Effect of a high fat intake on protein utilization during ontogenetic development

Male rats (Wistar strain, Velaz, Prague) aged 30, 90 and 150 days were fed 14 days ad libitum on a high fat diet (containing 40% margarine) and their growth (PER, NPR) and utilization (NPU, LPU) parameters of protein (casein) biological value were compared with those of animals given a standard gel containing 10% margarine (the diets were isoenergetic). The course of gluconeogenesis in their liver was also determined by measuring phosphoenolpyruvate carboxykinase (PEPCK) activity. A high fat intake had a negative effect on the growth parameters of protein biological value, PER and NPR, in all three age groups and on the utilization parameters NPU and LPU in 30- and 90-day-old rats. The nonsignificant increase in NPU and LPU in the oldest animals was evidently related to the equal protein intake compared with the control, indicating that proteins need to be utilized more economically in the presence of a raised fat intake; owing to their far lower fat intake compared with 90-day-old animals on a high fat diet, the fat had a less negative effect on their protein utilization than in the younger age group. The negative effect of a high fat intake was confirmed by high activation of gluconeogenesis in 30- and 90-day-old animals and by raised phosphoenolpyruvate carboxykinase activity in 150-day-old rats, in which the supposition that gluconeogenesis would be highly activated if the diet were administered for a period other than 14 days cannot be ignored. The biological and biochemical methods employed in this study can be used with a wider perceptual range of dietary nutrients to determine optimum nutrient values under different conditions.     

Age-correlation of protein utilization to saccharide intake

Male Wistar rats aged 30, 90, 150 and 360 days were fed ad libitum on diets with an optimum protein and fat content for their respective ages and an increasing saccharide content. Net protein utilization (NPU) was determined from the body nitrogen and protein intake values and the course of gluconeogenesis in the liver was measured by specific phosphoenolpyruvate carboxykinase (PEPCK) activity. According to the growth curve for the standard diet, animals aged 30 and 90 days have a high growth rate (3.245 g/day), 150-day-old rats grow more slowly (1.856 g/day) and 360-day-old animals put on scarcely any weight at all (277 mg/day). In 30-day-old rats, NPU attains maximum values in the presence of a 36% saccharide content in the diet, in 3- and 5-month-old animals in the presence of 51% saccharides and in one-year-old animals in the presence of 41% saccharides in their food. The course of gluconeogenesis also corresponds to these values. PEPCK activity in the youngest age group is greatest in the presence of 31% saccharides in the food, at 90 days it is stimulated in the presence of 31-46% saccharides, at 150 days the decisive concentration is 41 and 46% and at one year proteins are used for saccharide synthesis in diet with a 31 and 36% saccharide concentration. For optimum saccharide values, PEPCK activity is reduced in every age group; together with the maximum NPU values, this indicates that proteins are used for growth and building of the organism at an early age and for the renewal of tissues and organs and maintenance of the organism in adulthood.     

Determination of the optimum dose of fats in the food of rats of different ages

Over a 14-day period, male SPF Wistar rats with an initial weight of 60, 200 and 250 g (ages 30, 75 and 90 days) were given diets with a constant protein content (10% casein) and a mounting fat content (10, 15, 20, 25, 30, 40 and 50% margarine, at the expense of the saccharides in the standard diet). The utilization parameter of protein biological value (NPU) for the various diets was determined from protein intake and the body nitrogen values. The reciprocal relation of the intake of the two nutrients was determined on the basis of linearity between th growth parameter NPR and protein and fat intake and, after substituting the optimum protein intake, was used to compute the optimum fat content of the diet. From the aspect of the maximum NPU value the optimum fat contents were 30% for 30-day-old, 15% for 75-day-old and 10% for 90-day-old animals. In all three age groups (according to the growth curve for the standard Larsen diet animals with an equal growth rate of 3 g/day), protein utilization under optimum nutritional conditions was the same. The optimum fat content of the diet computed from the reciprocal relationship of fat and protein intake is in agreement with the value obtained by the biological method - 29.4% (49.5 energy %) for 30-day-old animals, 15,8% (30.4% of the total energy value of the diet) for 75-day-old animals and 11.83% (23.7% of total energy) for 90-day-old rats. By using a biological and a mathematical method, this study contributes to the determination of optimum physiological doses of nutrients.     

