WASHINGTON (AP) _ Joe had been stuffing himself on ice cream, pastries, steaks and butter, but was steadily losing weight.

He had AIDS and knew it, but had been trying to keep his weight up to stay as healthy as possible.

''I should be fat with all I'm eating,'' Joe said.

''It may sound hard to believe, but it's more likely that you will continue to lose weight on that diet,'' said Dr. C. Wayne Callaway, an endocrinologist and specialist in clinical nutrition.

Joe's problem was an AIDS-related bowel disease that prevented him from absorbing high-fat foods. He needed more calories, but the fat in the foods he chose exacerbated the bowel disease, causing extreme diarrhea and weight loss.

Callaway put him on a high-carbohydrate, low-fat diet and prescribed a resin to affect his intestinal tract. Within days, Joe was better and within three months his weight rose from 107 to 125 pounds.

Joe's story is one of several in Callaway's new book ''Surviving With Aids: A Comprehensive Program of Nutritional Co-Therapy,'' co-authored with Catherine Whitney.

Callaway says there is no evidence that AIDS itself can be treated with diet. And he admits that all these patients are terminally ill. But his research shows that diets can be prescribed that enable patients to both enjoy eating and guard against the rapid wasting that is typical of the disease.

''In 60 or 80 percent of (fatal) cases, starvation was making a big contribution to their death,'' Callaway said in an interview.

Callaway's book includes descriptions of typical eating disorders associated with AIDS and symptoms caused by specific nutritional deficiencies.

It offers a checklist for tracking weight loss, nutrient intake and eating patterns and for identifying food-related reactions, like diarrhea, changes in tastes and a quick sense of fullness.

The book also tells the reader what foods to eat and to avoid if certain symptoms exist, provides a list of menus and recipes and discusses what to do when tube or intravenous feeding becomes the only way to consume nutrients.

Callaway has been working with AIDS patients since the early 1980s when he was director of nutrition at the Mayo Clinic in Rochester, Minn. He said people were coming to him because of severe weight loss. When he discovered they had AIDS, they quit seeing him and went to the infectious diseases division of the clinic for drug therapy.

''At that time, we knew very little about the disease and even less about its nutritional complications,'' he said.

Later, when Callaway started private practice in Washington, he began seeing people already diagnosed with AIDS who wanted to know how to combat the disease nutritionally.

Bill, 39, was a 6-foot former athlete who dropped from 175 pounds to 155 pounds in six months and was suffering from chronic diarrhea. He said he had been diagnosed as HIV-positive quite some time before, but had no other problems except an infection under his nails.

He said he was always hungry, ate constantly, but grew continually weaker.

Callaway said the symptoms were those of someone starving to death. Bill was losing lean body mass, not fat.

The doctor put Bill on a low-fat diet which included a liquid protein supplement, since protein deficiency contributes further to muscle wasting. Callaway said that since Bill's blood selenium was low - a condition contributing to muscle wasting - he prescribed 200 micrograms of selenium as a daily supplement.

After five months, Bill had gained 13 pounds and had resumed regular exercise.

Callaway said Bill was a perfect example of one type of malnutrition seen in AIDS patients.

''His ability to reverse his body wasting and return to normal activity reinforced our belief that malnutrition in people with AIDS can be corrected nutritionally if it is treated in time,'' Callaway said.