To estimate the effectiveness of tailored physical activity and dietary interventions amongst adults attending colorectal and breast cancer screening. Five literature databases were systematically searched to identify randomised controlled trials (RCTs) of tailored physical activity and/or dietary interventions with follow-up support initiated through colorectal and breast cancer screening programmes. Outcomes included markers of body fatness, physical activity, and dietary intake. Mean differences (MDs) or standardised mean differences (SMDs) with 95% confidence intervals (CIs) were pooled using random effects models. Five RCTs met the inclusion criteria encompassing a total of 722 participants. Diet and physical activity interventions led to statistically significant reductions in body mass (MD - 1.6 kg, 95% CI - 2.7 to - 0.39 kg; I = 81%; low quality evidence), body mass index (MD - 0.78 kg/m , 95% CI - 1.1 to - 0.50 kg/m ; I = 21%; moderate quality evidence), and waist circumference (MD - 2.9 cm, 95% CI - 3.8 to - 1.91; I = 0%; moderate quality evidence), accompanied by an increase in physical activity (SMD 0.31, 95% CI 0.13 to 0.50; I = 0%; low quality evidence) and fruit and vegetable intake (SMD 0.33, 95% CI 0.01 to 0.64; I = 51%; low quality evidence). There is low quality evidence that lifestyle interventions involving follow-up support lead to modest weight loss and increased physical activity and fruit and vegetable intake. Due to the modest intervention effects, low quality of evidence and small number of studies, further rigorously designed RCTs with long-term follow-up of modifiable risk factors and embedded cost-benefit analyses are warranted (PROSPERO ref: CRD42020179960).