DIABESITY IS THE unification of the words diabetes, referring to type 2, and obesity. Just like the evocative “bromance,” it conveys the close relationship between these two ideas. Diabetes and obesity are truly one and the same disease. As strange as it may now sound, physicians did not always recognize this seemingly obvious and basic connection.

      Back in 1990, when grunge was taking over the music scene and fanny packs were growing in popularity beyond the middle-aged dad tourist, Dr. Walter Willett, now Professor of Epidemiology and Nutrition at Harvard’s School of Public Health, identified the strong and consistent relationship between weight gain and type 2 diabetes.

      The obesity epidemic had only just gotten underway in the late 1970s and was not yet the public health disaster it is today. Type 2 diabetes barely scratched the surface as a public health concern. Instead, AIDS was the hot topic of the day. And type 2 diabetes and obesity were not thought to be related in any way. Indeed, the Report of the Dietary Guidelines Advisory Committee issued by the U.S. Department of Agriculture in 1990 allowed that some weight gain after the age of thirty-five was consistent with good health.

      That same year, Dr. Willett challenged the conventional thinking, reporting that weight gain after age eighteen was the major determinant of type 2 diabetes.¹ A weight gain of 20–35 kg (44–77 pounds) increased the risk of type 2 diabetes by 11,300 percent. Gaining more than 35 kg (77 pounds) increased the risk by 17,300 percent! Even smaller amounts of weight gain could raise the risk significantly. But this idea was not an easy sell to a sceptical medical profession.² “We had a hard time getting the first paper published showing that even slight overweight greatly increased the risk of diabetes,” Willett remembers. “They didn’t believe it.”

       BODY MASS INDEX: THE RELATIONSHIP BETWEEN OBESITY AND DIABETES

      THE BODY MAS index is a standardized measurement of weight, and it is calculated by the following formula:

      Body mass index = Weight (kg)/Height² (m²)

      A body mass index of 25.0 or higher is considered overweight, while a body mass index of between 18.5 and 24.9 is in the healthy range.

      Table 4.1. Body mass index classifications

      However, women with a body mass index of 23–23.9 have a 360-percent higher risk of developing type 2 diabetes than women with a body mass index of less than 22, which is even more stunning since a body mass index of 23.9 is considered well within the normal weight range.

      By 1995, building on this new realization, researchers had determined that a weight gain of only 5.0–7.9 kg (11–17.5 pounds) increased the risk of type 2 diabetes by 90 percent, and a weight gain of 8.0–10.9 kg (17.5–24 pounds) increased the risk by 270 percent.³ By contrast, weight loss decreased risk by more than 50 percent. This result established an intimate relationship between weight gain and type 2 diabetes. But far more sinister, this excess weight also significantly increased the risk of death.⁴

      More supporting evidence would soon surface. Dr. Frank Speizer from the Harvard School of Public Health had established the original Nurses’ Health Study (NHS) in 1976. One of the largest investigations into risk factors for cardiovascular disease and cancer, this long-term epidemiological study included 121,700 female nurses from around the Boston area.

      Dr. Willett continued with the Nurses’ Health Study II, which collected data every two years on an additional 116,000 female nurses since 1989. At the start of the study, all the participants were relatively healthy, but over time, many of them developed chronic diseases such as diabetes and heart disease. By looking back at the collected data, some idea of the risk factors for these diseases emerged. In 2001, Dr. Willett⁵ showed that, once again, the single most important risk factor for the development of type 2 diabetes was obesity.

       GLYCEMIC INDEX: DIET AND DIABETES

      THE NURSES’ HEALTH Study II revealed that other lifestyle variables were also important. Maintaining a normal weight, getting regular physical exercise, not smoking, and eating a healthy diet could prevent a stunning 91 percent of type 2 diabetes. But the million-dollar question is: What is a “healthy” diet? Dr. Willett’s healthy diet was defined as high in cereal fiber, high in polyunsaturated fats, low in trans fat, and low in glycemic load.

      When digested, carbohydrates break down into glucose. The glycemic index measures the rise in blood glucose after ingesting 50 grams of carbohydrate-containing foods. However, the amount of carbohydrates contained in a standard serving varies enormously. For example, a standard serving of fruit may contain less than 50 grams of carbohydrates whereas a single pastry may contain far more. The glycemic load refines this measure by multiplying the glycemic index of a food by the grams of carbohydrate in a standard serving of that food.

      Generally, foods high in sugar and refined carbohydrates are high in glycemic load. Dietary fats and proteins, since they raise blood glucose very little, have minimal glycemic loads. Contrary to the low-fat diet recommended by all the medical associations around the world, Dr. Willett’s healthy diet was high in dietary fat and protein. His diet was about reducing sugar and refined carbohydrates, not reducing dietary fat.

      In 1990, the widespread belief was that dietary fat was evil, that dietary fat was a mass murderer, that dietary fat was vile. The term healthy fats did not exist. It was an oxymoron, like a jumbo shrimp. Fat-laden avocados? A heart attack in a fruit. Fat-laden nuts? A heart attack in a snack. Olive oil? Liquid heart attacks. Most people fervently believed fats were going to clog our arteries, but it was only an illusion.

      Dr. Zoë Harcombe, a Cambridge University–trained obesity researcher, reviewed all the data that had been available in the early 1980s, when low-fat guidelines were introduced in the U.S. and U.K. No proof had ever existed that natural dietary fats worsened cardiovascular disease. The evidence for the low-fat guidelines was simply a great work of fiction.⁶ The science was far from settled at the time the government decided to weigh in and make the final decision to vilify dietary fat. Yet this belief had become so entrenched both in the medical establishment and among the general public that it had become heretical to suggest refined grains and sugars were the problem rather than dietary fat.

      In the midst of our frenzied low-fat obsession, Dr. Willett’s assertion was considered high treason. But the truth could not be concealed forever. Today, we understand clearly that obesity is the main underlying issue behind type 2 diabetes. But the problem isn’t simply obesity. Rather, it is abdominal obesity.