High quality diets are protective of disease. However, defining a high quality diet is difficult, but some consensus has been reached in this regard from nutritional scientists. Generally, diets containing high concentrations of processed and manufactured foods with long shelf lives are of low quality. Such diets tend to contain high concentrations of both sugar and trans fatty acids, two known disease causing agents. Both trans fatty acids and sugar typify the modern Western diet, and both have been suggested to be the cause of Western disease. Long term consumption of poor quality foods produce poor quality humans that are susceptible to disease. This is because over time high intakes of particular foods accumulate in body tissues and this leads to changes in metabolic function. Fatty acids have been studies in this regard, and research has shown that the type and amount of fatty acids in the diet is reflective the type and amount of fatty acids stored in adipose tissue, and this may influence the risk of disease.
For example, researchers assessed the habitual fatty acid intake of 20 healthy subjects using 7 day food diariesSup>1. The researchers then analysed the fatty acid composition of triglycerides and phospholipid membranes in adipose tissue using biopsies. The subjects with the highest intake of saturated fatty acids had the highest concentration of saturated fatty acids in adipose tissue but also had the lowest concentrations of polyunsaturated fatty acids. Therefore the saturated to polyunsaturated fatty acid ratio in adipose tissue was significantly associated with the saturated to polyunsaturated fatty acid ratio of the diet. Carbohydrate intake of the subjects was related to the omega-6 content of adipose tissue, suggesting that plant diets rich in linoleic acid may also provide higher intakes of carbohydrates. High intakes of polyunsaturated fatty acids were associated with an increase phospholipid concentrations of polyunsaturated fatty acids. Higher levels of omega-3 fatty acids in phospholipids were also associated with higher concentrations of omega-6 fatty acids.
Therefore the dietary intake of fatty acids can influence the composition of both adipose tissue storage lipids and the membrane composition of phospholipids (in this case measured in phosphatidylcholine and phosphatidylethanolamine). Interestingly, this study found no significant relationship between dietary cholesterol and the amount of cholesterol found in adipose tissue or phospholipid membranes. The fact that lipids in the diet can accumulate in adipose tissue in not surprising as this has also been shown to be the case for lipid soluble vitamins and other compounds such as carotenoids. Of more interest is the ability to change the structure of the plasma membrane based on the intake of dietary fats. This study showed a positive association between omega-3 and omega-6 fatty acids and phospholipid membrane composition. Because both compounds can be converted to biologically active hormones that can alter cell function, this explains the ability of diet to alter membrane properties in cells.
So how does the fatty acid composition of adipose tissue and phospholipids relate to disease? One possibility is that trans fatty acids in the diet accumulate in these stores and interfere with normal tissue metabolism. The reason that trans fatty acid may be detrimental to health is likely because their structural characteristics allow them to interact with the enzymes required for the metabolism of other fatty acids. In particular, trans fatty acid may interfere with essential fatty acid metabolism. It is no surprise therefore to discover that the disorders and diseases associated with high intakes of trans fatty acids are similar to those encountered in essential fatty acid deficiencies. As trans fatty acids accumulate in adipose tissue a stored of disease causing chemicals is provided, that can over time can, be released to interact with metabolic pathways. The incorporation of trans fatty acids into cell membranes is also problematic because there is the potential for interference with membrane fluidity and changes to the characteristics of the membrane function.
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