This open label, single arm, prospective, interventional, weight loss trial evaluated a meal replacement beverage (Right Size® Smoothie) used to replace breakfast and lunch each day for 12 weeks (7 clinic visits) as part of a calorierestricted diet in overweight and obese adults. A total of 155 individuals were screened, 55 enrolled and 28 completed this 12 week study. Subjects were obese (mean weight: 206 pounds and BMI: 32.7 kg/m2) and the mean age was 40 years including 42 (76.4%) female and 13 (23.6%) male volunteers. The modified Intent to Treat and Completer groups lost an average of 10.6 and 13.8 pounds and reduced their average BMI by 1.7 and 2.2 kg/m2 respectively during this 12 week trial. The Per Protocol group lost 15.2 pounds and 2.4 kg/m2 and the Optimal Weight Loss group lost 18.5 pounds and 2.9 kg/m2. Using the Satiety Labeled Intensity Magnitude scale (SLIM) questionnaire, subjects reported feeling relatively hungry before they consumed the beverage, then feeling relatively full 15 minutes following the beverage with the sensation of some fullness lasting more than 2 hours and then feeling relatively hungry again at 3 hours after consuming the beverage. Study subjects reported significant improvements in physical functioning, general health, vitality and mental health as well as increased cognitive restraint of eating, reduced disinhibition and reduced hunger during the trial. The study beverages were well tolerated and no Serious Adverse Events (SAE) reported. This study suggests the study beverage aids in weight loss by helping to curb hunger during a reduced calorie diet program.