Changing perspectives on aging and energy requirements: aging and digestive function in humans, dogs and cats

Age-related digestibility of nutrients depending on the moisture content in aged dogs

Digestibility of pet food can affect the health of dog, especially of aged animals. To maintain the health of dogs in an overall good status it is necessary to provide nutritionally balanced food. For example, the digestibility of dogs was known to be decreased along aging. In addition, losing teethes is an often event in aged dogs that could induce a problem to eat a large size dry pet food. Nonetheless, few detailed information is available on the most suited feeding for aged dogs. As part of the nutritional study of food for aged dogs, in this study, we tested whether food type impacts on digestibility on adult versus senior dogs. The methodology to measure the digestibility of nutrients was chosen the index method using chromium oxide. Dogs were fed the same commercial dry or wet diets, which were supplemented with 0.5% chromium oxide. The wet food was prepared by adding twice volume of water in the dry food prior to incubated overnight (14-16 hours) at room temperature. After five days, their feces were collected up to a total weight of > 200 g which was the amount to analyze undigested nutrients in feces as 3 repeats. In the apparent total tract digestibility analysis of the experimental breed, no difference in the digestibility of crude protein, crude fat, crude fiber, ash, and energy was observed regarding the moisture content of the food. Noteworthy, the digestibility of nitrogen free extract was significantly increased in senior dogs fed dry dog food compared with adult dogs fed the same diet, whereas no difference was observed between senior and adult dogs fed wet food. The small breed dogs showed similar results to the experimental breed dogs. However, the digestibility of crude fat was additionally affected by age and food type unlike the experimental breed dogs. This finding suggests that the food moisture content affects the digestibility of nutrients in dogs with aging. Hence, it may be helpful to determine the nutrient contents in foods for senior dogs depending on the food type.

Healthy Ageing Is Associated with Preserved or Enhanced Nutrient and Mineral Apparent Digestibility in Dogs and Cats Fed Commercially Relevant Extruded Diets

Age-related changes in gastrointestinal function have been reported in companion animals, but the impact on digestive efficiency remains uncertain. Healthy dogs (n = 37; 2.6-14.2 years) received four diets varying in total dietary fibre (TDF; 6-29%, as fed). Healthy cats (n = 28; 1-13 years) received four diets with two fat (10-12%; 17-18%) and TDF (9 and 12%) levels. In a crossover design, diets were provided over four consecutive 10-day cycles, including a 4-day faecal collection. Apparent crude protein (CP), ether extract (EE), TDF, calcium (Ca), and phosphorus (P) digestibilities were determined. The effect of age was analysed as a continuous variable in dogs and as differences between adult (1-5 years) and senior (7-13 years) cats. In dogs, EE digestibility was unaffected by age (p > 0.10). Dogs of 6-12 years had higher digestibility of CP (p = 0.032), TDF (p = 0.019), Ca (p = 0.019), and P (p = 0.024) when fed the 6% TDF diet. Senior cats had greater digestibility of TDF (p < 0.01) and Ca (p = 0.024) but had lower EE and CP digestibility with one diet (17% fat; 9%TDF) (age, p > 0.10; diet × age, p < 0.001). Healthy ageing was associated with preserved nutrient digestibility in dogs and cats within the age ranges studied. The effect of ingredient sources in senior cats warrants further investigation.

First report of cystic echinococcosis caused by Echinococcus granulosus sensu stricto/G1 in Felis catus from the Patagonian region of Argentina

Two domestic cats from the Patagonia rural area in Argentina were found to be naturally infected with Echinococcus granulosus sensu stricto/G1 genotype; so far, the only species/genotype of E. granulosus sensu lato complex described to infect domestic cats. The felines developed abdominal disseminated larval disease; the diagnosis was performed by ultrasound, exploratory laparotomy, and molecular techniques. These results indicate that cystic echinococcosis must be considered for differential diagnosis of felines with abdominal distension and/or observation of vesicles through ultrasound, from endemic areas. Even though cats and dogs are carnivores, differences in digestive physiology and immunological characteristics between them could allow the development of larval or adult worm parasites. Domestic cats with cystic echinococcosis show to be environmentally infected with E. granulosus s. s./G1 eggs.

