Refined carbohydrates are associated with the development of insulin resistance which is a primary cause of metabolic syndrome. Development of the metabolic syndrome exposes an individual to a raft of diseases including type 2 diabetes and cardiovascular disease. Refined carbohydrates may be detrimental to glucose metabolism because they lack fibre which increases the rate of digestion and absorption of the glucose and results in increased glycaemic load. While this the most often considered line of reasoning when investigating insulin resistance, confounding variables exist which may call into question the significance of the role of fibre. High glycaemic index carbohydrates are associated with metabolic syndrome, and such carbohydrates have low amounts of fibre, but they also have low levels of micronutrients. One micronutrient in particular, chromium, is integral to the functioning of the insulin receptor, and deficiency may therefore play a role in development of insulin resistance.
Chromium deficiency is implicated in the development of diabetes in humans and animals. Feeding animals chromium deficient diets causes blood sugar and lipid abnormalities that resemble type 2 diabetes. Reintroduction of chromium to the diet of such animals reverses the diabetes-like symptoms and returns the animals to health. In humans, feeding patients parentally with inadequate chromium causes the same blood sugar and lipid abnormalities seen in animal models, and like animals, chromium supplements are able to reverse the condition. Chromium causes blood sugar and lipid abnormalities because it is required for the correct function of the insulin receptor. Dietary chromium forms an organic complex in animals known as the glucose tolerance factor (GTF), which activates the insulin receptor and therefore potentiates its action. Chromium intakes are generally low because the typical Western diet is devoid of chromium rich foods.
Increasing chromium intake may therefore be beneficial to preventing some blood sugar and lipid disorders. But can chromium effectively reverse type 2 diabetes in humans? Early research using brewer’s yeast as a source of chromium showed some benefits to those with type 2 diabetes. For example, one group of researchers1 used a double-blind randomised cross-over trial to assess the effects of brewer’s yeast, a chromium trichloride supplement and a placebo on the blood sugar and lipid metabolism of 43 men with type 2 diabetes. After 4 months of brewer’s yeast supplementation, the fasting plasma immunoreactive insulin levels of a sub-group of ketosis-resistant men was significantly enhanced in 9 out of 10 subjects following a meal. However, no other beneficial effects were seen for chromium in the diabetic patients. and no improvements were seen in plasma glucose or insulin for the majority of the patients.
These types of results are not unusual in that the benefits of brewer’s yeast and chromium supplements are equivocal when treating diabetic patients. Many other studies using brewer’s yeast have reported similar findings. However, analysis of the hair and red blood cell samples of the diabetic men showed that chromium pools were increased following both the organic (brewer’s yeast) and inorganic (chromium chloride) supplements of chromium. This rise was typically around 30 % for the hair and around 25 % for the red blood cell samples, but varied between sub-groups within the study. Brewer’s yeast was therefore able to improve the chromium status of the subjects but was not able to reverse the diabetic symptoms. From this it can be concluded that brewer’s yeast is a good source of chromium and can raise chromium pools in humans, but for some reason does not effectively reverse diabetic symptoms.
So while brewer’s yeast and other chromium supplements showed inconsistent results in early studies, it cannot be denied that some beneficial effects were observed. One reason that chromium might not produce clear benefits in type 2 diabetes may related to the fact that a clear chromium deficiency is not present in such individuals. For example, research published in 19872 in the American Journal of Clinical Nutrition assessed the mineral status of subjects with type 1 and type 2 diabetes. The results showed that neither type 1 nor type 2 diabetics had a deficiency of chromium (figure 1). Type 2 diabetes therefore does not appear to be a simple dietary chromium deficiency as supplements do not reverse its symptoms and tissue stores are not depleted. Interestingly, diabetic patients were deficient in zinc, which is required for insulin release from the β-cells of the pancreas. 
Figure 1. The mineral status of patients with type 1 and type 2 diabetes2.
However, more recently the role of chromium in insulin resistance, type 2 diabetes and gestational diabetes has been reappraised, and a role for chromium in the treatment of blood sugar disorders has been more firmly established. So why then did early studies fail to unequivocally establish brewer’s yeast and chromium as beneficial in the treatment of blood sugar disorders? Recent findings suggest that the requirement for chromium is related to the degree of insulin resistance. A large intake of chromium, around ~200 µg/d, is able to improve insulin resistance in those with mild symptoms, in the early stages of metabolic syndrome. However, those with more severe insulin resistance as found in fully developed metabolic syndrome or type 2 diabetes may require much higher concentrations. Therefore the earlier brewer’s yeast studies may simply have not provided enough chromium to produce benefits.
However, Brewer’s yeast remains a viable source of chromium for those wishing to maintain their chromium pool. While most foods are low in chromium, brewer’s yeast is known for its high content of chromium bound organically as its GTF form. The typical nutritional contents of brewer’s yeast is shown in figure 2. Even though brewer’s yeast has fallen out of favour with the nutritional science in recent years, it is still widely available and an excellent sources of micronutrients. Brewer’s yeast contains around 10 µg per 8.35g serving of chromium in its organically bound forms, and about 25 % of this chromium is absorbed. So while brewer’s yeast might not contain enough chromium to reverse sever cases of insulin resistance seen in type 2 diabetes, it should contain enough to prevent deterioration in those already healthy individuals who might have mild insulin resistance. 
Figure 2. A typical nutritional profile for brewer’s yeast1.
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