PHILADELPHIA - Just a few years ago, chef Matthew Kenney was ascending to the height of success and celebrity with a string of thriving New York City eateries, two well-received cookbooks, and, early on, a ranking by Food & Wine as one of the "Ten Best New Chefs in America."

But after Sept. 11, 2001, his empire collapsed in the economic fallout. And the French-trained chef took a surprising turn.

He gave up cooking. For raw food.

After a three-year culinary journey, he and his partner (in life and in the kitchen), Sarma Melngailis, have co-authored a diary cookbook, "Raw Food/Real World: 100 Recipes to Get the Glow" (Regan Books; 2005, $34.95), and opened a raw food restaurant, Pure Food and Wine in New York City.

Unlike many health-oriented cooks, Kenney, 40, and Melngailis, 32, both graduates of the French Culinary Institute, approached their raw food adventure from the standpoint of taste, after hearing about the culinary style while they were pondering their next project.

But the couple became hooked on a personal level, as the health benefits became evident. They had more energy, slept sounder, felt great.

"After a few weeks we realized that we weren't going back to regular cooking," Kenney said. "But it took a full year before we understood how food affected us. We experimented every single day."

They began reading and asking questions, learning all they could about raw foods, from nutrients to methods of preparation.

They learned, among other things, that raw food can be easier to digest than cooked food, that it can have more potent vitamins and minerals, since up to 80 percent of some nutrients are lost in cooking, and that otherwise healthy fats turn into trans-fatty acids when heated above 120 degrees.

After a year of navigating the nutritional maze, Kenney and Melngailis reached the point of deciding to share their newly developed food style with others. They opened their restaurant in June 2004 in the Flat Iron section of New York City, with a raw vegan menu that runs from sushi to stylized beet ravioli, green curry coconut noodles to flatbread pizza with hummus.

Heirloom tomatoes are among Kenney's favorite ingredients, and they star in some of his most popular dishes, including zucchini-tomato lasagna and tomato tartare.

Kenney and Melngailis don't miss "cooking" at all, he says, as they find preparing tasty raw food even more of a challenge.

Raw food recipes can be as simple as blender pureed soups or drinks. Their Watermelon-Tomato Gazpacho, for instance (for recipe go to http://go.philly.com/food), which uses watermelon, tomatoes, cucumbers, bell peppers, scallions, cilantro, ginger and jalapeno, can be easily blended "to taste."

Other raw food preparations can be labor intensive and ingredient-heavy (and not necessarily low-cal).

Nuts and grains are made more edible by soaking and sprouting. Some foods are slowly "cooked" at low temperatures by dehydration. The payoff is no greasy pans to scrub.

As for equipment, all you'll need, says Kenney, are a dehydrator, a powerful blender and good, sharp knives. The food processor is also useful. "And a juicer is good to have," Kenney says, "though I never got into juicing much. I just use a blender." Committed raw foodies can turn their ovens into storage space and use skillets for sprouting.

As exciting as the food is, it's the satisfying desserts that tend to lock in converts, says Kenney, items such as a dark chocolate ganache tart - one made with organic cacao beans but without the usual butter, eggs or sugar.

The new eating style may seem drastic, so Kenney suggests easing into it.

"In the beginning, keep it simple," he says.

"Take little bites of the philosophy. Go slowly. It can seem overwhelming. It did to us."

4 cups chopped, peeled cucumber (1 large English or a few Kirbys)4 cups chopped pineapple (1 large or 2 small)1 cup fresh pineapple juice1 small jalapeno pepper, seeded and diced1 green onion, white and 1 inch of green, chopped1 tablespoon lime juice2 teaspoons sea salt1 handful cilantro leaves, plus a few for garnish3 tablespoons avocado or macadamia oil1 handful finely chopped raw macadamia nutsIn a blender, add3cups each of the cucumber, pineapple, pineapple juice, jalapeno, green onion, lime juice and salt; blend smooth. Add the remaining cup each of cucumber and pineapple, the handful of cilantro and half of the oil. Pulse a few times, leaving the mixture chunky.Taste and adjust seasonings. Serve garnished with cilantro.Makes four to six servings.Per serving (based on 6): 242 calories, 2 grams protein, 23 grams carbohydrates, 18 grams sugar, 17 grams fat, no cholesterol, 652 milligrams sodium, 4 grams dietary fiber.

