Background and objectives Nonalcoholic steatohepatitis (NASH) is strongly associated with obesity. A weight loss of ≥10% is necessary to improve NASH severity, but this goal has rarely been achieved in published studies using different diet protocols. The effect of a ketogenic, hypocaloric, commercial diet (“Ideal Protein,” IP) on body weight, metabolic markers, and liver tests in a group of NASH patients is evaluated in this study. Daily calorie intake was tailored to achieve a weight loss of ≥10%. Methods We analyzed 38 patients with NASH who were placed on the IP diet between 2014 and 2018 and compared their outcomes with 6 control patients who declined the diet. All patients were evaluated by a trained health coach in weekly intervals throughout the study period. Clinical and laboratory data obtained before and at 6.5 months after intervention were compared using paired t-testing. Results The patients on the IP diet experienced a significant weight reduction (217 ± 8 lb vs. 194 ± 7 lb; mean ± S.E.M.), corresponding to an average weight loss of 9.7% ± 1.6%. Significant changes in systolic blood pressure (133 ± 3 mmHg vs. 123 ± 3 mmHg), triglycerides (200 ± 21 mmol/L vs. 132 ± 11 mmol/L), hemoglobin A1c (6.71% ± 0.29% vs. 5.74% ± 0.19%), SGPT (97.3 ± 11.1 IU/L vs. 44.2 ± 5.9 IU/L), SGOT (82.4 ± 10.5 IU/L vs. 32.8 ± 5.2 IU/L), and Fib-4 scores (2.25 ± 0.23 vs. 1.40 ± 0.13) were also observed (P<0.05 in all cases). In the IP group, 50.5% of patients lost ≥10% body weight. In contrast, no significant changes were observed in the control group. The IP diet was well tolerated, and no safety signals were noticed. Conclusions A ketogenic, hypocaloric resulted in striking weight loss and significant improvements in metabolic parameters and liver tests, suggesting that this approach carries promise for the dietary management of patients with NASH.