A period of 10 weeks of increased protein consumption does not alter faecal microbiota or volatile metabolites in healthy older men: a randomised controlled trial

Diet has a major influence on the composition and metabolic output of the gut microbiome. Higher-protein diets are often recommended for older consumers; however, the effect of high-protein diets on the gut microbiota and faecal volatile organic compounds (VOC) of elderly participants is unknown. The purpose of the study was to establish if the faecal microbiota composition and VOC in older men are different after a diet containing the recommended dietary intake (RDA) of protein compared with a diet containing twice the RDA (2RDA). Healthy males (74⋅2 (sd 3⋅6) years; n 28) were randomised to consume the RDA of protein (0⋅8 g protein/kg body weight per d) or 2RDA, for 10 weeks. Dietary protein was provided via whole foods rather than supplementation or fortification. The diets were matched for dietary fibre from fruit and vegetables. Faecal samples were collected pre- and post-intervention for microbiota profiling by 16S ribosomal RNA amplicon sequencing and VOC analysis by head space/solid-phase microextraction/GC-MS. After correcting for multiple comparisons, no significant differences in the abundance of faecal microbiota or VOC associated with protein fermentation were evident between the RDA and 2RDA diets. Therefore, in the present study, a twofold difference in dietary protein intake did not alter gut microbiota or VOC indicative of altered protein fermentation.

Cats Have Increased Protein Digestibility as Compared to Dogs and Improve Their Ability to Absorb Protein as Dietary Protein Intake Shifts from Animal to Plant Sources

This retrospective study used 226 dogs and 296 cats to evaluate whether protein absorption was influenced by species, and within species, what influence increasing the percentage of total dietary protein, as plant protein, had on protein absorption. Each food was evaluated by at least one study with a minimum of six dogs or cats assigned to each study. Dietary inclusion of animal and plant based protein was calculated by analysis of ingredients and dietary inclusion level. Both dogs and cats were able to digest dietary plant protein, with protein digestibility in dogs unchanged as plant protein increased, while in cats, eating dry food, an increase in plant protein, was associated with increased protein digestibility. When individual plant high-concentration protein sources (excluding the protein from whole grains) were evaluated (i.e., soybean meal, soybean protein isolate, corn gluten meal, and rice protein concentrate) there was no response to increasing protein from these sources in the dog. In the cat, there was a significant positive effect on protein digestibility associated with an increasing concentration of corn gluten meal. In summary, as the dietary protein shifted from striated muscle and other animal proteins to plant based proteins, there was no effect in the dog, while in cats, increasing dietary plant protein was associated with increasing protein digestibility (5.5% increase at 50% protein from plants in dry cat food). Protein digestibility of food in dogs and cats is similar, if not enhanced, when the plant protein sources are concentrated from soybeans (soybean isolate, soybean meal), corn (corn gluten meal), or rice (rice protein concentrate).

Nutritional assessment in the cat: Practical recommendations for better medical care

PRACTICAL RELEVANCE

Pet owners want dietary recommendations from their veterinarian. Providing a brief nutritional assessment for every cat at every visit will result in better medical care and build trust with clients.

CLINICAL CHALLENGES

Examination time is limited, and it can be challenging to ensure appointments are efficient, yet thorough. A range of practical assessment tools is available that can assist with this process.

PATIENT GROUP

Every cat can benefit from a screening nutritional evaluation as the fifth vital assessment (after temperature, pulse, respiration and pain assessment). Identifying patients with nutritional risk factors or nutrition-responsive diseases should prompt a more in-depth review of dietary needs.

AUDIENCE

This article is aimed at all veterinary health professionals and is accompanied by videos demonstrating the body condition scoring process for a series of cats ranging from ideal body weight through to obese.

