Herbs are the traditional treatment for many diseases. In many cases, the historical and contemporary writings of herbalists have been verified by peer review science. Of the herbs that have shown beneficial effect on human health, the allium family of plants is perhaps one of the most well studied. The physiological effects of garlic and onions have been particularly thoroughly reported, but beneficial effects have been found for other members including scallions, shallots, chives and leeks. In humans and other animals, allium vegetables have antioxidant effects as well as blood pressure, blood lipid and blood sugar lowering effects. They are therefore highly beneficial as a treatment for the metabolic syndrome. Other effects of allium vegetables include antithrombotic, anticarcinogenic, antimicrobial and antihelminthic effects. Allium vegetables are therefore suitable for the treatment of a wide variety of maladies, with the benefit of producing no serious side effects in those who consume them.
The ability of allium vegetables to lower blood glucose levels is well reported. For example, in one study1 researchers assessed the impact of water soluble extracts of shallots (Allium ascalonicum) and garlic (Allium sativum) on the fasting blood sugar levels and insulin sensitivity of rats. The rats were fed high fructose diets that consisted of fructose added to their drinking water. Control rats were fed normal rat chow with no added fructose. The fructose induced insulin resistance in the rats and caused a significant increase in their blood sugar levels within a few weeks. The rats were then fed 500 mg per kg body weight of either shallot or garlic extract for eight weeks. The supplements of allium vegetables significantly lowered the blood glucose levels of the rats and this likely resulted from the improvement in insulin sensitivity that were also observed. The data showed that of the two allium vegetables consumed by the rats the shallot extract was more effective at improving the blood glucose control.
While these results are relevant to rats, evidence in the literature shows that allium vegetables also have blood glucose modulating effects in humans, with garlic being the most widely reported. However, the chemistry of the allium vegetables is incredibly complex, and the main physiological effects are thought to derive from a group of sulphurous chemicals that are produced upon cutting or crushing (here). In this process, parent compounds such as allicin are enzymatically converted to a group of highly diverse sulphurous compounds, many of which exist only transiently. Because of the complexity of the chemicals produced from crushed allium vegetables, the main active ingredients that produce physiological effects in animals have not been fully identified. In addition to the sulphurous compounds, allium vegetables also contain a range of flavonoids, most notably quercetin. Red varieties of allium vegetables also contain anthocyanins, a group of flavonoids responsible for purple, red and blue colours in plants.
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