The many nutritional benefits of kiwifruitby Jennifer Bowden
Fuzzy or golden, the kiwifruit is good for our blood sugar and digestion.
In the half-century since the chinese gooseberry was renamed kiwifruit to increase its appeal in the US export market, it has become strongly identified with New Zealand. Our horticultural industry has invested heavily in the Actinidia deliciosa (the fuzzy green one) and Actinidia chinensis (the golden newbie). But both cultivars are sugar-rich, and shoppers are becoming increasingly conscious of sugar content in food. So what does this mean for our furry export darling?
Kiwifruit are packed with nutrients. They are especially rich in vitamin C – each berry contains 80-90mg, more than our daily requirement – and have produced some noteworthy results in clinical trials: in one, four gold kiwifruit a day for four weeks significantly reduced the severity and duration of cold symptoms; in another, women with low iron stores who ate two gold fruit a day with an iron-fortified breakfast cereal had significantly better iron stores after 16 weeks than a group that had the same cereal with banana.
Combining kiwifruit with breakfast cereal may also improve our glycaemic (blood glucose) response, according to Plant & Food Research. Carbohydrates break down during digestion into sugars that are absorbed into the bloodstream. But if this process happens rapidly, it can cause spikes and troughs in blood sugar levels, which is not good, particularly for people with diabetes: a slow release of sugars into the bloodstream is preferable.
To investigate what effect kiwifruit have on glycaemic response, Plant & Food combined kiwifruit with Weet-Bix cereal in clinical trials. Participants were given four different Weetbix meals: with sugar; with kiwifruit; with guar gum and sugars; and with guar gum and kiwifruit.
The meals had identical quantities of carbohydrate and sugars (as glucose, fructose and sucrose), but the blood-glucose spike that occurred after eating the cereal was significantly reduced when kiwifruit was included. What’s more, the kiwifruit-eating group did not have the later dip in blood-glucose levels that occurred when the wheat biscuits were consumed with sugar.
So kiwifruit is sweet, but its sugars do not have the same glucose-spiking effect as the added sugars found in table sugar, honey or maple syrup.
This is not unexpected: the sugars in the cellular structure of fruit and vegetables will almost always be digested and absorbed more slowly than “free” sugars. But kiwifruit may have the edge on other fruits because of the way its fibre disperses as it disintegrates during digestion.
Using a simulated gut for testing, the Plant & Food Research scientists found that kiwifruit’s fibre distributed itself widely through the gut contents. This is likely to slow absorption of both the fruit sugars and sugars from an accompanying breakfast cereal – or other foods present in the gut. In contrast, although the sugars in a firm-fleshed fruit such as apple would be slowly absorbed, the fruit itself may be less effective than kiwifruit at slowing the absorption of other sugars.
The good news doesn’t end there: the fibre in kiwifruit may also improve bowel function. A recent trial by University of Otago researchers revealed that eating two green kiwifruit a day improved bowel-motion frequency by two a week and helped to reduce gastrointestinal discomfort in constipated people.
New Zealand has every right to feel a bit smug about the kiwifruit. It is tasty, nutritious and, because it is widely available from April to January, fresh and economical. Enjoy.
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