Even if you’re eating a plant-based or vegan diet for health and wellbeing, you’re probably still using olive oil or other vegetable oil in your salad dressings or stir-fries, thinking that is a healthy move. But just because it's derived from plants doesn’t necessarily mean oil is healthy. If you're looking for optimal health, it may be time to toss the green bottle.

Vegetable oil is so ubiquitous in American cooking that you may not think twice about eating it. After all, it’s your go-to when you’re sauteing or roasting vegetables, and it's one of the top ingredients in chips and baked goods. Without checking the label, chances are you're getting oil several times a day, without even realizing it. It's time to take notice. Even though you can find studies to suggest that eating olive oil is healthy, numerous plant-based doctors will tell you: No way. Their message? No matter what kind, oil has no place in a healthy, plant-based diet, and the sooner you part ways with it, the better. Here’s the rationale for going oil-free.

How Oils Gained a Healthy Reputation

The health halo of vegetable oils dates back about a century ago when researchers first began to link the increased risk for heart disease and cancer to saturated fats, says T. Colin Campbell, Ph.D., professor emeritus of nutritional biochemistry at Cornell University in Ithaca, N.Y., and author of The China Study and the upcoming Future of Nutrition. As they compared data from different countries, they concluded that as fat in the diet increased, so, too, did the rates of heart disease and cancer. Cholesterol was also pinpointed as a trigger for these diseases.

The problem with this conclusion? “The chief cause wasn’t saturated fat or cholesterol but rather, the combination of an increase in animal protein and a decrease in plant-based foods,” Campbell says. This fact, however, was ignored and covered up. “People don’t want to question problems with animal protein, something humans have always, for lack of a better word, worshipped.” In fact, one of the first studies to prove the link between animal protein and chronic diseases was published in the early 1900s, but it garnered little attention.

Yet around the 1950s, a shift happened when researchers began to study the health impacts of a Mediterranean diet versus the Western diet. Again, they found that diets higher in saturated fat were consistent with higher rates of disease while polyunsaturated fats, found mainly in plants, were linked to less disease. So they concluded that “saturated fat was bad but unsaturated fat from plants, including the oil from plants, was good,” Campbell says. Butter was then out, and because the oil in liquid form couldn’t be slathered on bread, companies found a way to solidity and convert it to a spreadable form of a synthetic saturated fat called trans-fat. And the leftover liquid oil, which people still considered healthy because it was an unsaturated fat, became more popular for cooking.

Why Added Oils Are Bad for You

Because vegetable oils come from plants, it’s logical to assume they’re healthy. Not true. “Oil is the most refined, calorie-dense food in the grocery store,” says Cyrus Khambatta, Ph.D., co-founder of Mastering Diabetes and co-author of Mastering Diabetes. “Although some oils contain trace amounts of vitamins and minerals, oils don’t have carbohydrate, protein, fiber, and water, and the vast majority of vitamins, minerals, antioxidants, and phytochemicals have even been removed in the extraction process.” What you’re left with is a calorie-dense food containing minimal micronutrient value that’s “as refined as white table sugar,” he adds.

In addition, oil is high in omega 6 linoleic acid, which promotes inflammation in the body. “When consumed, omega 6 fatty acid is easily oxidized,” Campbell says. “As a result, it produces reactive oxygen species in the body, free radicals that damage the body by promoting cancer and laying down a foundation for heart disease.”

One of those foundations involves decreasing endothelial function, the endothelium being the thin membrane that lines the inside of blood vessels and the heart. “We have seen inflammation and endothelial dysfunction as significant contributors to chronic disease and even see how they negatively impact a healthy response to COVID infection,” says Kim Scheuer, M.D., plant-based lifestyle medicine physician and founder of DOKS Lifestyle Medicine in Aspen, Colo. This is one reason heart disease patients who go through the Heart Disease Reversal Program at the Cleveland Clinic run by Caldwell B. Esselstyn, Jr., M.D., are restricted from eating any oil.

