This toolkit discusses the following key nutrition issues regarding the prevention and treatment of obesity: environment; consumption; portion sizes; yo-yo dieting; intentional weight loss in older adults; low carbohydrate diets; low glycemic index and glycemic load diets; energy-restricted diets; comparing energy-restricted and low carbohydrate diets; meal patterns, timing, and frequency; effect of calcium and dairy products; effects of vegetable and fruit intake; effect of dietary fats,