I have a friend who's undergoing chemotherapy for cancer. He's making an effort to eat well, but lacks the strength to do much shopping or cooking. I want to help and yet feel frustrated because after I've spent time preparing something he says he will eat, he simply can't "stomach" it. What do you suggest?

A new book can be of help. "Nutrition for the Chemotherapy Patient," by Janet Ramstack and Ernest H. Rosenbaum, M.D. (Bull Publishing, $18.95), is written from the perspective of those who understand the nutritional problems that face cancer patients and their families. True, some sections of the book won't be relevant to your friend's case, since they describe different types of chemotherapy, their possible side effects and ways of dealing with them.

Also, some of the material is fairly technical. On the other hand, a quick skimming of the volume will offer you solutions and flexible alternatives to food-related issues your friend is experiencing. This book might be just what you need, and you can feel good in knowing that royalties from its sale go toward supporting breast-cancer research at Mount Zion Medical Center of the University of California, San Francisco.

I received an advertisement in the mail for a product containing "enzyme-rich" plant essences and microscopic sea vegetables. According to the brochure, enzymes are the missing link in the modern cooked-food diet, because they are destroyed by heat, and these preparations will supply them. I'm interested, but the capsules are expensive -- about $40 for a month's worth -- and I'd like your opinion.

First of all, we'd like to thank you for describing the advertising piece you received. That way, we can advise not only you, but also many others who get the same sort of mailing, not to throw your money away on this useless product.

The idea that enzymes are destroyed when food is processed, rendering the food nutritionally undesirable, has been used as a selling point for years. But it's false.

It's true that plants, like animals, produce enzymes, and that enzymes are necessary for millions of normal reactions. The ripening of fruits and vegetables is dependent on enzymes, for example, as is the spoilage process that results if ripening is allowed to go on too long. It's also true that heat destroys enzymes, which are proteins.

That said, let's make this critical point: The enzymes plants use and those used by man are different. Normally our bodies make all the enzymes we need. When they don't, special preparations, formulated to remain intact until they arrive at the appropriate site in the digestive tract, may be prescribed by a physician, not sent willy-nilly by a mail-order company.

The preparations so glowingly described in your brochure, which claim to contain a host of unspecified enzymes, are nothing more than a waste of money.

At a holiday party, the cheese tray contained an interesting cubed cheese the color of caramels. I liked its rather sweet taste and would like to buy some. Would you know its name?

You're probably talking about Gjetost (pronounced yay-toast), which for more than 100 years has been the national cheese of Norway. The other possibility is its close cousin, Mysost. Gjetost may be made solely from goat's milk or from a mixture containing mainly cow's milk and a small amount of goat's milk. Mysost is made from cow's milk.

Unlike most hard cheeses, they are made from whey rather than from casein-rich curds. The addition of lactose gives them a different nutritional profile than other hard cheeses. An ounce of gjetost has the same amount of milk sugar as a cup of milk, but less than half the protein of other hard cheese. On the other hand, its fat content, eight grams per ounce, is comparable to that in Edam, fontina, Swiss and other popular varieties.

Owing to its high lactose content (unlike most other hard cheeses), Gjetost will not be tolerated well by individuals with lactose intolerance.

You suggested a quick recipe for lentil soup that was tasty and low in fat. Can you provide the recipe again?

Gladly. We're fans of soup and are pleased to promote it as a healthful centerpiece of meals. Chop a medium onion and a stalk of celery, add to a saucepan with a tablespoon of oil and saute' about five minutes. Add a one-pound package of rinsed lentils and an eight-ounce can of crushed tomatoes or tomato sauce. Add water to a level twice the height of the lentils and simmer until tender, about an hour or so. Then add a bunch of chopped escarole and simmer five minutes, or until greens are just cooked. Season with salt and black pepper.

Divided among six people and served as a main dish, a portion would contain about 300 calories. Serve along with French bread and a salad, skim or low-fat milk and fruit for dessert, and you'll be hard-pressed to find a winter dinner that's lower in cost or easier to prepare.

To vary the flavor without adding appreciably to the caloric count, use beef or chicken stock as the liquid. Or brown a clove or two of minced garlic along with the onion or celery. Or add a sprinkling of Parmesan cheese at the time you serve the soup.

1991, Washington Post Writers Group