Low quality diets are increasingly being seen as the cause of Western lifestyle diseases such as cancer, cardiovascular disease and type 2 diabetes. In contrast, high quality traditional diets are protective of disease. Studying the changes that occur as population pass from their traditional eating patterns to more modern Western style practices gives us clues as to the cause of disease in Western nations. Generally, Western diets contain high amounts of processed foods, which can be thought of a adulterated versions of their whole food counterparts. Processing can involve the removal of substances necessary for health or formation of new substances that interact negatively with human biochemistry. Although refined carbohydrates are perhaps the most reported of the processed foods in the Western diet, proteins and fats are also present in chemically altered forms, and this is now thought to contribute significantly to biochemical imbalances.
That traditional diets contain low levels of refined carbohydrates including sugars is well reported. Refining cereal grains removes the bran and germ from the original plant material to leave only the starchy endosperm. This is problematic because the bran and germ contain the fibre and micronutrients required for the correct digestion, absorption and metabolism of the starch. Consumption of refined grains has been reported to be the likely cause of the insulin resistance that leads to the development of abdominal obesity and metabolic syndrome. Clinical trials show that adding fibre to refined carbohydrates causes a decrease in the glycaemic response, because a high fibre to carbohydrate ratio slows digestion. Sugars are also problematic when they are refined from their original plant material (such as fruits) because while the whole fruit contains fibre, the crystallised sugars do not. The increasing use of sugar in processed Western foods is mirrored by rises in obesity rates.
Refined oils are also problematic to human health. Polyunsaturated oils such as α-linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)) are very sensitive to light and heat. Long-term storage of such products is therefore problematic without refrigeration and opaque bottle because of rapid development of rancidity. To circumvent this problem, manufacturing companies refine the oils to create sterile deodorised supermarket oils with long shelf lives. These oils do not retain the original composition of the parent oils. Such oils may be hydrogenated to form margarine through a process that converts the liquid polyunsaturated fats to solid saturated fats. The oils are also often heated and pressurised during processing this chemically alters the oils, resulting in the production of lipid peroxides, trans fatty acids and other oxidised end products. Such oils are detrimental to the health because they lead to inflammation and oxidative stress when consumed.
Processed meats are created to allow elongation of shelf life, and often contain high levels of nitrites and nitrates which results in the formation of N-nitroso compounds (NOCs) in the gut. These compounds are now implicated in the development of gastric cancers when regularly consumed. Cooked meats can also result in the formation of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PCHs) and this is particularly evidence after pan frying, as is common in fast food preparation. The association between red meat and cancers of the gut is likely due to the confounding variable that is nitrate and nitrite preservatives in processed meat such as tinned and cooked meats as well as meat used in fast food, such as hamburgers. Processed meats are often cooked in refined oils and served with refined carbohydrates and this can significantly increase systemic oxidative stress and inflammation if consumed even sporadically.
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