The objective of this study was to assess if the amount of protein an overweight or moderately obese adult consumes while reducing their energy intake to lose weight affects their appetite. The study also assessed if using lean beef and pork vs. soy and legumes as the main sources of protein made a difference in these appetite responses. For 3 consecutive 4-week periods of time, overweight/ obese adults consumed diets that contained 750 Calories per day less than the amount of energy they needed for weight maintenance and contained 10%, 20%, or 30% energy from protein using lean beef and pork or soy and legumes as the main sources of protein. At the end of each 4-week period, they reported to a clinical laboratory, after an overnight fast, they consumed a test breakfast (breakfast sandwich containing English muffin, meat (lean beef and pork or meatless sausage patty) and cheese, fresh grapes and apple juice) that provided 25% of their prescribed daily energy and protein intakes. Blood samples were taken and appetite questionnaires were completed before consuming the meal and 15, 25, 60, 85, 120, 180, and 240 minutes post-meal. The results indicate that it is highly feasible for overweight/obese adults to successfully lose weight by consuming reduced energy diets that contain 10 to 30 percent of energy from protein, with lean beef and pork as the predominant sources of protein. These people experienced greater increases in plasma amino acids when they consumed greater amounts of protein in a meal, especially when the meal contained beef and pork vs. soy and legumes. Higher protein intake from both lean beef and pork or soy and legumes promoted decreased hunger and desire to eat and greater fullness responses after a meal. Ingesting a meal with 30% of energy from protein was superior to when the meals contained 10 or 20% of energy from protein. In conclusion, consuming higher amounts of protein from lean beef and pork foods helps overweight and moderately obese adults curb their appetite (reduce their hunger) after eating. Funding, wholly or in part, was provided by The National Pork Board, The Beef Checkoff, and NIH RR025761. For more information contact Wayne W. Campbell, PhD, Dept. of Nutrition Science, Purdue University, 765-494-8236, firstname.lastname@example.org.