Food additive testing

Relations between enzyme activities connected with energy metabolism and parameters of food energy utilization in young and adult rats. Part 1. Studies on dietary effects on weight, body composition and energy gain

Weaned male Wistar rats were fed ad libitum besides standard pellets a normal-protein (NP), a low-protein (LP) and a high-fat (HF) diet for different periods of time. In comparison to rats on the NP diet the body weight of the LP group was significantly lower after seven weeks feeding, not after a duration of about forty weeks. No remarkable diet-related differences were detected by determination of the mean body composition and of the relative gross energy content of the body neither after seven nor forty weeks. Total gross energy intake was practically identical both for the NP and LP rats irrespective on the duration of the feeding period. A significantly lower quotient of body energy gain/total gross energy intake under the protein-restrictive LP diet after seven weeks suggests the expression of an energy dissipation obviously no longer visible after a long time feeding period.

[Nutrient dependence of energy preservation requirements in rats. 1. Dependence of energy requirements for preservation in fully-grown rats on the type of nutrient offered as the sole energy source]

In two experiments with fully-grown albino rats (Wistar strain) the energetic utilization of glucose, sunflower oil and casein in the maintenance metabolism was determined under thermoneutral conditions of keeping the animals. The relative requirement of metabolizable energy for maintenance was, with either glucose, sunflower oil or casein being the sole energy source of the feed, in experiment 1 100:105:133 and in experiment 2 100:102:135. The absolute values of the maintenance requirement of metabolizable energy were in experiment 1 347 +/- 26, 364 +/- 61 and 460 +/- 33 resp., and in experiment 2 330 +/- 11, 337 +/- 21 and 446 +/- 27 kJ/kg LW 0.75 resp. The results are discussed in connection with the efficiency of ATP synthesis (metabolizable energy/mol ATP gain) in the oxidative decomposition of nutrients.

[Energy maintenance requirements and energy requirement for protein retention in growing rats and broilers. 1. Energy maintenance requirements of growing rats]

In 4 experiments with 3 times 3 male Wistar rats each, which received rations with different protein contents (10; 25 and 40% crude protein in the dry matter), in the growth range between approximately 65 and 180 g live weight and with an environmental temperature of 30 degrees C, a total of 226 measurings of the total metabolism were carried out on the energy level maintenance, partly also with the insertion of a fasting day. The most important results were: On the energy level maintenance with the simultaneous catabolisation of body fat there was considerable protein energy retention, which amounted to between 30 and 40% of the retention achieved in the growth periods. The energy maintenance requirement can be determined with good reproducibility (standard mean deviation: +/-6%). The average energy requirement directly measured at the feeding level maintenance of 437 kJ metabolizable energy (ME)/kg live weight 0,75.d (n=224) differs insignificantly from the average value obtained by means of multiple regression analysis from experiment periods with feeding for growth 423 kJ ME/kg live weight 0,75.d (n=437). Consequently it is not necessary to differentiate between energy requirement for maintenance and energy requirement connected correlatively with the live weight (metabolic weight of the body) under conditions of growth. Energy maintenance requirement proved to be insignificantly dependent on the amount of protein in the feed. The relative values of protein quotas of 10, 25 and 40% in the feed were 100, 101 and 103%; the expected values (derived from the efficiency of ATP synthesis in the oxidation of carbohydrates and protein) amount of 100, 104 and 109%. The problem of the thermogenous effect of protein, which is also of great importance to human nutrition urgently requires further experimental investigation. For growing rats the best adaptation of the energy maintenance over the investigated period of development is achieved if the 2/3 potence of the live weight is chosen as the expression of the metabolic body weight. With high probability this can also be transferred to the characterisation of protein metabolisation.

Effect of feeding pattern on the energy metabolism of rats given low-protein diets

1. The deposition of fat and protein and the utilization of energy by growing rats offered diets ad lib. or in controlled amounts by gastric intubation has been investigated. Diets contained 50, 75, 100 or 200 g protein/kg, mainly as casein. 2. Gain of body-weight and protein increased with increasing dietary protein concentration when animals received the same energy intake, although the reverse was true for fat deposition. However, the differences in live-weight gain were almost entirely due to changes in body water. The dry-matter content of the gain in animals given low-protein diets was 770 g/kg compared to 360 g/kg in those given the control diet. 3. Energy retention was unaffected by dietary protein level in groups given the same energy intake by gastric intubation. In Expt 1 daily heat production increased significantly (P smaller than 0-05) with increasing protein level (50, 75 and 200 g protein/kg diet) when energy intake was constant, but in Expt 2 there was no significant effect of protein level (50, 100 and 200 g protein/kg diet). Problems arose in the selection of a suitable basis for comparison of heat production between groups because of the differences in body-weight and body composition. 4. The energy requirement for zero energy balance was approximately 10 percent lower for the low-protein groups than for those given the diet containing 200 g protein/kg when food intake was just above the maintenance level. When the requirement was expressed per unit metabolic body size (W0-75 KG) dietary protein level had no significant effect. The mean values for Expts 1 and 2 were 452 and 456 kJ respectively. 5. The energy cost of weight gain increased as dietary protein level decreased in pairs of groups gaining at the same rate. The extra energy ingested by the animals given the lower protein level was converted to body tissue with an efficiency of at least 0-70. 6. Striking differences were observed in body composition and energy retention of the two pairs of groups used for the comparison of tube-feeding and ad lib. feeding. With the diet containing 50 g protein/kg, tube-fed rats gained significantly more weight (P smaller than 0-01) and more fat, dry matter and energy (P smaller than 0-001) than their ad lib, counterparts given an isoenergetic intake. 7. The results demonstrate that dietary protein level has little or no effecon the utilization of energy by growing rats when the pattern of intake is controlled by gastric intubation.