EVIDENCE BASE

Information in the review is drawn from the current scientific literature, as well as the clinical experience of the authors.

Pharmacokinetics of intravenous gentamicin in healthy young-adult compared to aged alpacas

The study objective was to evaluate the effects of age on aminoglycoside pharmacokinetics in eight young-adult (<4 years) and eight aged (≥14 years) healthy alpacas, receiving a single 6.6 mg/kg intravenous gentamicin injection. Heparinized plasma samples were obtained at designated time points following drug administration and frozen at -80°C until assayed by a validated immunoassay (QMS^® ). Compartmental and noncompartmental analyses of gentamicin plasma concentrations versus time were performed using WinNonlin (v6.4) software. Baseline physical and hematological parameters were not significantly different between young and old animals with the exception of sex. Data were best fitted to a two-compartment pharmacokinetic model. The peak drug concentration at 30 min after dosing (23.8 ± 2.1 vs. 26.1 ± 2 μg/ml, p = .043) and area under the curve (70.4 ± 10.5 vs. 90.4 ± 17.6 μg hr/ml, p = .015) were significantly lower in young-adult compared to aged alpacas. Accordingly, young alpacas had a significantly greater systemic clearance than older animals (95.5 ± 14.4 and 75.6 ± 16.1 ml hr^-1 kg^-1 ; p = .018), respectively). In conclusion, a single 6.6 mg/kg intravenous gentamicin injection achieves target blood concentrations of >10 times the MIC of gentamicin-susceptible pathogens with MIC levels ≤2 μg/ml, in both young-adult and geriatric alpacas. However, the observed reduction in gentamicin clearance in aged alpacas may increase their risk for gentamicin-related adverse drug reactions.

Effect of age, sex and body weight on the serum concentrations of cobalamin and folate in cats consuming a consistent diet

Objectives Multiple feline diseases involving the gastrointestinal tract, pancreas, liver and biliary tract are known to cause abnormal serum cobalamin and folate concentrations. Measuring the serum concentration of these vitamins can therefore be a helpful diagnostic tool. However, factors other than disease, in particular age, have also been suggested to have an effect on the serum concentration of cobalamin and folate. In previous studies, the dietary intake was not standardised, or even known, despite diet being the prinicpal source of both vitamins. Therefore, we evaluated the effect of age, sex and body weight on the serum concentration of folate and cobalamin in cats fed the same diet. Methods The serum cobalamin and folate concentrations were measured in 65 apparently healthy cats in a nutrition colony that had been fed an identical diet. A linear model was used to test the relationship between the serum concentration of cobalamin and folate with the variables age, sex and body weight. Results There was a large variation in the serum concentration of both folate and cobalamin, despite identical intake. Serum cobalamin was inversely associated with age ( P = 0.002), and males had higher concentrations than females ( P = 0.039). Serum folate was positively associated with age ( P = 0.01). Conclusions and relevance Independent of diet, serum cobalamin concentration decreases with age. Changes in gastrointestinal function, microflora or metabolism may be responsible. Older cats may be more susceptible to cobalamin deficiency secondary to inappetence or gastrointestinal disease.

The effect of age and carbohydrate and protein sources on digestibility, fecal microbiota, fermentation products, fecal IgA, and immunological blood parameters in dogs

