Clinicians lack the tools to incorporate physical activity into clinical care for Alzheimer's disease prevention. We tested a 52-week exercise and health education program (Lifestyle Empowerment for Alzheimer's Prevention [LEAP! Rx]) that integrates clinician referrals and community-based fitness resources. We randomized 219 participants to the LEAP! Rx (ie, exercise and monthly brain health education) or a standard-of-care control group and tested the effects on cardiorespiratory fitness, insulin resistance, body composition, lipids, and cognitive performance. Physicians were able to connect their patients to a community lifestyle intervention. The intervention group increased in cardiorespiratory fitness at 12 and 52 weeks (p=0.005). We observed no effects on secondary measures. Participants meeting 80% of weekly goals (150 min, moderate to vigorous activity) saw greater fitness improvements than those with less than 80% (p<0.001). These results hold promise for broad implementation of exercise interventions into larger healthcare systems and have implications for improved research recruitment strategies. NCT No. NCT03253341. Our community-based exercise program increased cardiorespiratory fitness. Our digital physician referral method increased the diversity of the participant sample. Our findings have implications for personalized dementia risk reduction strategies.