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The nutritional benefits of gold, green and red kiwifruit

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The familiar green and gold kiwifruit are nutritional powerhouses and a new red variety offers even more.

QUESTIONI’m a great believer in kiwifruit, both for vitamin C content and bowel regularity. Is the gold variety as nutritious as the green? And what about the new red strain?

ANSWER: The spectacular red kiwifruit made a dashing addition to Zespri’s kiwifruit range this season. The fruit, being developed by Plant & Food Research, is similar in taste to Zespri’s SunGold and is being trialled in some supermarkets.

All kiwifruit varieties are rich in vitamin, but SunGold, which has 161mg of the vitamin per 100g, has almost double that of the traditional Hayward green. Even that is nearly twice the 45mg recommended daily intake of vitamin C. Zespri hasn’t provided figures for the red variety, since it is still in development.

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Unlike the green and gold varieties, the red fruit contain an anthocyanin, a natural pigment responsible for their colour. Anthocyanins are a type of flavonoid, a class of compounds with health-giving antioxidant effects. They are also found in fruit such as cherries, grapes, blackcurrants and berries, as well as in red wine.

Kiwifruit are also rich in potassium, with one Hayward fruit providing about 220mg and a SunGold about 250mg. For a real potassium hit, however, a banana contains 400mg.

Kiwifruit also provide useful dietary fibre and many other nutritional and health benefits. The red variety has more fibre than the SunGold, but less than the green.

A 2018 review published in the European Journal of Nutrition highlighted kiwifruit as nutrient-dense and linked regular consumption to better nutritional status and digestive, immune and metabolic health.

The fruit also contain vitamin E, folate and a range of other antioxidants, phytonutrients and enzymes, all of which contribute to their nutritional goodness.

There is growing interest in the role kiwifruit may play in digestive health. In addition to fibre, the Hayward variety contains actinidin, a natural enzyme that breaks down a range of food proteins faster than our own digestive enzymes. Red kiwifruit also have moderate amounts of this activity.

The fruit have a mixture of insoluble and soluble – water-retaining – fibres, which help create a larger, softer stool that moves more quickly through the digestive system. A University of Otago clinical trial found that constipated people who ate two green kiwifruit a day had two more bowel motions a week and less gastrointestinal discomfort.

Another recent New Zealand clinical trial found that eating two SunGold kiwifruit daily for 12 weeks significantly raised plasma vitamin C levels in prediabetic study participants, and led to small improvements in several markers of metabolic and cardiovascular health. For instance, there were noticeable reductions in both diastolic (4mmHg) and systolic (6mmHg) blood pressure, as well as in waist circumference (3.1cm) and waist-to-hip ratio.

Previous clinical trials have also produced good results: four gold kiwifruit a day over four weeks significantly reduced the severity and duration of cold symptoms; and two gold kiwifruit a day with an iron-fortified breakfast cereal eaten by women with low iron levels resulted in better iron stores after 16 weeks compared with eating the same cereal with banana.

Green kiwifruit have also been shown to slow the absorption of sugars from an accompanying breakfast cereal, thereby reducing undesirable blood-sugar spikes.

Aside from being a nutritional powerhouse, kiwifruit are readily available almost year-round, being sold from April to January. Depending on the outcome of Zespri’s trial, increasing numbers of them may be red.

This article was first published in the June 8, 2019 issue of the New Zealand Listener.