Increasing consumption of calorically sweetened soft drinks has caused an increase in the consumption of fructose in the developed nations of the West. In addition, many foods are now sweetened with high fructose corn syrup and sucrose (table sugar) and this has also contributed to the increased consumption of fructose. The increase in the consumption of fructose mirrors the increase in the prevalence of obesity seen in these developed nations. A possible explanation for this is that fructose induced insulin resistance, as previously described, and the development of the insulin resistant state drives the metabolic changes that result in obesity. Feeding high fructose diets for as little time as 15 days has been observed to cause insulin resistance in animals, and feeding a little as 15 % of energy intake as fructose has been shown to reduce the binding capacity of insulin for its receptor in humans. Fructose is therefore implicated as a primary causative factor in the development of insulin resistance.
Cinnamon has been shown to improve insulin sensitivity and prevent the development of insulin resistance. This has been speculated to be due to either the mineral content of cinnamon, which includes the known insulin sensitising mineral, chromium, or because of the antioxidant polyphenols within the herb. The ability of cinnamon to prevent fructose induced insulin resistance has been demonstrated in rats. For example, in one study rats were fed either normal rat food or a diet of normal rat food containing 60 % of its energy as fructose, for three weeks1. Some of the rats fed the high fructose diet were also given cinnamon extract in their drinking water at a dose of 300 mg per day per kg body weight (equivalent to around 22.5 grams of cinnamon extract in a typical human). Fructose fed rats showed a 60 % decline in glucose disposal (as measured by disappearance of glucose from blood to cells under the influence of insulin) when compared to control rats, but cinnamon extract was able to reverse this decline.
Therefore cinnamon extract in physiologically relevant doses was able to reverse the detrimental effects of fructose on insulin sensitivity in rats. While rats are not humans, and care should always be taken to extrapolate such results, many studies have been performed on rats to show detrimental effects of fructose on insulin sensitivity. And these studies have also been repeated on humans. There is already therefore a large body of evidence to show the detrimental effects of high fructose diets on insulin sensitivity in rats and humans. Further, studies using cinnamon in humans have also shown insulin sensitising effects. The study authors noted that the phosphorylation rates for protein components of the insulin signal cascade were significantly lowered in fructose fed rats, but this was normalised with cinnamon feeding. As phosphorylation of proteins in one way that the insulin signal is transferred to the interior of the cell, disruption of this process by fructose may be pivotal in the development of insulin resistance.
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