A
front page story in today's Washington Post suggests that increased consumption of soft drinks by children and adults helps to explain America's obesity crisis. It also suggests that this finding lends support to efforts to ban vending machines in schools.
First, it is clear that if you drink alot of regular soft drinks, you will probably gain weight--an increase in calories consumed without offsetting increases in calorie expenditures leads to increased weight. Second, it appears that liquid calories are processed differently in the body from food colories--whereas food calories tend to displace the desire for other calories to at least some extent (a snack tends to decrease your appetite at meals), liquid calories do not offset to the same extent. Third, the science suggests that high fructose corn syrup is especially problemmatic, in that it appears that the body does not metabolize it the same way as sugar, and thus it gets converted into weight gain more rapidly.
But can the increase in obesity be explained by an increase in soft drinks? Kelly Brownell thinks so. "This is a strong study, which joins a number of others in showing that soft drink consumption is related to poor diet and obesity, yet the soft drink industry says the opposite," said Kelly Brownell, who is director of the Yale University Center for Eating and Weight Disorders. "They lose credibility by the day. Reducing soft drink consumption may be a powerful means of addressing the obesity crisis." Brownell, of course, has argued without trace of irony that America's toxic food culture simultaneously causes anorexia and obesity.
But what does the data show on soft drink consumption? Note the following graph on beverage consumption, taken from the USDA's food disappearance data (the standard data set for tracking these sorts of things):
(If you have trouble reading the chart because it is small, just click on it and it opens in a new larger window.)
As this quite plainly shows, soft drink consumption has been largely constant for about 15 years (as has diet sodas). Ironically, bottled water is the fastest-growing component of beverage consumption.
Studies also indicate that soft drink consumption for children at all ages has been largely constant over this period as well. There does seem to be some increase in the consumption of fruit drinks, such as fruit boxes, which may account for some of the problem.
What about vending machines? Well, according to the data, only 4 percent of soft drink consumption by children, and only 3 percent of children purchase soft drinks from vending machines. See Simone A. French, Biing-Hwan Lin, and Joanne F. Guthrie, National Trends in Soft Drink Consumption Among Children and Adolescents Age 6 to 17 years: Prevalence, Amounts, and Sources, 1977/1978 to 1994/1998, 103 J. AM. DIETETIC ASSOC. 1326, 1329 (2003). About half of soft drink consumption comes at home and most of the remainder comes at restaurants. Thus, the overwhelming majority of soft drink consumption by children comes under parental supervision. There is thus little reason to believe that removing vending machines from schools will do much at all to reduce childrens' obesity.
In fact, children's soft drink consumption--like all aspects of children's diets--has followed exactly the same trends in recent years as their parents. In short, kids eat--and drink--what their parents eat and drink. I have a chart showing this in
my powerpoint presentation that I gave at Cato in June.
Once I finish up my series on direct shipment of wine, I'll discuss these issues in greater depth.
Update:
Matthew Malewski at FROG takes me to task for my overly-casual presentation of the science of HFCS in my earlier post. I plead guilty and refer you to Matthew's blog for a more precise statement of the science involved. I agree that the research is inconclusive at this point, but my impression is that the hypothesis is plausible enough to warrant further testing.