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Americans are growing Hispanic, not heavier

One of the myths that the media propagates is that America has an obesity epidemic. Every year we’re getting fatter, and it’s because we eat too much bad food, too many McDonald’s hamburgers and the like.

I have previously expressed my doubts about this because the whole story stinks of lousy fact checking and some kind of strange political correctness. See my two previous posts: Are Americans really fat? and Americans are NOT getting fatter.

Unlike the typical news media article, I have actually done some research, and therefore, unlike most of what I post in my blog, this post contains real news that you haven’t read anywhere else.

Based on one line of reasoning from my previous posts, I explored the question of whether the changing demographics of America are affecting our average weight. The answer is a resounding yes.

I used the National Longitudinal Survey of Youth 1997 (NLSY97) to determine the average weights of young Americans. This is a survey of nearly ten thousand young people. I used the 1999 questionnaire for this inquiry, so the ages of those in the survey were 15 to 19.

For each racial group, I computed the average body mass index (BMI). The BMI is defined as kilograms/meters^2. To help you understand better what the numbers mean, a difference of one BMI is about six pounds for women and seven pounds for men.

Note that the average BMIs shown below are slightly higher than the median BMIs. The median BMI would be a more useful number if you wanted to know what a typical person of a certain height should weigh. But the average BMI is fine for our purposes here.

The races white, black and Asian exclude Hispanics.

The results:

As we can see from the tables above, Hispanics and blacks are both heavier than whites, while Asians are thinner. Because one’s body weight is strongly influenced by genetics, it is probable that the racial differences are in large part due to genetic differences between the races.

Because of the different average BMIs for the different races, it is wrong for our health authorities to not take race into account when making weight recommendations. A young woman who is 5’5” tall and 137 pounds would be average if she were black (5’5” and 137 pounds is the median height and weight for black females in the NLS survey), but overweight if she were Asian.

Furthermore, BMI doesn’t tell us if the weight is fat or muscle. Nor does it distinguish the wide boned from the narrow boned. I strongly suspect that some of the extra weight that blacks have with respect to whites is extra muscle. This would help explain why blacks are a lot better at sports compared to whites. If it were all extra fat, then blacks would be worse at sports.

The following data, pulled from the special U.S Census report “Demographic Trends in the 20th Century,” shows the changing racial composition of America:

Don’t try to see if the percentages add up to 100. They don’t because I didn’t include races besides white, black and Asian, and those races include Hispanics because Hispanics are considered an ethnicity and not a race, so there are white Hispanics and black Hispanics. (It doesn’t really make much sense to me, but that’s the way they do it.)

The data clearly shows that whites are a declining percentage of the population, while Hispanics are a rapidly growing percentage of the population. Because Hispanics, on average, have a higher BMI than whites, this partially explains why Americans are, on average, getting heavier.

Asians have a lower BMI than whites, and Asians are also a rapidly growing percentage of the population, but they are not growing as fast as Hispanics. From 1980 to 2000, Asians increased by 2.23% of the population, while Hispanics increased by 6.1% of the population.

In the future I hope to analyze additional data from the NLS surveys and present more brilliant insights that have never been published before.

posted Friday, July 16, 2004