After six months, all four diet groups averaged a six-kilogram weight loss, or 7 percent of their original weight, which ever diet they were on. All again began to regain weight after 12 months. After two years, the average weight loss was about four kilograms for all groups. Earlier studies had claimed that higher protein intake reduced appetite and sustained muscle mass better during weight loss. The Harvard researchers’ conclusion: A diet program’s benefits result from the degree to which people stick with them, not from any specified energy reduction formula.