The current menu of new diet and nutrition books reads like a $6.95 all-you-can-eat buffet -- plentiful, varied and likely to lead to indigestion.

With tips on how to nourish your heart, your brain or your libido, diet books have blossomed from the single premise of weight loss to the wider promise of good health and long life. Whether you want to lower your cholesterol, raise your child's IQ or protect yourself from low-level radiation, there's a book to tell you which foods can do it.

Reflecting the latest fads and research findings in nutrition, these books differ in their emphasis, purpose and accuracy. The authors all agree, however, that diet is important for good health. Yet what that ne plus ultra diet consists of is not so easy to ascertain.

One book, for example, tells you to get 20 percent of your daily calories from fat, another says 30; one says that the latest findings on cholesterol in shellfish make it acceptable for a cholesterol-restricted diet, another recommends stringent limitation of shrimp and scallops. And there is a wide range among authors of what is considered a toxic level of various vitamins and minerals.

Many "better living through eating" guides follow the same formula as popular fad diet books of the past. First, the author presents the problem, followed by why solutions other than this one are doomed to fail. Then come the plan and the recipes.

There is nothing wrong with this, as long as the plan isn't based on too narrow a premise or inconclusive research. Yet zealous testimonials and a strident call for action are often standard features of many of these books. Aided by author appearances on talk shows and an aggressive marketing approach that targets non-traditional outlets such as supermarkets and drugstores, these books are often the type that quickly make the best-seller lists.

The highly criticized "Fit for Life" by Harvey and Marilyn Diamond, for example, sold almost 2 million copies, making it 1986's second-best seller in hardcover nonfiction, reported Publishers Weekly. The book, based on the unproven theory of food combinations, claims that one key to being fit for life is to eat fruit on an empty stomach. The Diamonds have just written another book, "Living Health," which delves into more of their unorthodox ideas on air, water and sunshine. (They contend, for example, that spanking a child at birth to stimulate breathing causes asthma and other respiratory impairments in later life.)

These books appeal to the public's desire for a dietary magic bullet. People want "the black, the white, the yes, the no," said Patricia Moriarty, spokeswoman for the American Dietetic Association. A book with all the answers, she says, leaves dieters with "no decisions to make."

But when it comes to how foods work to reduce the risks of various diseases, the science of nutrition still has a lot of "mays" and "seems." While researchers are often reluctant to draw conclusions until all the facts are in, authors need definitive answers in their eating guides. Moderation, variety and common-sense advice to eat less, exercise more and stop smoking don't make for particularly entertaining copy. Gimmicky eating plans, simple solutions and promises to sort out nutrition controversies do.

At the same time, not enough of the critics from the scientific establishment are fighting back. The ADA, for example, which is always quick to criticize trendy diet books, publishes no nutrition guide of its own.

While reputable dietitians and physicians are increasingly co-authoring guides with successful results ("The New American Diet" by Sonja L. Connor, MS, RD, and Dr. William E. Connor was one of last year's noteworthy books), popular writing is generally difficult for professionals.

As Dr. Johanna Dwyer, professor of medicine and community health at Tufts University and director of the Frances Stern Nutrition Institute, said: "I've never seen a scientist have a hard time writing a proposal for a $600,000 grant, but what he would tell his Aunt Minnie to eat is another story."

Besides, impressive credentials don't always guarantee an accurate book. Dr. Stuart M. Berger, a graduate of Tufts University and the Harvard School of Public Health and author of the highly successful "Dr. Berger's Immune Power Diet," has been criticized by the mainstream medical and nutrition community for his claims that people are overweight because hidden food sensitivities cripple their immune systems.

Given all the caveats, then, what can and can't you expect from any of these books?

For one, you can't expect a book to address your individual situation. By following a particular eating regimen, the author might have shed allergies and learned the meaning of life, but that doesn't mean you will.

You also can't expect that reading a nutrition book will guarantee prevention of a disease. You can only play the probabilities and remember that what you eat is only one part of a healthy life style -- and only one factor among many in the development of diseases.

If you lower your expectations, however, some of the books may provide you with motivation and incentive to watch your diet. You can also expect some practical information, such as good recipes, even from the most worthless guides. (The reverse may be true, too; authors who know the intricacies of the body don't necessarily know the workings of a kitchen.)

And as with any book, you can expect some of them to be excruciatingly boring or inadvertently funny ("Maggie's Food Strategy Book," for example, details the size, shape and type of mirror to buy for examining yourself nude every morning.)

With all this in mind, here is a sampling of the latest eating-for-health guides. Total Body Health

"Jean Carper's Total Nutrition Guide" By Jean Carper (Bantam, $12.95)

Carper's premise is that "a good diet, not pills, is the ultimate solution to poor nutrition," but she is not totally anti-supplement. She takes into account the needs of special populations and situations -- and realizes that supplements, in moderation, can serve as possible insurance against vitamin and mineral deficiencies. But she advises against "megadoses" -- 10 times the federal recommended dietary allowances (RDAs) or higher.

