Reference
Bellafiore M, Pintaudi AM, Thomas E, et al. Redox and autonomic responses to acute exercise-post recovery following Opuntia ficus-indica juice intake in physically active women. J Int Soc Sports Nutr. 2021;18(1):43.
Design
A randomized, double-blind, placebo-controlled crossover study that investigated whether the juice of Opuntia ficus-indica (OFI) might affect plasma redox balance and heart rate variability (HRV) parameters following a maximal effort test in young women.
Participants
Eight women completed the study out of an initial 10 recruited. Following are the characteristics of those who completed the study:
- Age: 23.25 ± 2.95 years
- Weight: 54.13 ± 9.05 kg
- Height: 157.75 ± 0.66 cm
- Body mass index (BMI): 21.69 ± 0.66 kg/m2.
During their first assessment, all the participants were in the luteal phase of their menstrual cycle (corresponding to the lowest physiological reactive oxygen species [ROS] production levels in women). All participants exercised regularly with resistance training 3 to 4 times per week. Two of the 10 subjects who began the study did not complete it and so were excluded from the final analysis.
Study Medication and Dosage
The participants were divided into 2 groups, designated as OFI and placebo. The OFI group received 50 mL (about 1.5 oz) of concentrated commercially manufactured juice made from peeled fresh fruits of Sicilian Opuntia ficus-indica (NopalRed), which was diluted with water to 170 mL. The placebo group received 170 mL of a similar-tasting beverage that did not contain O. ficus-indica juice. Investigators instructed participants to consume their assigned juices along with breakfast daily for the 3 days before their maximal effort test and then continue to take it for 2 more consecutive days until after completion of a second testing procedure. The participants were subjected to a graded exercise test on a cycle ergometer until exhaustion. Each participant cycled for 4 min at a constant work rate of 50 W, and then the cycle ergometer work rate increased by 25 W/min until the participant reached her tolerance limit. The pedal rate was maintained at 60 revolutions per minute (rpm) throughout the test.
Outcome Measures
One week before the participants started the supplementation, investigators tested all participants to determine baseline measurements. They collected each variable of interest at specific time points during the trial period: 1) baseline, 2) pre-effort test, 3) posteffort test, 4) 24 hours after the end of the effort test, and 5) 48 hours after the end of the effort test.
Investigators collected plasma hydroperoxides concentration, antioxidant capacity, skin carotenoid score, and heart rate variability at baseline, day 3 (pretest and posttest), day 4 (24 hours posttest), and day 5 (48 hours posttest) of each period. There were 2 test periods separated by a 15-day washout period, and groups switched from placebo to OFI or the reverse.
Participants performed all tests between 8 a.m. and 10 a.m., after a 12-hour overnight fast. Investigators measured stature and body mass at baseline. They recorded oxygen uptake (VO2) with a breath-by-breath measurement system and defined maximal oxygen uptake (VO2 max) as the highest consecutive 30-second averaged value achieved during the test. A short-range radio telemetry system recorded heart rate. Investigators monitored heart rate and VO2 throughout exercise, recovery time, and rest. They stopped the test when either VO2 max plateaued <2.2 mL/Kg/min or participants were unable to maintain the required work rate.
Investigators collected HRV parameters at baseline, immediately after the maximal graded test, and 24 hours and 48 hours after the end of maximal effort test.
Key Findings
The data show reduced production of hydroperoxides and increased antioxidant capacity in the OFI juice–supplemented group compared to the placebo before the exercise test and also at 48 hours after the end of the test. Plasma antioxidant testing (PAT) values of the OFI group significantly increased compared to those of the placebo group pretest and 48 hours posttest. Skin carotenoid score (SCS) did not differ between groups. Low-frequency (LF) heart rate variability was significantly lower in the OFI group 24 hours after the end of the test, whereas root mean square of successive differences (RMSSD) was significantly higher in the OFI group 48 hours posttest (P=0.0117), suggesting better autonomic recovery from exercise.
Lower hydroperoxide concentrations were observed in the OFI group compared to the placebo group in all the examined conditions. In detail, the OFI group showed a significant decrease pretest (P=0.0013), posttest (P=0.0030), and at 48 hours posttest (P=0.0230) compared with the corresponding conditions of the placebo group. Baseline hydroperoxide concentrations did not differ significantly between placebo and OFI groups in pre- and posttest conditions (P>0.05).
