The Western diet is increasingly being implicated in the development of Western lifestyle disease such as cardiovascular disease, obesity, type 2 diabetes, cancer and dementia. Investigators have analysed the components of the Western diet and found that the lack of micronutrients, the lack of fibre and the presence of energy dense foods may all contribute to disease. However, the Western diet also contains high concentrations of modified fats and sugars and these components may be particularly damaging to animal physiology. Trans fats are modified fats formed during the hydrogenation process, and no lower limit of safety is known for their consumption. Trans fats may interfere with normal fatty acid regulation and lead to the development of nonalcoholic fatty liver and insulin resistance, the underlying physiological changes that cause the metabolic syndrome. Evidence suggests that fructose from sugar contributes to these changes and also modifies normal appetite regulatory mechanisms.
A number of well designed studies have investigated the effects of trans fats and fructose on the metabolism of mammals. For example in one study1, researchers investigated the effects of trans fats and fructose (in the form of high fructose corn syrup) on the normal metabolic regulation in mice. The ability to exercise was removed from the mice by modification of their cages. Mice fed high trans fat diets developed detrimental changes to their livers within 16 weeks of beginning the diet, including the development of hepatic steatosis. The trans fed mice also became obese, which was reflected in an increase in plasma leptin levels. Plasma enzymes, suggestive of tissue damage, including alanine aminotransferase, also increased in the trans fat fed mice. Markers of inflammation and other markers of tissue injury (procollagen mRNA) also became elevated. The mice also developed elevated fasting blood glucose levels and impaired glucose intolerance within 4 weeks of beginning the high trans fat diet.
Substitution of the trans fats for lard ameliorated the detrimental effects of the high fat diet suggesting that it was the trans fats that were responsible for the changes and not the macronutrient content of the diet. When the rats were fed a high fructose corn syrup diet, the researcher observed that the mice became obese and developed insulin resistance. In addition however, the high fructose corn syrup also caused changes to the appetites of the mice such that they started to overeat. These data taken as a whole suggest that trans fats and fructose, two components of the typical Western diet, contribute significantly to the development of obesity and the metabolic changes seen with the development of metabolic syndrome, particularly fatty acid accumulation in the liver, and peripheral and central insulin resistance. The evidence showing that high quality diets devoid of trans fats and fructose reverse these changes, further supports the contention that these metabolic poisons contribute significantly to Western diseases.
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