With that philosophy, the author of nine books on health and nutrition launches into a concise, intelligent and extensive analysis of macronutrients (protein, carbohydrates and dietary fat), micronutrients (vitamins and minerals) and the U.S. Department of Agriculture's latest nutrient data.

Each chapter is divided into easy-to-read sections that answer questions about cooking losses, food sources, toxicity levels and nutrient interactions. Carper examines who -- if anyone -- needs to worry about a deficiency. She also uses the USDA's nutrient data to compile useful charts, among them how to get the most nutrients for the fewest calories.

If there's anything to criticize about Carper's book, it's that it may be too complete. It contains so many facts and figures that people may have trouble identifying the practical implications of them all. For example, it's interesting that foods containing phytates block the absorption of zinc, but is it important enough to refrain from nibbling corn chips and oysters at the same cocktail party? The book seems best geared for readers with a specific vitamin or mineral concern, or for professionals who want intrepretations of the USDA data.

"How to Be Your Own Nutritionist" By Dr. Stuart M. Berger (William Morrow, $16.95).

Dr. Stuart Berger is a master at manipulating the mind. Whether he is equally proficient in dispensing information about the rest of the body is another matter.

After criticizing the medical establishment and the vast inadequacy of the RDAs, Berger writes in cult-leader fashion:

"My role in this book is to act as your trusted guide and mentor, to show you the way, to make the complex simple and easy to understand -- in short, to give you all the emotional support you need on your journey."

Yet Berger gives readers a false sense of control, as he proceeds to prescribe a litany of vitamin and mineral supplements, with dosages often many times higher than the RDAs. The recommendations, divided by "personal micronutrient prescriptions" are meant to give the impression of individualized attention; nonetheless, they are no more than generalized categories, such as "caffeine consumers," "dieters" and "men."

Berger's dietary advice -- when disentangled from the supplement section -- is relatively sensible, and the quizzes scattered throughout the book are fun to take. But learning how to be your own nutritionist largely means learning how to follow Berger's nutrition advice.

"Maggie's Food Strategy Book" By Maggie Lettvin (Houghton Mifflin, $17.95).

Because of age, state of health, activity level, environment and personal likes and dislikes, Lettvin believes that "no one eating strategy is right for everyone." This is a sensible enough proposition, but her book is so full of downright silly ideas and unappetizing eating tips that it's unlikely Lettvin's strategies are right for anyone.

Lettvin introduces eight diets for eight types of eaters -- the sweet diet, the regularity diet, the raw diet, the anti-stress diet, the two-minute diet, the high-protein, low-carbohydrate diet, the pocket diet and the lean, clean machine diet. One seems more outlandish than the next.

The anti-stress diet, for example, in which Lettvin says that she knows of "no diet that makes you look better and feel better so rapidly" includes a high cholesterol regime of kidneys and sweetbreads for breakfast. The raw diet outlines a daily intake of oysters, clams, tuna, bass and other uncooked fish. And the two-minute diet consists of various drink mixes consumed eight times daily, among them milk and tomato paste, milk and canned liver paste and tomato juice and tofu.

Heart Health

"Eater's Choice: A Food Lover's Guide to Lower Cholesterol" By Ron and Nancy Goor (Houghton Mifflin, $17.95).

At 31, "I was a heart attack just waiting to happen," Ron Goor writes in the introduction to "Eater's Choice." With a strong family history of heart disease and the discovery that his own cholesterol was abnormally high, Goor knew he had to give up his daily Italian sub.

One thing led to another, and he eventually ended up turning his health into a career, becoming the coordinator of both the National Institute of Health's Coronary Primary Prevention Trial and its National Cholesterol Education Program. He then teamed up with his wife to write a book that is one of this year's most readable, realistic and practical guides to lowering cholesterol via diet.

The plan concentrates on trimming saturated fat, the most potent dietary influence on blood cholesterol levels. Using the American Heart Association's guidelines to get 10 percent of daily calories from saturated fat, you establish your "sat-fat budget." If your daily caloric intake is 1,800, for example, then your sat-fat budget would be 180.

By following the sat-fat tables in the book, you choose foods that fit within that budget. Low-fat and high carbohydrate foods are emphasized, but splurge foods are permitted as long as they fit into your budget. (A cup of vanilla ice cream is 80 sat-fat calories, for example.)

The appeal of "Eater's Choice" is that it offers the flexibility of individual food preference within a quantitative framework. It is one of the few educational materials that give readers the opportunity -- in fact, the responsibility -- of designing their own diets under a set of calorie guidelines.

