The secret to a healthy old age may lie in the trillions of "friendly bacteria" that live in the guts of 60-plus people, reveal scientists.
With the food eaten affecting the types of bugs that thrived, something as simple as eating a varied diet rich in fruit and vegetables could help ward off a host of ills from frailty to memory loss, their study suggests.
"This work gives people strong motivation not to just give granny enough calories and vitamins - diversify it because you are feeding the bacteria in granny's intestine," the Daily Mail quoted the researchers as saying.
The advice comes from scientists who had asked 178 men and women aged between 64 and 72 for information about their diet, then analysed the bugs in their guts and put them through a battery of health tests.
Some of the volunteers lived at home, while others were in hospital.
The study found that those who had been in hospital for more than six weeks had less variety of bugs in their guts than the others. They were also in poorer health and had less varied diets.
They ate a smaller variety of fruit and vegetables, and ate more sugary and fatty foods, more meat and smaller amounts of wholegrain breads and cereals.
According to the University College Cork researchers, it wasn't that the people were being given inferior food, the menus had been varied, but the pensioners had made less exciting choices, with problems with their teeth or digestion or loss of interest in what was going on around them leading them to subsist on snacks such as tea and toast.
Researcher Paul O'Toole said that there were several ways the bugs in people's guts that help keep pensioners fit.
Some bugs helped release energy from fruit and vegetables and keep the bowels healthy.
Other bugs are thought to strengthen muscles and keep the brain working quickly, both essential in preventing slips and falls.
O'Toole said that more effort should be made to ensure those in long-term care eat a varied diet.
And if they can't eat the foods on offer, the food industry might be able to come up with easier to eat alternatives.
"A substantial proportion of the population are tea and toasters that's not enough," Researcher Dr Fergus Shanahan said.
Another author of the study, Professor Paul Ross said that "this was undoubtedly one of the major ways in which diet affected health and was a landmark study."
"Few of us in our research make a difference. This is one time in my career when I can see making a difference to a substantial sector of society," O'Toole added.