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The Journal of the International Society of Sports Nutrition recently published the results of a randomized and double-blind controlled clinical trial evaluating the effects of high-intensity interval training (HIIT) and probiotic supplementation, separately and together, on cardiorespiratory fitness and other markers of metabolism among middle-aged women with obesity. Forty-seven women took part in this 8-week study, each with a body fat percentage greater than 35%, and were assigned into one of 4 groups with approximately equal distribution: control, probiotic, HIIT, and probiotic and HIIT.
An incremental intensity treadmill exercise test was administered at baseline to determine cardiorespiratory endurance (including VO2 max and time to exhaustion (TTE)) and again at the end of the study period, along with anthropometric data and serum lipids and glucose. HIIT was targeted at 85–90% VO2 max, characterized by 7 cycles of 2 minutes on and a 1-minute rest period, performed 3 times per week. Women receiving either a placebo or probiotic consumed one packet every morning while fasting, with the latter comprised of Lactiplantibacillus plantarum (TWK10) at a dose of 6 × 1010 CFU per day.
After 8 weeks, somewhat surprisingly, waist circumference increased in the group performing only HIIT, while in women taking probiotics (with and without HIIT), it did not differ significantly from the control group. Women in the group receiving probiotics and HIIT had significant reductions in hip circumference compared to all other groups, while HIIT (with or without probiotics) significantly improved TTE. Postintervention calorie consumption was significantly reduced in the probiotics/HIIT group as well, as estimated by three-day dietary food records pre- and post-intervention, though participants were told not to change their typical diet. Lipid and glucose changes were minor, but included a slight increase in fasting glucose in the HIIT group, though the mean was well within the normal range pre- and post-intervention. This increase was not observed among women taking probiotics in addition to HIIT.
Overall, the results are consistent with what might be expected, i.e., generally favorable effects of HIIT, although an increase in fasting glucose and waist circumference in the HIIT group was unexpected, and seemingly mitigated by probiotic supplementation. This probiotic strain has been previously shown to enhance exercise performance, limit exercise-induced inflammation, and promote an improvement in body composition (e.g., greater muscle mass proportion and lower fat mass) without changing body weight. Unfortunately, although this more recent study set out to evaluate body composition via DEXA testing, technical errors prevented any post-intervention measurement.
A small study also suggests that this strain may have an endurance benefit, as marked by a greater performance on a treadmill running test by amateur runners. It may also have “postbiotic” effects, i.e., favorable effects with supplementation of inactive (heat-treated) bacteria. Immune modulation, enhanced gut integrity, and a reduction in fatigue have been demonstrated with other Lactobacillus species, including strains of Lactococcus lactis, Lactobacillus gasseri, and Lactobacillus brevis. Heat-inactivated TWK10, the strain of Lactiplantibacillus plantarum used in this study, was shown to improve grip strength and muscle weight in a small but controlled study of young men.
The authors of this recent study also suggest that the increase in fasting glucose levels could possibly be attributed to increased gastrointestinal permeability and endotoxin (LPS) production, as a result of the rapid increase in exercise intensity (HIIT was initiated at 85–90% VO2 max, rather than increased gradually), with the associated inflammation leading to a rise in plasma glucose. This speculation was not in any way verified by this study, and there may be stronger evidence for reverse causality, i.e., elevated fasting glucose may damage intestinal mucosa integrity. Nonetheless, it’s possible that if HIIT were responsible for elevated plasma glucose, this could be a mechanism by which probiotic supplementation mitigated the rise, as observed in this study.
There is very little evidence for the use of probiotics combined with HIIT, so this study offers encouraging, if limited, support for their combined use. A previously published study using a different strain of Lactiplantibacillus plantarum (PS128) also suggested that a reduction in exercise-induced inflammation and oxidative stress may be a distinct mechanism of action of this species. This was a small but randomized and placebo-controlled study that enrolled members of triathlon teams into one of two exercise protocols, both with probiotic supplementation (and both placebo-controlled). Both were 8-week training periods, with the last 3 to 4 including probiotic supplementation. Post-intervention testing indicated that creatine kinase, thioredoxin, and myeloperoxidase indices, as well as markers of inflammation (TNF-α, IL-6, and IL-8), were improved with probiotic supplementation, and branched-chain amino acid plasma levels were increased (potentially reducing fatigue). Improvements in both anaerobic and aerobic exercise capacities were also noted in this study.
While these studies are small with multiple limitations, they suggest that Lactiplantibacillus plantarum may mitigate some of the adverse effects of high-intensity exercise. Although HIIT has numerous benefits, it is associated with increases in oxidative stress and inflammation, as well as muscle damage, that could potentially be mitigated with probiotic supplementation.
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