For the tomato sauce:2 cups sun-dried tomatoes, soaked 2 hours or more1 medium tomato, diced¼ small onion, chopped2 tablespoons lemon juice¼ cup extra-virgin olive oil1 tablespoon plus 1 teaspoon agave nectar*2 teaspoons sea saltPinch of hot pepper flakesFor the basil-pistachio pesto:2 cups packed basil leaves½ cup pistachios¼ cup plus 2 tablespoons extra-virgin olive oil1 teaspoon sea saltPinch of fresh black pepperFor assembling the lasagna:3 medium zucchini (trim ends)cup extra-virgin olive oil1 tablespoon minced oregano1 tablespoon fresh thymePinches: sea salt, black pepper2 cups Pignoli Ricotta (below)3 medium heirloom tomatoes, halved and slicedWhole basil leaves for garnishTo prepare the tomato sauce, squeeze and drain as much of the water from the soaked sun-dried tomatoes as possible. In a high-speed blender, puree the tomatoes and remaining ingredients until smooth. Set aside.To prepare the basil-pistachio pesto, place the pesto ingredients in a food processor and blend until slightly chunky.Assemble the lasagna. Cut the zucchini crosswise in half, or into 3-inch lengths. Using a mandoline or vegetable peeler, cut the zucchini lengthwise into very thin slices. In a medium bowl, toss the zucchini slices with the olive oil, oregano, thyme, salt and pepper.Line the bottom of a 9-by-13-inch baking dish with a layer of zucchini slices, each slightly overlapping another. Spread a third of the tomato sauce over it. Top with small dollops of pignoli ricotta and basil-pistachio pesto, using a third of each. Repeat layers twice.Garnish with basil and serve at once or cover with plastic and let stand at room temperature for up to three hours.For individual servings: Overlap three zucchini slices in the center of each plate to make a square shape. Spread tomato sauce over zucchini, top with dollops of ricotta and pesto and small tomato slices. Repeat layers twice. Garnish and serve.Makes six servings.Pignoli ricotta:In a food processor, combine 2 cups raw pine nuts (pignoli, soaked for an hour), 2 tablespoons lemon juice, 2 tablespoons nutritional yeast and 1 teaspoon sea salt. Pulse to combine. Gradually add 6 tablespoons filtered water while processing until fluffy, like ricotta.*Agave nectar, a natural sweetener, is the amber liquid of agave cactus and is found in natural- and health-food stores.Per serving: 662 calories, 19 grams protein, 30 grams carbohydrates, 5 grams sugar, 58 grams fat, no cholesterol, 1,777 milligrams sodium, 9 grams dietary fiber.

