By now, many, if not a majority, of the Americans who vowed to lose weight in 2008 have fallen off the proverbial wagon. But it's still only late January. Plenty of time to start anew.

The problem is deciding how to do it.

By commercial diet plan? By diet book? By computer? Or how about one of the hospital weight clinics in Pittsburgh?

The short suggestion from one local weight-loss expert: Do whatever works for you -- as long as it's of no longer duration than three to six months.

"I don't endorse any particular diet plan for everyone. Some do better with Weight Watchers; others with meal replacements. Others don't like meetings, so they have Internet diets. Some go to commercial centers," said Dr. Jorge Vazquez, director of medical nutrition at the Allegheny Center for Digestive Health, a part of AGH located on Federal Street on the North Side.

"The other option is buy a book and do it on your own. The popular one is the South Beach Diet, even Atkins, and the Zone. There are so many books around. Each has some strengths, some weakness. My main concern is people almost never complete the program. ... They don't follow with the behavioral part or exercise. Practically all of them have gimmicks."

Dr. Vazquez, who also is an associate professor of medicine at Drexel University Medical School, noted there has been no real study showing one commercial diet is better than another, and he is of the same opinion.

"I don't have any problem with people using any of the diets, except they have to stay with them. ... They have to follow everything," he said.

"Some people have expressed concern about side effects of some of these diets, but they are all safe for the short term.

"My concern is for the long term. If you can lose 20 pounds doing the Atkins diet, fine. But what diet are you going to do the rest of your life? For example, the Atkins diet eliminates many fruits or vegetables for life. South Beach says there are some good veggies and some bad, but there's no evidence that is true. All fruits and veggies are good for you. ... That's what concerns me in the long term," Dr. Vazquez said.

"In the long term, what you need is a well-balanced diet, fruits and vegetables, calorie control and exercise.

"We know the recommendation for exercise is to accumulate 10,000 steps a day. That's five miles. ... We want people to exercise five days a week. We want it to be aerobic rather than weight lifting. If you go to a gym, swim, walk, run, jog, row. It doesn't matter as long as you do enough to do the equivalent [of 10,000 steps]."

There also should be what Dr. Vazquez calls a "behavioral component, including a way to control the urges to eat, why people eat."

At the AGH center, as at most hospital-based weight management clinics, the emphasis is on custom-designed programs.

"What I usually do, is go over issues with them, their physical activity, the type of diet they eat," Dr. Vazquez said. "Based on that I try to come up with a program that meets their needs.

"I believe one of the easiest programs to follow is a meal replacement plan."

The meal replacement program used by AGH -- and Forbes -- is HMR-in-Home. (The HMR is short for Health Management Resources.)

"Patients who decide to follow that program consume three liquid supplements, two pre-packaged meal entrees and then, as a minimum, five fruits or vegetables daily," Dr. Vazquez said. "That's a lot of food [but only] 1,200 calories."

Other tools include medications such as the fat blocker orlistat (marketed at prescription-strength as Xenical and over-the-counter as Alli) and appetite suppressants like Meridia (generic name is sibutramine) and Adipex (generic phentermine).

In cases of extreme overweight, weight-loss, or bariatric, surgery is suggested, Dr. Vazquez said.

"Most of these people are 100 pounds over their recommended weight."