A massive survey by Consumer Reports found six key behaviors that help people lose weight and keep it off.

Two out of three American adults are overweight, and adults gain an average of 20 pounds between ages 25 and 55. Yet some people are able to lose weight permanently, and others never seem to gain a pound.

Consumer Reports interviewed 21,000 readers to find out their secrets to losing weight.

Diane Lobel said she found that exercise and eating right were the keys to losing 40 pounds and keeping it off for three years.

"The doctor is even happy. He thought I was a completely different patient. He had to check his records to make sure it was me," Lobel said.

Consumer Reports staffers broke down eating right and exercising into six key behaviors.

No. 1 is one we all know but don't want to hear – watching portions and not eating everything you want.

"People who've always been thin typically aren't sitting around eating potato chips," said Jamie Koph, of Consumer Reports. "Only 3 percent of the thin people we surveyed said they ate whatever they pleased and never exercised."

"Portion control is a given. I have to make sure I don't go overboard on anything that I eat," Lobel said.

Like Lobel, most of the successful dieters lost weight without the help of a diet program, pills or a medical treatment. Their strategies were similar to those of the naturally thin.

No. 2, after portion control, is that they eat lots of fruits and vegetables. The more days that respondents ate five or more fruits and veggies, the lower their average body mass index (BMI) was.

Strategy No. 3: People with lower body weights consistently opted for whole-wheat breads and other whole grains, rather than white flour.

Next, No. 4: limit fat. Restrict it to less than a third of your daily calorie intake.

Exercise – No. 5 – is, of course, another secret of successful dieters. Although vigorous exercise is especially effective, the survey shows that any physical activity is helpful.

Finally, the survey found that those who weigh less eat out less. And as a bonus, eating home-cooked meals can also save you money.

Consumer Reports has suggestions for cooking healthy meals on a budget.