WHAT’S LEFT TO EAT? by Sue Gebo, McGraw-Hill, 278 pages, $12.95, paperback.

At the conclusion of one of her lectures on sodium and high blood pressure — during which nutritionist Sue Gebo had revealed the dismayingly high sodium content of many common foods — an elderly man with high blood pressure problems approached the author and asked perplexedly, “What’s left to eat?” From his worried question was derived the title of this reassuring, authoritative guide to food safety, and its ramifications. “A recent survey shows that a whopping 83 percent of American adults are concerned about the health effects of what they eat,” comments the author.

Gebo, who is greatly respected by her peers, received her degrees in nutrition from Cornell University and the University of Michigan. Affiliated with both the University of Connecticut Medical School and Wesleyan University, she also serves as consultant to such giant corporations as Honeywell and United Technologies, and is in great demand on the lecture circuit. “The purpose of this book,” she explains, “is to educate you about food-related risks … some familiar … some new … all part of our world, and inescapable as breathing.”

With the ease of one completely conversant with her subject, the author pilots the reader through the shoals of additives, sugar substitutes, salt, natural food toxins, food-related poisons, pros and cons of food irradiation, that reduce health risks.

She clarifies the confusing subject of cholesterol which she describes as “a necessary life-sustaining compound that our bodies actually manufacture.” Cholesterol is found in our blood, she continues. “It’s part of the little fat packages called lipoproteins which our bodies use to transport fat around in the bloodstream. The cholesterol in the blood is what causes health problems.” But it is essential to understand that one type of fat package (lipoprotein) is called LDL (low-density lipoprotein) and is the “bad” cholesterol. The other is HDL (high density lipoprotein) and is the “good” cholesterol. That, says the author, acts as a scavenger in our blood vessels, scooping up cholesterol and taking it out of harm’s way before it can get dumped into artery walls.

The five links in the bracelet of this book are Food Safety, Preventing Disease, Making Food Selections, Safe and Healthy Menus, and Recipes, and a lengthy Resource Corner in which the author promises the reader will find listed a treasury of “truly fine publications you can trust” that run the gamut from mail-order organic food suppliers, newsletters, magazines and books, to computer software and lead-testing kits.

Gebo repeatedly emphasizes that one cannot think in absolutes if one is to accept the realities of a risk-laden world. “Many of these risks are infinitesimally small, such as the risk of cancer from consuming apple juice made with Alar-sprayed apples,” she writes, “but some risks are considerable, at room temperature.”

Rachel Carson’s outcry in “Silent Spring,” published in the ’60s, against the lethal pesticide DDT, comes in for high praise as does the government’s quick action to toughen pesticide regulations. Gebo also lauds the voluntary action of farmers who, under the aegis of an integrated pest management program, monitor their crops and spray only when there is actual need; and she applauds the efforts of grape growers who now control the use of pesticides by spraying their fields with larvae of the green lacewing predator of crop-damaging insects. The Food and Drug Administration has stepped up its vigilance and closely monitors new products, as well.

Simplesse, a fat substitute, is one of the new products that gained the FDA’s coveted approval in 1990. A creamy substance made of egg white and-or milk protein, Simplesse is employed in the making of chilled foods and frozen desserts.

Olestra, a much more spectacular (and scarier) artificial oil-like fat substitute called sucrose polyester (a molecule so complex that human digestive enzymes can’t digest it, and hence passes out of the body without being absorbed) has yet to receive the royal nod from the FDA. The alluring Olestra offers consumers the seduction of unrestrained indulgence in deep-fat fried foods such as french fries, potato chips, doughnuts, and so on, without any of the usual punishing penalties to the body. But the FDA is wary: What else will that “undigested fatlike stuff” carry away with it? Cautiously, the FDA is conducting long-term animal studies, including testing of genetic effects over several generations, reports the author.

Gebo’s guide not only soars into the rarefied stratosphere of nutrition, it dips down to the terra firma of such essentials as why one must scrub the outside skin of a cantaloupe with a vegetable brush before cutting it open; the reason for keeping honey on the verboten list of foods for infants; and the wisdom of avoiding green-tinged potatoes. In every sense of the word, “What’s Left to Eat?” reflects the zeitgeist of the ’90s and its ever-increasing focus on the wisdom of the apothegm that you are what you eat.

Bea Goodrich’s reviews are a regular feature in the monthly Books in Review section. Goodrich also writes a review column, and is the author of the award-winning nature story series, “Happy Hollow Stories by Judge Tortoise.”