On Obesity

A couple of recent NBER papers:

Body Composition and Wages

In the first, John Cawley of Cornell and Feng Liu of Shanghai University look at the relationship between body fat, lean body mass, and wages. The researchers eschew the traditional use of Body Mass Index in these types of studies, arguing that BMI could consider a person overweight even though they're perfectly healthy as BMI doesn't distinguish between body fat and muscle.

They find that for most ethnic and gender groups, wages take a hit from higher body fat but get a boost from muscle mass.

A one kilogram (2.2 pounds) increase in [body fat] reduces wages by about 1 percent for [Latino] males and [Latino] females, and about 0.9-1.0 percent for white males and white females. The effects of [body fat] on the wages of black males and females are smaller and only significant for females. The wages of black females go down by about 0.6 percent in response to a one kilogram increase in body fat.

When the [muscle mass] is raised by one kilogram, the wages increase by about 0.7 percent for white males and [Latino] males and about 1.3 percent for white and [Latino] females. Again, the effects on black males and females are smaller and both coefficients are insignificant. These results indicate that, while an increase in body size that is due to an increase in [body fat] will hurt wages, [muscle mass] is actually beneficial.

Do Working Mothers Lead to Fat Children?

Recent work has shown that about 8 percent of the rise in childhood obesity over the last four decades can be attributed to infants whose mothers work.

Roy Wada of The Rand Corporation and Erdal Tekin of Georgia State University try to find out how this happens using data from the American Time Use Survey:

We find that maternal employment is associated with a lower probability of, and reductions in time spent, grocery shopping and cooking, and a higher probability of purchasing prepared foods. Moreover, we find that when wives work husbands spend significantly less time grocery shopping and are more likely to purchase prepared foods.

We also find that working mothers are less likely to eat with their children. This is relevant for childhood obesity because eating meals as a family is associated with children consuming a less fatty and more nutritious diet.

Finally, we find that employment is associated with mothers spending less time engaged in child care, supervising children, and less time overall spent with children. This is relevant for childhood obesity because there is evidence that unsupervised children consume more calories.

To clarify, our intent is not to calculate the net benefits of maternal employment, but to identify possible mechanisms that explain the observed correlation between maternal employment and childhood obesity.

Related:

- Chubby Gets A Second Look

- The Stomach-Surgery Conundrum