The present study compared the effects of diets formulated with fibers of different fermentability and protein sources of animal or vegetable origins on old and adult dogs. The experiment was organized in a 3 (diets) × 2 (ages) factorial arrangement, totaling 6 treatments. Thirty-six Beagle dogs were used (18 old dogs [10.2 ± 1.0 yr] and 18 young adult dogs [2.6 ± 0.9 yr]), with 6 dogs per treatment. Three diets with similar compositions were used: a nonfermentable insoluble fiber source (sugarcane fiber) and chicken byproduct meal (nonfermentable fiber [NFF] diet), a fermentable fiber source (beet pulp) and chicken byproduct meal (fermentable fiber [FF] diet), and soybean meal as a protein and fiber source (soybean meal [SM] diet). Data were evaluated using the MIXED procedure and considering the effects and interactions of block, animal, diets, and age. Means were compared using Tukey's test ( < 0.05). Age × diet interactions were evaluated when < 0.1. Old dogs had a reduced coefficient of total tract apparent digestibility of DM, which was explained by the age and diet interaction of CP and fat digestibility that was lower for old than for adult dogs fed the FF diet ( < 0.05). The SM diet obtained higher DM, OM, CP, and fiber digestibility compared with the NFF diet ( < 0.05). The feces of dogs fed the NFF diet had increased DM content ( < 0.05). The short-chain fatty acids (SCFA) did not change by age group and were higher for dogs fed the FF and SM diets compared with dogs fed the NFF diet ( < 0.05). An age and diet interaction was observed for lactate and was increased in the feces of old dogs compared with adult dogs fed the FF diet ( < 0.05). Fecal putrescine, cadaverine, and spermine were increased for old dogs compared with adult dogs ( < 0.05), and the spermidine fecal concentration was increased for dogs fed the SM diet regardless of age ( < 0.05). Old dogs had reduced peripheral T and B lymphocytes ( < 0.05). An age and diet interaction was observed for fecal IgA ( < 0.001). Adult dogs fed the SM diet had increased IgA in feces compared with animals fed the NFF and FF diets ( < 0.05). However, for old dogs, both the FF and SM diets induced increased IgA compared with the NFF diet ( < 0.05). In conclusion, beet pulp may reduce digestibility and induce increased lactate in the feces of old dogs. The protein and oligosaccharides of soybean meal are digestible by dogs, induce the production of SCFA and spermidine, and increase fecal IgA. Old dogs had increased putrecine, cadaverine, and spermine fecal concentrations.

Influence of feeding a fish oil-containing diet to young, lean, adult dogs: effects on lipid metabolites, postprandial glycaemia and body weight

The aim of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight in young, lean, adult dogs. Eight female Beagles were randomly assigned to one of two isonitrogenous and isoenergetic diets, Control or FO, in a crossover design. At the beginning of the experiment and at 30 and 60 d, a baseline blood sample was collected and the dogs then were fed their daily ration. Nitrogen balance began at 07:00 h on day 63 of each experimental period and ended at 07:00 h on day 69. On day 66 of each period, a single dose (7.5 mg/kg) of (15)N-glycine was administered orally to each dog via gelatin capsule. Postprandial glycaemia did not differ between treatments or among sampling days within treatment. Cholesterol concentration was increased (p<0.05) on the Control treatment throughout the experiment when compared to values of day 0. Dogs fed the FO treatment had higher plasma triglyceride and ghrelin concentrations than those fed the Control treatment. Body weight and food intake did not differ between dietary treatments. Faecal excretion was increased (p<0.05) in the FO treatment. Dry matter digestibility was decreased (p<0.05) and fat digestibility tended (p<0.10) to decrease in the FO treatment. Overall, feeding a FO-containing diet showed a protective effect against the rise of plasma cholesterol and it increased plasma ghrelin concentration. However, FO supplementation did not appear to affect protein metabolism or postprandial glycaemia in adult lean dogs.

Digestion and Postprandial Metabolism in the Elderly

The elderly are an increasing segment of the population. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that decrease quality of life and accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. Yet despite the importance of nutrition, relatively little is known of the impact of advancing age on the gastrointestinal function, the digestive responses, and the post-meal metabolic adaptations that occur in response to ingested food. Knowledge of the age-related differences in digestion and metabolism in the elderly is essential to the development of appropriate nutritional recommendations for the maintenance of optimal health and prevention of disease.

