The role of protein and calorie restriction in outcome from Salmonella infection in mice

"Feed a Cold, Starve a Fever?" A Review of Nutritional Strategies in the Setting of Bacterial Versus Viral Infections

PURPOSE OF REVIEW

Some data, mostly originally derived from animal studies, suggest that low glucose intake is protective in bacterial sepsis but detrimental in overwhelming viral infections. This has been interpreted into a broad belief that different forms of sepsis may potentially require different nutritional management strategies. There are a few mechanistic differences between the host interactions with virus and bacteria which can explain why there may be opposing responses to macronutrient and micronutrient during the infected state. Here, we aim to review relevant evidence on the mechanisms and pathophysiology of nutritional management strategies in various infectious syndromes and summarize their clinical implications.

RECENT FINDINGS

Newer literature - in the context of the SARS-CoV-19 pandemic - offers some insight to viral infections. There is still limited clinically applicable data during infection that clearly delineate the role of nutrition during an active viral vs bacterial infections. Based on contrasting findings in different models of viruses and bacteria, the macronutrient and micronutrient needs may depend more on specific infectious organisms that may not be generalizable as bacterial versus viral. Overall, the metabolic effects of sepsis are context dependent, and various host-specific (e.g., age, baseline nutritional status, immune status, comorbidities) and illness variables (phase, duration, and severity of illness) play a significant role in determining the outcome besides pathogen-specific (virus or bacterial or fungi and combined infections) factors. Microbe therapy (probiotics and prebiotics) seems to have therapeutic potential in both viral and bacterial infected states, and this seems like a promising area for further practical research.

Calorie restriction partially attenuates sickness behavior induced by viral mimetic poly I:C

Calorie restriction (CR) has been shown to extend the mean and maximum lifespan in both preclinical and clinical settings. We have previously demonstrated that CR attenuates lipopolysaccharide (LPS)-induced fever and sickness behavior. CR also leads to reductions in pro-inflammatory and increases in anti-inflammatory profiles. LPS is a bacterial mimetic; however, few studies have explored this phenomenon utilizing a viral mimetic, such as polyinosinic:polycytidylic acid (poly I:C). Dose-dependently, poly I:C induced an increase in core body temperature (Tb), with the largest dose (5000 µg/kg) resulting in a 1.62 °C ( ± 0.23 °C) Tb increase at 7 h post-injection in ad libitum mice and was associated with reduced home-cage locomotor activity. We then investigated the effect of 50% CR for 28 days to attenuate fever and sickness behavior induced by a poly I:C (5000 µg/kg) viral immune challenge. CR resulted in the partial attenuation of fever and sickness behavior measures post-poly I:C. The freely fed, control mice demonstrated a 2.02 °C ( ± 0.22 °C) increase in Tb at 7 h post-injection compared to the CR poly I:C group which demonstrated an increase in Tb of 0.94 °C ( ± 0.27 °C). Locomotor patterns post-injection were different, CR mice displayed a reduction in activity during the light phase, and the control group displayed a reduction during the dark phase. CR moderately attenuated the neuroinflammatory response with a reduction in microglial density in the ventromedial nucleus of the hypothalamus. The fever and sickness behavior attenuation seen after CR may be driven by similar anti-inflammatory processes as after LPS; however, further investigation is required.

Larval diet affects adult reproduction, but not survival, independent of the effect of injury and infection in Drosophila melanogaster

