The relationship of carbohydrate metabolism to protein metabolism. IV. The effect of substituting fat for dietary carbohydrate

Studies on the protein metabolism of cestodes

The dry weight and nitrogen content of Hymenolepis diminuta were studied after a period of 15 days‘ growth in rats receiving different diets. The special diets were fed during the last 7 days of this period, that is, while the major part of growth is occurring but before shedding proglottids.

Replacement of all the protein (casein) of the diet by carbohydrate resulted in greater development of the worm. However, replacement of casein by fat had no effect on worm development, indicating that removal of protein is not a significant factor, whereas addition of carbohydrate is effective.

Since exchange of casein by the nutritionally incomplete protein zein did not affect worm development significantly, protein quality appears not to be a factor in growth of H. diminuta.

The addition of tryptophan and lysine to the meal containing zein, in order to raise its nutritional value to that of casein, did not influence the growth of the parasite. However, the feeding of the same amounts of these two amino acids at times other than those of giving zein depressed the growth of the parasite. This was not due to type of protein (zein) fed in the rest of the diet, since a similar phenomenon occurs when casein is the dietary protein, or when a protein-free diet rich in carbohydrate is given. Addition of these amino acids, singly, either to diets containing protein or deficient in protein, had significant actions on worm growth, which was sometimes stimulated and in other circumstances reduced.

The nitrogen balance of the host was unaffected by the worm burden.

We are deeply indebted to Dr C. A. Hopkins for providing facilities, for infection of rats with the cestode, and for his helpful advice. Miss M. Cowan provided skilled technical assistance during the feeding of the animals and analysis of the host and parasite tissues. One of us (D.F.M.) gratefully acknowledges the Award of a Commonwealth Bursary from the Royal Society and the Nuffield Foundation.

Differential effects of high-fat diets varying in fatty acid composition on the efficiency of lean and fat tissue deposition during weight recovery after low food intake

The energetics of body weight recovery after low food intake was examined in the rat during refeeding for 2 weeks with isocaloric amounts of high-fat (HF) diets providing 50% of energy as either lard, coconut oil, olive oil, safflower oil, menhaden fish oil, or a mixture of all these fat types. The results indicate that for both body fat and protein, the efficiency of deposition was dependent on the dietary fat type. The most striking differences were found (1) between diets rich in n-3 and n-6 polyunsaturated fatty acids (PUFA), with the diet high in fish oil resulting in a greater body fat deposition and lower protein gain than the diet high in safflower oil; and (2) between diets rich in long-chain (LCT) and medium-chain triglycerides (MCT), with the diet high in lard resulting in a greater gain in both body fat and protein than the diet high in coconut oil. Furthermore, the diet high in olive oil (a monounsaturated fat) and the mixed-fat diet (containing all fat types) were found to be similar to the fish oil diet in that the efficiency of fat deposition was greater (and that of protein gain lower) than with the diet high in safflower oil. Neither the efficiency of fat gain nor that of protein gain were found to correlate with fasting plasma insulin, the insulin to glucose ratio, or plasma lipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Does intravenous fat spare nitrogen in the injured rat?

The role of glucose versus fat as a source of energy in parenteral nutrition is controversial, particularly when administered after trauma, injury or in sepsis. In the present series of experiments, rats undergoing laparotomy and jugular vein cannulation were infused with hypertonic glucose or Intralipid with and without amino acids. The results demonstrate that the combination of amino acids and glucose has a better nitrogen-conserving ability than amino acids and fat, lasting at least 4 days after injury. However, when infused without amino acids, fat had the same nitrogen-conserving quality as glucose. The authors attribute the improved nitrogen-conserving quality of amino acids and glucose to the specific carbohydrate influence on amino acid metabolism, an action which is specific in both protein-free and protein-containing meals but has only very limited effect in the absence of simultaneously infused or fed amino acids. In the moderately to severely injured rat, a glucose calorie is significantly more effective in sparing nitrogen than a fat calorie.

Influence of starches from different sources on protein utilization in rats

1. The role of the starch component of cereals and legumes on the utilization of casein-protein was studied. 2. In comparison with maize starch the legume and potato starches caused a significant lowering of net protein utilization (NPU). And this reduction in NPU could be partially restored by cooking the diets before they were fed to the rats. 3. It is suggested that in NPU studies involving rats the experimental diet should always be cooked so that the conclusions drawn may be applicable to human diets.

Glycerol: major contributor to the short term protein sparing effect of fat emulsions in normal man

Intravenous fat emulsions have been advocated as acceptable alternatives to hyperosmolar glucose solutions in parenteral nutrition. The ability of a fat emulsion (soy bean oil suspended in glycerol) to produce nitrogen sparing in the absence of nitrogen intake was examined in normal man. The protein conservation obtained by the fat emulsion can be duplicated by the infusion of glycerol alone in the same amount as that available from the fat emulsion.

Studies on the nutrition of marine flatfish. The metabolism of glucose by plaice (Pleuronectes platessa) and the effect of dietary energy source on protein utilization in plaice

1. The effects of dietary energy level and dietary energy source on protein utilization by plaice (Pleuronectes platessa) were examined by giving diets containing 400 g crude protein/kg to nine groups of fish. Five of these diets contained only lipid as a source of energy (in addition to protein) and their energy contents were varied by increasing the lipid level in a step-wise manner from 56 to 176 g/kg. The remaining four diets contained both lipid and carbohydrate (glucose plus dextrin) together as energy sources: two levels of carbohydrate (100 and 200 g/kg) being used at each of two (56 and 86 g/kg) lipid levels. 2. Weight gains of plaice given the diets containing only lipid as an energy source did not differ significantly from each other. Weight gains of plaice given diets containing carbohydrate as well as protein and lipid were superior to those given diets lacking carbohydrate. 3. Values obtained for protein efficiency ratio (PER) and net protein utilization (NPU) increased with increasing dietary energy level in both those fish given the diets containing carbohydrate and those given diets lacking it. Both PER and NPU values were greater for plaice given diets containing carbohydrate than for fish diets without carbohydrate even when the total energy content of the diets was approximately the same. 4. Liver glycogen levels were significantly higher in plaice given diets containing 200 g carbohydrate/kg than in plaice given diets without carbohydrate. Blood glucose levels and hepatic hexokinase (EC 2-7-1-1) levels were not significantly different in plaice given these diets. No glucokinase (EC 2-7-2-2) was detected in plaice given either diet. 5. The metabolic fate of glucose carbon in plaice was investigated by injecting the fish intraperitoneally with [U-14C] glucose and examining, 18 h afterwards the distribution of radioactivity in different biochemical fractions from the fish. 6. Glucose was respired much less rapidly in the carnivorous plaice, irrespective of dietary treatment, than in omnivorous mammals (mouse and rat). The rate of production of 14CO2 from (U-14C) glucose by plaice given diets containing carbohydrate was not significantly greater than that by plaice given diets lacking carbohydrate. 7. More glucose was incorporated into liver glycogen when plaice were given carbohydrate in their food than when it was absent. Otherwise no differences were apparent in the fate of glucose C by plaice which could be related to the diets used. 8. No mortalities occurred nor was any histopathology observed in the plaice as a consequence of the inclusion of carbohydrate in the food.