Kiwifruit and Metabolic Health
Dr. John Monro
The New Zealand Institute for Plant & Food Research, New Zealand
A ripe kiwifruit is a luscious, sweet, carbohydrate-rich food – the kind of food that would be expected to raise blood glucose concentrations. However, kiwifruit is also nutrient dense and capable of promoting health in numerous ways.
We therefore faced two questions:
- What is the true glycaemic potency of whole kiwifruit – the capacity of the whole fruit to raise blood glucose?
- What effect does the interaction of kiwifruit with other components of a meal have on the meal’s glycaemic impact?
We addressed these questions in a research sequence involving in vitro and human intervention studies, and found:
(a) The non-digested dietary fibre remnants from kiwifruit that had been digested in vitro occupied about four times their original volume in the intact fruit. They would therefore surrounded and extensively interact with other foods in the limited volume of the gut.
(b) Within the dispersion of pre-digested kiwifruit remnants several processes important to the glycaemic response were substantially retarded in vitro, including:
- sugar diffusion
- mixing of intestinal contents
(c) In a human intervention study we found the glycaemic impact of kiwifruit to be relatively low; 100 g of kiwifruit would have about the same effect on blood glucose as only 6 g of glucose.
(d) The low in vivo glycaemic impact could be partly attributed to the carbohydrate in kiwifruit being fruit sugars, but the kiwifruit also caused changes in the blood glucose response curve that indicated improved homeostatic blood glucose control due to factors other than sugar, consistent with effects of kiwifruit remnants on intestinal processes indicated by the in vitro studies above (in c).
(e) Analysis of the effects of equal carbohydrate, partial substitution of kiwifruit for highly glycaemic foods – such as those based on cereal starch – showed it is an effective strategy for improving intake of nutrients such as vitamin C, with the added benefit of reducing glycaemic impact.
(f) The glycaemic benefit was greatest when kiwifruit were consumed about 30 mins before a cereal food meal, substantially lowering both the amplitude of the response (the “spike”) compared with consuming the two foods together, while inducing a lower total response (area under the curve) compared with an equal carbohydrate amount of the non-substituted food.
The study concluded that equal carbohydrate (isoenergetic) inclusion of kiwifruit in the diet by partial substitution of cereal starch-based staples, such as potatoes and rice, is an effective dietary strategy to simultaneously reduce exposure to glycaemia while improving nutrient profile of the diet.
View presentation about Glycaemic Control and Nutrient Enhancement by Dr John Monro from Kiwifruit Symposium