Most popular weight-loss diets keep lists of forbidden foods—foods you must not eat. Ever. Low-fat diet gurus say we must not eat any high-fat foods if we hope to get leaner. No bacon, no cheese, no oil-based salad dressing. Glycemic control diet gurus say we must not eat any high-glycemic foods or else we’ll never reach our goal weight. No peaches, no potatoes, no pasta. And so forth.
A reality check indicates that such forbidden food lists are both longer than they really need to be and too narrowly defined. In my view, a food should not be forbidden to dieters unless it meets two criteria: 1) it is eaten most frequently by the fattest people and least often by the leanest and 2) its consumption is associated with significant long-term weight gain. Not all high-fat foods or high-glycemic foods or high-whatever foods meet these criteria. Only four foods do: fast food, soft drinks, fried food, and snack chips.
Hamburgers and French fries purchased from fast food restaurants may be the biggest individual food contributors to weight gain in America. The average American gets 11.3 percent of his or her calories from fast food. But normal-weight persons tend to eat less fast food while fat people eat more. For every 100 calories a normal-weight American gets from fast food, an obese American gets 125.
Longitudinal research demonstrates that this association is not coincidental but causal. A 2005 study from the University of Minnesota reported that, over a 15-year period, people who ate fast food two or more times per week gained 10 more pounds than did people who ate fast food less than once a week.
Most fast foods have a very high fat content. A Burger King Whopper contains 37 grams of fat and gets 333 of its 650 calories from fat. A medium order of french fries at Burger King contains 18 grams of fat and gets 162 of its 410 calories from fat. It would be a mistake, however, to caution against eating high-fat foods in general rather than fast food specifically. After all, nuts and yogurt are high in fat, but people who eat lots of these foods tend to be slimmer than those who eat less of them.
It would also be a mistake to steer weight-loss seekers away from only high-fat fast foods. There are low-fat foods that are just as fattening—or one, anyway: soft drinks. Adults who drink at least on soda per day are 27 percent more likely to be overweight or obese than are those who never drink soda. As you know, all of the calories in most soft drinks come from sugar. But it would be a mistake to caution dieters against consuming all foods high in sugar. Many fruits are high in sugar, but people who eat lots of fruit are leaner than those who eat little fruit.
In fact, it’s not even necessary to include candy on a list of foods forbidden to the weight-loss seeker. Fat people do not eat more candy than the general population. Because candy is energy dense and not terribly satiating, in principle it has the potential to be quite fattening. But in practice candy is seldom the main culprit in individual cases of weight gain because candy doesn’t invite gorging the way fast food meals do. People routinely consume 1,000-plus calories of fast food in a single sitting. People do not routinely eat four and a half bags (i.e. 1,000 calories’ worth) of Skittles in a single sitting, or even in a single day.
Fried foods and snack chips, on the other hand, are even more energy dense and even less satiating than candy and they do tend to be eaten in larger amounts. Unlike candy, fried foods and snack chips are eaten most frequently by the fattest people and therefore they are much better candidates for inclusion on our sensible lost of foods forbidden to the weight-loss seeker.
A 2013 study by Spanish researchers found that, within a population of 9,850 adult males, those who ate fried food four or more times per week were 37 percent more likely to be overweight or obese than were those who ate fried food two or fewer times per week. A well-known 2011 study from the Harvard School of Public Health found that potato chips were associated with more weight gain in a population of nearly 120,000 American adults over a 20-year period than was any other food or food type. Doritos and other snack chips were not looked at in this particular study, but I’m confident they have similar effects.
There are many successful dieters—not to mention people who have never been overweight—who don’t forbid themselves anything. They just don’t eat much of whichever foods they consider most fattening. I am one such person, and there are no forbidden foods in the “agnostic healthy eating” approach I recommend to others. But I’m aware that declaring certain foods completely off limits works for some people. If you belong to this psychological type—if you insist on not eating certain foods—then I encourage you to select these four: fast food, soft drinks, fried food, and snack chips.
There are plenty of items not on this list that you should not eat often—e.g. sweets, refined grains, processed meats—but both real-world and scientific evidence suggest that complete abstinence from these foods won’t aid your weight-loss efforts any more than moderation. As eaters, it’s easier for us to say “yes” than “no.” So keep your “no’s” to a minimum. If you can avoid fast food, soft drinks, fried food, and snack chips for the rest of your life without going crazy, great. But focus the rest of your attention on saying “yes” to foods that make you leaner when you eat more of them, such as vegetables, fruit, nuts and seeds, whole grains, yogurt, and fish.