In a recent study published in Obesity Research & Clinical Practice researchers at York University in Toronto analyzed a large body of data on diet, physical activity, and body weight that had been collected from American adults between 1971 and 2008 and concluded that a person who eats a given number of calories and does a given amount of exercise today is likely to have a body mass index (BMI) 10 percent greater than the same person with the same habits 20 or more years ago.
Predictably, this startling finding has led to attention-grabbing headlines such as “Why It Was Easier to Be Skinny in the 1980s” (The Atlantic) and “Young People Must Eat Less, Exercise More to Avoid Weight” (Newsmax). The study’s authors framed their own conclusion somewhat less starkly, writing, “Factors other than diet and physical activity may be contributing to the increase in BMI over time.”
The idea that things other than overeating and sedentariness may cause weight gain is not new. Past research has suggested that modern realities such as poor sleep, exposure to pesticides and other chemicals, and use of antibiotics may be fattening us up. Some studies even suggest that excess body weight is passed from mothers to infants through epigenetic mechanisms, causing our societal weight problem to snowball over generations.
The York University researchers admit that, so far, there is little evidence of these factors being powerful enough to cause such a huge difference in BMI. But there is plenty of evidence that American adults do eat more—a lot more—than they used to. A 2011 study out of the University of North Carolina, for example, found that average daily food intake among American adults increased by 570 calories between 1977 and 2006.
Metabolic modeling studies performed by Kevin Hall of the National Institutes of Health and others have shown that this increase easily accounts for all of the weight gain that Americans have experienced over the course of the “obesity epidemic.” When the obvious culprit of overeating is properly accounted for, there is little to nothing left for pesticides or other ancillary factors to explain and no reason to believe that we need to eat less and work out more than our parents did to get the same results.
Less scientific—yet no less powerful—evidence that diet and exercise are every bit as effective as they used to be comes from clinical weight-loss specialists who have been working directly with weight-loss seekers over the full span of the obesity epidemic. One such specialist is Laurie Beebe, RD, a Florida-based diet coach. “In the past 30 years of practicing as a registered dietitian,” she says, “I have not come across anything that makes me think people need to exercise longer and harder or eat fewer calories to lose weight. One thing that has definitely changed is that people do eat more and move less.”
What really needs to be explained, then, is not why we are so much heavier than we used to be but why the York University researchers missed the obvious explanation. According to Stephan Guyenet, PhD, an obesity researcher and author of the Whole Health Source blog, the York University study relied on self-reported food intake data, which is notoriously inaccurate, whereas more credible estimates of how much food we eat are based on “food disappearance” data from the USDA. “If you look at the calorie intake numbers they report in the paper,” Guyenet says, “you can see that they’re implausible, particularly the numbers for women.”
This brings up another question: Why would the York scientists rely on notoriously inaccurate data for their analysis? They defended the choice in their paper on the grounds that the degree to which people underreport their food intake has remained consistent over time, so that such data is still a reliable indicator of trends in consumption (not unlike how a bathroom scale that consistently subtracts 5 pounds from your actual weight is still a reliable indicator of whether you’re gaining or losing weight).
The fact remains, however, that a more trusted and objective source of information on changes in food intake was available. Guyenet sees the decision to ignore it as possibly symptomatic of a fatalistic streak in the new generation of obesity researchers, some of whom “think we’re just better off accepting excess weight and trying to be as healthy as possible at the higher weight, rather than making ourselves miserable with unsuccessful weight loss attempts.”
Guyenet hastens to add that he appreciates the compassion motivating this agenda. But people who earnestly seek a healthier life are always best served in the end by the truth, whatever it may be. Though arrived at with the best of intentions, the idea that it takes ever more calorie cutting and exercise to reach an ideal weight is probably less likely to make people who are struggling to lose weight feel better about themselves than it is to discourage them from doing the only things that have ever worked.