Show of hands, please: How many of you pay careful attention to your car's maintenance, with periodic oil changes and regular tune-ups?Good, good. Put your hand down now. People are staring.Here's a tougher one: How many of you are equally devoted to your body's upkeep, to periodically flushing out its sludge and keeping it running in tip-top condition?Ahh. We thought not."We're overfed and, really, undernourished," says Colorado Springs, Colo. naturopathic physician Glen Nagel. "People will change their car's oil every 3,000 miles to a T, but ask them what they've done to maintain their health, and. ..."Like a car, our bodies rely on fuel, consumed as food or the food facsimiles that increasingly populate grocery store shelves. If your body is running more like a Pinto than an MX-6, chances are that subpar nutrition is taking its toll."The only way you get energy is, you combust it -- you burn fuel and you produce by-products," Nagel says. "Your body has to deal with those."To help your body cleanse itself of such physical sludge, consider an old idea that's been modified and dressed up in new language. Detoxification -- the process of clearing toxins from the body, neutralizing or transforming them -- has much in common with the ages-old notion of fasting. "The true fast is a water fast," Nagel says. "That's the most severe, because it allows the body to really detox, so a lot is dumped, and that can really overload detoxification processes. The body can only detoxify stuff so quickly."Here's a primer to help you understand the thinking behind detoxification: We live in a world of pollutants, including not only environmental toxins, but processed and chemically altered foods. The body, too, produces toxins through normal, everyday function; stress can increase the level of these biochemical bad boys."The proper elimination of these toxins is essential," writes California Dr. Elson M. Haas in The Detox Diet ($9.95, Celestial Arts). "The healthy human body can handle certain levels; the concern is with excess intake or production of these toxins, or a reduction in the elimination process."The liver and the gastrointestinal tract are the body's anti-toxicity workhorses. When they're overloaded, symptoms begin to appear, including headaches, fatigue, congestion, backaches, aching or swollen joints, digestive problems, mood swings and muddled memory and concentration."Many of the toxicity symptoms can be related to so many things," Nagel says. "Generally, what I look at is prescription medications -- if they've been on many of them for a long time. When your liver is overworked trying to detoxify those drugs, it won't have the chance to do all the things it has to do: making hormones, breaking down internal wastes, storing vitamins and glycogen for short-term energy for the brain."And, I look at the diet -- processed food, processed fats, all the things that stimulate the liver detoxification pathways. Alcohols, smoking, saturated fats, processed foods. That gives you a pretty good understanding that they're going to have some kind of problem."'NUTRITIONAL SUICIDE' So, here you sit, you who were so smug just three minutes ago about the conscientious care you give your car. Wondering, now, when your poor, neglected body will betray your abuse -- if it hasn't already."With a lot of people, there's a sense of invincibility -- especially young people," Nagel says. "You don't think about your body until it breaks."If your body has already broken -- or, if you're getting warning signs that a breakdown is imminent, you may feel powerless to make any real change. That, in itself, may be another sign of toxic build-up -- and the best possible reason to reform yourself now, before any damage becomes permanent."There is something that you can call nutritional suicide, and we're on that path," Nagel says. "The more your body is fed the wrong fuel, the more it's going to affect your attitude: 'It doesn't really matter. We're all going to die anyway.' ...Because we're a poorly fed nation, we have a poor attitude."Well, snap out of it. A detoxification regimen -- followed by a commitment to a healthier, less toxic diet -- can make a big difference, according to doctors who prescribe this dietary remedy."We detoxify/cleanse for health, vitality and rejuvenation -- to clear symptoms, treat disease and prevent future problems," Haas writes. "A cleansing program is an ideal way to help us reevaluate our lives, make changes or clear abuses and addictions."Detox regimens vary widely, from a short, water-only fast to a 21-day group program Nagel tailors to patients who want to share resources and support."They have to address resting and repairing the body," says Nagel, who advises detoxers to get away to a quiet spot if possible. "Resting really has to involve all the aspects of physical, emotional and nutritional health. To make it a complete program, you have to put both your physical body in it and your mind in it."Longer regimens typically involve a gradual stepping-down to progressively healthier, less congestive foods, as in Nagel's 21-day program. For a typical American food junkie, it might begin with a decrease in sugar, caffeine, fried foods, meats and dairy, followed by a diet of fruits, vegetables, whole grains, nuts and legumes, followed by a regimen of raw foods only, then fruits and vegetables only, then juices, and, finally, water only.Some detoxers may be unable to tolerate this last step; for many, a juice fast, which provides easily accessible nutrients, including glucose fuel for the brain, is better. In either case, the idea is to eliminate the intake of toxins, and to give the body a chance to clear the sludge that's accumulated."The body is able to focus its attention on correcting what's wrong," Nagel says. "A tremendous amount of energy is spent on digesting food, and, if you're not eating, then the body can turn inward."There's another advantage, Nagel says."You would be amazed at how much of your day is spent in finding food, making food and digesting food. It (not eating) gives you, like, three more hours a day. So you have all that energy you're able to use in other ways."The fast or modified fast is followed by a gradual return to a more sustainable diet, ideally one that reduces the body's toxicity burden. According to Haas, a nontoxic diet stresses organic foods, filtered water, a diverse menu and seasonal cuisine. It includes plenty of fruits, vegetables, whole grains, legumes, nuts and seeds, and, if you're an omnivore, low- or non-fat dairy products, fresh fish and organic poultry. It avoids or minimizes red meats, cured meats, organ meats, refined foods, canned foods, sugar, salt, saturated fats, coffee, alcohol and nicotine.Nagel recommends undergoing a detoxification regimen at least twice a year, preferably during warm weather, when the body can better spare the heat generated by digestion."If you've been really great in your life, you may be able to do it less frequently," he says. "And some people will never do it at all, because to them, the concept is so foreign."Some people would just rather suffer, be sick and die of some disease than have to deprive themselves of food."