Fat digestibility is reduced in old cats with subnormal cobalamin concentrations

Fat digestibility is decreased in old cats for unknown reasons. Subclinical gastrointestinal diseases and pancreatic dysfunction, both related to ageing, can affect food digestibility. The aim of the present study was to elucidate the prevalence of subnormal cobalamin concentration and pancreatic disease in old cats and study the relationship between both markers and fat digestibility. A total of sixty-four cats without evident signs of gastrointestinal disease were included and grouped according to age: (1) fifteen middle-aged (MA), aged 3–7 years; and (2) forty-nine old, aged 10–17 years. All cats were tested for serum cobalamin, specific feline pancreatic lipase (fPL) and feline trypsin-like immunoreactivity. Then, sixteen of the old cats were selected and grouped according to cobalamin and fPL concentrations: control (normal cobalamin and fPL); low vitamin B₁₂ (cobalamin <290 ng/l; normal fPL); and high fPL (normal cobalamin; fPL >4 µg/ml). A food digestibility trial with a high-fat diet (21·6 %) was performed. In the old group, cobalamin was lower and fPL higher than in MA cats. Of the old cats (n 49), 14 % had subnormal cobalamin, 8 % had a severe increase in fPL, 2 % had both alterations and 14 % had a slight increase in fPL. By contrast, MA cats did not have cobalamin deficiency or an increase in fPL concentrations. Fat digestibility was lower in low vitamin B₁₂ cats than control cats. Decreased fat digestibility is not present in all old cats but could be a characteristic of subclinical chronic gastrointestinal disease. Cobalamin concentration, as a marker of gastrointestinal disease, could be useful for the routine evaluation of old cats.

Seasonal and age effects on energy requirements in domestic short-hair cats (Felis catus) in a temperate environment

There is little information known about the energy requirements of cats in temperature climates. Energy requirement of domestic short-haired cats was determined using three groups of mixed gender - old kept outside (approximately 9.9 years of age; 4.8 kg; n = 9), young kept outside (approximately 3.1 years of age; 3.9 kg; n = 8) or young kept inside (approximately 3.1 years of age; 3.9 kg; n = 8). Cats were housed individually for 5 weeks during summer (18.5 ± 0.5 °C) and winter (8.5 ± 0.4 °C) and were fed a commercially available maintenance diet ad libitum. In both periods, energy expenditure was determined from the rates of (2) H and (18) O elimination for blood H2 O over a 12 day period, from a doubly labelled water bolus (2) H2 O (0.7 g/kg BW) and H2 (18) O (0.13 g/kg BW) administered intravenously. During the summer period, macronutrient digestibility was determined. Older cats had a reduction (p < 0.05) in apparent digestibility of dry matter (approximately 9%), energy (approximately 8%) and protein (6%). There was a significant effect of age and season on energy intake and energy expenditure. While lean mass was affected by age and season, there was no effect of age or season on energy expenditure when expressed as a proportion of lean mass. Possible seasonal differences in nutrient digestibility may explain these results.

Old beagle dogs have lower faecal concentrations of some fermentation products and lower peripheral lymphocyte counts than young adult beagles

The effects of age on microbiota composition, gut fermentation end-product formation and peripheral lymphocyte numbers were compared between old and young adult Beagle dogs fed four kibble diets differing in yeast cell wall contents. The experiment had a double 4 × 4 Latin square design, one with four mature dogs (4 years old) and the other with four old dogs (10 years old), with four replicates (diets) per dog. In each period a 15 d adaptation period preceded a 5 d total collection of faeces for the digestibility trial. On day 21, fresh faecal samples were collected for the determination of bacterial enumeration, pH, biogenic amine and short-chain fatty acid. Flow cytometry was used for immunophenotypic evaluation. Dogs were fed four kibble diets with similar composition with 0, 0.15, 0.30 and 0.45 % of yeast cell wall (as-fed), respectively. Data were evaluated using general linear models of Statistical Analysis Systems statistical software (P < 0.05). No evidence of a difference in faecal bacteria counts between ages was found (total aerobes, total anaerobes, Bifidobacterium, Lactobacillus, Clostridium and Escherichia coli: P>0.15). Faecal concentrations of butyrate, histamine, agmatine and spermine were lower (P ≤ 0.05) and faecal pH was higher (P = 0.03) in older dogs than in mature adult dogs, suggesting an alteration in bacterial metabolic activity, or in the rate of intestinal absorption of these compounds. Concentrations of T-lymphocytes, T-cytotoxic lymphocytes and B-lymphocytes were also lower (P ≤ 0.01) in older dogs than in mature adult dogs. The study confirmed alterations in peripheral lymphocytes and revealed a reduced concentration of some fermentation end products in the colon of old dogs.