Early-life conditions have profound effects on many life-history traits, where early-life diet affects both juvenile development, and adult survival and reproduction. Early-life diet also has consequences for the ability of adults to withstand environmental challenges such as starvation, temperature and desiccation. However, it is less well known how early-life diet influences the consequences of infection in adults. Here we test whether varying the larval diet of female Drosophila melanogaster (through altering protein to carbohydrate ratio, P:C) influences the long-term consequences of injury and infection with the bacterial pathogen Pseudomonasentomophila. Given previous work manipulating adult dietary P:C, we predicted that adults from larvae raised on higher P:C diets would have increased reproduction, but shorter lifespans and an increased rate of ageing, and that the lowest larval P:C diets would be particularly detrimental for adult survival in infected individuals. For larval development, we predicted that low P:C would lead to a longer development time and lower viability. We found that early-life and lifetime egg production were highest at intermediate to high larval P:C diets, but this was independent of injury and infection. There was no effect of larval P:C on adult survival. Larval development was quickest on intermediate P:C and egg-to-pupae and egg-to-adult viability were slightly higher on higher P:C. Overall, despite larval P:C affecting several measured traits, we saw no evidence that larval P:C altered the consequence of infection or injury for adult survival or early-life and lifetime reproduction. Taken together, these data suggest that larval diets appear to have a limited impact on the adult life history consequences of infection.

Viral susceptibility across host species is largely independent of dietary protein to carbohydrate ratios

The likelihood of a successful host shift of a parasite to a novel host species can be influenced by environmental factors that can act on both the host and parasite. Changes in nutritional resource availability have been shown to alter pathogen susceptibility and the outcome of infection in a range of systems. Here, we examined how dietary protein to carbohydrate altered susceptibility in a large cross-infection experiment. We infected 27 species of Drosophilidae with an RNA virus on three food types of differing protein to carbohydrate ratios. We then measured how viral load and mortality across species was affected by changes in diet. We found that changes in the protein:carbohydrate in the diet did not alter the outcomes of infection, with strong positive inter-species correlations in both viral load and mortality across diets, suggesting no species-by-diet interaction. Mortality and viral load were strongly positively correlated, and this association was consistent across diets. This suggests changes in diet may give consistent outcomes across host species, and may not be universally important in determining host susceptibility to pathogens.

Feed Restriction Modulates Growth, Gut Morphology and Gene Expression in Zebrafish

A reduction in daily caloric or nutrient intake has been observed to promote health benefits in mammals and other vertebrates. Feed Restriction (FR), whereby the overall food intake of the organism is reduced, has been explored as a method to improve metabolic and immune health, as well as to optimize productivity in farming. However, less is known regarding the molecular and physiological consequences of FR. Using the model organism, Danio rerio, we investigated the impact of a short-term (month-long) FR on growth, gut morphology and gene expression. Our data suggest that FR has minimal effects on the average growth rates, but it may affect weight and size heterogeneity in a sex-dependent manner. In the gut, we observed a significant reduction in gut circumference and generally lower mucosal heights, whereas other parameters remained unchanged. Gene Ontology (GO), EuKaryotic Orthologous Groups (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified numerous metabolic, reproductive, and immune response pathways that were affected by FR. These results broaden our understanding of FR and contribute towards growing knowledge of its effects on vertebrate health.

Dietary Supplementation With High Fiber Alleviates Oxidative Stress and Inflammatory Responses Caused by Severe Sepsis in Mice Without Altering Microbiome Diversity

In this study, we demonstrated the effects of a high-fiber diet on intestinal lesions, oxidative stress and systemic inflammation in a murine model of endotoxemia. C57BL/6 mice were randomly assigned to four groups: the control group (CONTROL), which received a commercial normal-fiber rodent diet comprising normal fiber; a CLP group, which received a commercial normal-fiber rodent diet and underwent caecal ligation puncture (CLP); a high-fiber group (HFG), which received a commercial high-fiber rodent diet; and a high fiber + CLP group (HFCLP) which received a commercial high-fiber rodent diet and underwent CLP (30%). The sepsis model was created via CLP after 2 weeks of dietary intervention. Notably, dietary high-fiber supplementation in HFCLP group improved survival rates and reduced bacterial loads, compared with CLP alone. In the HFCLP group, dietary fiber supplementation decreased the serum concentrations of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6) and high-mobility group protein 1 (HMG-1) but raised the concentration of interleukin 10 (IL-10), compared with the levels in CLP mice. Meanwhile, high-fiber supplementation increased the relative proportions of Akkermansia and Lachnospiraceae. These data show that dietary high-fiber supplementation may be therapeutic for sepsis-induced lesions.

