The logic seems impeccable: In 1980, the U.S. government officially recommended that all Americans eat a low-fat diet. The entire country fell in line. Food manufacturers cranked out low-fat versions of everything from pastries to pork (“the other white meat”). Nutrition scientists published studies in support of higher-carb, lower-fat diets. The media jumped on board (even Men’s Health referred to fat as “artery-clogging”).
You know what happened next: Americans got really fat, really fast. The obesity rate tripled, and with it came a tsunami of type 2 diabetes. The dual epidemics even got a clever name—“diabesity”—making it the Brangelina of diseases. More to the point, it caught everyone by surprise, including the experts who thought no one could get fat on a low-fat diet.
Next came a low-carb backlash, with diets like Atkins, South Beach, and paleo ascending and low-fat diets dismissed as relics of an era when we were naïve enough to believe the experts.
Many people today, including legitimate scientists like David Ludwig, M.D., of Harvard University, argue that the guidelines weren’t merely misguided. They actually caused the obesity and diabetes epidemics by forcing us to focus on the wrong target. As a consequence of cutting fat, we massively overate foods that were high in processed carbohydrates, like white bread and soda.
Does that argument hold up?
No, says Stephan Guyenet, Ph.D., an obesity researcher and author of The Hungry Brain: Outsmarting the Instincts that Make Us Overeat. which comes out in February. Understanding the reasons why will tell you what you need to know to manage your own weight.
The American diet has been crappy for more than a century
The U.S. has been issuing nutrition guidance since 1894, Guyenet says, and if you check out the first one, you’ll find this familiar-looking complaint about contemporary diets:
“[O]ur diet is one-sided and … we eat too much. The food which we actually eat … has relatively too little protein and too much fat, starch, and sugar. This is due partly to our large consumption of sugar and partly to our use of such large quantities of fat meats. … How much harm is done to health by our one-sided and excessive diet no one can say. Physicians tell us that it is very great.”
Arcane language aside, it doesn’t sound like much has changed in the past 122 years. What made the 1980 guidelines different, Guyenet notes, is their emphasis.
“Previous guidelines were general, tended to focus on food groups, and usually focused on eating more of things,” he says, “whereas the 1980 guidelines had specific nutrient targets such as total fat, saturated fat, and cholesterol, and focused on eating less of things.”
But did they make us fat? For that to be true, Guyenet argues, you have to show two things:
First, that Americans actually ate less fat in response to the guidelines. Second, that those who followed the guidelines were more likely to be obese and unhealthy as a result.
Guyenet answers the first question with this list of the top 10 sources of calories in the U.S. diet, according to the USDA’s 2010 Dietary Guidelines for Americans Report:
- Grain-based desserts (like cakes, cookies, and donuts)
- Breads made with yeast
- Chicken and chicken dishes
- Soda and sports drinks
- Alcoholic beverages
- Pasta and pasta dishes
- Mexican dishes
- Beef and beef dishes
- Dairy desserts (like ice cream and cheesecake)
“Can anyone look at this list and tell me with a straight face that the 1980 dietary guidelines, which emphasized eating whole foods and less fat and sugar, are what made us fat?” he say. “When our number-one source of calories is cake, number four is soda, number five is pizza, and number six is booze? To me, this idea doesn’t even pass the laugh test.”
That alone is pretty good evidence that the obesity epidemic was the predictable result of Americans gorging on unprecedented quantities of highly processed foods. But it also gave some low-carb advocates an opportunity to claim we now eat less fat.
It’s true that fat, as a percentage of total calories, went down, while the percentage of calories from carbs went up. But it’s deceptive. “Our absolute intake of fat never declined,” Guyenet says.
Low-fat diets don’t make us fat
That brings us to the second question: Did the call to eat less fat actually hurt the people who complied?
Researchers have tackled this question a couple of different ways. Just last month, for example, a study in the American Journal of Clinical Nutrition graded nearly 12,000 Canadians on their adherence to the U.S. guidelines.
Their conclusion is unequivocal: Those whose came closest to the government-sanctioned model were the least likely to be obese, despite diets that are relatively high in carbs (53 percent of calories) and low in fat (28 percent).
The least compliant, who ate 43 percent carbs and 37 percent fat, were twice as likely to be obese. (Here’s the full truth about how carbs affect your weight.)
To be sure, population-level studies like these are notoriously dependent on self-reported food intake, which can skew the data. The heavier participants will often claim they eat a lot less food than they actually do. So studies like this one throw out data from people who’re obviously lying, based on their age, gender, weight, and reported activity level (which might also be more aspirational than operational).
But more carefully controlled studies, Guyenet points out, show pretty much the same thing. “Low-fat diets aren’t fattening,” he says. “They aren’t super-effective for fat loss, but they certainly don’t cause fat gain.” (In fact, many high-fat foods are good for you.)
The real enemy is within
There’s yet another side to all of this: The people with the crappiest diets aren’t eating that way because they’re confused about nutrition guidelines.
“The main problem isn’t the information,” Guyenet says. “It’s the assumption that the information will change behavior. We don’t drink soda, eat pizza, or eat ice cream because we think they’re healthy and slimming. We eat those things because we like them, despite the fact we know they’re fattening. That’s not the guidelines’ fault. It’s simply human nature.”
But there’s an even bigger problem, one that Guyenet tackles in his soon-to-be-published book. “Our brains contain circuits that are playing by the rules of a survival game that no longer exists,” he says, “and those circuits tell us to crave fattening foods.”
The first step to breaking those circuits is to acknowledge they exist, and to recognize when they’re pulling us toward a bad decision, one that we’ll soon regret. The second step, Guyenet says, is to re-engineer our home and work environments to help us avoid those temptations in the first place.
That takes time and effort, and for many it will never happen at all. Either way, it’s foolish to blame a problem caused by the intersection of calorie-seeking brains and profit-seeking food producers on guidelines issued almost four decades ago.