If you've tried fad diets, over-the-counter diet pills, liquid diets, and specialty diet foods and products and haven't lost weight, there's still hope. Eat less fat and exercise more may seem like old-fashioned advice, but they are among the most effective ways to lose weight according to new research.

Researchers at Beth Israel Deaconess Medical Center analyzed data collected from over 4,000 obese people picked from the 2001-2006 National Health and Nutrition Examination Survey (NHANES) conducted by the Centers for Disease Control and Prevention. This survey is used to assess the health and nutritional status of people in the United States.

More than a third of Americans are obese and 50 to 70 percent are trying to lose weight... Just a 5 percent reduction in weight can improve health,

People included in the study had a body mass index (BMI) of 30 or greater 12 months prior to their interview with researchers, and they were all over 20 years old. Among those surveyed, 2,523 reported attempting to lose weight. Forty percent said they had lost 5 percent or more of their weight, and 20 percent reported losing at least 10 percent of their body weight.

The common denominator among those who experienced weight loss was that they exercised more and ate less fat. These individuals lost significantly more weight. Those who joined weight loss programs also had greater weight loss success, giving credence to the importance of structure in a weight loss plan. A small number of the study participants reported weight loss using prescription drugs.

The researchers, led by Jacinda M. Nicklas, MD, MPH, MA, found that people who used popular diets, liquid diets, nonprescription weight loss pills, and diet foods/products did not have success with weight loss. "There are a lot of fad diets and expensive over-the-counter medications that haven't been proven to be effective," said Christina Wee, MD, MPH, a senior author of the research in a press release. The fact that most of the weight loss methods that are successful are both inexpensive and easily accessible is encouraging: Eat less fat and exercise more.

More than a third of Americans are obese and 50 to 70 percent are trying to lose weight. The health risks associated with obesity are significant and include high cholesterol, high triglycerides, type 2 diabetes, heart disease, stroke, high blood pressure, sleep apnea, osteoarthritis, and gallstones. Just a 5 percent reduction in weight can improve health, according to Dr. Nicklas.

The research appears in the April 10, 2012 online issue of the American Journal of Preventive Medicine.