Resveratrol-Induced Xenophagy Promotes Intracellular Bacteria Clearance in Intestinal Epithelial Cells and Macrophages

Autophagy is a lysosomal degradation process that contributes to host immunity by eliminating invasive pathogens and the modulating inflammatory response. Several infectious and immune disorders are associated with autophagy defects, suggesting that stimulation of autophagy in these diseases should be beneficial. Here, we show that resveratrol is able to boost xenophagy, a selective form of autophagy that target invasive bacteria. We demonstrated that resveratrol promotes in vitro autophagy-dependent clearance of intracellular bacteria in intestinal epithelial cells and macrophages. These results were validated in vivo using infection in a transgenic GFP-LC3 zebrafish model. We also compared the ability of resveratrol derivatives, designed to improve the bioavailability of the parent molecule, to stimulate autophagy and to induce intracellular bacteria clearance. Together, our data demonstrate the ability of resveratrol to stimulate xenophagy, and thereby enhance the clearance of two invasive bacteria involved life-threatening diseases, Salmonella Typhimurium and Crohn's disease-associated Adherent-Invasive Escherichia coli. These findings encourage the further development of pro-autophagic nutrients to strengthen intestinal homeostasis in basal and infectious states.

Influence of diet and metabolism on hematopoietic stem cells and leukemia development following ionizing radiation exposure

PURPOSE

The review aims to discuss the prominence of dietary and metabolic regulators in maintaining hematopoietic stem cell (HSC) function, long-term self-renewal, and differentiation.

RESULTS

Most adult stem cells are preserved in a quiescent, nonmotile state in vivo which acts as a "protective state" for stem cells to reduce endogenous stress provoked by DNA replication and cellular respiration as well as exogenous environmental stress. The dynamic balance between quiescence, self-renewal and differentiation is critical for supporting a functional blood system throughout life of an organism. Stress-conditions, for example ionizing radiation exposure can trigger the blood forming HSCs to proliferate and migrate through extramedullary tissues to expand the number of HSCs and increase hematopoiesis. In addition, a wealth of investigation validated that deregulation of this balance plays a critical pathogenic role in various different hematopoietic diseases including the leukemia development.

CONCLUSION

The review summarizes the current knowledge on how alterations in dietary and metabolic factors could alter the risk of leukemia development following ionizing radiation exposure by inhibiting or even reversing the leukemic progression. Understanding the influence of diet, metabolism, and epigenetics on radiation-induced leukemogenesis may lead to the development of practical interventions to reduce the risk in exposed populations.

A theoretical exploration of dietary collective medication in social insects

Animals often alter their food choices following a pathogen infection in order to increase immune function and combat the infection. Whether social animals that collect food for their brood or nestmates adjust their nutrient intake to the infection states of their social partners is virtually unexplored. Here we develop an individual-based model of nutritional geometry to examine the impact of collective nutrient balancing on pathogen spread in a social insect colony. The model simulates a hypothetical social insect colony infected by a horizontally transmitted parasite. Simulation experiments suggest that collective nutrition, by which foragers adjust their nutrient intake to simultaneously address their own nutritional needs as well as those of their infected nestmates, is an efficient social immunity mechanism to limit contamination when immune responses are short. Impaired foraging in infected workers can favour colony resilience when pathogen transmission rate is low (by reducing contacts with the few infected foragers) or trigger colony collapse when transmission rate is fast (by depleting the entire pool of foragers). Our theoretical examination of dietary collective medication in social insects suggests a new possible mechanism by which colonies can defend themselves against pathogens and provides a conceptual framework for experimental investigations of the nutritional immunology of social animals.