Nevertheless, not everyone has the concentration, motivation or necessity to eat by number. For those who are not into counting sat-fat calories, there are some interesting recipes and good general information about the fat content of various foods.

"The Eight-Week Cholesterol Cure" By Robert E. Kowalski (Harper & Row, $15.95).

Any book with a title that promises both a "cure" and a time frame in which it will occur should be looked at with skepticism.

Medical writer Robert Kowalski had two coronary bypass operations by the time he was 41. Since then, he has kept his blood cholesterol under control and written an overenthusiastic testimonial that promises to control weight, lower cholesterol dramatically and "vastly improve your chances for living a long, long life."

Aside from exercise and a low-fat diet, the book recommends a regimen of oat bran and niacin to lower cholesterol. While eating three oat bran muffins a day won't hurt you -- indeed, some studies show it may lower cholesterol -- medicating yourself with nicotinic acid might.

Doctors prescribe nicotinic acid, a form of niacin, for certain patients with high cholesterol, but its side effects include flushing, elevation of blood sugar and a rise in uric acid, says Dr. John C. La Rosa, dean for clinical affairs of George Washington University Medical Center. In the doses that Kowalski advises, nicotinic acid should be considered a drug, La Rosa added.

Most nutrition books hedge advice by recommending that readers consult a physician before proceeding with any regimen. One wonders if anyone ever does, but particularly with this book, one hopes they do.

"The Good Fat Diet" By Robert Gold, MD and Kerry Rose-Gold (Bantam, $14.95).

If last year was the year of the calcium book, 1987 is the year of the omega-3 fatty acid guide. Omega-3 fatty acids, found in fish such as salmon and bluefish, have been shown to be protective against heart disease.

Learning to eat more fish has always been a wise idea, because it is both low in calories and low in saturated fat. But "The Good Fat Diet," whose cover flashes "The New 14-Day Low-Fat, Low-Cholesterol Rapid Weight-Loss Program based on Omega-3, Nature's Proven Fat," hypes the omega-3 fatty acid idea. Relying on a rigid eating plan, the book promises rapid and significant weight loss in a short period of time as well as preventing or halting your risk of heart disease.

The book outlines a rigid eating plan of 1,200 calories a day that includes eating fish high in omega-3 fatty acids eight out of 14 days. While virtually any low-fat 1,200-calorie diet adhered to strictly would promote weight loss, "The Good Fat Diet" emphasizes the added bonus of protecting your heart.

The book fails on both levels, however. As a weight-loss guide, there is very little information on behavior modification and exercise. As a healthy-heart eating book, it overemphasizes the importance of fish containing omega-3 fatty acids while offering too little advice about other low-fat foods.

Vitamins and Supplements

"The Right Dose" By Patricia Hausman (Rodale, $19.95).

After much rumination, Hausman, a local nutritionist and author, has concluded that an inadequate diet plus a safe supplement program is better than an inadequate diet alone.

In a chatty writing style, Hausman proceeds into a lengthy recitation of side effects and case studies of supplement toxicity, ostensibly to reach a decision about the dose people should take. It is a major work, compiled from an extensive search of the available medical literature. And Hausman writes that there are probably more cases than she found, since supplement toxicity is not always reported to public health authorities.

In many ways, however, the author defeats her own purpose. The book devotes so much space to the acute ailments, long-term problems and hidden consequences of taking various supplements that it dilutes the case for taking them in the first place. The frequently gory case studies (i.e., from taking 500 milligrams daily of vitamin B-6, a woman "began to have the sensation of electric shocks shooting down her spine . . .") offer some pretty grim illustrations of the risks of vitamin and mineral megadoses.

Weight Loss

"The Popcorn-Plus Diet" By Joel Herskowitz, MD (Pharos, $14.95).

"Unpopped kernels, dating back 2,000 years, have been found in the Bat Cave in New Mexico," writes Dr. Joel Herskowitz, popcorn historian, humorist and fetishist.

What appears to be an incredibly gimmicky book is not quite as ridiculous as it sounds. Herskowitz, a pediatric neurologist at Boston City Hospital and assistant professor at the Boston University School of Medicine, promotes a realistic 1,200-to-1,600-calorie-a-day diet with a weight-loss goal of 1 to 2 pounds per week. And although he doesn't delve terribly meaningfully into any of the ideas, he does discuss the importance of behavior modification, exercise and goal setting.

Herskowitz's premise is that having popcorn readily available prevents you from impulsive, unwise food choices. While this is a sensible idea, given the fact that popcorn -- if air popped without saturated oils -- is a low-calorie, high-fiber food, his advice to carry around five to 10 cups of the stuff in a plastic breadbag is more than a bit impractical. (Can you imagine how crowded the subways would get?)

