‘Hotel’ Pays Guests for Experiments : Health: Tufts University runs experiments with volunteers, mainly older people. For $50 to $3,000, depending on the study, subjects are fed and monitored.

Pat Phillipps is staying in downtown Boston for a few months, in a room with a view of the theater district. At her disposal are a swimming pool, library and exercise room, and she gets three meals a day.

Rather than pay room and board, Phillipps will get about $2,100. But then, most tourists aren’t called back if they don’t clean their plate.

Phillipps, 68, and about 11 other people are housed not at the Sheraton or the Meridien, but a Tufts University laboratory. “You’ve got a private room, private bath, and you don’t have to make up your bed if you don’t want to,” she said. “Of course, I make up mine.”

Tufts’ Nutrition Research Center on Aging, funded by the U.S. Department of Agriculture, runs experiments and studies with volunteers, mainly older people. For $50 to $3,000, depending on the study, subjects are fed and monitored.

The center, in an effort to slow the aging process through diet and nutrition, studies ways to impede the decay of the human body by osteoporosis, arteriosclerosis, cataracts, and overall loss of physical capacity.

“There are life-threatening situations as people age, debilitating situations,” said Judy Frazier, metabolic research unit manager and director of nursing. “There really has to be a better way.”

The studies can last from two months to five years, including follow-up experiments. The center, since its inception in 1983, has completed 76 studies, is working on 18, and has seven ready to go.

The main focus, naturally, is on diet, and meals are monitored rigorously. Portions are carefully weighed and measured so the staff knows exactly how much protein, cholesterol, body fat and other elements the subjects are eating.

“We look at food as chemicals,” said research dietitian Nadine Sahyoun. “We are really a lab, not a kitchen.”

Some studies require two identical meals, one that ends up poured into a blender to be mixed together and inspected for overall content.

If a subject doesn’t eat everything the study calls for, even a dab of gravy left on the plate, the “rinse and scrape” method is implemented. The plate is squirted with a bit of water, and the volunteer scrapes the plate with a spatula to ensure that every last bit of food is consumed. If a volunteer is found to have dropped a pound or two, his or her meals are enlarged.

Most of the participants, aside from the money, like to contribute to the center’s research and come from all over the country.

“It’s a great organization, great people,” said Richard Harris, a retiree from El Paso, Tex. “That makes it more pleasant than anything.”

Harris, who participated in a Vitamin B-6 study last fall and was back this year for a follow-up, said he would receive $3,000.

The center offers guided boat tours, museum outings and other diversions, and the nearby theaters provide entertainment. Chaperones used to keep the volunteers from sneaking over to Chinatown for a plate of sweet and sour pork, but most subjects welcome the chance to find out if they’ve been eating right.

And, of course, there are other reasons. Phillipps, whose Walpole home doesn’t have air conditioning, likes to take part in summer experiments so she can get some knitting done without her hands getting sweaty.