The relationship between protein retention and energy requirements in rats of different ages

Male Wistar rats aged 30, 75 and 150 days were fed for 14 days ad libitum on diets with an optimum protein content (15% for 30-day-old, 12.5% for 75-day-old and 10% for 150-day-old animals) and a mounting fat content (from 5 to 40%), supplemented by saccharides (from 76 to 41%). Net protein utilization was determined for each of the diets from the body nitrogen and protein intake values. Protein retention values were determined from protein intake on the basis of net protein utilization (NPU). Energy intake was computed from fat and saccharide intake, using energy coefficients. The optimum fat content of the diet, evaluated from the maximum protein retention value per day and the minimum amount of energy needed for the retention of 1 g protein, is 30% at 30 days, 15% at 75 days and 10% at 150 days. Protein retention per kg body weight falls with advancing age--mildly at 75 days compared with 30 days, but markedly at 150 days. From their smaller weight increments and NPU values and also from their lower protein retention, 150-day-old animals are characterized by slower growth and higher protein requirements for maintenance of their organism likewise demonstrated by the growth parameter net protein ratio (NPR). Energy requirements for total protein retention/day per kg body weight diminish with age. In old age a small amount of energy is needed only for the maintenance of body functions. This study contributes to the expression of the interrelationship of energy requirements and protein retention.     

Determination of the optimum proportion of saccharides in the diet of adult rats

SPF male Wistar rats weighing 250-260 g and aged 90 days were fed 14 days on diets with a constant 10% protein (casein) content, a constant 11% fat (margarine) content and mounting saccharide (rice starch: sugar: potato starch - 6.4: 1.2: 1) contents of 31, 36, 41, 46, 51, 56, 61 and 66%. Protein intake and the body and liver nitrogen values were used to determine the utilization parameters of protein biological value, i.e. NPU (body) and LPU (liver), for the individual diets. Liver gluconeogenesis was also studied by measuring specific phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1.6-diphosphatase (FDP-ase) activity. On the basis of linearity between the growth parameter NPR and protein and saccharide intake we determined the reciprocal relationship of the intake of the two nutrients and used it to compute the optimum saccharide concentration for the diet. The 51% saccharide diet gave the best protein utilization (the maximum (net) protein utilization value) in the 90-day-old rat organism. This was confirmed by the course of gluconeogenesis, which was significantly activated in the presence of 31-46% saccharide diets. By substituting the optimum protein intake in the reciprocal saccharide-protein intake relationship we obtained the optimum saccharide intake, which corresponded to a 49% concentration in the diet. With its use of a biological, biochemical and computation method, the study is a contribution to the determination of optimum nutrient values.     

Determination of the optimum doses of nutrients in a diet.

For 14 days, SPF male Wistar rats with an initial weight of 60 g were given isocaloric diets (1.7 MJ/100 g diet) containing 10% protein (casein) and 5, 10, 25 and 40% fat (margarine). Two utilization parameters of the protein biological value--net protein utilization (NPU) and liver protein utilization (LPU)--were determined from protein intake and body and liver nitrogen. These results were supplemented by a study of the course of the antithetical processes of gluconeogenesis and glycolysis, of the citric acid cycle and transamination processes and of the liver and muscle amino acid spectrum. A high (40%) fat diet significantly reduced the protein biological value parameters NPU and LPU and liver and muscle amino acid values, stimulated gluconeogenesis and inhibited glycolysis and the citric acid cycle, together with associated transamination processes in the liver. Activation of these processes in the muscles provided substrates for increased gluconeogenesis. The negative effect of a low fat + high carbohydrate diet was less marked. The optimum diet for weaned rats is thus a diet containing 10% protein and 10--25% fat. The study, which submits several possible ways of determining optimum nutrient intakes under different physiological conditions shows that diets with more detailed nutrient concentrations should be used.     

