Whole grain consumption is associated with improved healthy. Consistently it has been shown that those with the highest whole grain intakes are the least likely to be obese, suffer from cardiovascular disease, or have blood sugar problems. The reason that whole grains are considered a high quality food relates to the way that they differ from refined grains. Cereal grains such as wheat, oats and barley possess three main layers in the kernel, the germ, the bran and the endosperm. While the endosperm layer contains the starch that provides energy, the bran and the germ layer contains fibre, vitamins and minerals. During the digestive and absorptive process the fibre contained within the bran layer acts to reduce the rate of starch digestion and absorption and this has beneficial glycaemic effects. During metabolism of the absorbed glucose the vitamins and minerals are required to help flux through metabolic pathways and therefore contribute to normal metabolic regulation.
In contrast, refined grains are stripped of their bran and germ layers during processing. This reduces the fibre and micronutrient content of the grain considerably. Studies have shown that this has detrimental glycaemic effects that can alter metabolic regulation and lead to insulin insensitivity. Reductions in insulin sensitivity are the likely reason that refined grains increase the risk of cardiovascular disease, type 2 diabetes and obesity. Whole grains are increasingly being seen as a good source of antioxidants. In particular, wheat barley and rye contain a group of antioxidants including the alkylresorcinols and ferulic acid. The presence of antioxidants in cereal grains may explain some of the health benefits they confer. A number of studies have looked at the health effects of the antioxidants in whole grain cereals and found that consumption modifies biochemistry and may cause beneficial effects. In particular, reductions in oxidative stress, insulin resistance and inflammation may occur from regular whole grain consumption.
For example, in one study1, researchers investigated the metabolic effects of whole grain consumption by feeding 80 healthy but overweight subjects either whole grains or refined grains for 8 weeks. Researchers then tested a number of metabolic parameters over the course of the study. The results showed that whole grain consumption resulted in increased serum levels of dihydroferulic acid (DHFA; 4-fold) and ferulic acid (FA; 2-fold) compared to refined grain consumption. In addition, urinary levels of FA doubled only following consumption of whole grains. Whole grain consumption also caused a reduction in plasma levels of tumour necrosis factor α and an increase in interleukin-10 compared to refined grain consumption. The authors also reported that whole grain consumption altered gut bacteria levels, with bacteroidetes and Firmicutes increasing in number, and this increase was associated with faecal ferulic acid levels. Whole grains antioxidant may therefore favourably alter certain metabolic parameters.
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