Practice Implications
This study brings another potential therapeutic food to our kitchens, one that many of us are unfamiliar with. Opuntia species are tropical or subtropical cacti that grow in arid areas of Mexico, Latin America, Africa, and Mediterranean countries. These cacti have been widely used as food and as a source of botanical medicines in these regions. Both the fruit and leaves can be converted into many types of edible products. This study used juice made from the fruits, though others have used flour made from the leaves.1 Opuntia ficus-indica, the specified plant used in this trial, is a domesticated variety of opuntia grown as a crop, but wild species of opuntia are also eaten. The fruit itself goes by various names including prickly pear, cactus pear, nopal fruit, tuna, sabra, Barbary fig, and Indian fig. The fruit ranges in color. Even among Opuntia ficus-indica, the fruit can be white, green, purple, yellow, red, or even orange.2
The opuntia are of interest because they contain high levels of bioactive phytochemical compounds — in particular, betalains.3 Systematic reviews have reported that supplementation with these cactus species may affect obesity, type-2 diabetes mellitus,4 and cardiovascular risk factors such as body weight and composition, serum triglycerides, cholesterol, blood glucose, and blood pressure. A 2020 systematic review examining effects on vascular health and endothelial function describes a potential increase in vasodilation and serum nitric oxide and a reduction in vascular stiffness and blood pressure. A number of human studies showed a reduction in heart rate as well as an increase in heart rate variability. Although these findings appear to indicate improvement in vascular health, randomized human intervention studies to identify mechanisms are lacking.5
The fruit itself goes by various names including prickly pear, cactus pear, nopal fruit, tuna, sabra, Barbary fig, and Indian fig.
There is general consensus that exercise exerts a beneficial effect on health and wellbeing. It is in the details related to exercise duration and intensity where exercise advice gets tricky. Exercise induces production of reactive oxygen species (ROS). Moderate exercise generates ROS that, in turn, induce an adaptive response to exercise training; this adaptive response is responsible for functional improvements that result. Yet too much exercise or exercise at too high of an intensity may result in an overproduction of ROS.6 Such ROS overproduction can cause havoc, upsetting the cell redox balance and activating redox-dependent transcription factors that induce formation of inflammatory proteins, leading to inflammation and further enhancing ROS formation.7
Moderate-intensity exercise, on the other hand, appears to prevent oxidative stress. Time and rest, though, are not always enough to restore redox balance after more intensive workouts.8 Healthy food choices and nutritional supplements can play a useful role in moderating the oxidative stress triggered by too much or too intense exercise.9 Juice and other food products derived from OPI are getting attention because they have notable antioxidant action and decrease inflammatory markers and oxidative damage.10 OPI juice, as the results of the present study evidence, appears to be particularly good at this. These results suggest that the OPI juice can counteract the oxidative stress induced in a single bout of maximal exercise. Other studies have shown similar benefits from this juice at modulating redox balance after a range of different exercise types, including an intermittent yo-yo maximal aerobic test11 and after a maximal anaerobic test.12
We should take note of the protocol used in this current study to achieve maximum protection postexercise and during recovery: Participants began dosing with the juice 3 days before the maximal exercise test. This might translate in clinical practice to suggesting that patients who are planning on a maximal exercise event—for example, running a marathon—mimic this strategy and begin drinking this juice 3 days prior.
We should also note that this study only used short-term intake. Apparently chronic supplementation with antioxidants may blunt the adaptive effect of exercise training, interfering with the endogenous antioxidant response to ROS, and so may have a detrimental impact on athletic performance and recovery.13 Antioxidants should be reserved for acute high-intensity exercise; using them this way appears to enhance exercise performance.14
Of course, we can think of several other foods with similar antioxidant effects that have been studied with exercise. Cherries, blueberries, pomegranates, and chocolate all may aid in muscle recovery after strenuous exercise.15-18 A meta-analysis published August 2021 suggests that any fruit or vegetable providing anthocyanins may offer similar protection.19 The advantage opuntia provides is that it can be grown in hot, dry parts of the world where these other food crops cannot be grown, offering a potential commercial opportunity to areas not usually considered hospitable to agriculture.
