In 1890 a survey of 5,000 US citizens revealed that only 3.4% of Americans were obese and they were typically isolated to the upper class. This compares to a contemporary rate of 32%. Two thirds of Americans are either overweight or obese. This includes one third of school children. This obesity rate has doubled since 1976 (CDC Source). The rapid increase in girth cannot be explained by genetics. Johnson feels that the rapid change in the frequency of obesity exonerates genetics as the cause, he states that the human genome has been relatively stable going back a few thousand years.
This leaves an environmental change. He then considers and discards changes in physical activity as the etiology. This is supported by the most recent analysis revealed at the 2009 European Congress on Obesity.
Johnson goes on to implicate fructuse. He states that fructose intake has increased 30% since the 1970's. Fructose is the main source of sugar in fruit. It is half of the molecule sucrose, table sugar. In 1970 the average American consumed half a pound of High Fructose Corn Syrup. By 2000 that had increased to 42 pounds a year. Though HFCS consumption has risen by two orders of magnitude, fructose exposure has only gone up by 30%. This likely means that HFCS has largely replaced the prior source of fructose in the diet, table sugar. The authors don't address that inconsistancy in this chapter.
Fructose causes obesity through multiple mechanisms:
- fructose causes more and faster weight gain than seen with other sugars
- fructose does not satisfy your appetite resulting in more calorie intake
- increased fructose dulls the brains responce to the normal satiety signals so that following chronic fructose exposure subjects eat more as they don't sence "fullness"
- fructose upregulates enzymes which promote obesity
- hypertension: 73 million Americans
- diabetes: 20 million Americans (CDC Source)
- kidney disease: 20 million Americans
- liver disease: emergence of NASH, now effect 2-5% of Americans (NIDDK Source)
- metabolic syndrome 55 million Americans
- fructose is the only sugar which increases the production of uric acid which leads to hypertension
- fructose increases the production of triglyceridesand lowers HDL
- fructose causes insulin resistance
- fructose causes kidney disease