The Effect of Starting the Protein-Sparing Modified Fast on Weight Change over 5 years

Summary

This Cleveland Clinic-affiliated study followed 1,403 patients who were eligible for a protein-sparing modified fast program over 5 years to answer the question the original 1970s PSMF literature could not: does the dramatic short-term weight loss persist? Of those eligible, 879 (63 percent) actually initiated PSMF; the remaining 524 (37 percent) pursued other dietary approaches and served as a comparison cohort. The 1-year outcomes were dramatic and favored PSMF: -7.6 percent body weight in the PSMF arm versus -1.8 percent in the comparison arm, a 5.8-percentage-point difference (p less than 0.01). At 3 years, PSMF still showed an advantage but smaller: -2.3 percent vs -0.9 percent, a 1.4-point difference. By 5 years, the difference had effectively disappeared: -1.4 percent vs -1.0 percent (p=0.64, not statistically significant). The proportion achieving clinically meaningful (≥5 percent) weight loss told the same story: PSMF was strongly favored at 1 and 3 years, equivalent at 5 years. The honest conclusion: PSMF produces substantial short-term weight loss with good durability through year 3, but by year 5 the advantage over conventional dietary care is gone.