Federal Trade Commission officials have rejected a consumer group's call for an investigation into whether Coca-Cola, Pepsico and other manufacturers have falsely advertised that artificially sweetened soft drinks and food products help people lose weight. The California-based group, U.S. Right to Know , filed citizen petitions in April asking the agency and the U.S. Food and Drug Administration to stop companies from branding products with the word "diet" if they contain an artificial sugar substitute, including those containing aspartame, the most widely used sweetener.