Friday, May 27, 2011

One (not Two!) Kiwi(s) A Day Keeps Doctors Away! Golden Kiwi Boosts Vitamin C Status, Reduces Lipid Oxidation and DNA Damage.

Image 1: Golden and green Kiwi
fruits (image by Zespri)
In the pseudo-scientific camp of hardcore low-carbers fruit is getting a real bad rep, lately. Only a few weeks ago, Hunter et al. (Hunter. 2011) had published a review of the anti-oxidant potency of kiwi fruits, which puts into question, whether abstaining from fruit consumption altogether is necessary or even just beneficial for healthy, active human beings in the long run. A more recent study conducted by a group of scientists from various European countries (Brevik. 2011) does now provide experimental evidence that the good old saying "An Apple a day keeps the doctor away!" may be just as or even more applicable to kiwifruits in general and the particularly phytochemical rich golden variety Actinidia chinensis var. Hort 16A, in particular.

The scientists recruited 24 men and women (20-57 years, BMI 20-30 kg/m²), specifically selecting subjects who already consumed modest amounts of fruits and vegetables in their diet and excluding subjects, who used contraceptive pills, medicines or supplements, were on a diet aimed at weight correction, had diagnosed diabetes, cancer or cardiovascular disease, consume >30 units (15 glasses of wine) of alcohol/week, habitually or undertook >6h of vigorous exercise/week. All that half of  the subjects had to do was eat one additional golden Kiwi per day (in a second period the dosage was "escalated" ;-) to 2 kiwis). This turned out to be a dietary intervention with significant effects on antioxidant status, malondialdehyde levels and DNA damage in circulating lymphocytes:
Plasma vitamin C increased after supplementation as did resistance towards H2O2-induced DNA damage. Purine oxidation in lymphocyte DNA decreased significantly after one kiwifruit per day, pyrimidine oxidation decreased after two fruits per day. Neither DNA base excision nor nucleotide excision repair was influenced by kiwifruit consumption. Malondialdehyde was not affected, but plasma triglycerides decreased. Whole blood platelet aggregation was decreased by kiwifruit supplementation.

Before you run to your local fruit store and buy their whole stock of golden kiwi, I just want to mention that there was no clear dose-dependent effect (cf. figure 1) in this or previous studies done by the same or other researchers.
Figure 1: Effects of supplementation with one or two kiwis a day
on glucose, cholesterol and triglycerides (data adapted from Brevik. 2011)

In other words, eating an additional 100 kiwis a day, won't make you any healthier than eating one or two; and the additional fructose (over-)load may in fact turn against you, as the increases in blood glucose and the smaller decrease in triglycerides even with the consumption of only two kiwis shows (cf. figure 1). So, as "golden" and rich in phytochemicals Actinidia chinensis var. Hort 16A may be, as so often: moderation is key.