Refined crystalline sugar induces insulin resistance in mammals. Rat experiments have shown that feeding fructose at high intakes causes insulin resistance in just a few short weeks (here, here and here). Fructose can induce insulin resistance because it increases flux through the de novo lipogenesis pathway, and this increases the production of fatty acids from non-fat sources, particularly carbohydrates. However, it is not clear if the fructose acts as a substrate or is meanly able to increase flux through the pathway for other substrates. Either way, the resultant fatty acids can accumulate in the liver, or alternatively are exported to skeletal muscle as triglycerides on the very low density lipoprotein (VLDL) particle, where they are released as fatty acids by lipoprotein lipase. The accumulation of fatty acids in skeletal muscle and liver tissue increases the accumulation of intracellular lipids and this is thought to lead to interference with the insulin signal cascade, which ultimately reduces the sensitivity of the signal.
Epidemiological studies have demonstrated that coffee consumption is inversely associated with obesity and type 2 diabetes. It has been suggested that the caffeine content of the coffee may explain the beneficial metabolic effects, but decaffeinated coffee also shows the same association. Therefore other components of the coffee may be responsible for the beneficial effects. Antioxidant polyphenols improve insulin sensitivity in humans, and a number of polyphenols are present in coffee. The possibility arises therefore that it is the polyphenol within coffee that are responsible for the protective effects against obesity and type 2 diabetes, because of the antioxidant protection they confer. Evidence for this line of reasoning comes from data showing that coffee may reduce the intracellular accumulation of lipids and that coffee drinking is associated with a lower risk of developing non-alcoholic fatty liver disease (NAFLD). However, to date most of the research in this area has come from animal studies using mice.
Chlorogenic acid is polyphenolic compound found in coffee that is bioavailable in humans and may possess antioxidant properties. Studies on animals show that chlorogenic acid has protective effects against insulin resistance. Human studies confirm the beneficial effects of chlorogenic acid on glucose homeostasis. For example in one study1, researchers fed healthy subjects a high fructose diet (4 grams per kg of body weight per day) to induce hepatic fatty acid production. In response to the fructose the subjects experienced a 16 % increase in hepatic glucose production. These changes were indicative of a reduction in the insulin sensitivity of the subjects. However, caffeinated coffee high in chlorogenic acid, decaffeinated coffee high in chlorogenic acid, or decaffeinated coffee with regular amounts of chlorogenic acid all decreased hepatic glucose production, suggesting that insulin sensitivity had been improved. However the coffee treatments were not able to prevent the intrahepatocellular accumulation of fats.
Dr Robert Barrington’s Nutritional Recommendation: In this study the reduction in the hepatic glucose production was indicative of a reversal of hepatic insulin resistance. That caffeine was not required for this effect suggests that other components of the coffee were responsible. Evidence from other studies suggest that the chlorogenic acid may possess insulin sensitising effects. That both the high and normal chlorogenic acid coffee were beneficial might suggest that moderate intakes of coffee may have beneficial effects at protecting from insulin resistance. The lack of an effect on intrahepatocellular lipids may be indicative of the short-term nature of the study. Had the subjects been observed for longer, the beneficial effects on the liver may have become more apparent. Drinking fresh filter coffee is a healthy endeavor and numerous studies attest to the health benefits of drinking coffee. Regular coffee drinkers should therefore be encouraged to continue a moderate intake of this antioxidant rich beverage.
RdB
