For about 70 years, scientists have known that restricting how much laboratory rats eat, while at the same time maintaining their nutrition, extends significantly how long the unhappy rodents will live.

In the mid-1990s, Leonard Guarente, a molecular biologist at MIT, discovered a gene in yeast and worms (called SIR-2) that responds to caloric restriction by producing an enzyme that shuts down long stretches of DNA involved with metabolism and aging.

Today, a small number of people try to trigger the therapeutic benefits of SIR-2 by practicing caloric restriction with optimal nutrition, CRON, or more simply, CR.

But the holidays are traditionally the time for gastronomic overindulgence. We pine for turkey, gravy, and pies. What's a poor CRONer to do? We asked two of them, April Smith and Michael Rae, what they ate for Christmas dinner. They generously offered not only their recipes -- but also to test-drive their holiday meal, and take a few pictures of the results for our viewers [click here to see photos].

Like many CRONers, Michael and April want to dispel the most common perception about caloric restriction: that it makes people miserable. Lenny Guarente recently told us, "Most people who have tried the diet find it unpleasant. It makes them cold, it makes them hungry, they're irritable."

Not so, say April and Michael. April is 31 years old, and lives in Philadelphia, where she's the director of organizing for the Pennsylvania Association of Staff Nurses and Allied Professionals. She has been practicing CR since spring 2004. Most days, she eats around 1,200 calories. "The short term benefits of CR have been incredible for me. I never get sick. I sleep much, much better, and have more energy. I feel great in my body," she says. Smith adds: "I have also experienced some emotional effects that are harder to explain. I am a more easy-going person. Stress affects me much less than before, and I am more patient, less likely to become irritated or lose my temper."

Michael is 35 years old and lives with in Philadelphia with April. He's the research assistant to Aubrey de Grey, the British theoretical biologist who believes he has found a "cure" for aging (see "Do You Want to Live Forever?"). Ordinarily, Michael eats a little more than 1,800 calories. Michael is less sanguine about the possibilities of CR. "It's clear from the research that, even under the most optimistic scenario, adult-onset CR at a manageable level can only grant another decade or two of healthy life over and above the 5 years or so to be gained by leading an unusually healthy lifestyle," he says. For him, "CR [is] as a bridge into a future in which emerging biotech will ultimately allow for a greatly extended youth."

Here's Michael and April's Christmas dinner. (All measurements are per person.)

Christmas Salad with Hazelnut-Nutmeg Dressing

20 g arugula: 5 calories

37 g red pepper, diced: 10 calories

Dressing:

1 teaspoon hazelnut oil: 80 calories

4 g hazelnuts: 26 calories

1 tablespoon balsamic vinegar: 8 calories

Nutmeg: 0 calories

Directions: Arrange the arugula on a salad plate. Decorate with red pepper. Drizzle with hazelnut oil, balsamic vinegar. Dust with nutmeg. Arrange hazelnuts on top.