Calorie restriction in rodents: Caveats to consider

The calorie restriction paradigm has provided one of the most widely used and most useful tools for investigating mechanisms of aging and longevity. By far, rodent models have been employed most often in these endeavors. Over decades of investigation, claims have been made that the paradigm produces the most robust demonstration that aging is malleable. In the current review of the rodent literature, we present arguments that question the robustness of the paradigm to increase lifespan and healthspan. Specifically, there are several questions to consider as follows: (1) At what age does CR no longer produce benefits? (2) Does CR attenuate cognitive decline? (3) Are there negative effects of CR, including effects on bone health, wound healing, and response to infection? (4) How important is schedule of feeding? (5) How long does CR need to be imposed to be effective? (6) How do genotype and gender influence CR? (7) What role does dietary composition play? Consideration of these questions produce many caveats that should guide future investigations to move the field forward.

Differential alternative splicing coupled to nonsense-mediated decay of mRNA ensures dietary restriction-induced longevity

Alternative splicing (AS) coupled to nonsense-mediated decay (AS-NMD) is a conserved mechanism for post-transcriptional gene regulation. Here we show that, during dietary restriction (DR), AS is enhanced in Caenorhabditis elegans and mice. A splicing mediator hrpu-1 regulates a significant part of these AS events in C. elegans; knocking it down suppresses DR-mediated longevity. Concurrently, due to increased AS, NMD pathway genes are upregulated and knocking down UPF1 homologue smg-2 suppresses DR lifespan. Knockdown of NMD during DR significantly increases the inclusion of PTC-containing introns and the lengths of the 3′UTRs. Finally, we demonstrate that PHA-4/FOXA transcriptionally regulates the AS-NMD genes. Our study suggests that DR uses AS to amplify the proteome, supporting physiological remodelling required for enhanced longevity. This increases the dependence on NMD, but also helps fine-tune the expression of metabolic and splicing mediators. AS-NMD may thus provide an energetically favourable level of dynamic gene expression control during dietary restriction.

Alternative splicing coupled to nonsense-mediated decay (AS-NMD) is a conserved mechanism for post-transcriptional gene regulation. Here, the authors provide evidence that AS-NMD is enhanced during dietary restriction (DR) and is required for DR-mediated longevity assurance in C. elegans.

Short-Term Dietary Restriction Rescues Mice From Lethal Abdominal Sepsis and Endotoxemia and Reduces the Inflammatory/Coagulant Potential of Adipose Tissue

OBJECTIVES

Visceral adipose tissue is a major site for expression of proinflammatory and procoagulant genes during acute systemic inflammation. In this study, we tested whether the loss of fat mass by dietary restriction would remove the major source of these factors resulting in improved tolerance to sepsis and endotoxemia.

DESIGN

Prospective, laboratory controlled experiments.

SETTING

Aging and critical care research laboratory in a university hospital.

SUBJECTS

Middle-aged (12-month old) male C57BL/6 mice.

INTERVENTIONS

Mice were subjected to 40% dietary restriction for 3 weeks followed by induction of abdominal sepsis or endotoxemia by intraperitoneal injection with cecal slurry or lipopolysaccharide, respectively.

MEASUREMENTS AND MAIN RESULTS

Compared with freely fed mice, dietary restricted mice exhibited dramatically improved survival (80% vs 0% after sepsis; p < 0.001 and 86% vs 12% after endotoxemia; p = 0.013) and significantly reduced visceral fat-derived messenger RNA expression of interleukin-6, thrombospondin-1, plasminogen activator inhibitor-1, and tissue factor, which positively correlated with fat mass. Plasma levels of interleukin-6 were significantly reduced by dietary restriction and correlated with adipose interleukin-6 messenger RNA levels and fat mass (p < 0.001; R = 0.64 and 0.89). In vitro culture of visceral fat explants from naive dietary restricted mice showed significantly reduced interleukin-6 secretion compared with that from freely fed mice in response to lipopolysaccharide. Analysis of major adipose immune cell populations by flow cytometry demonstrated that macrophages were the only cell population reduced by dietary restriction and that CD11c/CD206 (M2-type) and CD11c/CD206 (double negative) macrophages, in addition to T cells, are the major immune cell populations that produce interleukin-6 in middle-aged mice during systemic inflammation.