Feeding old cats--an update on new nutritional therapies

Aging is associated with a wide variety of physiological changes that compromise the ability of the body to respond to stress or change, and ultimately contribute to morbidity and mortality. Much research has been done on the aging process in humans and experimental animals, and the impact of diet, but there is relatively little data from companion animal studies. However, although many of the aging changes are likely to be similar between different mammals, it is known that there are some differences with cats. In contrast to dogs and humans, elderly cats experience an increase in their maintenance energy requirements rather than a continued decline, which may be mediated partly through a better-maintained basal metabolic rate but also through progressive compromise in fat and protein digestion. Old age is also associated with a progressive loss of lean body mass that may be mitigated in part by feeding higher protein levels. Diets designed for healthy elderly cats should therefore concentrate on being energy dense, highly digestible and with an increase in the proportion of protein calories, and being fed with the aim of supporting optimal body weight. There is also strong evidence emerging that dietary manipulation in cats may be able to modify aspects of the aging process, with a long-term longitudinal study of cats demonstrating both survival and health benefits from feeding a diet supplemented with antioxidants, fatty acids, and a prebiotic source.

Weight loss in the elderly cat. Appetite is fine and everything looks normal

PRACTICAL RELEVANCE

Improvements in general health care and nutrition have meant that more cats are living to an advanced age. Weight loss is one of the most common presenting signs in the older cat. Many causes of weight loss in older cats are at least amenable to supportive care and some are curable.

CLINICAL CHALLENGES

Weight loss is a non-specific change and, while often a sensitive indicator of ill health, does not readily point to the diagnosis. Careful history taking and physical examination may indicate a specific cause but, as discussed in this article, further tests are generally required to confirm the diagnosis. In those cats where common causes of weight loss have been eliminated by initial tests, it is often harder to reach a diagnosis. A logical approach to case-solving is required, making use of imaging and advanced laboratory tests. Occult gastrointestinal disease should be suspected and investigated in cats where another cause of weight loss cannot be found.

PATIENT GROUP

While the average lifespan of a pet cat is probably around 13-14 years, many will live longer than this if well cared for, and some considerably longer. Recently, the life stages have been redefined to help predict the changes that might be occurring in terms of a cat's physical and mental health. Cats are considered 'senior' at 11-14 years old and 'geriatric' at 15 years and above.

AUDIENCE

Geriatric medicine is forming an increasing part of the case load of first opinion and many referral veterinarians.

The reduction of protein intake observed in old rats depends on the type of protein

Previous experiments have shown in Lou/c/jall rats growing old a deleterious reduction of protein intake, which occurs earlier in males than in females. We previously showed that this decrease could not be attributed to a loss of regulation of protein intake with age. Present studies were designed to investigate if the age-related decrease of protein intake was dependent on the type of protein used. In a first sectional study, adult, middle and old-aged Lou/c/jall rats were submitted to a self-selection procedure. They were fed successively with casein, whey protein and fish flour as protein. In a second longitudinal study, self-selected males and females were tested each 4 months (at 3, 7, 11, 15, 19, 23 and 27 months of age) with only casein and whey protein as protein. In the two experiments, the type of dietary protein had an influence on the protein intake: when casein is offered, the well-established decrease in protein consumption was seen after 15 months of age in male groups. The introduction of whey protein induced maintenance of protein intake in old male groups at the level of female's protein intake. Moreover, young females showed an obvious preference for casein versus whey protein. This preference disappeared in old ages. These data showed that casein, even if it was an appropriate protein for young animals, could become inadequate for old animals and could result in a protein aversion in old rats. On the contrary, whey protein seemed to be a more appropriate protein than casein for old rats.

