From the archives: Red kiwifruit have finally hit our supermarkets, but are they any better than your average green and golds? Jennifer Bowden investigates the classic autumn fruit.
Question: l eat at least two kiwifruit a day and prefer the gold variety to the green. I know the gold has more vitamin C than the green, but is there any information on the new red kiwifruit for comparison?
Answer: Red kiwifruit have a higher concentration of vitamin C than the gold variety, which has double the amount of the green, according to data supplied to the Listener by kiwifruit marketing company Zespri. Vitamin C is necessary for growing, developing and repairing body tissue, proper functioning of the immune system, and wound healing. A deficiency can result in adverse moods and cognitive effects, a recent review found. Low vitamin C levels are also linked to depression. Yet one kiwifruit a day can maintain your total vitamin C needs.
University of Otago researchers recently published a Zespri-funded study investigating the effects on vitality in adults with low vitamin C levels of consuming either a vitamin supplement or two gold kiwifruit a day. They found that eating the golden fruit improved “subjective vitality” in adults with low vitamin C levels. Although the supplements resulted in similar improvements, the changes reported from eating kiwifruit suggest other factors in the fruit may contribute to “improved vitality”. Red kiwifruit contain polyphenols such as anthocyanins, which are coloured water-soluble pigments. These polyphenols add to the fruit’s antioxidant capacity, along with the vitamin C content.
Red kiwifruit contain similar levels of potassium, but have more than double the folate of the green and gold varieties. The red variety has a slightly higher glycemic index (GD) rating than the green and gold, but it is still classified as a low-GI fruit. The glycemic index is a measure of how different carbohydrate-containing foods affect blood- glucose levels; this information is vital for people with diabetes, who need to control their blood sugar. Kiwifruit are also fantastic for gut health. Numerous studies have shown that they help with the digestion of protein and improve bowel function. For starters, the green variety contains 3g of fibre per 100g of flesh.
Kiwifruit fibre has a mixture of insoluble and soluble fibres with unique properties that help with digestion by bulking up stools, retaining more water and creating a larger, softer stool that moves more quickly through the gut. Clinical trials have shown that green kiwifruit significantly improve digestive health, increasing frequency of bowel movements and reducing bowel transit times in healthy adults, older adults and people with constipation, including constipation caused by irritable bowel syndrome.
A recent US clinical trial found green kiwifruit were as effective as prunes and psyllium in treating chronic constipation. Furthermore, kiwifruit had the lowest rate of adverse effects in the trial and the lowest level of patient dissatisfaction. Green kiwifruit also contain actinidin, a natural enzyme that breaks down food proteins faster than our digestive enzymes, which helps with digestion. A study published recently in the European Journal of Nutrition noted that the Hayward green kiwifruit variety could facilitate protein digestion from a beef. So, whether you prefer the green, the gold or the red, you’re undoubtedly getting a significant nutrient boost.
This story was originally published in the March 27-April 2, 2021 issue of the New Zealand Listener.
