Mayor Bloomberg wants to ban large sodas. The Institute of Medicine wants to tax unhealthy folks. As John Goodman showed in a previous post, it’s hard to justify any of this. Here are some additional considerations.
Population obesity seems to have plateaued. The National Health and Nutrition Examination Survey (NHANES) shows no trend in US child and adolescent BMI since 1999. US men and women have had constant obesity rates and mean BMI since 2003. NHANES BMI measurements date suggest that the growth in U.S. overweight occurred between 1976-80 and 1988-94.
In 1997, the government made 35.4 million adults overweight overnight. It redefined overweight as a BMI greater than or equal to 25 regardless of age. Before that, overweight was BMI ≥ 27 for those 35 or older. Kathleen Flegal of the National Center for Health Statistics estimates that the change increased the fraction of overweight adults from roughly a third of the population to over half of it.
There are a variety of ways to measure overweight and they don’t necessarily agree. Burkhauser et al. (2009) found that when obesity is measured using skinfold tests, overweight has apparently been increasing since at least 1960.
Americans gained weight while following national dietary guidelines. In 1961, the American Heart Association proposed reducing dietary fat intake as a way to reduce blood cholesterol. People complied. The fat consumed by American children fell from 36-37% of calories in 1973 to about 32 percent of calories in 2000. Milk consumption declined by 25 percent between 1965 and 1996. High fat milk was replaced with low fat soft drinks and fruit drinks. When advised to cut sugar intake, Americans obeyed. They reduced their intake of added sugars from 18.1 percent of total energy intake in 1999-2000 to 14.6 percent of total energy intake in 2007-08.
National definitions of overweight are based on the BMI distribution of people aged 20-29 despite evidence suggesting that as people age, the lowest mortality occurs at progressively increasing weights. Prior to 1980, healthy weight standards were based on the Metropolitan Life Insurance Company (MLIC) calculations of distributions of weight-for-height associated with minimal deaths for healthy people aged 25-59 who applied for life insurance policies from 26 life insurance companies in the U.S. and Canada. A 1985 federal consensus panel defined obesity as BMI ≥ 27.8 for men and ≥27.3 for women because these were the sex-specific 85th percentile of the BMI distribution of people aged 20-29 years old in NHANES II. Twenty-year-olds were selected as the reference population because “young adults are relatively lean and the increase in body weight that usually occurs with age is due almost entirely to fat accumulation.” The 1985 standards corresponded to weights 20% above the ideal weight for a medium frame given in the MLIC standards. By 1995, federal experts had redefined healthy weight for adults of all ages as BMI 19-25. Kuczmarski and Flegal write that this “is equivalent to weights that are only 10% and 12% above the 1983 MLIC weight-for-height tables for men and women, respectively.”
Absent identifiable pathogens, any regime to classify foods as good or bad based on current evidence will be arbitrary, encouraging crony capitalism and unproductive rent seeking. There is little hard evidence showing that calories from any one kind of food cause more weight gain. Overweight seems to depend on the total quantity of calories ingested rather than on the kinds of calories people eat.
American taxpayers pay almost as much for government feeding programs as overweight and obesity generate in excess medical costs. US Department of Agriculture programs spend $115 billion a year encouraging low income people to eat more via the Supplemental Nutrition Assistance Program, the Women Infants and Children (WIC) program, and the school lunch and breakfast programs. In 2010, the Department of Health and Human Services reported that low family income is “strongly associated with overweight and obesity.” To put this in perspective, the Society of Actuaries estimated that the total cost of excess medical care caused by overweight and obesity in the United States and Canada was $127 billion in 2009.