Makes four servingsFor the tomato tartare:5 red heirloom tomatoes, seeded and diced1 shallot, minced2 tablespoons finely diced green mango½ cup ripe mango, diced small1 tablespoon minced fresh galangal or ginger1 small handful Thai basil, julienned2 tablespoons extra-virgin olive oilCoarse sea salt and cracked black pepper, to tasteFor the assembly:Green mango relish (below)Macadamia milk (below)Walnut hemp crackers, optionalMicrobasil, microgreens or herbs for garnishIn a mixing bowl, combine all the tartare ingredients, seasoning with salt and pepper to taste.To assemble, place a 2½-to 3-inch ring mold in the center of a coupe bowl or shallow dish and fill with Tomato Tartare, packing it in with the back of a spoon. Carefully slip off the mold. Top tartare with a small spoonful of Green Mango Relish.Foam the macadamia milk with a hand blender or whip at medium-high speed (or seal and shake vigorously) to aerate it.Pour the foamed milk around the tomato mold. Garnish with greens and, if desired, a cracker. Drizzle oil on the milk.Green mango relish: In a bowl, mix one finely diced green mango, ¼ cup diced ripe mango, 1 tablespoon julienned Thai basil, ½ teaspoon sea salt and a pinch of cayenne.Macadamia Milk: in a high-speed blender, combine 1 cup macadamia nuts (soaked for an hour), 4 cups filtered water, and 2 pitted dates (or 2 tablespoons agave nectar). Whip for at least two minutes. Strain the milk through multiple layers of cheesecloth. Season with 2 tablespoons lemon juice, a pinch of cayenne and sea salt to taste. Transfer to a covered container and chill until ready to use. Makes about 4 cups.Per serving: 403 calories, 5 grams protein, 31 grams carbohydrates, 22 grams sugar, 33 grams fat, no cholesterol, 380 milligrams sodium, 7 grams dietary fiber.Raw food as an alternative lifestyle has been promoted since the 1950s. In recent years, the success of raw-food restaurants in California has spread the concept nationwide.With "Raw" (Ten Speed Press, 2003), two visionary chefs - Charlie Trotter in Chicago, Roxanne Klein in San Francisco - created a landmark volume celebrating raw food, giving it gourmet glam and nudging it into the culinary mainstream.Certainly, eating some raw food is natural and healthful; raw-food vegetarian diets can promote health and healing. But questions of long-term success, and possible vitamin deficiencies, remain. Face it, the concept runs counter to evolution and thousands of years of cooking.If that's not enough to stir controversy, add the nutritional complexities to the mix and you could have a food war on your hands.Here are a few of the pros and cons:Raw food contains live enzymes that aid digestion, says chef-author Matthew Kenney. Heated past 118 degrees, those enzymes begin to die, leaving only the enzymes our bodies produce to digest what we eat. When the body supplies those enzymes, some believe, it speeds up the aging process.Research has shown that a raw food diet can have a major effect on health, normalizing weight and increasing energy. Raw foods can be more easily digested, producing less acid and bile. Combining raw and cooked foods at the same meal, however, may cause indigestion.There is some concern that raw foods have higher pesticide levels than cooked foods, thus use of organic ingredients is recommended for raw food dishes.A small supplement of Vitamin B12 is suggested with vegetarian diets since that nutrient is found primarily in meat.Nuts, seeds and sprouts are good sources of protein. But because plant proteins don't have the "balanced" amino acid profile found in animal protein, it is best to include a variety of protein sources, with a variety of sprouts, in vegetarian diets.For essential fatty acids, Omega 3, typically found in fish, is very important. A precursor of Omega 3, alpha-linoleic acid, is found in grean leafy vegetables and walnuts.Take note: While eating most foods raw won't hurt you, the nutritional benefits of eliminating cooked foods, or for that matter, of going vegan and cutting all meat and dairy items from your diet, remains a subject of controversy for dietitians and doctors.Katherine Tallmadge, spokeswoman for the American Dietetic Association, has said that a raw food diet is apt to be nutrient-poor, protein-deficient and "dangerous," especially for people whose systems are under stress such as growing children, pregnant women, the elderly, or those with impaired immune systems.For those interested in learning more about raw foods, here are several books to explore:"Complete Book of Raw Food: Healthy, Delicious Vegetarian Cuisine Made with Living Foods" by Lori Baird (Healthy Living Books, 2003) - More than 350 uncooked recipes from more than 40 top raw food chefs worldwide, with tips for making elegant and healthy meals, from preparation to presentation."Living Cuisine: The Art and Spirit of Raw Foods" by Renee Loux Underkoffler (Avery Publishing, 2004) - A comprehensive introduction to a raw-foods lifestyle, including tools, techniques, nutrition and safety tips and more than 300 gourmet vegan recipes from the former chef/co-owner of Raw Experience in Maui."Raw Food/Real World" by Matthew Kenney and Sarma Melngailis (Regan Books, $34.95) - A practical guide to the alternative raw food lifestyle, from the couple's personal journey and home dining to their gourmet restaurant recipes."Raw Gourmet" by Nomi Shannon (Alive Books, 1999) - A certified health educator's guide highlighting the benefits of raw food and the importance of organics, with a wide range of recipes."Sunfood Cuisine: A Practical Guide to Raw Vegetarian Cuisine" by Frederic Patenaude (Maul Brothers, 2002, $29.95) - France's leading raw-gourmet chef on the basic techniques of raw cuisine. Among his tips:Wash produce, even organicsIf not organic, wash with soapWash nonorganic fruits, even if you're not going to eat the peel.