Vegetable Oil

The increased consumption of industrially produced seed oils in modern diets could be one of the largest casual factors in the current epidemic of degenerative diseases.

Research suggests they play a role in modern diseases such as: heart disease, cancer, diabetes and auto-immune illnesses.

Sources of Vegetable Oil

Overview of Polyunsaturated Fats

Polyunsaturated Fatty Acids (PUFAs) is the group name for the omega 3, omega 6 and omega 9 fats.

Omega 3 and 6 have vital functions for human health. They are referred to as ‘essential fats’ as they cannot be synthesised by the body and must be obtained through the diet.

Omega 3

  • There are many forms of omega 3, the most common forms are Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA), Alpha-linolenic acid (ALA).
  • EPA and DHA are found in animal foods, particularly oily fish, and provide most of the known benefits of Omega 3.
  • ALA is found in plant foods like seeds and nuts. ALA can be converted in the body to EPA or DHA, but the conversion is not very efficient, so it is mostly used for energy.
  • Omega 3 is involved in the formation of cell membranes, controlling inflammation, brain health, mental health, preventing asthma, bone health and weight management.

Omega 6

  • The most common form is Linoleic Acid (LA).
  • Omega 6 is involved in the control of inflammation.

What are the health concerns with PUFAs?

There are 2 main points to understand:

  1. The ratio of omega 6 to omega 3 in modern diets has risen considerably as compared to ancestral diets.
  2. The high level of PUFAs in modern diets is mostly in the form of oxidised oils.

Pont 1: The ratios of PUFAs in your diet

The ratio of omega 6 to omega 3 was probably around 1:1 for most of human evolution, but in modern diets the ratio is estimated as being between 15:1 and 20:1.

A high ratio of omega 6 to omega 3 is thought to be pro-inflammatory, while a more equal ratio reduces inflammation.

Chronic inflammation promotes the development of many modern diseases, and the increased consumption of omega 6 coincides with a massive rise in heart disease, cancer, osteoporosis, obesity, diabetes, Alzheimer’s and auto-immune illnesses.

The modern diet, even a whole foods diet with no processed food, generally contains more omega 6 than 3.

  • Pork and chicken contain much higher amounts of omega 6 linoleic acid than meat from ruminants (goats, cattle, sheep). The amount of linoleic acid in pork and chicken is further increased if the animals are fed corn or other foods high in linoleic acid, which is standard practice.
    • Pork from pigs fed a grain free diet can have a ratio of omega 6 to omega 3 in the region of 5:1.
    • Pork from pigs on a high PUFA diet can have a ratio of omega 6 to omega 3 in the region of 30:1.
    • Chicken thighs or drumsticks with skin on can have a ratio of omega 6 to omega 3 in the region of 12:1.
    • Chicken fed corn or other grains high in omega 6 is likely to contain more omega 6 than pastured chicken.
  • From 1961-2018 in Western Europe and North America per capita consumption of pork and chicken has increased, while consumption of red meat has decreased.
  • Grain fed red meat contains less omega 3 than pastured meat, though the total amount of PUFAs in red meat is still relatively small.

Whole foods high in omega 6, e.g. seeds and nuts, are probably beneficial in small amounts. However, our ancestors did not have access to 1 kg bags of nuts or bake cakes with almond flour. They probably ate a few seeds and nuts opportunistically.

Even if you are only eating unprocessed whole foods, the ratio of omega 6 to 3 could still be higher than ideal if you eat a lot of fatty cuts of pork or chicken, seeds and nuts.

Point 2: Most PUFAs in the modern diet are in the form of oxidised oils.

Industrially produced polyunsaturated oils only came into our diet around 1865 when they started to be mass produced as a cheap cooking oil. Previously the main sources of fat in Western diets were butter, lard and beef tallow, all of which are predominantly saturated fats.

‘Vegetable oil’ consumption in the US has increased by more than 150 times since 1909.

Vegetable oil can describe a number of different types of oil. Typically it’s made from seeds or nuts, the most common being sunflower, rapeseed, cottonseed, safflower or soy bean. These oils are high in PUFAs, particularly omega 6.

PUFAs are easily oxidised by heat, light and oxygen.

The processing involved in producing commercial oils causes huge amounts of oxidisation.

High temperature cooking, such as frying with PUFA rich oils also causes oxidisation. Even if the oil is a cold pressed oil and not an industrially processed oil, it will still become oxidised at high temperatures.

Oxidised PUFAs are thought to be a driver of many modern diseases:

  • Obesity
  • Heart disease
  • Inflammatory bowel disease
  • Non-alcoholic fatty liver disease
  • Rheumatoid arthritis
  • Alzheimers
  • Cancer
  • Diabetes
  • Autoimmunity

Where are oxidised PUFAs likely to be found in the modern diet?

  • Cooking oils made from seeds or nuts containing PUFAs.
  • Processed food, check ingredients for ‘vegetable oil’.
  • Sauces, curry pastes, marinades.
  • Hummus.
  • Mayonnaise.
  • Anti-pasti (jars of roasted peppers, artichokes and other such treats).
  • Olive oil blends sneakily pretending to be olive oil.
  • Baked goods.
  • Gluten free products.
  • Restaurant foods (large amounts are used in fried foods, often the oil is used repeatedly, increasing oxidisation).
  • Tinned fish.
  • Probably loads of other places if you read the labels.


The ‘processed foods’ listed above contain high amounts of oxidised PUFAs which are known to be a significant factor in the increase many modern diseases.

Even whole foods such as seeds, nuts, fatty cuts of pork and chicken can lead to an unfavourable ratio of omega 6 to omega 3 which may be pro-inflammatory.


  1. Fatty Acids From Fish: The Anti-Inflammatory Potential of Long-Chain omega-3 Fatty Acids
  2. Polyunsaturated Fatty Acids and Inflammation
  3. Polyunsaturated fatty acids in the food chain in the United States
  4. An Increase in the Omega-6/Omega-3 Fatty Acid Ratio Increases the Risk for Obesity
  5. Evolutionary aspects of diet, the omega-6/omega-3 ratio and genetic variation: nutritional implications for chronic diseases
  6. Health Implications of High Dietary Omega-6 Polyunsaturated Fatty Acids
  7. Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century
  8. Oil for food – the global story of edible lipids
  9. Consumption of vegetable oils worldwide from 2013/14 to 2019/2020, by oil type
  10. Fatty Acid Comparisons of Grain and Forage-Fed Pork – Practical Farmers of Iowa
  11. Fatty acid composition in pork fat: De-novo synthesis, fatty acid sources and influencing factors a review
  12. Cortinas L, Villaverde C, Galobart J, Baucells MD, Codony R, Barroeta AC. Fatty acid content in chicken thigh and breast as affected by dietary polyunsaturation level. Poult Sci. 2004;83(7):1155-1164. doi:10.1093/ps/83.7.1155
  13. Effect of feeding systems on omega-3 fatty acids, conjugated linoleic acid and trans fatty acids in Australian beef cuts: potential impact on human health
  14. A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef
  15. Food and Agriculture Organization of the United Nations (FAO) (2020)
  16. Heated vegetable oils and cardiovascular disease risk factors
  17. The harmful effects of consumption of repeatedly heated edible oils: a short review
  18. Impact of consumption of repeatedly heated cooking oils on the incidence of various cancers- A critical review