You have no doubt heard about America’s obesity epidemic. Due to our poor diet, our sedentary lifestyle, the evil machinations of the fast food-industrial complex, and our foolishly thrifty preference for getting value for the dollar when we go out to eat, we are said to have a huge public health problem requiring legislative and judicial remedies.

Basically, Americans are too fat. Perhaps not every single one of us, but there’s obesity in virtually every family (he is heavy, and he’s my brother).

I guess I’ve been predisposed to believe this story, for a variety of reasons. The Objectivist in me would simply note the evidence of the senses here. I seem to see a lot of fat people around – and not just those with glandular or other medical conditions, but folks who simply appear to eat to much and exercise too little. Also, I’ve seen lots of research over the years comparing lives lost or diminished by poor diet and exercise to those lost or diminished by abusing tobacco, alcohol, or illegal drugs. The studies seemed persuasive.

According to an article by Mark LaRochelle in the latest issue of Consumers’ Research, however, I should have been exercising a different part of my body here – my brain. It turns out that many of the most extravagant claims about obesity in America are based on cooked statistics and politically flavored rhetoric.

Most researchers have described people as overweight if they weigh more than the national average weight for their height. Obesity, as a subset of overweight, is usually defined as having 25 percent or more body fat for men, and 30 percent or more body fat for women. By these definitions, the National Institute of Health has charted a clear increase in both overweight and obese Americans in the past 20 years. From 1980 to 2000, the proportion of Americans who are overweight rose from around 45 percent to 64 percent. The obese doubled to around 30 percent during the same period, with childhood obesity tripling to 15 percent.

Sounds pretty bad, right? Too many super-sized fries and super-sized TVs. Only these numbers are suspect. For one thing, the NIH changed its definitions of overweight and obesity during the period, reclassifying a man at the average height (5 feet 9 inches) who weighed 175 pounds or more as overweight, when the threshold used to be 190 pounds. Similarly, the threshold for the average woman (5 feet 4 inches) went from 160 pounds to 145 pounds. These changes made 35 million Americans overweight “with the stroke of a pen,” LaRochelle wrote – something that the fast food-industrial complex could only dream about.

The author also noted that these federal survey data don’t comport with weight data gathered by private insurers, who typically get them from actual weigh-ins by medical personnel rather than volunteered estimates by survey respondents. Furthermore, LaRochelle found, another set of federal data from the U.S. Department of Agriculture show that the average caloric intake of Americans — 2,344 a day for men, 1,638 for women – is significantly below the recommended daily intake levels for the average man (2,538) and woman (1,982). In other words, if there is a huge and growing obesity epidemic, it must be coming from our couches rather than our curly fries.

Finally, LaRochelle exposes a problem with the obesity numbers: they don’t adequately differentiate fat from muscle. The percentages of “body fat” I mentioned above are actually a “body mass index” that consists of a ratio of height to weight. Very muscular people, those who work out incessantly and generally make the rest of us looking shrimpy, will often show up with high body-mass indices, by even the NIH’s admission. Bruce Willis and Harrison Ford are overweight according to this BMI measurement, for example, while Sylvester Stallone and Arnold Schwartzenegger are officially obese.

Now, I heard these gentlemen called “fatheads” but I doubt this is what their critics had in mind. Next time, I pledge to taste a statistical claim before I swallow it, and I recommend you do the same.

Hood is president of the John Locke Foundation and publisher of Carolina Journal.