Adiponectin is a cytokine released from adipose tissue and its circulating levels are inversely associated with the body fat mass of the individual. Adiponectin acts via the adenosine monophosphate-activated protein kinase (AMPK) secondary messenger systems to convert the acetyl-Co A carboxylase enzyme to its inactive form, thus decreasing fatty acid synthesis. The subsequent decrease in malonyl-CoA levels remove the inhibition on the carnitine shuttle enzyme palmitoyl transferase, which increases transport and oxidation of fatty acids into the mitochondria. It is not known what controls levels of adiponectin and the biochemical mechanisms of action are not fully understood, however, it is speculated that various foods may inhibit or stimulate the release of adiponectin from adipocytes. Dietary fibre is known to decrease the risk of developing obesity, diabetes and cardiovascular disease and so its possible links to adiponectin plasma levels are intriguing.
Fibre is composed of a large group of plant derived carbohydrates that are not digestible by human enzymes. Their beneficial effects appear to be multifacorial but increases in gut transit time, blood lipid altering properties and conversion to short chain fatty acids in the colon by bacterial degradation are well researched mechanisms of actions. Research published in the American Journal of Clinical Nutrition in 20031 investigated the effects of a high fat, a high carbohydrate, and a high carbohydrate high fibre meal on circulating levels of cytokines in diabetic and non-diabetic subjects. Consumption of the high fat meal reduced adiponectin levels in all subjects, but only the diabetic subject had reduced levels of adiponectin with the high carbohydrate meals. Interestingly, adiponectin did not significantly change after consumption of the high carbohydrate-high fibre meal.
In this study, the diabetic subjects had lower levels of adiponectin compared to matched non-diabetic subjects at baseline even though the subjects were matched for body fat. The stable adiponectin levels on consumption of the high fibre meal suggest that another possible mechanism by which fibre may protect from obesity and diabetes. Interestingly the high fat meal was the most detrimental both in terms of the degree of reduction of adiponectin and because the effect was evident in both diabetic and non-diabetic individuals. However, the high fat meal contained the lowest levels of fibre of all of the meal (just 2.8 grams compared to 4.5 grams in the high carbohydrate meal and 16.8 in the high carbohydrate high fibre meal). High fat and high carbohydrate meals not accompanied by reasonable levels of fibre appear therefore to inhibit fatty acid oxidation by reduction in adiponectin levels.
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