Comparison of cheese with and without Propionibacterium freudenreichii subsp. shermanii LMGT 2951 on off-season muscle strength and VO2 max development in Nordic skiers: a randomized clinical trial.

Background and objective: Nordic skiers represent a low-impact, weight-sensitive sport and may be inclined to engage in weight-controlling behavior, hence increasing their risk for low energy availability and impairment in health and performance. Jarlsberg cheese (J) is rich in vitamin K₂ from fermentation by Propionibacterium freudenreichii subsp. shermanii LMGT 2951 (Pf) and lactic acid bacteria and increases the osteocalcin (OC) level. Vitamin K is essential for activating OC, which is described to be associated positively with muscle strength, whereas propionic acid bacteria are found to enhance endurance. Except for Pf and its by-products, J and Norvegia (N) cheeses have almost identical nutrient content. The objective of this study was to compare the effects of Jarlsberg and N as potential supplements to training on muscle strength (MS), lean body mass (LBM) and VO₂ max.

Methods: Thirty female and 30 male Nordic skiers were block randomized 1:1 to either J or N and studied during a 24-week offseason training schedule. The Norvegia group served as a control group. Females and males were treated with 75 and 90 grams/day, respectively. MS by seated pulldown and half-squat, LBM by DXA, and VO₂ max were measured at baseline and after the 24 weeks off-season period. Dietary intake and training hours were registered and monitored at baseline and every eight weeks during the study.

Results: MS significantly increased in both groups after 24 weeks (p < 0.01). The mean increase difference in MS-upper body favored Jarlsberg by 0.95 kg (95% CI: -0.02-1.46), approaching significance (p = 0.06). No significant difference was found between groups in MS-lower body. LBM and VO2-max both increased significantly in each group (p ≤ 0.05), with no notable differences between groups. Correlation analysis identified LBM as the dominant outcome variable at both baseline and 24 weeks. Endurance training was the dominant input variable and correlated significantly positively both multiply and partially to LBM, (p = 0.04, p = 0.02), respectively. At baseline and 24-weeks sex, endurance training along with OC-level explained 65% and 68% of the LBM variations, respectively.

Conclusion: Both Jarlsberg cheese, characterized by its unique Propionibacterium freudenreichii content, and Norvegia cheese, when combined with off-season training, led to increases in LBM, VO₂ max, and MS, with no significant differences observed between groups. However, there was a trend toward greater improvements in MS in the Jarlsberg group. Overall, increases in LBM through structured training appear to be a key driver of gains in both muscle strength and aerobic capacity.

Protocol number: XCS-Jarlsberg/IIA.

Clinicaltrial.gov: NCT06688032.