potatoes. The study participants were 2 adults—a 25-y-old
man and a 28-y-old woman. The potato diet was supplemented
with butter or pork fat and a few fruits (apples
and pears), and tea and black coffee with sugar were consumed
occasionally. The man consumed w6 g nitrogen
(37.5 g protein)/d, and the woman consumed 3.5 g nitrogen
(21.9 g protein)/d. Both individuals lost w2 kg of body
weight during the course of the study. The digestibility
[(diet N 2 fecal N/diet N) 3 100] of the potato diet averaged
66% and 75% in the man and woman, respectively.
This level of digestibility is comparable to that reported
for beans, maize, and millet (11). Both individuals achieved
nitrogen balance over the entire study. However, the woman
took longer than the man to achieve nitrogen balance. The
results substantiated previous claims that a potato-based
diet can support nitrogen balance in adults, but the capacity
of potato protein to support growth was still questioned despite
these results.
In 1981, Lopez de Romaña et al. (12) evaluated the capacity
of potato-based diets to rehabilitate Peruvian infants and
children with severe malnutrition. Diets supplying 50%,
75%, or 84% of total energy from potatoes were tested.
The 50% potato diet was well accepted, but the children
were unable to tolerate the 84% potato diet over a prolonged
period of time. The diets providing 50–75% of total energy
and 80% of nitrogen requirements from potatoes supported
growth in the children while maintaining normal serum albumin
concentrations. Thus, long-term consumption of potato
protein is of sufficient quality to support growth in
undernourished infants and children as well as to maintain
nitrogen balance and body weight in adults.
The protein quality of a food is determined by its amino
acid composition in addition to digestibility. Amino acid
quality is estimated from the amino acid score of a food