Popcorn as one part of a well-planned diet may be useful. That said, you'd be better off spending money on Orville Redenbacher than on Joel Herskowitz.

"The 35-Plus Diet for Women" By Jean Perry Spodnik and Barbara Gibbons (Harper & Row, $15.95).

The book has an appealing title for the millions of women 35 and over who are battling weight, but the diet doesn't seem substantially different from the low-calorie, high-protein regimes that often lead to quick weight loss and then rapid regaining of weight.

Spodnik, the chief clinical dietitian at Kaiser Permanente in Cleveland, presents a three-phase plan that begins with a 900-calorie-a-day diet composed of 27 percent carbohydrates, 40 percent protein and 33 percent fat. It is designed to put the dieter on "the brink" of ketosis {a complication of starvation that results from the incomplete combustion of fatty acids}, but "not actually in it," Spodnik writes. (How one can measure being "on the brink" of ketosis is questionable.)

After one to two weeks, dieters proceed to phase two, which is slightly lower in protein (36 percent) and marginally higher in daily calories (950). In phase three, carbohydrates are gradually increased, with the promise of not gaining back excessive water or fat.

While the diet is probably not unsafe, the directive to follow the dietary percentages exactly seems difficult at best. In addition, the three-phase theory, which is the basis of the diet, comes from Spodnick's study of 20 women -- a small group by scientific standards. In all, "The 35-Plus Diet" may help women lose weight, but whether it teaches the tools for permanent weight loss is another matter.

"The Diet Principal" By Victoria Principal (Simon and Schuster, $17.95).

Now that Dallas' Pam Ewing was in a car accident and Victoria Principal doesn't have a fulltime job anymore, let's hope she maintains her 110-pound figure. The last time she waited for a good script, she gained 40 pounds, Principal writes in her latest book.

In a writing style as simplistic as an elementary school text, Principal explains how she successfully shed those pounds. Her philosophy is essentially a good one -- that the word "diet" means a nutritious way of eating, rather than a regimen of deprivation. But when it comes to the specifics of moderation and balance, Principal shows that every actress who wears a size six isn't necessarily a nutrition expert.

In her lists of "(almost always) forbidden foods," for instance, she recommends staying away from mayonnaise. "If you want to use it, put it on your face to add oil to your skin." Or cheese: "If you insist on eating it, you might as well spread it on your thighs, because that's where it will surely show up anyway, sooner than later." For some reason, rice also appears on the list of foods that Principal "almost always never" eats. So do polyunsaturated oils, such as corn and safflower, while butter, a saturated fat, is on the "maybe/sometimes" list.

She also stresses that she doesn't believe in crash diets, then outlines an extremely low-calorie "Bikini Diet," which promises a weight loss of 5 to 10 pounds in a week.

Principal's book, while containing enough of its share of Rodeo Drive eccentricities, isn't as quirky as one might expect -- and some of the recipes sound fairly tasty. But as for being an important nutritional work, she should concentrate on screenplays.

Healthy Cookbooks

"The Rotation Diet Cookbook" By Martin Katahn, PhD, and Terri Katahn (W.W. Norton, $18.95).

"The Rotation Diet" that took the country by storm last year was Norton's largest selling book -- ever. Katahn, the Vanderbilt University psychology professor who had entire cities on his diet, has now resurfaced with a cookbook written with his daughter.

Whatever the legitimacy of his diet (some experts believe its premise is not physiologically proven and that it is too low in calories during the first and third weeks), this is not a bad recipe book.

Whether or not you are on the diet, there are some decent-sounding low-calorie dishes. New Yorker and Far Side cartoons help break up the text.

But one wonders why the chapter entitled "The Efficient Kitchen" was included. In it, the Katahns dispense information that surely even the biggest kitchen clod already knows: "Don't clutter work space on your counter tops with kitchen equipment," and "Keep frequently used items as close as possible to their point of use."

"Eat Smart for a Healthy Heart Cookbook" By Dr. Denton A. Cooley and Carolyn E. Moore, PhD, RD (Barron's, $18.95).

Dr. Denton Cooley, surgeon-in-chief of the Texas Heart Institute, and the first doctor to implant an artificial heart, has teamed up with a nutritionist and 16 of Houston's top restaurateurs to create this elegant cookbook for heart-healthy eating. It illustrates that good food and food that is good for you needn't be mutually exclusive.

It's unclear how much Dr. Cooley actually wrote, however, as the bulk of the book is recipes and eating tips. His contribution appears to be primarily in providing biographical information and snapshots.

In fact, there are as many pages devoted to himself as there are to atherosclerosis and heartdisease. He is pictured with Princess Grace (1979), Prince Philip (1982), his 1962 Rolls-Royce and his springer spaniel Atticus.

Carole Sugarman writes about food and nutrition for The Washington Post's food section.