New Harvard research has found that not all trendy low-carb diets are equal when it comes to maintaining weight — some may even make you gain a few pounds.

People who consume low-carb diets that emphasize plant-based proteins and healthy fats have a better chance of keeping excess weight gain at bay than those who eat low-carb diets comprised mostly of meat and unhealthy fats, according to results of a decades-long study published Wednesday in JAMA Network Open.

“Our study goes beyond the simple question of, ‘To carb or not to carb?’” lead study author Binkai Liu, a research assistant in the university’s Department of Nutrition, said in a 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,” she explained.

123,332 healthy adults self-reported their diets and weights every four years.

Carbs represented 38-40% of the daily calorie intake in each of the five diets studied:

Participants who adhered more to the total low-carb, animal-based, or unhealthy low-carb diets on average gained more weight compared to those who partook in the healthy low-carb diet.

Liu told CNN that the unhealthy low-carb dieters gained, on average, 5.1 pounds over four years.

The healthy low-carb dieters, meanwhile, lost an average of 4.9 pounds over the same period.

The weight differences were most pronounced among participants who were younger than 55 years old, overweight or obese, and/or less physically active.

The vegetable-based low-carb diet, meanwhile, offered mixed results.

“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 the nutrition department, said in a statement.

Sun continued: “Our findings 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.”