By Claire McDonnell Liu, Nutritionist at Leafie.org Medical review by Dr Rod Tayler
Seed oils, widely used in homes and restaurants for cooking, sauces, ready meals, and spreads, may not be as harmless as once believed.
Seed, or vegetable oils — made from canola, soybean, corn, sunflower, and safflower seeds — are often recommended for heart health, as they may help lower low-density lipoproteins (LDL) cholesterol, often called “bad cholesterol.” However, it’s unclear if this cholesterol-lowering effect leads to fewer heart problems or deaths, as updated research challenges the idea that cholesterol levels alone determine heart health.
Nina Teicholz – ‘Vegetable Oils: the Unknown Story”
There are growing concerns over the potential health risks associated with these industrially processed fats, which are being consumed in ever-increasing amounts.
Here’s a quick overview of the main issues linked to vegetable oils.
Chronic Inflammation from Excessive Omega-6
Dr Chris Knobbe: ‘Are Vegetable Oils the Primary Driver of Obesity, Diabetes, and Chronic Disease’
Seed oils are high in omega-6 fatty acids, especially linoleic acid. Omega-6 fatty acids are essential fats, meaning our body needs them, but they must be balanced with omega-3 fatty acids to maintain optimal health. An imbalance, specifically, a diet too high in omega-6 and too low in omega-3, has been linked to inflammation and various health issues.
While we need omega-6, too much throws off the balance with omega-3s, which are essential for reducing inflammation. Chronic inflammation has been linked to heart disease, arthritis, and autoimmune disorders (1: Weinberg, S. L. (2004). The diet-heart hypothesis: a critique. Journal of the American College of Cardiology, 43(5), 731-733.).
Questionable Heart Health Claims
Prof. Tim Noakes: ‘The Cholesterol Hypothesis
The diet-heart hypothesis has been a subject of debate for many years. The diet-heart hypothesis is the idea that eating saturated fat and dietary cholesterol raises blood cholesterol levels, which in turn increases the risk of heart disease. Despite widespread adoption, the evidence supporting this hypothesis has been inconsistent, with scientific reviews challenging the decades-old recommendation to swap saturated fats for seed oils to protect heart health.
Promotion of low-fat, high-carbohydrate diets, by major health organisations, has not yielded the expected benefits in reducing heart disease incidence. These carbohydrate-heavy promoted eating patterns may even contribute to metabolic syndrome—a cluster of conditions increasing the risk of heart disease, stroke, and diabetes.
Some studies suggest replacing saturated fats with polyunsaturated fatty acids (PUFAs), a type of fat found in certain foods, does not necessarily reduce heart disease risk, as oxidized seed oils may contribute to arterial damage and heart disease (Chowdhury et al., 2014).
Other studies suggest that repeatedly heating these cooking oils may raise blood pressure, and cause inflammation in blood vessels, all of which may lead to heart disease. pubmed.ncbi.nlm.nih.gov
Focusing solely on reducing dietary fat and cholesterol may be overly simplistic, with researchers advocating for exploring wider dietary factors and lifestyle changes to effectively combat heart disease and metabolic health conditions.
Oxidized Fats Can Damage Cells
PUFAs, the predominant fat found in most seed oils, are highly unstable and oxidize easily when exposed to heat, air, or light. When consumed, these oxidized fats may trigger oxidative stress, damage cells and potentially increase the risk of cancer and neurodegenerative diseases (Guéraud et al., 2010).
Potential Cancer Risk
When heated, seed oils can produce toxic compounds like aldehydes and lipid peroxides, which have been linked to DNA damage and an increased risk of cancer. Some research suggests that a diet high in omega-6 fatty acids may promote tumour growth in cancers like breast and prostate cancer (Hursting et al., 1990).
Insulin Resistance and Obesity
There’s growing research that excessive seed oil consumption could play a role in metabolic dysfunction. High levels of linoleic acid have been linked to insulin resistance and obesity, making weight loss more difficult (Ramsden et al., 2013).
Hormonal Disruptions
Some studies indicate that excess omega-6 intake from seed oils could disrupt hormonal balance by affecting insulin, estrogen, and testosterone production. This could contribute to conditions like PCOS, fertility problems, and endocrine disorders (Ailhaud et al., 2006).
Potential Effects on Brain Health
Since the brain is mostly made of fats, the type of fats we eat matters. High omega-6 consumption has been linked to increased neuroinflammation, which is associated with Alzheimer’s, depression, and anxiety (Dyall, 2015).
Final Thoughts
The much-promoted notion that seed oils are healthy is being challenged by emerging science. The long-term health consequences of consuming these fats in large amounts—especially in processed foods—are unsettled. Whilst some studies and critics suggest that these oils contribute to inflammation, metabolic issues, and other health risks opting for more stable fats, such as butter, ghee, tallow, lard, coconut oil, and cold-pressed olive oil, may be a safer long-term choice.
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