain, and increasing the risk for heart disease and diabetes.

According to a review published in Mayo Clinic Proceedings, the health hazards of eating too many of these oils include a suppressed immune system; lower “good” HDL cholesterol; a more dangerous, oxidized form of “bad” LDL cholesterol; and increased risk for prostate, pancreatic, colon, and breast cancers.

Related: The Health Benefits of Black Seed Oil

Benefits of Eliminating Seed Oils

“It’s like a fog has lifted.” That’s what many people tell Dr. Cate after they stop eating seed oils. Other benefits include unlocking the ability to burn body fat, fewer headaches, a better mood, less anxiety, and overall enhanced mental performance. Less craving for sugar is another perk, which is why Dr. Cate calls these oils “the gateway drug to sugar addiction.” When you eat them, the resulting combination of locked-up body fat and depleted mental energy makes you reach for junk food—especially the sugary or starchy kind.

The good news is that it’s relatively easy to upgrade your oils with healthier options full of good-for-you fats. These are Dr. Cate’s top choices of multipurpose oils that can be eaten cold and used for all types of cooking:

• Almond oil
• Avocado oil
• Butter
• Cocoa butter
• Coconut oil
• Ghee
• Macadamia nut oil
• Olive oil
• Peanut oil
• Tallow and lard

In addition to the above oils, hemp culinary oil can be eaten cold or used for low-heat cooking. Flax and walnut oils are healthy fats that shouldn’t be exposed to heat, so they’re best used for dressings and dips.

Shopping Tips

Organic versions of harmful seed oils are becoming more popular in packaged foods. Organic standards help to reduce toxins from chemicals used in agriculture and refining, but they don’t change the molecular structure of PUFAs—so organic versions of unhealthy seed oils will produce the same harmful reactions in the human body as regular versions. The key to better health is simply to avoid these oils altogether, says Dr. Cate.

When shopping for Dr. Cate’s healthier upgrades, keep in mind that refining turns good oils bad—healthy fats degrade when they’re refined and can go rancid during shipping or storage. So look for fresh, unrefined, cold-pressed products to make sure you’re getting the health benefits you want.