Experimental details

1. Subjects
Twenty-one male university students served as the subjects in these three series of experiments. They lived in a metabolic ward of our laboratory throughout the experiment. During the study, they continued their daily routine activities but were not allowed to do any hard physical work. Characteristics of the students are shown in table 1.

2. Diets
Each subject was given, successively, four levels of low-protein diets. Protein sources were cod fish (as a standard) for eight subjects, a soybean protein isolate (Supro) for five subjects, and a 50:50 mixture of both for eight subjects. Among these, five men received both the cod and mixed protein diets (see table 1). The fish and Supro were prepared as paste products (kamaboko) and fed in equal amounts three times a day. An example of the diet composition is shown in tables 2 and 3.

Each experimental period consisted of one day on a protein-free diet and ten days

TABLE 1. Characteristics of the Subjects

TABLE 2. Diet Composition (Example). Subject: 65 kg; mixed protein 0.55 g/kg; energy 45 kcal/kg.

* For composition of the kamaboko, see table 3. The nitrogen contents are as follows: Dried cod 89.6 mg/g; dried Supro 147.2 mg/g; cod kamabako 18.45 mg/g; Supro kamaboko 26.6 mg/g. Nitrogen intake was 2.86 g/day equally in cod and Supro.

TABLE 3. Composition of Kamaboko Products

Total 129.5 100.0 114.5 100.0 on the experimental diet, followed by three days on a free choice (ad libitum) diet. Four periods were included in the study, with 0.35, 0.45, 0.55, and 0.65 9 protein/ kg/day fed to each man in a random order. Energy intake was constant for each individual to maintain body weight (mean + S.D. = 44.6 + 2.4 kcal/kg; range = 38.4 to 49.8).

3. Measurements and Indicators

a. Anthropometry: body weight, height, arm and leg circumferences, skin-fold thickness.
b. Blood analyses: RBC and WBC count, haemoglobin, haematocrit.
c. Plasma analyses: total proteins (Biuret), albumin (dye-binding, HABCA), urea (indophenol colour reaction), glucose (Somogyi-Nelson), triglyceride (Van Handel), total cholesterol (Zak-Hanly), Na and K (atomic absorption), SGOT and SGPT (Reitman-Frankel). d. Urine analyses: urea (urease-indophenol), ammonia (phenol-hypochlorite), creatinine (Folin-Wu), uric acid (phosphotungstic acid), Na and K (atomic absorption).
e. Nitrogen balance: total nitrogen in diets, faeces, and urine was measured with a semi-micro-Kjeldahl technique during the last five days of each ten-day period on the experimental diets.