The Atwater energy equivalents overestimate metabolizable energy intake in older humans: results from a 96-day strictly controlled feeding study

The Atwater energy equivalents of 16.7, 16.7 and 37.7 kJ/g of protein, carbohydrate and fat, respectively, are the standard values used to calculate the macronutrient intakes required to meet a person's metabolizable energy requirement. The aim of this study was to compare in older people the measured metabolizable energy intake (MEI(MEAS)) required to achieve and maintain stable body weights with the MEI estimated using the Atwater energy equivalents (MEI(AT)). During a 96-d (14-wk) strictly controlled dietary period, 11 men and 17 women (55-78 y old) were each provided a MEI(AT) to maintain body weight within +/- 0.5 kg of baseline weight. The MEI(MEAS) was determined retrospectively from the gross energy contents of food, urine and feces samples collected during week 14. Resting energy expenditure was measured using indirect calorimetry. At wk 14, MEI(AT) overestimated MEI(MEAS) by 26%. These results suggest that the Atwater energy equivalent values may overestimate the actual MEI of older people.

Senescent terminal weight loss in the male F344 rat

Loss of weight, often of unknown cause and culminating in death, commonly occurs in humans at advanced ages. Rats that live to old ages, such as the Fischer 344 (F344) strain, also exhibit a terminal loss in body weight. A presently held hypothesis is that the terminal weight loss in the F344 rat model is due to reduced food intake because of an alteration in hypothalamic function resulting in early satiation. We report findings on terminal weight loss and food intake in male F344 rats fed ad libitum (AL group) or a life-prolonging dietary regimen in which caloric intake was restricted (DR group). Rats in both dietary groups that did not exhibit a terminal weight loss died at younger ages than those exhibiting the loss. Terminal weight loss in the AL group was not associated with decreased food intake; indeed, half of the rats in this group had an increased food intake during the period of terminal weight loss. This finding is not in accord with the presently held hypothesis. In the DR group, terminal weight loss was associated with reduced food intake. Pathology (renal disease and neoplasms) did not explain the presence or absence of the association between reduced food intake and weight loss in either dietary group. The duration of the period of terminal weight loss was similar for the AL and DR groups. Apparently, restricting calories delays the occurrence but does not affect the duration of senescent terminal weight loss.

Protein digestibility and quality in products containing antinutritional factors are adversely affected by old age in rats

The protein digestibility-corrected amino acid score (PDCAAS) has been recommended to be the most suitable method for routine evaluation of protein quality of foods by FAO/WHO. The PDCAAS method includes the use of young rats for predicting protein digestibility of foods for all ages including the elderly. To assess the usefulness of protein digestibility in old rats in the calculation of PDCAAS for the elderly, the influence of age on the digestibility of protein in 5-wk-old and 20-mo-old rats by the balance method was studied. Fifteen protein products were tested. Each protein product was fed as the sole source of 10% dietary protein. A protein-free diet was also included to obtain an estimate of metabolic fecal protein. Protein digestibility values (corrected for metabolic fecal protein loss) in old rats were significantly (P < 0.05) lower than in young rats for most products; however, these differences were small (up to 3%) for properly processed animal products (casein, whey protein concentrate, whey protein hydrolysate, lactalbumin and skim milk powder). Similarly, the differences attributed to age were not large (up to 5%) for properly processed vegetable protein products (soy protein isolate and autoclaved soybean meal, black beans and fava beans). However, digestibility values in old rats were considerably lower (7-17%) than in young rats when fed products containing antinutritional factors, that is, mustard flour containing glucosinolates; alkaline/heat-treated soy protein isolate and lactalbumin-containing lysinoalanine; raw soybean meal and black beans containing trypsin inhibitors; and heated skim milk powder containing Maillard compounds. Therefore, the inclusion of protein digestibility data obtained using young rats in the calculations of PDCAAS may overestimate protein digestibility and quality of these products for the elderly. For products specifically intended for the elderly, protein digestibility should be determined using old rats.