Determination of optimum fat intake

In a 14-day experiment, adult rats weighting 250-260 g were given ad libitum diets with a constant protein content [casein - 10 %] and a mounting fat content [margarine - 0, 10, 20, 30 and 40 % - added at the expense of carbohydrates]. The growth parameters of protein biological value - PER and NPR - were determined and together with weight increments in correlation to protein an fat intake [a linear correlation] they were used on the basis of their regression equations to calculate the reciprocal relationships of fat and protein intake [for equality y]. By substituting the optimum protein intake [43.3 g/14 days - according to NPU], the optimum fat intake for adult rats was found to correspond to dietary fat concentrations of 9.72 % [y = weight increments], 12,82 % [y = PER] and 11.83 % [y = NPR]. These results wee verified in a biological experiment in which adult animals, for 14 days, were given a limited amount [31 g/animal per day] of diets containing 10 % protein [casein] an d9, 10, 11, 12, and 13 % fat [margarine - at the expense of carbohydrates] with the aim of studying the effect of a mounting fat intake on optimum protein intake [43.4 g/14 days]. The correctness of the mathematical method for determining the optimum fat intake was verified by a biological method [the optimum net protein utilization , NPU, which is highest in diets containing 11 % fats, i.e. 22.5 % of the total energy value of the diet]. It was also found that this method, both along and in conjunction with other methods [especially the one using the NPR parameter], was suitable for the determination of optimum nutrient values.     

Age dependence of the utilization of different quality proteins in animal experiments.

Male rats aged 45, 85, 145 and 270 days (daily body mass increments on an optimal diet containing casein were 6.73, 2.88, 0.53 and 0.31 g respectively) were fed 15 days ad libitum on a diet with a nutrient content physiological for their age, in which the protein source was milk casein (ratio of essential to nonessential amino acids E/N = 0.79, compensation coefficient K = 14) or wheat gluten (E/N = 0.30, K = -8). In the case of gluten, net protein utilization (NPU) fell markedly in rapidly growing animals aged 45 and 85 days (33 and 30% more than with casein), indicating that without essential amino acid compensation, gluten is inadequate for animals of this age, whose organism requires fully ensured proteosynthesis for growth and development. In adolescence and adulthood (145 and 270 days), the utilization of proteins is not dependent on their quality (the decrease in NPU 13 and 12%--is nonsignificant). That means that a smaller amount of essential amino acids, including the limiting amino acid in uncompensated protein, is sufficient for the maintenance and renewal of organs and tissues, i.e. for proteosynthesis. The activation of gluconeogenesis (phosphoenolpyruvate carboxykinase activity in the liver) after the intake of plant protein confirms the effect of proteins on catabolic processes.     

Protein utilization in correlation to protein intake

In a 14-day experiment, weaned and adult rats were given ad libitum isocaloric diets with a mounting casein content (5, 10, 15, 25 and 40% by weight) and growth parameters of protein biological value, PER and NPR, and the utilization parameters NPU (body protein) and LPU (liver protein) were determined together with phosphoenolpyruvate carboxykinase (gluconeogenetic enzyme) and pyruvate kinase (glycolytic enzyme) activity in the animals' liver. The decrease in all the biological value parameters in weaned rats on 25% and 40% casein diets and in adult rats on 15%, 25% and 40% casein diets shows that these concentrations are too high for the organism. The decrease in PER and diminished weight and body and liver nitrogen increments in both age groups in animals with a low protein intake is evidence that 5% casein is an inadequate concentration. The optimum diet for weaned rats is thus a 15% casein diet and for adult rats a 10% casein diet, as confirmed by the linear correlation between weight increments, body and liver nitrogen and protein intake and also by gluconeogenetic enzyme activity. Under the given experimental conditions the study is a contribution to the determination of optimum physiological doses of proteins.     

Body growth and substrate partitioning for fat and protein gain in weaned BALB/c mice treated with growth hormone

Previously we have found that recombinant human growth hormone (rhGH) (GH; 74 ng g body wt.(-1)) administration to weaned BALB/c male mice (fed 12% or 20% protein diet) induced a growth lag and subsequent repletion similar to the catch-up growth process. We studied the partitioning of feed and protein intakes between adipose and protein body stores through the linear relationships among them. The non-linear relationship of protein intake with body fat gain/protein gain (FG/PG) ratio was especially adequate in determining the partitioning of substrates. rhGH induced an increase in feed and protein intake utilization for body weight gain (50%) and fat gain (75-140%) over saline; macronutrient utilization was the greatest in rhGH-treated mice fed 20% protein. However, growth recovery of rhGH mice was anomalous and protein intake was derived primarily for fat gain. Mice fed 12% protein (treated and control) also derived protein intake in preference to fat stores. Treatment and diet had a cumulative effect with the result that rhGH-treated animals fed 12% protein showed the greatest FG/PG ratio (1.6), and therefore, the lowest efficiency to gain protein. Weaning is a critical stage in mice when treating with rhGH, as this could provoke a growth lag. The study showed that a high protein level is required to surpass the rhGH-induced lag, but it is not enough to obtain an enhanced protein deposition. Feeding a 12% protein diet was even worse as mice did not improve on the growth lag and substrates were directed mainly to body fat.     

