Abstract
Kefir is an acidic, carbonated, and fermented dairy product produced by fermenting milk with kefir grains. The Lactobacillus species constitutes an important part of kefir grains. In a previous animal study, kefir effectively improved exercise performance and had anti-fatigue effects. The purpose of this research was to explore the benefits of applying kefir to improve exercise performance, reduce fatigue, and improve physiological adaptability in humans. The test used a double-blind crossover design and supplementation for 28 days. Sixteen 20–30 year-old subjects were divided into two groups in a balanced order according to each individual’s initial maximal oxygen uptake and were assigned to receive a placebo (equal flavor, equal calories, 20 g/day) or SYNKEFIR™ (20 g/day) every morning. After the intervention, there were 28 days of wash-out, during which time the subjects did not receive further interventions. After supplementation with SYNKEFIR™, the exercise time to exhaustion was significantly greater than that before ingestion (p = 0.0001) and higher than that in the Placebo group by 1.29-fold (p = 0.0004). In addition, compared with the Placebo group, the SYNKEFIR™ administration group had significantly lower lactate levels in the exercise and recovery (p < 0.05). However, no significant difference was observed in the changes in the gut microbiota. Although no significant changes in body composition were found, SYNKEFIR™ did not cause adverse reactions or harm to the participants’ bodies. In summary, 28 days of supplementation with SYNKEFIR™ significantly improved exercise performance, reduced the production of lactic acid after exercise, and accelerated recovery while also not causing any adverse reactions.
Highlights
During long-term or high-intensity exercise, considerable energy is consumed, when energy cannot maintain a stable supply, it may cause fatigue and reduce exercise performance [1]
Fatigue can be divided into central fatigue and peripheral fatigue, the latter of which is defined as the inability to maintain power output and strength, thereby impairing body functions [2]
Kefir was shown to effectively reduce fatigue after exercise and promote the improvement of exercise performance, which might be affected by changes in the gut microbiota [19]
Summary
During long-term or high-intensity exercise, considerable energy is consumed, when energy cannot maintain a stable supply, it may cause fatigue and reduce exercise performance [1]. The physical and psychological effects of exercise depend on the type, intensity, duration, and energy expenditure of the exercise [3]. These factors are used to describe the decline in bodily function and the actual/perceived difficulties associated with tasks or increased exercise [4]. The excessive production and accumulation of metabolites such as lactic acid and urea nitrogen can lead to muscle failure [5]. Biochemical indicators, including lactic acid, have been used to assess skeletal muscle fatigue, showing that the serum urea nitrogen (BUN) levels increased, and the glucose (GLU) levels decreased [6]
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