CONCLUSIONS

Short-term dietary restriction drastically improved the survival outcome of middle-aged mice during both polymicrobial sepsis and sterile endotoxemia. Improved survival was accompanied by a significantly attenuated inflammatory response in adipose tissue, which is likely due to alterations of both fat mass quantity and qualitative changes, including a reduction in macrophage populations.

Dietary Supplementation With Nonfermentable Fiber Alters the Gut Microbiota and Confers Protection in Murine Models of Sepsis

OBJECTIVES

Links between microbial alterations and systemic inflammation have been demonstrated in chronic disease, but little is known about these interactions during acute inflammation. This study investigates the effect of dietary supplementation with cellulose, a nonfermentable fiber, on the gut microbiota, inflammatory markers, and survival in two murine models of sepsis.

DESIGN

Prospective experimental study.

SETTING

University laboratory.

SUBJECTS

Six-week-old male C57BL/6 wild-type mice.

INTERVENTIONS

Mice were assigned to low-fiber, normal-fiber, or high-fiber diets with or without antibiotics for 2 weeks and then subjected to sepsis by cecal ligation and puncture or endotoxin injection. Fecal samples were collected for microbiota analyses before and after dietary interventions.

MEASUREMENTS AND MAIN RESULTS

Mice that received a high-fiber diet demonstrated increased survival after cecal ligation and puncture relative to mice receiving low-fiber or normal-fiber diets. The survival benefit was associated with decreased serum concentration of pro-inflammatory cytokines, reduced neutrophil infiltration in the lungs, and diminished hepatic inflammation. The high-fiber diet also increased survival after endotoxin injection. Bacterial 16S ribosomal RNA gene sequences from each sample were amplified, sequenced, and analyzed. Fiber supplementation yielded an increase in relative abundance of the genera Akkermansia and Lachnospiraceae, taxa commonly associated with metabolic health. Administration of antibiotics to mice on the high-fiber diet negated the enrichment of Akkermansia species and the survival benefit after cecal ligation and puncture.

CONCLUSION

Dietary supplementation with cellulose offers a microbe-mediated survival advantage in murine models of sepsis. Improved understanding of the link between diet, the microbiota, and systemic illness may yield new therapeutic strategies for patients with sepsis.

Permissive Underfeeding of the Critically Ill Patient

The rise in the popularity of nutrition support in the 1970s was associated with the concept of "hyperalimentation." This concept was based on the early findings that increased metabolic rates were observed in various disease states such as trauma, sepsis, and burns. The aim was to feed 40% to 100% above the basal metabolic rate to avoid weight loss associated with critical illness. Since that time, several observations have indicated that permissive underfeeding may be beneficial because: (a) the metabolic rate is not markedly increased in most patients with critical illness except burns; (b) weight gain during nutrition support in critical illness is not caused by a gain in nitrogen but fat; (c) energy intake as glucose in excess of needs causes increased carbon dioxide production and a fatty liver; (d) hyperglycemia increases the risk of infective complications; and (e) a controlled trial of preoperative nutrition in which patients received 1000 kcal above the metabolic rate increased infectious complications.

Disseminated infections with antibiotic-resistant non-typhoidal Salmonella strains: contributions of host and pathogen factors

Non-typhoidal Salmonella enterica serovars (NTS) are generally associated with gastroenteritis; however, the very young and elderly, as well as individuals with compromised immunity, are at risk of developing disseminated infection that can manifest as bacteremia or focal infections at systemic sites. Disseminated NTS infections can be fatal and are responsible for over 600 000 deaths annually. Most of these deaths are in sub-Saharan Africa, where multidrug-resistant NTS clones are currently circulating in a population with a high proportion of individuals that are susceptible to disseminated disease. This review considers how genome degradation observed in African NTS isolates has resulted in phenotypic differences in traits related to environmental persistence and host-pathogen interactions. Further, it discusses host mechanisms promoting susceptibility to invasive infection with NTS in individuals with immunocompromising conditions. We conclude that mechanistic knowledge of how risk factors compromise immunity to disseminated NTS infection will be important for the design of interventions to protect against systemic disease.

