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Fat As A Storage Compound

Fatty acids are a group of non-polar (non-water soluble) molecules that comprise of a carbon chain with a hydroxyl group and oxygen molecule at one end and a methyl group at the other. The chain lengths vary, but generally the shorter the chain length, the more polar (water soluble) the fatty acid becomes. Formic acid and acetic acid with 1 and 2 carbon are actually short enough to be water soluble. Nutritionally important fatty acids have even numbers of carbons in their chain, with chain lengths of common dietary fatty acids varying in chain length from short chain fatty acids with fewer than 6 carbons, to medium chain fatty acids having between 6 and 12 carbons, to long chain fatty acids having between 12 and 22 carbons and to very long chain fatty acids having more than 22 carbons in their chain. Adipose tissue is composed primarily of stearic acid, an 18 carbon saturated fatty acid, the same fatty acid that predominates in the fat tissue of most animal, which can be seen on red meat as a white solid fat.

Fatty acids are stored in adipose tissue in the form of triglycerides. Triglycerides (also called triacylglycerols) comprise of three fatty acids joined to a molecule of glycerol. Triglycerides provide 9 kcals per gram when oxidised, which is higher than both carbohydrate and protein, which yield 3.75 and 4.1 kcal per gram, respectively. This makes triglycerides a highly efficient storage substance from an energy perspective. The fact that triglycerides can also be stored in the absence of water, further increases the efficiency of storage when compared to glycogen, with every gram of glycogen having 2 to 3 grams of water associated with it. Although many consider body fat to be unsightly, body fat is necessary, for as adipose tissue falls below 3 % of total body weight the risk of death increases significantly. The disadvantage of storing fatty acids is that they cannot be oxidised in the absence of oxygen like carbohydrate, and for this reason are not a good source of instant energy in short duration activities of high intensity.

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Fruit Juice And Insulin Resistance

Fruit contains high amounts of sugars, particularly fructose and sucrose. Sucrose is a disaccharide made up of a molecule of glucose joined through a glycosidic bond to a molecule of fructose. Therefore fructose is the primary sugar in fruit, its name actually meaning fruit sugar. Fructose has been shown to cause insulin resistance in mammals including mice, rats, monkeys and humans in a short amount of time, perhaps a few weeks, when consumed in high concentrations. The amount of fructose used in studies to induce insulin resistance in animals has been shown to be equivalent to the high intakes of fructose associated with soft drinks. Soft drinks are rich in fructose, either in the form of sugar or high fructose corn syrup, in Europe and the United States, respectively. Soft drinks are associated with obesity and have been shown to cause insulin resistance in humans. However, fruit does not cause insulin resistance, despite the fact that it contains high amounts of fructose.

The reason that fruit does not cause insulin resistance, as mentioned previously, is that it contains fibre. Fibre slows the digestion and absorption rate of any concomitantly eaten carbohydrates and this reduces the nutrient overload experienced by the cells. Although fruit does not cause insulin resistance, fruit juice does, and this is a reflection of the fact that the fibre has been removed. Studies show that fruit juice is no less detrimental to the health than soft drinks and high intakes of fruit juice may induce insulin resistance and lead to obesity. Many people consume fruit juice and give it to their children under the impression that it is a healthy food, but increasingly it is being shown that the decision to consume fruit juice is not a sound nutritional one. Consuming fruit juice with high fibre foods may negate some of the detrimental effects as the fibre in the gut can limit the absorption of the fructose and inhibit nutrient overload in the cells. However, the nutritional literature suggests that consumption of fruit juice should be severely limited.

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