When it comes to keeping warm, the old adage applies: You are what you eat.

So says Althea Zanecosky, a registered dietitian who knows about nutrition from A to Z.

In her day job, Zanecosky, 48, does public relations work for a dairy organization. But she is also a volunteer food and nutrition expert for the American Dietetic Association. A Pennsylvania State University graduate, she taught high school home economics for six years and received a master's degree in nutritional biochemistry from Drexel University in Philadelphia.

However, she's no food cop. Her philosophy: "There are no bad foods, only bad diets." Many so-called bad foods, such as red meat and eggs, contain nutrients that are vital and protective. The stearic acid in chocolate, for example, may actually lower cholesterol, she says, and there's evidence that the fat in peanuts may be healthy for the heart.

Food is not the only factor in longevity, and longevity is not the only factor in quality of life. "It's important to eat well but it's also important to enjoy the foods you love," Zanecosky says. "If you stay active, you can have your cake and eat it, too."

She also has a theory about how food can help someone stay warm. It involves three basic principles:

* Hot is better than cold.

* Carbohydrates are better than protein.

* Liquid is better than solid.

Hot food is better than cold for obvious reasons: It actually warms the organs as it goes down, she says. Then there's the psychological effect--the comfort of holding a steaming cup of cocoa, for instance, in icy fingers after a day on the slopes.

Carbohydrates (sugars, starches, etc.) are better than protein because they burn more efficiently and generate more constant heat, according to Zanecosky. Protein, by contrast, is the fuel of last resort, what the body consumes when it sputters out of glucose. Because protein is difficult to break down, it takes more energy to metabolize-- energy that could be used to warm the body. That's why runners feel crummy at the end of a marathon; their bodies, plumb out of carbs, have switched to protein, cannibalizing their muscles.

Liquid food is better than solid because nutrients from liquids exit the stomach and enter the blood faster.

How does this translate to real life? Zanecosky and I concocted an ideal menu for a day of such cold-weather pastimes as shoveling snow and cross-country skiing:

* For breakfast: A bowl of oatmeal topped with honey and washed down with hot chocolate. (Coffee is hot, too, but the caffeine helps cause dehydration, which is not good because water helps burn fuel more efficiently.)

* For lunch: A bowl of chili, a couple slices of corn bread, a mug of hot apple cider, with rice pudding for dessert. Spicy foods such as chili are excellent heat generators, Zanecosky says, because they contain capsaicin, which acts as a vasodilator, warding off chills by bringing blood to the surface of the skin.

* For dinner: This is a good time to stock up on protein, assuming you won't be tobogganing or building snowmen in the dark. If your iron level is low, eat plenty of beans or slice into a steak. Iron deficiency makes people feel cold, Zanecosky says.

CAPTION: Chili is the sort of hot, spicy food that's ideal on a cold day.