Effect of dietary threonine on laying performance and intestinal immunity of laying hens fed low-crude-protein diets during the peak production period

Threonine (Thr) may be a limiting amino acid for laying hens fed diets with lowered protein level. An experiment was conducted to examine laying performance, and the intestinal immune function of laying hens provided diets varying in digestible Thr levels. Lohmann Brown laying hens (n = 480), 28 weeks of age, were allocated to six dietary treatments, each of which included five replicates of 16 hens. Dietary crude protein (CP) 16.18% diet was offered as the positive control diet. L-Thr was added to the negative diet (14.16% CP) by 0, 1.0, 2.0, 3.0 and 4.0 g/kg, corresponding 0.44%, 0.43%, 0.49%, 0.57%, 0.66% and 0.74% digestible Thr. At 40 weeks, a reduction in CP level decreased laying performance (p < 0.05). In the low CP, increasing dietary Thr increased (p < 0.05) egg production and egg mass and rose to a plateau between 0.57% and 0.66%. The hens fed 0.66% Thr showed the lowest value (p < 0.05) of feed conversion ratio (FCR). Serum level of uric acid showed the lowest values (p < 0.05) at 0.57-0.66%. In addition, serum-free Thr maximized (p < 0.05) between 0.66% and 0.74%. Digestive trypsin activity decreased (p < 0.05) when hens fed the low-CP diet compared with hens fed CP (16.18%) and hens fed 0.57-0.66%. Expressions of ileal MUC2 mRNA maximized (p < 0.05) at 0.66% Thr. Occludin mRNA increased with increasing Thr level (p < 0.05). sIgA mRNA reached to the maximum level (p < 0.05) at 0.66% and 0.74% Thr. INF-γ mRNA reached to the lowest level (p < 0.05) at 0.65%. Expressions of ileal IL-2, IL-6, IL-1β mRNA decreased with increasing Thr level (p < 0.05). In conclusion, Thr supplementation resulting in optimal laying performance and stimulated the mucosal immune system, suggesting that it is a limiting amino acid in the low-crude-protein diet of laying hens during the peak production period.

Dietary restriction improves repopulation but impairs lymphoid differentiation capacity of hematopoietic stem cells in early aging

Dietary restriction (DR) improves health, delays tissue aging, and elongates survival in flies and worms. However, studies on laboratory mice and nonhuman primates revealed ambiguous effects of DR on lifespan despite improvements in health parameters. In this study, we analyzed consequences of adult-onset DR (24 h to 1 yr) on hematopoietic stem cell (HSC) function. DR ameliorated HSC aging phenotypes, such as the increase in number of HSCs and the skewing toward myeloid-biased HSCs during aging. Furthermore, DR increased HSC quiescence and improved the maintenance of the repopulation capacity of HSCs during aging. In contrast to these beneficial effects, DR strongly impaired HSC differentiation into lymphoid lineages and particularly inhibited the proliferation of lymphoid progenitors, resulting in decreased production of peripheral B lymphocytes and impaired immune function. The study shows that DR-dependent suppression of growth factors and interleukins mediates these divergent effects caused by DR. Supplementation of insulin-like growth factor 1 partially reverted the DR-induced quiescence of HSCs, whereas IL-6/IL-7 substitutions rescued the impairment of B lymphopoiesis exposed to DR. Together, these findings delineate positive and negative effects of long-term DR on HSC functionality involving distinct stress and growth signaling pathways.