Old as mature LOU/c/jall rats enhance protein selection in response to a protein deprivation

Previous experiments have shown a strong decrease in protein consumption as rats grow old. This result could be induced by an impaired regulation of feeding behaviour. Present study investigated the ability of ageing rats to adapt their protein intake to protein requirements. Four groups of self-selecting LOU/c/jall male and female rats (4, 16, 22, 28 months at the beginning of the experiments) were submitted to 4-days of protein deprivation periods while their macronutrient intakes were monitored. Moreover, they were submitted to a 4-day fasting period. After reintroduction of proteins, old and senescent rats were able to increase their protein intake in response to the specific protein need created by the protein deprivation. They were also able to increase caloric intake after the fasting period. These results led to the conclusion that the loss of appetite for protein observed with ageing reflects rather an adaptation than an impairment of the regulation of macronutrient choice. Another important observation was that older animals did not recover initial body weight after a body weight loss even if they ate as many calories as younger animals. This data supports a decrease in the efficacious utilization of body fuels in old and senescent rats.

Prolonged longevity in naked mole-rats: age-related changes in metabolism, body composition and gastrointestinal function

Aging is characterized by declines in all physiological processes and concomitant changes in body composition. Age-related changes in metabolism, body composition and gastrointestinal function were investigated in naked mole-rats (Heterocephalus glaber), rodents that exhibit extended longevity. Maximum lifespan of these 40 g rodents (>27 year) is approximately 9 times greater than predicted allometrically. We investigated changes in basal metabolic rate (BMR), body composition and intestinal glucose transport in 1, 5, 10 and 20-year-old male individuals. Body composition was measured using dual X-ray absorptiometry and activity of sodium glucose co-transporters (SGLT1) determined using everted gut sleeves. One-year-olds had lower body mass than other age cohorts, as they had not attained full adult form. Among the 5, 10, and 20-year-olds, no age-related changes in body mass, BMR, percentage body fat, fat-free mass or bone mineral density were found. SGLT1 activity declined moderately (<20%) from 5 to 20 years and was similar at 10-20 years, whereas age-related declines are 40-60% in mice. Although mole-rats have low metabolic rates, their prolonged longevity results in a lifetime energy expenditure more than 4 times that of mice. Since lifetime energy expenditure is an important index of potential exposure to oxidative damage, naked mole-rats may be valuable for studying mechanisms of aging.

Aging does not influence feeding behavior in cats

The aim of this investigation was to see whether aging influences feeding behavior in cats. Two studies were carried out. In the first study, a standard canned cat food was fed to six young adult and six senior cats for 10 d on an ad libitum basis. Feeding behavior was monitored during the final 5 d. In the second study, diets enriched with beef tallow, olive oil or sunflower oil were fed at an equivalent energy intake for 21 d. Feeding behavior was monitored during the final 5 d. The results of both studies indicated no significant differences between the young and old cats in the number of meals consumed, the amount consumed at each meal or the duration of each meal when fed either ad libitum or at equivalent energy intakes. Daily feeding patterns were similar for each of the 5 d for each cat, with cats tending to consume regular small meals throughout the day and night. The only significant differences noted were among the fat-enriched diets. The diet enriched with beef tallow had fewer refusals compared to the diets enriched with olive oil and sunflower oil, indicating a possible palatability differential. It was concluded that cats of all ages are habitual feeders with similar daily feeding patterns, which may be altered only with a change in diet. Given that no differences were seen between the young and senior cats, it cannot be assumed that feeding patterns are responsible for the previously observed age-related decreases in apparent digestibility.