Results from animal studies should always by treated with caution because humans and animals have physiological differences. However, some animal studies are interesting from a nutritional point of view because certain types of study that may be considered unethical in humans can be performed on animals, and this can give insight for future human studies. Vitamin depletion studies are one such research tool that can be problematic in humans, and so animals studies are often used in the first instance in order to collect preliminary data. Vitamin E deficiencies are rare, mainly because tocopherols and tocotrienols are stored in adipose tissue and released to circulation as dietary intake falls and normal adipose tissue turnover occurs. Much of the data regarding the metabolism of vitamin E has therefore come from animals studies because rat diets can be strictly controlled.
Research published in the Journal of the American College of Nutrition1 adapted rats to a starch based diet for 7 weeks before randomly dividing them into a control group with no supplemental vitamin E, a wheat germ supplemented group and a wheat germ oil supplemented group. Rats were fed these diets for three weeks and the two wheat germ diets were designed to provide the same quantity of vitamin E. The antioxidant contents of the three diets is shown in figure 1. Rats receiving the wheat germ diet had significant increases in plasma vitamin E, when compared to the control diet. This increase in vitamin E was associated with a reduced susceptibility of the liver, heart and plasma to undergo lipid peroxidation. No differences were found between wheat germ and the wheat germ oil, suggesting that both provided beneficial levels of vitamin E.
Figure 1. The antioxidant content of the food provided to the rats. The control group received no added vitamin E, other than that present in the diet mainly as corn oil. The wheat germ rats received 200g/kg diet wheat germ and the wheat germ oil group received 10g/kg diet wheat germ oil. Numbers in parentheses represent the dietary intake for the rats in the respective groups.
These results suggest that wheat germ is a good sources of vitamin E which can supply an intake of vitamin E capable of reducing lipid peroxidation in rats. The wheat germ in this study contained mainly α- and β-tocopherol, measured at roughly 13 and 10mg/100g of germ, respectively. Alpha-tocopherol may be absorbed and utilised more favourable than other isomers of vitamin E in humans due to the presence of the α-tocopherol transfer protein, that preferentially incorporates the α-isomer of vitamin E into very low density lipoproteins for transport around the body. Alpha tocopherol therefore appears to be the main biologically active form of vitamin E that accumulates in tissues and is may be the form most actively involved in preventing lipid peroxidation. The control diet (with corn oil) was not able to prevent lipid peroxidation, perhaps due to the high γ-tocopherol content of corn oil.
However, the high unsaturated fat content of wheat germ may cause the fresh germ to auto-oxidise over the course of a few days. Stabilisation of the germ is therefore required through heat treatment in order to denature particular enzymes present, and this can prevent rancidity to some degree, elongating shelf life. The wheat germ in this study was heat treated in this way. The advantage of using the oil, is perhaps that this rancidity caused by lipid peroxidation is less evident. The high unsaturated fat content of the germ however, is a suitable vehicle to allow efficient absorption of the vitamin E, as it has been shown that α-tocopherol is not efficiently absorbed from a low fat meal. The dietary fibre present in wheat germ may have beneficial effects on blood lipids, although no effects were reported to have occurred to the rats in this study.
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