Compared to a placebo control, participants who ingested blackcurrant extract had a significantly lower post-exercise heart rate than those who had consumed the placebo despite no overall difference in the distance rowed.
In addition, participants who ingested the extract exhibited a decrease of some markers of oxidative stress compared to the placebo.
These were the results reported from two trials by researchers at the New Zealand Institute for Plant and Food Research, a New Zealand government-owned research company. For the first trial, they investigated the time- and dose-dependent bioavailability of blackcurrant extract in 36 individuals. In the second, they investigated the effects of supplementation using New Zealand-grown, anthocyanin-rich blackcurrant extract on the oxidative stress and neutrophil function of 32 individuals after a 30-minute rowing exercise.
Because of its small sample size, the researchers characterized their study as a pilot. “This study provides data to underpin a larger study designed to evaluate the efficacy of timed blackcurrant extract consumption on post-exercise recovery and innate immunity,” they wrote in the paper, published last week in the journal Frontiers in Nutrition.
They found that consumption of the extract caused a time- and dose-dependent increase of plasma anthocyanins, which means that the anthocyanin content found in the study participants’ blood was varied according to how long-ago supplementation occurred and how much of the extract per body weight was ingested.
By two hours after exercising, consumption of 1.6 mg/kg blackcurrant extract prior to exercise caused a significant 34 and 32% decrease in some markers of oxidative stress—post-exercise plasma oxidative capacity and protein carbonyl levels, respectively, compared to placebo.
Can antioxidants actually help with recovery?
Whether antioxidant supplementation can aid in post-workout recovery is still up in the air, the researchers argued.
“It is still debatable whether or not consuming foods that exhibit powerful inherent antioxidant properties actually results in increased human plasma antioxidant capacity that is capable of attenuating oxidative stress resulting from exercise,” they wrote.
In a 2016 study published in The Journal of Physiology, for example, researchers from the Energy Metabolism Laboratory at the Swiss Federal Institute of Technology posited that antioxidant supplements interfere with skeletal muscle adaptation to exercise training.
However, in the present study, “we found that the consumption of the [blackcurrant extract] had no impact on overall plasma antioxidant capacity prior to, or during recovery from, a 30-minute rowing,” the New Zealand researchers reported.
“Our preliminary findings are supported by [previous studies, which] demonstrated that the ingestion of a fruit drink enriched in polyphenolics 15 min prior to a 90-minute cycle had no effect on overall plasma antioxidant status despite mediating a significant decrease in post-exercise plasma protein carbonyls.”
These results indicate that the facilitated recovery from exercise-induced oxidative stress is unlikely to be due to the inherent antioxidant properties of the ingested anthocyanin extract. Instead, they posited that the extract may activate cellular redox-sensitive mechanisms that up-regulate antioxidant systems to increase antioxidant capacity.
The first trial, investigating time- and dose-dependent bioavailability, was non-blinded, meaning both participants and investigators knew what the intervention product (in this case blackcurrant extract) was.
Six female and six male participants donated blood samples before consuming two opaque gelatin capsules containing the extract. All participants conducted the trial at the same time of day, and had eaten the same breakfast (a One-Square Meal cereal bar and water). After supplementation, further blood samples were taken at half an hour, one hour, two hours, and six hours after ingestion.
To examine dose-dependence, a different set of 24 participants were randomly assigned to four groups with six in each—placebo group, or one of the different doses of blackcurrant extract groups (0.8, 1.6, or 3.2 mg/kg of weight). Anthocyanins were measured the same way as the previous portion.
The second trial applied knowledge from the first to a set of 32 physically active individuals. It was double-blinded, meaning neither participants nor investigators knew if an individual ingested the placebo or extract.
Blood samples were taken at the beginning. Afterwards, the participants ingested 1-2 gelatin capsules with water. Then, participants conducted a 30-minute exercise on a row machine. Blood samples were collected at two and six hours after the workout.
Funding for the study was provided by a grant from the New Zealand Ministry for Business Innovation and Employment specifically for ‘New Healthy and Flavorsome Berries and Products,’ as the grant program is called. The authors declared that there are no royalty agreements associated with sales of New Zealand blackcurrant products.
Source: Frontiers in Nutrition – Sports and Exercise Nutrition
Published online 29 May 2019, https://doi.org/10.3389/fnut.2019.00073
“Consumption of an Anthocyanin-Rich Extract Made From New Zealand Blackcurrants Prior to Exercise May Assist Recovery From Oxidative Stress and Maintains Circulating Neutrophil Function: A Pilot Study”
Authors: Roger D. Hurst, et al.