Increasing protein at the expense of carbohydrate in the diet down-regulates glucose utilization as glucose sparing effect in rats

High protein (HP) diet could serve as a good strategy against obesity, provoking the changes in energy metabolic pathways. However, those modifications differ during a dietary adaptation. To better understand the mechanisms involved in effect of high protein diet (HP) on limiting adiposity in rats we studied in parallel the gene expression of enzymes involved in protein and energy metabolism and the profiles of nutrients oxidation. Eighty male Wistar rats were fed a normal protein diet (NP, 14% of protein) for one week, then either maintained on NP diet or assigned to a HP diet (50% of protein) for 1, 3, 6 and 14 days. mRNA levels of genes involved in carbohydrate and lipid metabolism were measured in liver, adipose tissues, kidney and muscles by real time PCR. Energy expenditure (EE) and substrate oxidation were measured by indirect calorimetry. Liver glycogen and plasma glucose and hormones were assayed. In liver, HP feeding 1) decreased mRNA encoding glycolysis enzymes (GK, L-PK) and lipogenesis enzymes(ACC, FAS), 2) increased mRNA encoding gluconeogenesis enzymes (PEPCK), 3) first lowered, then restored mRNA encoding glycogen synthesis enzyme (GS), 4) did not change mRNA encoding β-oxidation enzymes (CPT1, ACOX1, βHAD). Few changes were seen in other organs. In parallel, indirect calorimetry confirmed that following HP feeding, glucose oxidation was reduced and fat oxidation was stable, except during the 1(st) day of adaptation where lipid oxidation was increased. Finally, this study showed that plasma insulin was lowered and hepatic glucose uptake was decreased. Taken together, these results demonstrate that following HP feeding, CHO utilization was increased above the increase in carbohydrate intake while lipogenesis was decreased thus giving a potential explanation for the fat lowering effect of HP diets.     

Stress induced differential intake of various diets and water by rat: the role of the opiate system

The purpose of this study was to explore the effect of acute mild stress (12–48 hour food and water deprivation) and acute severe stress (12 hour food and water deprivation followed by 10 min swim in water at 4°) on the intake of different isocaloric dietary regimes. Each group of experimental animals was given only one particular diet. Rats subjected to mild stress showed very little preference of dietary regimes. When the food intake was measured during 3 hour period, following 48 hours of fasting, animals showed 2 to 3 fold increase in the food and water intake but no particular dietary preference. However, when rats were subjected to severe stress, there was an increase in the food intake of 154% (control diet); 174% (high-carbohydrate diet); 310% (high protein diet) and 423% (high fat diet) compared to animals subjected to mild stress. In terms of the absolute quantity of food, the animals subjected to severe stress ate more high-fat diet than any other diet; the consumption of high fat diet was 142% more than high-protein diet, 180% more than control diet and 258% more than high carbohydrate diet. Animals subjected to severe stress and given high-carbohydrate and high fat diet also showed 80% increase in the water intake. Prior administration of naloxone (1 mg/kg body weight, i.p.) reduced the stress induced increase in the intake of food and water. Naloxone inhibited the intake of high-fat diet more than any other diet. The ability of naloxone to block the increase in the intake of high-fat diet, and the reported increase in the concentration of β-endorphin in the different regions of brain of the animals subjected to the cold swim, suggest that endogenous opioid system in body is activated during stress. An activation of the endogenous opioid system leads to a preferential increase in the intake of palatable foods.     

Body composition and physiological casein and wheat gluten protein requirements of 180-day-old rats

Six-month-old male rats were given diets with mounting casein and wheat gluten protein concentrations from 0% to 40% and after 14 days the optimum and minimum physiological doses were determined from changes in body nitrogen, body water, body weight and protein intake. The optimum dose for casein protein was 1.54 g/d (5% protein in the diet) and for wheat gluten protein 2.10 g/d (7.5% protein in the diet). The minimum casein and wheat gluten protein doses for 180- to 194-day-old rats, determined from body nitrogen changes, were 1499 mg/d (4.86%) and 1995 mg/d (7.12%) respectively, from body water changes 1561 mg/d (5.06%) and 2027 mg/d (7.23%) and from body weight changes 1333 mg/d (4.32%) and 1951 mg/d (6.06%). It should be noted that, unlike younger animals aged 35-49, 75-89 and 120-134 days, the optimum and minimum doses for six-month-old rats were approximately the same.     

