In this chapter, Lieberman argues that obesity due to overabundance of energy is the largest problem in the US currently. Type 2 diabetes and heart disease are mismatch diseases related to obesity. Once food is eaten, the excess energy is stored to fuel the body later on. Humans are able to endure long periods of negative energy balance by relying on these fat stores, and until recently, humans went long periods with negative energy balances. Lieberman explains that humans are adapted to store a lot of fat, because our large brains require a constant flow of sugar to the brain. Compared to other primates, humans store way more fat in the body. Lieberman explains the thrifty phenotype hypothesis, which suggest that if a pregnant woman is not getting enough nutrients, the baby will be predisposed to store fat in preparation for an environment with limited resources. However, this does not explain why children born to healthy or overweight women also develop obesity. Lieberman explains that the reasons why some people store more fat that others is not known. It is important for more research on the subject, especially because the numbers of people who are obese are rising. Although people are eating more than they ever have, Lieberman explains that another reason for increased obesity is the types of food that are eaten. Insulin rises when blood sugar levels rise, and allows fat cells to store the sugar as fat. Insulin rises when glucose is eaten, and current processed food is high in glucose, and low in fiber, which slows the rate of digestion and increases satiation. Additionally, fructose is processed by the liver, and without fiber, an abundance of fructose can overwhelm the liver. Hunter gatherers would only be able to acquire such large amounts of sugar in honey, so our digestive system is simply not adapted to process large amounts of sugar. Additionally, Lieberman explains that exercise alone is not a good way to lose weight, because it burns relatively few calories and then stimulates hormones to make you hungry. Additionally, it is difficult to lose weight because someone must be in a negative energy state, which increases hunger. Type 2 diabetes is also a chronic mismatch disease that results in insulin resistance. Excess visceral fat, or fat around the internal organs, is a risk factor for type 2 diabetes. However, losing this visceral fat is able to even reverse the early stages of type 2 diabetes. But Lieberman explains that the problem is people wait until they are seeing symptoms before making changes, when it would be more effective to make changes earlier. Another chronic mismatch disease is heart disease, which results from high LDL cholesterol. It is common because of the same factors that cause diabetes: inactivity, poor diet, and obesity. This disease can also be mitigated by regular exercise and a good diet. Lieberman points out that just being overweight is not a guarantee of a problem, instead better predictors of health are where you store fat, how you eat, and how much you exercise.