Each year around 45 million Americans go on a diet. But only about 20 percent of us keep the weight off for four years or longer. There are dozens of different diet plans to choose from — but which one offers the greatest chance of long-term success?

A recent Harvard University study points to the qualities your diet needs to help you maintain the weight-loss you've worked hard to achieve. It's not only low in carbohydrates and high in proteins, but also includes fats and carbohydrates that come from plant-based sources.

“Our study goes beyond the simple question of ‘to carb or not to carb?’” lead author of the study, Binkai Liu, research assistant in the Department of Nutrition at Harvard T.H. Chan School of Public Health, said in a press statement. “It dissects the low-carbohydrate diet and provides a nuanced look at how the composition of these diets can affect health over years, not just weeks or months.”

Replacing refined carbohydrates like white bread or sugary cereals with whole grain foods and cutting back on animal-based fats and proteins helped dieters keep weight off over the four-year period.

To come up with a successful diet plan, the team of researchers reviewed the diet and weight of over 123,000 healthy adults. The data were taken from three large studies done between 1986 and 2018: the original Nurses' Health Study, the Nurses' Health Study II and the Health Professional Follow-Study.

Everyone included in these three studies gave information on their diet and weight every four years.

The researchers scored the participants' diets based on how well they stuck to five categories:

  • Whole grains, such as oatmeal, whole grain pasta or breads.
  • Fats from vegetable oils, though not including tropical types such as coconut or palm oils (because of they are high in saturated fat.)
  • Plant proteins such as beans, nuts and soy.
  • Fruits
  • Vegetables

They found that replacing refined carbohydrates like white bread, white rice or sugary cereals with whole grain foods and cutting back on animal-based fats and proteins appeared to reduce the amount of weight folks gained over the four-year period. They recommend diets based on lentils and legumes like pinto, cannelloni or garbanzo beans; whole grain cereals and soy products; as well as vegetable oils, avocados and seeds; combined with fruits and vegetables and low-fat dairy products.

It's not about “to carb or not to carb” — it's about the kinds of carbohydrates you eat.

There are some limitations to consider. Most of the participants were white women, so it's not known whether the findings would be the same for other groups. Also, the dietary information and people's weights were based on self-reports which may be flawed.

This large study offers valuable information despite these caveats. “The key takeaway here is that not all low-carbohydrate diets are created equal when it comes to managing weight in the long-term,” senior author Qi Sun, associate professor in Harvard's Department of Nutrition, said in a press statement. “Our finding could shake up the way we think about popular low-carbohydrate diets and suggest that public health initiatives should continue to promote dietary patterns that emphasize healthful foods like whole grains, fruits, vegetables, and low-fat dairy products.”

If you want to lose weight and keep it off, in addition to following a particular low carbohydrate diet, the Centers for Disease Control recommend having regular physical activity, getting the recommended hours of sleep each night, reducing stress, and speaking with your health care provider about whether medications or surgery are a good idea for you.

The study is published in JAMA Network Open.