Writing in the Springer Nature publication Cureus, researchers from California Northstate University College of Medicine evaluated the existing science on spinach extract, physical performance and body composition, in addition to assessing its safety profile as supplement.

“Spinach extract exhibits promising physical performance advancements and is a safe ergogenic aid,” they reported. “These benefits are primarily ascribed to enhanced nitrate (NO3-) bioavailability, which age, dietary patterns and athletic history can influence.”

Spinach for sport

The benefits attributed to spinach extract’s NO3- content and are explained by its conversion into nitric oxide (NO-) in the body through a multi-step process. NO- is a key regulatory molecule that functions across systems as vasodilator, anticoagulant, skeletal muscle modulator, antioxidant and insulin modulator.

“NO3- has become a popular supplement for sports, given its potential to increase health and physical performance,” the researchers wrote. “However, the literature shows mixed results, with some studies showing improved cardiovascular endurance via increased time-to-exhaustion and improved aerobic performance at varying distances. It also decreases the oxygen cost of submaximal intensity exercises in inactive and recreational men and women.”

While beetroot juice has become the most established source of dietary NO3- and is one of the supplements recognized by the International Olympic Committee as sports food, the review noted that there are many other sources of dietary NO3-, notably leafy greens such as spinach, Chinese flat cabbage and arugula.

“However, spinach extract (red/amaranth and green/spinacia) contains a rich amount of NO3- and several other bioactive compounds such as carotenoids, calcium, antioxidants and polyphenols that may offer additional benefits,” the researchers added. “Green spinach also contains a high ecdysteroid content, demonstrating anabolic strength and muscle mass benefits.”

Considering the data

The review carried out a systematic search of PubMed, Embase and Cochrane Library for English-language randomized controlled trials (RCTs) reporting on physical performance parameters after spinach extract supplementation in populations of all ages.

Of the 409 initial studies returned for screening, three studies investigating red spinach and one with green spinach remained, providing a total of 94 participants (45.7% male, 54.3% female) between the ages of 20 and 59. Follow-up time ranged from seven to 84 days and dosages from 1 g to 2 g of spinach extract.

The selected studies evaluated effects on cycle time in recreationally active men and women, resistance-trained men, male collegiate baseball athletes and skeletal muscle fitness in adults over the age of 50. There were no common performance parameters among the trials.

“The main findings in this study were that [spinach extract] demonstrated significant improvements in physical performance parameters across most measured outcomes, mixed results on body composition and no complications noted,” the researchers reported. “These results suggest that spinach extract supplementation has practical ergogenic usability.”

They suggested that future research prioritize standardizing baseline patient demographics and investigate optimal dosing and timing of supplementation, effects in different populations and impact on short-term and long-term physical performance.

Source: Cureus. doi: 10.7759/cureus.77840. “Effect of Spinach Extract on Physical Performance: A Systematic Review of Randomized Controlled Trials. Authors: Jimmy Wen et al.