Endogenous N-excretion and minimal protein requirement for maintenance of the common marmoset (Callithrix jacchus)

The protein requirement for maintenance of the marmoset Callithrix jacchus was investigated by factorial calculation via the N balance technique. Six adult male marmosets were fed a protein-free pelleted diet for 22 days. When a low protein diet (6%) was fed in the preperiod, only 7 days were necessary and when fed a higher protein diet (18%) 10 days were necessary to reach a minimum of N excretion during protein depletion. Body weight losses averaged 11% and food intake was 21% lower in the protein free period. The average endogenous urine N (EUN) was 62.1 mg N and endogenous fecal N (EFN) 49.2 mg N/kg W0.75. Body surface losses (BSN) were assumed to be 20 mg N/kg W0.75. The total endogenous loss of 131.3 mg N/kg W0.75 is similar to that of other species. Net protein utilization (NPU) of well balanced proteins, determined near the N equilibrium, was 51.8%. The calculated net protein requirement amounts to 313.6 mg N/kg W0.75, which corresponds to a dietary protein content of 6% in a diet of high caloric density, (about 19-20 MJ/kg dry matter) when the food intake is 3.3% of body weight.     

The influence of sulphur,molybdenum and cadmium exposure on the growth of goat,cattle and pig

A three factorial designed feeding experiment with common carp (Cyprinus carpio L.) was carried out in an intensive experimental rearing system. Fish (initial body weight 200 g) were fed on two different levels of dietary energy (16 and 18 MJ DE/kg DM), two different levels of protein (320 and 420 g CP/kg DM) and also two different feeding intensities (100% and 75% of the maximum intake). The experiment was terminated when fish reached a mean body weight of 1300 g.

Growth, feed utilization and nutrient composition of the whole body and fillet were observed. The highest growth was obtained when the fish were fed on the diet containing high dietary energy and high dietary protein with satiation feeding. High dietary energy, high dietary protein and restriction of feed intake improved feed conversion ratios. High dietary energy, low dietary protein and restrictive feeding increased energy utilization. Low dietary protein and restrictive feeding resulted in better protein utilization.

Fish fed with high dietary energy contained more fat and less protein in their carcasses. A lower fat content but higher protein and higher ash content in fish carcasses was shown when fish were fed with a diet high in protein and fed restrictively.     

Protein Utilization and Caloric Intake of Rats with Fatty Liver Due to an Amino Acid Imbalance

The effect of partial threonine deficiency on protein and calorie utilization and its relation to liver fat accumulation were studied. The retained nitrogen of the threonine deficient group dcreased but the ratio of the caloric intake to the retained nitrogen increased.

The liver fat content of rats fed on the threonine deficient diet decreased with each decrease in their caloric intake.

Present results support the earlier concept of the authors that the fatty liver caused by feeding rats such an amino acid imbalanced diet is due to a disproportionately high intake of calories in relation to the intake of balanced protein.     

Phospholipid and Ganglioside Composition in Rat Brain After Chronic Intake of Ethanol

Abstract: A total of 18 60-day-old male Wistar rats were divided into three groups of six animals each. One group was fed a basal diet containing high levels of protein, fat, carbohydrate, vitamins, and minerals and separately a solution of 25% sucrose-32% ethyl alcohol (wt/vol). A second group was offered water as the only drinking fluid and a similar solid diet, except that carbohydrate replaced ethanol isocalorically. A third group was maintained on the basal diet ad libitum . All groups of animals were killed in a sober state after 6 months of chronic ethanol treatment and lipid analyses were performed on brain homog-enates. Chronic treatment of the animals with ethanol produces statistically significant modification of the phospholipid and ganglioside patterns in rat brain. A statistically significant decrease of the total phospholipid content and of some of the investigated fractions, i.e., phos-phatidylcholine and phosphatidylserine, as well as an increase of phosphatidylinositol were observed. Chronic alcohol consumption was associated with a statistically significant increase in the total amount of ganglioside in rat brain. An increase in most of the investigated ganglioside fractions was indicated but the difference was statistically significant only for trisialoganglioside GT_1b. The amount of disialoganglioside GD_1a in these brains was decreased after chronic intake of ethanol.     

