In a letter to the editor of the Lancet (1983) Dr. Wayne Martin wrote: “In early 20th century Britain and the United States everyone cooked and baked with butter or lard, and death from what we now call myocardial infarction was so rare that it had no name or medical recognition. The oilseed industry was founded shortly before 1920 and by 1926 was injecting into the national diet trainloads of new vegetable fats which, in the concept of the “prudent” diet are now the “good” fats. I suggest that the introduction of trans-trans linoleic acid in the 1920s in margarines and refined vegetable oils was the main cause of the pandemic of myocardial infarction and that since 1960 orthodox medicine has been fostering a cause of this disease as the cure.”
Powerful words, and subsequent research has shown that Dr. Martin was indeed right. So right that food processors and manufacturers are now tripping over themselves in their haste to remove trans fats from their products. If fat is removed, however, then something must replace it. In some cases the replacement might be sugar or other refined carbohydrate (a bad choice). In other cases, the replacement is usually a non-hydrogenated vegetable oil, rich in linoleic acid, otherwise termed omega-6 fatty acid.
It’s been shown that the average person consumes roughly 10 times more vegetable oil than was the case 50 years ago. Expressed oil simply wasn’t available back then. The problem with excessive omega-6 is that it can interfere with omega-3 uptake (already in short supply), resulting in serious potential for conditions including inflammation, platelet aggregation, reduced HDL cholesterol levels, increased gallstone formation, predisposition to lipid peroxidation, hypertension, depressed immune function, cancer, abdominal weight gain and age-related macular degeneration.
Omega-6 and cancer
Linoleic acid is the only fatty acid to exhibit an unequivocal cancer-enhancing effect in rodents, impacting mammary, pancreatic and colon cancer. A number of nutrients show tumour-enhancing properties, but excessive levels of intake are usually required. This is not the case with linoleic acid as only five times the amount needed for optimal growth will bring about mammary tumour development in rats. Research shows the more linoleic acid in a product (corn oil for example), the more carcinogenesis enhancement compared to low-linoleic acid foods like dairy fat, beef tallow and fish oils.
Researchers have looked at the influence of maternal diet on breast cancer risk among female offspring and determined that a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat, and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. The same may be true regarding prostate cancer risk in male offspring.
A 2006 study found that a diet rich in omega-6 fatty acids appeared to promote the spread of prostate cancer, while a diet rich in omega-3 impeded the spread.
Other related conditions
Several other conditions are linked to excessive linoleic acid intake such as asthma, eczema, allergic rhinitis and hay fever. It has also been proposed that changes in fatty acid composition of ingested fats have been determinants in the increasing prevalence of childhood overweight and obesity. You can’t help but wonder if the rise in cancers of the breast, prostate and colon are linked to the rise in linoleic acid consumption. While vegetable oil intake was on the increase, consumers were urged to sharply reduce the amount of cancer-fighting, CLA-rich animal fats in their diet.
Thomas Edison once said, “The doctor of the future will give no medicine, but will interest his patients in the care of the human body, in diet and in the cause of prevention of disease.”
Though Edison was no nutritionist, I think he was on to something. Don’t avoid linoleic acid in your diet — it’s essential! Just avoid diets that are excessive — in anything.
Helen Bishop MacDonald is a consulting nutritionist in the agriculture industry