Oils Can Cause Inflammation

There’s another downside to that omega 6s. Consuming just a small amount increases your overall omega-6 to omega-3 ratio, which not only ramps up inflammation but also reduces your production of EPA and DHA, anti-inflammatory fatty acids that are crucial for optimal brain function and eye health, Khambatta says.

Now factor in saturated fat, the primary content of coconut oil and most vegetable oils, and you’ll not only face an increased production of LDL (bad cholesterol) in your liver, insulin resistance may also be another concern. “Small amounts of saturated fat can impair the function of insulin receptors in your muscle and liver within hours of a single high-fat meal,” Khambatta says. In fact, people who have insulin-dependent diabetes, even those with prediabetes, type 2 diabetes, and gestational diabetes, find that small amounts of oil in a single meal significantly increase their blood glucose about two to six hours after the meal. One to four days after that meal, they need more exogenous insulin.

Now let’s talk weight. “Because oil is the most calorie-dense food available, eating oil-rich foods contribute to weight gain,” Scheuer says. Fat has nine calories per gram versus four calories per gram in protein and carbohydrates, which means that in one tablespoon of oil, you’ll get 120 calories of fat. To be even more clear, while vegetables typically contain about 100 calories per pound and fruits about 300 calories per pound, oil has about 4,000 calories per pound.

Not only will you consume more calories, but you also risk overheating oil-rich foods. When you eat fruits, vegetables, legumes, and whole grains, their fiber and water content will make you mechanically and nutritionally full before you become calorically full. “This means that when your stomach begins to distend, it will send a neurological impulse to your brain that says ‘slow down’ or ‘stop eating’,” Khambatta says. Oil, however, doesn’t trigger this same satiety mechanism so you could easily eat too much without knowing it.

Are All Oils Bad for You?

Oil is oil, and “you should avoid all if you want to strive for optimal health,” Scheuer says. This includes olive oil, a cornerstone of the Mediterranean diet, even though studies show that people eating a Mediterranean diet have lower rates of chronic illnesses like heart disease and cancer. Yet it’s not because of the olive oil. “It’s because they’re eating a predominantly vegetarian diet, consuming high amounts of fruits and vegetables,” Campbell says, adding that the olive oil industry often works in the background to promote its products.

There’s another reason olive oil gets touted as healthy. “This idea comes from research showing that eating a Mediterranean diet is more beneficial than eating a standard American diet, but that doesn’t mean it’s as healthy as eating an oil-free diet,” Scheuer says. She points to the tobacco industry which once claimed that smoking was healthy, namely because there wasn’t a massive difference in risk from smoking 10 versus seven packs a day. Yet there is a tremendous difference in smoking 10 packs per day compared to no packs. The same goes for some versus no oil.

How to Eat an Oil-Free Diet

Eliminating added oils from your diet might seem impossible. But with just a few tweaks, you can cook and bake – even go out to eat – without consuming oil. “Once you get used to cooking without oil, you won’t miss the flavor,” Scheuer says.

For cooking, saute vegetables dry (put the onions in first so they naturally sweat their juices) or use low sodium vegetable broth (or water) instead of oil, Scheuer says. If you want to roast vegetables, add moisture from a low-sodium vegetable broth (use a silicone mat or parchment paper to prevent sticking) or slow roast in a foil bag. Rather than making salad dressings with oils, blend seeds or nuts to make a creamy dressing, and in other sauces, use a liquid base of flavored vinegar or juice. For baking, unsweetened applesauce, mashed bananas, or ground flax seeds make suitable oil substitutes.

And when going out to eat, politely ask if the restaurant can cook a meal without oil (or go light on oil, if all else fails, Scheuer says). “Most of the time, your server or chef will impress you with a fun, creative presentation of what you ordered,” Khambatta says.

Yet what if you’re an otherwise healthy individual who wants to eat a little oil? “If you’re healthy, not overweight, void of chronic disease and don’t have food addictions, having a little processed oil in your diet may not be dangerous, but I wouldn’t consider it healthful,” Scheuer says.

That’s a sentiment Campbell echoes. “I can’t say I never use a drop of oil but do try to avoid it, as oil is not a health food, and you don’t need it,” he says.