In recent months, seed oils have been a subject of debate, with online assertions claiming they are "toxic" and linked to chronic health conditions. On January 7, Robert F Kennedy Jr, United States secretary of health and human services, announced the 2025–2030 US dietary guidelines, emphasizing "real food" and promoting protein, saturated fats, and whole foods.
Kennedy has previously stated seed oils were "poisoning Americans," and the new guidelines suggest alternative oils and fats for cooking.
Understanding Seed Oils
Seed oils, often marketed as vegetable oils, are derived from seeds. Commonly criticized types, referred to as the "hateful eight," include canola, corn, cottonseed, grapeseed, rice bran, safflower, soy, and sunflower oils. These oils are widely available, affordable, and some have high smoke points, making them suitable for cooking.
Seed oils contain monounsaturated and polyunsaturated fats, including omega-3 and omega-6 fatty acids. Critics assert that seed oils cause inflammation due to their high omega-6 content.
Omega Fatty Acids and Inflammation
Unsaturated fats are essential and must be obtained through diet. Polyunsaturated fats include omega-3s (found in fatty fish, chia seeds, walnuts) and omega-6s (common in vegetable oils, seeds, nuts).
Traditionally, omega-3s were considered anti-inflammatory, and omega-6s pro-inflammatory.
However, Dr. Emma Beckett, a senior lecturer of nutrition and food science, states this concept is outdated.
A recent study by Dr. Daisy Crick from the University of Queensland indicated that omega-3 fatty acids might also increase some inflammation biomarkers, and higher omega-6 to omega-3 ratios could contribute to a low-grade inflammatory state. Dr. Beckett suggests focusing on the overall quality of foods rather than isolated inflammation markers.
Correlation Versus Causation
Arguments that increased seed oil consumption correlates with rising chronic disease rates have been disputed by experts.
Professor Clare Collins of the University of Newcastle highlights that correlation does not imply causation, citing other factors like increased car ownership and air pollution.
A 2022 meta-analysis found no link between omega-6 fatty acids and the risk of cardiovascular disease. The World Cancer Research Fund also found no evidence that moderate consumption of vegetable and seed oils increases cancer risk. Instead, experts suggest the rise in high body weight and obesity, largely due to ultra-processed foods, has a more significant impact on chronic disease risk.
Seed Oils in Processed Foods and Trans Fats
Ultra-processed foods, which are often lower in micronutrients and higher in calories, commonly use seed oils due to their low cost. These foods often contain saturated fats and trans fats.
Trans fats, linked to cardiovascular disease, diabetes, and cancer, should constitute no more than one percent of daily calories. While naturally occurring in some animal products, trans fats are primarily consumed in processed foods where unsaturated fats have been hydrogenated to become solid, like in pastries or crackers.
Hydrogenation can convert any oil, including seed oils, into trans fats, making them behave like saturated fats.
Dr. Beckett emphasizes that hydrogenated oils are not the primary way seed oils are consumed and that demonizing seed oils is not a comprehensive solution; instead, the focus should be on the overall dietary context.
Dietary Guidelines and Recommendations
Health organizations, including the World Health Organization, Australian Dietary Guidelines, and Dietitians Australia, recommend that fats constitute approximately 30 percent of daily energy intake.
Polyunsaturated and monounsaturated fats should be the primary source, with saturated fat intake limited to less than 10 percent of total energy intake.
The new US dietary guidelines also advise keeping saturated fat intake below 10 percent of daily calories, despite suggesting the use of olive oil, butter, and beef tallow for cooking.
Saturated fats, typically solid at room temperature, are not inherently detrimental in small doses, but high intake is linked to increased levels of LDL (low-density lipoprotein) cholesterol, which raises cardiovascular disease risk. All health bodies recommend limiting trans fats to less than one percent of daily calories, citing their link to a 34 percent increased risk of death and no known health benefits.