Why Diet and Exercise Fail demonstrates that traditional theories of weight gain cannot fully explain rising rates of obesity in the United States. Agricultural workers are among the most physically active people in California, yet they have one of the highest rates of obesity. The Inuit, or Eskimo, traditionally received 75% of their calories from fat and stayed lean, but eating a high fat diet did not produce weight loss in all the followers of the Atkins diet. In the 1950s, the rural Thai ate a diet with 80% of its calories from white rice, a refined carbohydrate, yet they remained thin. Low calorie diets have been tried since the beginning of the twentieth century to little effect. Over 99% of people who lose weight on low calorie diets return to their previous weight within three years. The problem with these diets is that they do not take into account how different types of food affect hunger levels. To see what could be influencing hunger, the book looks at obesity research that identifies factors which can cause weight gain. Soda consumption tends to predict weight gain, but diet soda consumption is an even stronger predictor of weight gain than is regular soda. Sleep deprivation predicts weight gain and is associated with increased hunger. In fact, people who are overweight tend to have higher levels of hunger than people of normal weight, despite the fact that they have already eaten too much. Increased hunger seems to be the mechanism by which prescription drugs and stress can lead to weight gain. However, hunger does not appear to explain why overweight people are less able to use stored fat and why food makes them feel less full, compared to people who are thin. The American diet underwent huge changes beginning in the twentieth century. Many of these have had profound nutritional implications of which we are not aware. Almost all of the bread products in the United States, including those labeled whole wheat, have had their grain oils removed. This extends their shelf life, but it radically alters their nutrient content. Caffeine, food additives, refined sugars, and chemical pesticides have a profound nutritional impact as well. In addition, the types of fats in the modern diet are different from those which we ate historically. Giving our livestock commercial feed made from corn and soy, instead of grass, has radically altered the types of fats we eat, as has consuming refined vegetable oils. Some of these changes in our diet can cause sleep deprivation, stress, increased hunger, and reduced use of stored fat. Although they are conventional wisdom, many common theories about nutrition are incorrect. While dietary fiber is believed to lower cholesterol and body weight, defatted fiber has no such effect. A nutrient stored in the fat in fiber appears to be responsible for fibers beneficial effects. Also, while omega-6 rich oils are supposed to be unhealthful and omega-3 rich oils healthful, this is not always the case. A highly anti-inflammatory oil rich in omega-6 is largely removed from the American diet during food processing. Its absence has probably contributed to increasing rates of chronic inflammatory diseases and insulin resistance. While healthful eating is supposed to be difficult, there are relatively easy changes to our diet that can have a profound impact on our weight and our health.