People are more likely to stick to eating plans that restrict calories and portions rather than ones that cut the fats and carbs. In fact, good, ol' stick-to-itiveness is critical to shedding pounds regardless of the weight-loss program, according to a new study.

Researchers at Tufts University's Human Nutrition Research Center on Aging compared the highly popular Atkins (carbohydrate restriction), Ornish (fat restriction), Weight Watchers (calorie and portion size restriction), and Zone (high-glycemic-load carbohydrate restriction and increased protein) weight-loss programs over a year's time.

"The bottom line was that it wasn't so much the type of diet followed that led to successful weight loss, but the ability of participants to stick with the program for the entire year's time," said Ernst Schaefer, one of the lead researchers.

The researchers assigned 160 overweight or obese volunteers to one of the four diet plans. At the one-year mark, the average weight loss was 7.3 pounds for Ornish, 7.0 pounds for the Zone, 6.6 pounds for Weight Watchers, and 4.6 pounds for Atkins. What's more, people on all four plans realized a 10-percent improvement in the balance of "good" and "bad" cholesterol levels, but only if they stuck to their plans for the full study.

In addition, only half of the volunteers stuck with the Atkins and Ornish plans, which experts generally consider the more extreme of the modern weight-loss programs. In contrast, almost two-thirds were able to complete the more moderate Weight Watchers and Zone plans.

Study participants also slashed their risk factors for heart disease by 20 percent. According to the researchers, for every one percent of weight loss a person achieves, there will be a two percent, or twice as much, reduction in heart disease risk factors.

The study was partly paid for by the federal government's Agricultural Research Service.

Future studies will focus on identifying practical ways to get people to stick to their weight-loss plans and how to match people with programs that best suit their food preferences and lifestyles, Schaefer said.

However, one federal government nutritionist said, an eating plan isn't the only part of a successful weight-loss program. In addition, lifestyle practices that help people maintain healthy body weights, incorporate the right balance of foods and appropriate portions, and increase their physical activity are keys to long-term weight management, said Molly Kretsch, a nutritionist with the Agricultural Research Service.