Concerns that the phytoestrogens (isoflavones) in soy may feminize men continue to be raised. Several studies and case-reports describing feminizing effects including lowering testosterone levels and raising estrogen levels in men have been published. For this reason, the clinical data were meta-analyzed to determine whether soy or isoflavone intake affects total testosterone (TT), free testosterone (FT), estradiol (E2), estrone (E1), and sex hormone binding globulin (SHBG). PubMed and CAB Abstracts databases were searched between 2010 and April 2020, with use of controlled vocabulary specific to the databases. Peer-reviewed studies published in English were selected if (1) adult men consumed soyfoods, soy protein, or isoflavone extracts (from soy or red clover) and [2] circulating TT, FT, SHBG, E2 or E1 was assessed. Data were extracted by two independent reviewers. With one exception, studies included in a 2010 meta-analysis were included in the current analysis. A total of 41 studies were included in the analyses. TT and FT levels were measured in 1753 and 752 men, respectively; E2 and E1 levels were measured in 1000 and 239 men, respectively and SHBG was measured in 967 men. Regardless of the statistical model, no significant effects of soy protein or isoflavone intake on any of the outcomes measured were found. Sub-analysis of the data according to isoflavone dose and study duration also showed no effect. This updated and expanded meta-analysis indicates that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects TT, FT, E2 or E1 levels in men.

Purpose: Over recent years, multiple studies have tried to optimize the exercise intensity and duration of work intervals in high-intensity-interval training (HIIT) protocols. Although an optimal work interval is of major importance to facilitate training adaptations, an optimal HIIT protocol can only be achieved with an adequate recovery interval separating work bouts. Surprisingly, little research has focused on the acute responses and long-term impact of manipulating recovery intervals in HIIT sessions. This invited commentary therefore aimed to review and discuss the current literature and increase the understanding of the moderating role of recovery durations in HIIT protocols. Conclusion: The acute responses to manipulations in recovery durations in repeated-sprint training (RST), sprint interval training (SIT), and aerobic interval training (AIT) protocols have recently begun to receive scientific interest. However, limited studies have manipulated only the recovery duration in RST, SIT, or AIT protocols to analyze the role of recovery durations on long-term training adaptations. In RST and SIT, longer recovery intervals (≥80 s) facilitate higher workloads in subsequent work intervals (compared with short recovery intervals), while potentially lowering the aerobic stimulus of the training session. In AIT, the total physiological strain endured per training protocol appears not to be moderated by the recovery intervals, unless the recovery duration is too short. This invited commentary highlights that further empirical evidence on a variety of RST, SIT, and AIT protocols and in exercise modalities other than cycling is needed.