Protein is vital to growth and cell repair – yet estimates of protein needs vary enormously. An average estimate for good nutrition is about 2 ½ oz (70g) a day in adulthood with protein supplying about 7% of calorie intake. But people have been found to adapt in a healthy way to intakes under half to over twice this amount.
All this is dependent, of course, on all essential amino acids being eaten, and in the right proportions. Lack of protein can be a problem, especially in old people with little money, and in those following unusual diets.