Taking HMB shortly before or after exercise is linked to changes in the activity of certain genes in muscle tissue that help regulate the body's daily biological rhythms.

We analyzed the available evidence on whether HMB affects circadian rhythm genes in human muscle, and what we’ve found so far is limited but consistent. One assertion suggests that taking HMB shortly before or after exercise is linked to changes in the activity of certain muscle genes involved in regulating the body’s daily biological rhythms [1]. There are no studies in our review that contradict this observation. The term “circadian rhythm genes” refers to genes that help control your body’s internal clock — things like when you feel awake or tired, and how your muscles repair or use energy over a 24-hour cycle. The evidence we’ve reviewed does not say how strong or lasting these changes are, nor does it explain whether they improve recovery, performance, or sleep. It only notes a connection between HMB timing around exercise and shifts in gene activity. Because only one assertion was analyzed, and no studies directly measured outcomes like sleep quality, hormone cycles, or muscle function tied to these gene changes, we cannot say whether this effect matters in real life. The number of supporting assertions is high — 45.0 — but this appears to reflect repeated references to the same single observation rather than multiple independent studies. We don’t know if HMB taken at other times of day has the same effect, or if people who don’t exercise see similar changes. There’s also no information on whether these gene changes are temporary or if they build up over time. What we’ve found so far is a single, unchallenged observation that HMB around exercise may influence muscle genes tied to daily rhythms. Without more research, we can’t say what this means for health or fitness. If you’re taking HMB and wondering if timing matters, this suggests it might be worth experimenting with taking it close to your workout — but don’t assume it will change your sleep or energy levels.