The free radical theory of obesity suggests that nutrient overload in the cells of the body induces the production of free radicals. This occurs because the energy that floods the cells increases flux down the electron transport chain and this overwhelms the antioxidant defences of the cell. As the free radicals accumulate, protective mechanisms are enacted to reduce the influx of nutrients to the cell. This includes the down regulation of the insulin receptor, the main facilitator of glucose entry to the cell. This feedback mechanism protects the cell in the short term at the expense of the organism as a whole in the long term. Insulin resistance is an insidious condition that causes the slow deterioration of the metabolic regulatory pathways and ultimately ends in the development of a Western lifestyle disease. In particular, insulin resistance increases the risk of diabetes, obesity and cardiovascular disease. The ability of plants to provide antioxidants that bolster endogenous defences explains their insulin sensitising effects.
Cinnamon has particular insulin sensitising effects. The reason for the effectiveness of cinnamon at sensitising the insulin system in not fully known. However, cinnamon contains biologically active antioxidant chemicals that confer protective effects against oxidative stress in humans, and these antioxidant effects have been investigated in humans with impaired fasting blood glucose levels1. Overweight and obese subjects (body mass indices ranging from 25 to 45 km/m2) were administered either a 250 mg cinnamon water extract twice per day or a placebo for 12 weeks. The results of the study showed that the antioxidant capacity of the plasma of the subjects improved considerably during this time in the treatment group compared to the control group. In addition the cinnamon group also experienced a concomitant decrease in lipid peroxidation. The fall in the levels of lipid peroxidation was associated with improvements in the fasting plasma glucose levels of the subjects.
Current evidence supports the role for antioxidant nutrients from plants as insulin sensitising agents. Of the herbs tested, cinnamon has been reported to be particularly effective in this role. Obesity is associated with increased oxidative stress and the aetiology of obesity may in some way be caused by free radical damage. Based on the assumption that oxidative stress is a causative factor in insulin resistance, the ability of plant antioxidants such as cinnamon to reverse insulin resistance may therefore be through their free radical scavenging ability. Diets high in plant foods containing antioxidant nutrients are effective at preventing and reversing the oxidative stress and insulin resistance associated with obesity. Such diets also cause weight loss suggesting that one of the main problem with the Western diet is its ability to cause oxidative stress. Oxidative stress, may therefore directly cause insulin resistance and good evidence suggests that oxidative stress is the common cause of many Western lifestyle diseases.
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