What if you could live past 100, but feel like you're in your 40s?

A growing number of Americans believe it is possible by eating a special kind of diet. Now there is new research that just may prove them right.

If you have a Big Mac, large fries and a big Coke, you will get 1,400 calories with just one meal.

But if you eat grain cereals, salad, tuna and vegetables, you still get 1,400 calories, but it is three meals.

While there is no doubt which option is healthier, there is now evidence that all those nutritious unprocessed foods may add decades to your life.

"I think I will probably live much longer than most people who don't give much thought to what they eat," said Sarah Kretchmer.

Kretchmer said she expects to live well past 100 years old, but not in a wheelchair.

"I don't want to be old and turning into some kind of puddle, you know," Kretchmer said.

So, Kretchmer embarked on a life-altering regimen, and her lunch of cod, greens and melon was just one meal in a way of life known as calorie restriction.

She eats fewer calories than even nutritionists recommend. Some people cut their intake by 40 percent.

"I actually have printouts of today's values. I am at about 1,400 a day," Kretchmer said.

Studies prove that in animals, calorie restriction works.

Monkeys, rodents and fish sometimes live up to twice as long when they are forced to eat less.

The initial human research suggests that even exercise can't compete with cutting calories when it comes to living longer.

The calorie cutters in the studies had almost zero heart attack risk and the blood pressure and cholesterol levels of a teenager. These people were in their 50s.

Dr. Luigi Fontana of St. Louis' Washington University, who is one of the researchers, said the results are so promising that they now want to know if calorie restriction can actually reverse aging.

"You don't have to be so extreme. You can have major changes by changing quality of your diet," Fontana said.

Kretchmer's parents are also part of the research, and their lunch of a huge plate of fruits and vegetables is only 499 calories -- the same as two raisin bagels.

"We're just very, very selective in the types of food we do eat," said Dick Kretchmer.

Now in their 60s, the Kretchmers may live far longer than many of their friends, but if the theory is correct, Sarah Kretchmer will live even longer.

There are enough die-hard believers in the program that there is now a Calorie Restriction Society. Illinois member David Stern eats 1,200 to 1,400 calories a day.

"Cut back 10 percent and see what happens to your weight. If you get down to something you're happy with, fine. If not, cut back another 10 percent, see what happens," Stern said.

Stern lost more than 50 pounds.

"My blood pressure dropped to normal range," Stern said.

But skeptics include University of Chicago geriatrician Daniel Brauner, who is not convinced by the human research.

He doesn't think the diet would work for most Americans.

"This would be something, if it did work -- be something that only a small number of people could adhere to. Because we eat more than just to live, it might take some of the pleasure from eating," Brauner said.

But, science aside, the people on this diet said they are sold, especially because of the way they feel.

"I sleep better. I sleep like a stone," Dick Kretchmer said.

"The energy is better," said Carla Kretchmer.

"I went off all my medicine after two years," Stern said.

"I rarely get sick. I just feel like it's a healthier way of being. I feel better," Sarah Kretchmer said.

Related Resources:

CalorieRestriction.org

Walford.com

Psychology Today: The Skinny On Calorie Restriction

ScienceDaily.com: Calorie Restriction May Prevent Alzheimer's