Previously we discovered that routine periodic fasting was associated with a lower prevalence of coronary artery disease (CAD). Other studies have shown that fasting increases longevity in animals. A hypothesis-generating analysis suggested that fasting may also associate with diabetes. This study prospectively tested whether routine periodic fasting is associated with diabetes mellitus (DM). Patients (n = 200) undergoing coronary angiography were surveyed for routine fasting behavior before their procedure. DM diagnosis was based on physician reports of current and historical clinical and medication data. Secondary end points included CAD (physician reported for ≥1 lesion of ≥70% stenosis), glucose, and body mass index (BMI). Meta-analyses were performed by evaluation of these patients and 448 patients from a previous study. DM was present in 10.3% of patients who fasted routinely and 22.0% of those who do not fast (odds ratio [OR] 0.41, 95% confidence interval [CI] 0.17 to 0.99, p = 0.042). CAD was found in 63.2% of fasting and 75.0% of nonfasting patients (OR 0.42, CI 0.21 to 0.84, p = 0.014), and in nondiabetics this CAD association was similar (OR 0.38, CI 0.16 to 0.89, p = 0.025). Meta-analysis showed modest differences for fasters versus nonfasters in glucose concentrations (108 ± 36 vs 115 ± 46 mg/dl, p = 0.047) and BMI (27.9 ± 5.3 vs 29.0 ± 5.8 kg/m², p = 0.044). In conclusion, prospective hypothesis testing showed that routine periodic fasting was associated with a lower prevalence of DM in patients undergoing coronary angiography. A reported fasting association with a lower CAD risk was also validated and fasting associations with lower glucose and BMI were found.