No single food provides everything, so the best diet is a mix of dairy items, whole grains, fruits, vegetables, and protein. You don't have to eliminate favorite foods, just eat less of them. What really matters is the total diet consumed over several days. Here is an example of a balanced meal plan. The elderly often have a diminished sense of thirst and don't realize they need water.
Dehydration can gradually develop and is a serious problem.
Getting enough of the more than 40 nutrients needed for good health can be hard for people who are eating small amounts. For example, to process calcium, the body needs vitamin D, which is provided by sunlight. But many elderly people get little exposure to the sun, and when they do, their skin doesn't absorb vitamin D as well as it once did. Food may not be very appealing or enjoyable, because taste and smell become less sharp with age. Disease and medications can affect these senses too.