By this time of year, many peoples’ best-laid New Year’s Resolutions have died, just seven short weeks after they were born. One reason why it’s difficult to lose weight—the most common resolution—is that dieting is so confusing.

For instance, the American Heart Association's recommended diet is one of the most effective food plans out there. It’s also one of the most complicated. It requires, according to a recent study, “consuming vegetables and fruits; eating whole grains and high-fiber foods; eating fish twice weekly; consuming lean animal and vegetable proteins; reducing intake of sugary beverages; minimizing sugar and sodium intake; and maintaining moderate to no alcohol intake.” On top of that, adherents should derive half of their calories from carbs, a fifth from protein, and the rest from fat—except just 7 percent should be saturated fat. (Perhaps the goal is to keep people busy doing long division so they don't have time to eat food.)

It’s a lot to remember, and nutritional information is already notoriously contradictory. So rather than put people on a complex diet, a group of researchers recently decided to test whether they could still get people to lose weight and boost their heart health by telling them to do just one thing: Eat more fiber.

Researchers found 240 participants and divided them into two groups. One group was instructed to eat the American Heart Association, or AHA, diet, including shaving 500 to 1,000 calories off of their normal food intake. The other was simply told to eat more fibrous foods. High-fiber foods include fruit, legumes, whole grains, and some vegetables. (It’s recommended that adults eat about 25 to 30 grams of fiber per day, but very few people do this.)

After a year, the more-fiber group had lost 2.1 kilograms, or about 4.6 pounds, according to results published recently in the Annals of Internal Medicine. The AHA group, which had been following a much more complicated eating regimen, lost just half a kilogram more, or six pounds. It was a pretty small difference, but the AHA group suffered greatly for it: They were cutting more than twice as many calories per day, around 400, as the fiber group had been. Fiber is also a part of the AHA diet, but the fiber group was eating about twice as much of it as the other participants. There was no difference in blood pressure or fasting glucose levels between the groups at the end of the experiment. In other words, the people killing themselves to meet a raft of rules did roughly as well as the people who were simply eating more beans and apples.

Changes in Weight and Insulin Levels Over Time

Annals of Internal Medicine

“A dietary intervention focusing on a targeted fiber goal may be able to achieve clinically meaningful weight loss similar to the widely applied, but more intense, AHA dietary guidelines,” the authors, who were from the University of Massachusetts and elsewhere, wrote. They think this might be because, as past studies have suggested, it’s easier to follow one dietary rule than it is to adhere to a whole new life plan.

This might seem like yet another dubious miracle cure of the sort peddled by TV doctors, but it’s really not. Most people eat only about half as much fiber as they should. Foods that are high in fiber tend to be filling and, as far as caloric impact goes, are more of a swan dive than a cannon ball. A handful of high-fiber carrots can produce a feeling of satiety, but they don’t cause as much waistline damage as the same number of KFC hot wings.

Of course people should strive to eat as overall healthfully as they can, or desire to. Americans have been steered wrong by one-note dietary guidelines before. Still, we are nonetheless always on the hunt for one simple trick for weight loss. Fiber isn’t necessarily one, but it’s a good place to start.