Soluble and insoluble fractions from nopal (Opuntia ficus) cladodes improve postprandial glycaemic regulation: a crossover randomized study in healthy volunteers

Abstract: Background and objectives: Type 2 diabetes has been increasing all over the world. A healthy diet, including particular functional foods is an effective strategy to prevent this form of diabetes. Nopal (Oputia ficus) is a cactus plant that, according to traditional medicine, has antidiabetic properties. The objective of this research was to examine the effects of different fractions of nopal cladodes on postprandial glycaemic regulation in healthy volunteers. Methods: Nopal cladodes flour was separated by centrifugation into two fractions (a water insoluble and a soluble fraction). The fractions were incorporated into two different test breads, i.e. insoluble fraction bread (INB) and soluble fraction bread (SNB), and evaluated with respect to acute glycaemic properties in 17 healthy subjects with normal body mass index, applying a randomized cross-over study design. The effects on glycaemic and insulinaemic responses were compared with the responses after a control product, which composed of a similar bread lacking the nopal fractions (white wheat bread, WWB). The products were characterized with respect to starch and dietary fibre content. In addition, starch hydrolysis index (HI) was determined with an in-vitro method in order to predict glycaemic index (pGI),and elucidate possibly underlying mechanisms on postprandial glycaemia. Results: Results regarding glycaemic regulation show that insoluble nopal fractions had a beneficial effect on postprandial glucose regulation. Consequently, the incremental area under the postprandial blood glucose curve (iAUC) after INB was significantly reduced compared to after intake of the WWB during the time periods 0 – 45 and 0 – 60 minutes (p < 0.05). In addition, the iPeak value, i.e. the individual highest incremental peak concentrations, was significantly lowered after INB compared to WWB (P < 0.05). Regarding the postprandial insulin secretion, both SNB and INB lowered the postprandial iAUC compared to the WWB during the time period 0 – 45 and 0 – 60 minutes (P < 0.05). On the other hand, only the INB significantly reduced the insulin iPeak value compared to WWB (P < 0.05). In terms of HI, INB had lower HI and pGI compared to WWB and SNB. Also, INB exhibited highest total, soluble and insoluble dietary fibre contents. Conclusion: The INB promoted lower postprandial glucose and insulin response, while SNB showed beneficial effects only on postprandial insulin secretion. The beneficial effects of nopal on glycaemic regulation might be to some extent explained by the dietary fibre content, especially the INB. However, with respect to the improved postprandial insulin economy observed after the SNB, additional mechanisms are probably involved.