Dieters could not live on hamburger- and-cottage-cheese plates alone. Science wouldn't let them. Not in today's dieting age of behavior modification and biochemical breakthroughs. Not when eating Lean Cuisine and jogging are national pastimes.

But we tend to forget the days when being fat meant simply that you were an uncontrollable glutton, that to lose weight all you had to do was to eat less. Back then, those high-protein, high-fat hamburger-and-cottage-cheese plates were as stylish as surf 'n turf.

Pound for pound, dieting has become more complex. And we have become more sophisticated.

"Patients have changed," says Dr. Arthur Frank, clinical assistant professor of medicine at George Washington University and an internist who supervises an obesity management program. "They're more food conscious, more health conscious, more literal in nutritional terms."

The fact is, we may not even realize the sensibility we have about weight loss nowadays. The problem is still the same; the way we look at it is different. What seems like common sense to many of us, what we now take for granted as the axioms of dieting, wasn't always so.

It's time to take a look back a decade or two, to remember where we came from and to rehash where we are. A "then and now" of dieting, let's call it -- at least until the next wave, at least until the "nows" become the "thens."

Then: You are fat because you have no willpower. You are fat because you have low esteem, because you're inadequate. Doctors used to reinforce that belief, says Suzanne Goddard, a 33-year-old Washingtonian who recently lost 133 pounds under the care of Dr. Frank. But Goddard remembers the diet specialists of the past with their "blaming attitudes" and "guilt trips." It just compounded the problem, she says.

Now: Diet specialists recognize that obesity is a very complex interaction between culture, psychology and physiology, says Kelly Brownell, co-director of the University of Pennsylvania Obesity Research Clinic.

There has been an acknowledgement that getting fat in our society is easy, that food makes people feel better and that there are strong physical reasons why some people don't lose weight as quickly as others, says Brownell. The problem is looked at more as a disease.

Specialists now explore why people eat, how they eat and how they use food as part of their lives, adds Frank.

Then: You are fat because you eat too much. Follow this low-calorie diet and you will lose weight.

Now: In better identifying the causes of being overweight, experts now know that its treatment has to be more complicated. Food intake alone is not the answer. Exercise, behavior modification, social support and proper nutrition are all used jointly to tackle the problem, says Brownell.

In addition, experts agree, there has been the growing recognition that because the reasons people are fat differ, each person must be treated with an individualized approach.

While it remains true that you need to consume fewer calories as part of a weight-loss plan, Dr. Aaron Altschul, director of the Georgetown University Diet Management and Eating Disorders Program, said those calories are looked at more selectively nowadays. The important thing is not just to reduce calories, but to reduce those that are caloric-dense, such as fats, says Altschul.

Then: Taking the weight off is the tough part. Once you lose the weight, the problem goes away.

Now: Dieting is more of a way of permanent eating rather than a meal plan to be followed for a short period. It's a complete alteration in food choices, eating habits and behavior. It never ends.

People are into long-term weight loss, says local nutritionist Anne Molofsky. People used to be willing to go on a diet for a month. Now, says Molofsky, they realize the importance of follow-up.

Then: If you don't lose weight on this diet, it's surely because you cheated.

Now: Those people who were "shunned" as being closet nibblers were probably telling the truth when they said they didn't cheat, says Frank. It is "clear medically" that some people have different metabolic rates, that some people's bodies fail to generate heat and dispose of calories, says Frank.

Then: Exercise is good for your health but if you're trying to diet, it will increase your appetite. Anyway, the diet should take care of it. Besides, being athletic isn't for fat people, it's for athletes.

Now: As we readily know, exercise has become not only a national fetish but also is stressed on practically every kind of weight-loss program. Goddard says she used to laugh about exercising. "Not me" was her attitude. Not anymore; Goddard now makes sure she jogs regularly.

Brownell says that previously it was thought that the only advantage to exercising was that it would burn off fat. Now scientific evidence shows that exercise can help to raise your metabolic rate even when you're not exercising. In addition, he said, at lower levels of activity, it has been shown to decrease appetite, not heighten it.

Then: Follow this diet -- Have orange juice, black coffee and dry toast for breakfast. Eat tunafish and lettuce for lunch. Don't get near any "forbidden" foods.

Now: There has been an easing of regimentation from following strict food plans, say diet specialists. Dieters today assume much more personal responsiblity when it comes to planning their own menus and making specific food choices, says Dr. Reva Frankle, director of nutrition at Weight Watchers International.

It's part of "educating" the dieter, says Frankle, because if a dieter is following a specific plan because a doctor told him too, chances are he won't follow it once the doctor isn't around.

In addition, now many experts and dieters are receptive to the idea of trade-offs; that a diet of total deprivation from all your favorite foods can turn into a diet of frustration and failure.

And, adds Altschul, there is evidence that eating five or six small meals is better than one big one, or even three.

Then: If you want to go on a diet, the food will be boring, monotonous, unattractive, not to mention tasting pretty awful. How many times can you buy diet fruit cocktail and Carnation Slender? It will take a long time to cook something interesting at home too.

Now: The element of creativity is easier for dieters. Supermarkets are filled with low-this, low-that foods -- pegged to a mass audience interested in health and nutrition -- that merge with the needs of consumers seeking weight loss. High-fiber foods, fresh fruits and vegetables, fish and poultry are advised for everyone. Dieters are no longer singled out. There is the emphasis that low-calorie food can and should look pretty, and that it can also taste good.

Then: You're on a diet and you're eating at a restaurant? Thank goodness they have the Dieters Delight: creamy cottage cheese and a juicy hamburger. Dieters need a lot of protein for satiety. Remember not to order a baked potato or anything "starchy." Those are fattening foods.

Now: People realize that foods high in protein are frequently high in fat, says Frankle. Word has spread that diets high in fat are calorie dense and that high-fat diets are high risks for heart disease and elevated cholesterol.

In addition, the potato myth got started, Frankle theorizes, because the vegetable's high-calorie additions became inseparable from the plain potato. In addition, she says, people associated all carbohydrates in one lump -- simple carbohydrates such as pies and cakes with complex carbohydrates such as grains and bread. Carbohydrates got a bad name.

Then: There are magical foods, miracle weight loss programs and magical books that will cure your problems.

Now: About the same. Fad diets are as popular as ever, diet specialists agree -- even though people have much more access to knowledge about proper nutrition. The only difference may be that fad diets today play off of current trends, says Beila Kunis, a dietitian and director of Nutrition Counselors, Inc., in Chicago.

Frank says the information age may in fact have made dieters more confused, that they're hearing so much from different sources that it's hard to sort it all out. It all makes them easily prone to fad diet "hookum," he says. People are more easily trapped by things that give them "simplistic answers to complicated questions."

So where has this all taken us? According to government figures, there are just as many overweight people in this country as there were 20 years ago. If we're not getting skinnier then, are we at least getting smarter?