Dysmorphogenesis of the inner ear: disruption of extracellular matrix (ECM) formation by an L-proline analog in otic explants

L-azetidine-2-carboxylic acid (LACA), a l-proline analog, disrupts collagen secretion by cells and prevents normal morphogenesis of in vitro developing organ rudiments. Otic explants derived from 10.5-through 14-day-old mouse embryos were continuously exposed to LACA in the nutrient medium at concentrations of 75, 150, and 300 micrograms/ml. LACA disrupted normal in vitro otic morphogenesis in inner ears explanted from embryos of 10.5 through 13 days' gestation. Development of 14-day-old otic explants were not affected by LACA at the concentrations tested. There was a direct correlation between the embryonic age of the explant when exposed to LACA, and the severity of otic dysmorphogenesis. The younger explants (10.5-to 12-day-old) developed abnormalities of both vestibular and auditory structures, but with increasing embryonic age of the explants (12-to 13.5-day-old) abnormalities were confined more to the auditory portion of the inner ear. Disruption of collagen secretion of connective tissue cells of the otic explants are a major teratogenic action of LACA on inner ear development. Disrupted collagen secretion alters otic extracellular matrix production, which in turn affects the tissue interactions that regulate the progressive expression of otic morphogenesis and differentiation.     

Effects of increasing amounts of hempseed cake in the diet of dairy cows on the production and composition of milk

This study explored the potential for using seed cake from hemp (Cannabis sativa L.) as a protein feed for dairy cows. The aim was to evaluate the effects of increasing the proportion of hempseed cake (HC) in the diet on milk production and milk composition. Forty Swedish Red dairy cows were involved in a 5-week dose-response feeding trial. The cows were allocated randomly to one of four experimental diets containing on average 494 g/kg of grass silage and 506 g/kg of concentrate on a dry matter (DM) basis. Diets containing 0 g (HC0), 143 g (HC14), 233 g (HC23) or 318 g (HC32) HC/kg DM were achieved by replacing an increasing proportion of compound pellets with cold-pressed HC. Increasing the proportion of HC resulted in dietary crude protein (CP) concentrations ranging from 126 for HC0 to 195 g CP/kg DM for HC32. Further effects on the composition of the diet with increasing proportions of HC were higher fat and NDF and lower starch concentrations. There were no linear or quadratic effects on DM intake, but increasing the proportion of HC in the diet resulted in linear increases in fat and NDF intake, as well as CP intake (P < 0.001), and a linear decrease in starch intake (P < 0.001). The proportion of HC had significant quadratic effects on the yields of milk, energy-corrected milk (ECM) and milk protein, fat and lactose. The curvilinear response of all yield parameters indicated maximum production from cows fed diet HC14. Increasing the proportion of HC resulted in linear decreases in both milk protein and milk fat concentration (P = 0.005 and P = 0.017, respectively), a linear increase in milk urea (P < 0.001), and a linear decrease in CP efficiency (milk protein/CP intake; P < 0.001). In conclusion, the HC14 diet, corresponding to a dietary CP concentration of 157 g/kg DM, resulted in the maximum yields of milk and ECM by dairy cows in this study.     

Elimination of oxalate by fat sand rats (Psammomys obesus): wild and laboratory-bred animals compared

Wild fat sand rats (Psammomys obesus) can feed exclusively on plants containing much oxalate, but little calcium; oxalate intake may exceed 300 mg/d, while calcium intake is approximately 30 mg/day. By contrast, for generations, laboratory bred P. obesus have been fed a low-oxalate (<100 mg/day), high-calcium (approximately 150 mg/day) rodent chow. We compared oxalate intake and excretion between wild and laboratory-bred animals, both fed the natural high-oxalate diet, to determine whether these different dietary histories are reflected in the animal's ability to eliminate dietary oxalate. Since both wild and laboratory-bred P. obesus harbor intestinal oxalate-degrading bacteria, we predicted that their oxalate intake and excretion would be similar. Indeed, we found no significant differences in oxalate intake or excretion between the groups fed either saltbush or alfalfa (p>0.05). However, due to the differences in dietary calcium intake between the two diets, in both groups only part (23-25%) of the ingested oxalate was excreted when the animals were fed the oxalate-rich saltbush, yet most (87-90%) was excreted when feeding on calcium-rich alfalfa. Thus, even after generations of feeding on a commercial low-oxalate diet, fat sand rats maintain intestinal oxalate-degrading bacteria that appear to increase in number and activity when presented with their natural diet.