Background: Investigate the effectiveness of the scientific 4 Phases Method, a methodology developed by EMAGRECENTRO, which is based on a ketogenic approach (total carbohydrate intake <40 g/day; including fibers) associated with health coach assistance, in promoting reductions in body weight, body mass index (BMI), and waist circumference after 5 weeks of methodology application. Methods: Record files from 354 individuals, both sexes, aged between 18 and 67, who took part in the 4 Phases Method were used to develop this study. Age, sex, weight, height, BMI, waist circumference measurement, and the presence of ketone bodies in the urine were evaluated before (baseline) and after 5 weeks of the 4 Phases application. Results: In general, a significant reduction in body weight (−7.8 ± 1.2 kg, p < 0.0001), BMI (−2.8 ± 0.4 kg/m², p < 0.0001), and waist circumference measurement (−7.6 ± 0.4 cm, p < 0.0001) was found after the application of the 4 Phases Method, regardless of age, gender, and BMI. Conclusions: Taken together, our results demonstrated that the 4 Phases Method was able to promote significant body weight, BMI, and waist circumference reductions in the short term, particularly by associating a ketogenic intake strategy with a regular close follow-up weekly consultation with a health coach assistance.