Evidence shows that well-being for mental health in prison is an important component of prison rehabilitation efforts—including notably lowering recidivism rates after release. While support for well-being initiatives in U.K. prisons has grown, few prison programs offer a health-promoting focus or invest in well-being interventions. Therefore, this study seeks to replicate and extend emerging data on an innate health intervention. Volunteers from HMP Nottingham ( N=127) participated in normal prison programming. The intervention group ( n=66) received an additional 3-day intensive. This study found higher levels of innate health, self-control, well-being, and prosocial behavior and lower levels of aggression within the intervention group and as compared with the control group. Next, we conducted a mediation analysis to test if innate health, self-control, and/or social desirability bias could explain these positive changes. Importantly, innate health did play a mediating role equivalent to and/or partnering with self-control, whereas social desirability bias did not.