Losing weight has always been a problem for overweight and obese people. There are so many books, so many TV shows teaching people how to choose the diet that best suits them. There are so many studies on the efficiency of each diet and yet so many people complain they cannot maintain their weight.

The latest study in the field notes that people can lose weight no matter what their diet is as long as they consume fewer calories. It was conducted by experts at the Harvard School of Public Health in Boston and the Pennington Biomedical Research Center in Baton Rouge, part of the Louisiana State University system.

Frank Sacks, a lead author of the study and professor of cardiovascular disease prevention at Harvard said “it’s not a question of eating a particular type of diet. To lose weight, it comes down to how much you put in your mouth.”

For the study, the researchers recruited 811 overweight or obese older adults and randomly assigned them on four diets: two low-fat diets with 20 percent of calories from fat and two high-fat diets with 40 percent of calories from fat. The calories from carbohydrates ranged from 35 percent to 65 percent. Protein was either 15% or 25% of calories. Each plan cut about 750 calories from a participant’s normal diet, but no one ate fewer than 1,200 calories a day.

The participants were asked to engage in 90 minutes of moderate exercise per week and all had diet counseling. They were followed for two years, much longer than most studies. After two years, they lost on average 9 pounds and took 2 inches off their waistline, regardless of which diet they were on.

“There's no special diet that's better for weight loss than any other. As long as it's healthy for you -- high in unsaturated fats, high in whole grains and fiber, low in junk foods and high carb-junk foods, and low in fatty meats -- any of these variations will be fine for losing weight,” Sacks said.

The study found that in six months, the participants lost on average of 13 pounds no matter their diet. Also they had improvements in heart-disease risk factors, including increases in the HDL (good) cholesterol, and decreases in LDL (bad) cholesterol and triglycerides (blood fats) at six months and two years. No matter their diet, people reported similar levels of fullness, hunger and satisfaction.

“Find a diet that's heart-healthy. Follow it, and really be mindful of your intake. Get some support from other people in your life or from organized groups,” Sacks advises people who want to lose weight.

The findings are published this week in The New England Journal of Medicine.