Video: Diet foods – what's good, what's bad?

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SEATTLE - Right now, one in three Americans is overweight, but a new study says that all Americans will be overweight in 40 years.

Billions of dollars are spent each year on diet foods.

But some choices are better than others.

"There's never going to be one particular food that's marketed to help you lose weight that's going to do it," said Dr. Ann Kulze, nutrition and wellness expert.

Low-calorie frozen meals are usually a good choice, but not always.

"Avoid the great white hazards, these refined carbs, white flour, white rice, white potatoes, sugar," Kulze said.

Another diet food loser is the liquid lunch.

"Liquid calories simply do not suppress the human appetite to the same degree of solid food calories," Kulze said.

Low-carb foods? Proceed with caution.

"Just because something is labeled low-carb does not mean it's going to be low in calories or even healthy for you," Kulze said.

Fat-free foods have also lost steam.

"The only fat-free food I recommend to anyone -- people that want to lose weight or people that are healthy weight -- is fat-free milk," she said.

Another loser: Sugar-free food.

"It's probably a classic example of labeling schizophrenia at its finest," Kulze said.

The first ingredient listed is white flour.

"White flour in the human body is handled exactly like if you sat there and ate sugar out of the bowl," Kulze said.

Even sugar-free soda is risky. One study shows your risk of being overweight rises more than 40 percent with every diet soda you drink.

The quickest way to slim down is to choose foods like whole grains, beans, veggies, fruits and lean meats. And make sure to get at least 15 grams of protein and seven grams of fiber in every meal.