The randomised, double-blind, cross-over study saw 25 overweight or obese boys aged 14–18 given 50 g of freeze-dried strawberry powder or a control powder every day for a week.
This was equivalent to 500 g of fresh-weight strawberries, or an estimated three servings.
Published in the British Journal of Nutrition, the results suggested strawberries could provide vascular health benefits in heavier teenage boys.
This California Strawberry Commission (CSC)-funded study is the first time the effects of a strawberry powder-based drink on cardiovascular health in overweight adolescents have been explored.
Nitrate notch up
Measuring markers of vascular health at baseline and one hour after drinking the strawberry mix, the researchers saw improvements in some of the participant's nitrite levels.
“As a group, fasting nitrate/nitrite levels did not significantly change after one week of control or FDSP [freeze-dried strawberry powder] intake.
“However, for those individuals where fasting nitrate levels increased after short-term FDSP intake compared with controls, an increase in reactive hyperaemia index (RHI) was observed, whereas RHI was unchanged in those individuals who did not have a significant increase in nitrate.”
The reactive hyperaemia index – measuring the blood flow to different tissues in the body – is used as a marker of endothelial function.
Supplementation with inorganic nitrate found in many vegetables and fruits has been associated with significant improvement in endothelial function, measured by flow-mediated dilation.
Dietary nitrate may serve as a source of the "potent vasodilator"– a blood vessel widener – nitric oxide.
“Strawberries contain high levels of nitrate when compared with other types of fruits, and this may be responsible, in part, for the favourable changes noted in vascular function in our study,” the researchers from the University of California in the US said.
They also said polyphenols found in strawberries may have helped.
Teenage angst
Yet one key limitation to the study remained.
The teenage participants said they had taken the drinks, but they were not required to give back their used packets for verification.
Future research should have more rigorous measures to make sure the participants took the full dose of the powder given to them, the researchers said.
Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114516002348
“Effects of a dietary strawberry powder on parameters of vascular health in adolescent males”
Authors: D. Djurica, R. R. Holt, J. Ren, A. W. Shindel, R. M. Hackman and C. L. Keen