The Role of Steroid Hormones in the Modulation of Neuroinflammation by Dietary Interventions

Steroid hormones, such as sex hormones and glucocorticoids, have been demonstrated to play a role in different cellular processes in the central nervous system, ranging from neurodevelopment to neurodegeneration. Environmental factors, such as calorie intake or fasting frequency, may also impact on such processes, indicating the importance of external factors in the development and preservation of a healthy brain. The hypothalamic-pituitary-adrenal axis and glucocorticoid activity play a role in neurodegenerative processes, including in disorders such as in Alzheimer's and Parkinson's diseases. Sex hormones have also been shown to modulate cognitive functioning. Inflammation is a common feature in neurodegenerative disorders, and sex hormones/glucocorticoids can act to regulate inflammatory processes. Intermittent fasting can protect the brain against cognitive decline that is induced by an inflammatory stimulus. On the other hand, obesity increases susceptibility to inflammation, while metabolic syndromes, such as diabetes, are associated with neurodegeneration. Consequently, given that gonadal and/or adrenal steroids may significantly impact the pathophysiology of neurodegeneration, via their effect on inflammatory processes, this review focuses on how environmental factors, such as calorie intake and intermittent fasting, acting through their modulation of steroid hormones, impact on inflammation that contributes to cognitive and neurodegenerative processes.

The complex contributions of genetics and nutrition to immunity in Drosophila melanogaster

Both malnutrition and undernutrition can lead to compromised immune defense in a diversity of animals, and "nutritional immunology" has been suggested as a means of understanding immunity and determining strategies for fighting infection. The genetic basis for the effects of diet on immunity, however, has been largely unknown. In the present study, we have conducted genome-wide association mapping in Drosophila melanogaster to identify the genetic basis for individual variation in resistance, and for variation in immunological sensitivity to diet (genotype-by-environment interaction, or GxE). D. melanogaster were reared for several generations on either high-glucose or low-glucose diets and then infected with Providencia rettgeri, a natural bacterial pathogen of D. melanogaster. Systemic pathogen load was measured at the peak of infection intensity, and several indicators of nutritional status were taken from uninfected flies reared on each diet. We find that dietary glucose level significantly alters the quality of immune defense, with elevated dietary glucose resulting in higher pathogen loads. The quality of immune defense is genetically variable within the sampled population, and we find genetic variation for immunological sensitivity to dietary glucose (genotype-by-diet interaction). Immune defense was genetically correlated with indicators of metabolic status in flies reared on the high-glucose diet, and we identified multiple genes that explain variation in immune defense, including several that have not been previously implicated in immune response but which are confirmed to alter pathogen load after RNAi knockdown. Our findings emphasize the importance of dietary composition to immune defense and reveal genes outside the conventional "immune system" that can be important in determining susceptibility to infection. Functional variation in these genes is segregating in a natural population, providing the substrate for evolutionary response to pathogen pressure in the context of nutritional environment.

Intermittent fasting promotes bacterial clearance and intestinal IgA production in Salmonella typhimurium-infected mice

The impact of intermittent fasting versus ad libitum feeding during Salmonella typhimurium infection was evaluated in terms of duodenum IgA levels, bacterial clearance and intestinal and extra-intestinal infection susceptibility. Mice that were intermittently fasted for 12 weeks or fed ad libitum were infected with S. typhimurium and assessed at 7 and 14 days post-infection. Next, we evaluated bacterial load in the faeces, Peyer's patches, spleen and liver by plate counting, as well as total and specific intestinal IgA and plasmatic corticosterone levels (by immunoenzymatic assay) and lamina propria IgA levels in plasma cells (by cytofluorometry). Polymeric immunoglobulin receptor, α- and J-chains, Pax-5 factor, pro-inflammatory cytokine (tumour necrosis factor-α and interferon-γ) and anti-inflammatory cytokine (transforming growth factor-β) mRNA levels were assessed in mucosal and liver samples (by real-time PCR). Compared with the infected ad libitum mice, the intermittently fasted infected animals had (1) lower intestinal and systemic bacterial loads; (2) higher SIgA and IgA plasma cell levels; (3) higher mRNA expression of most intestinal parameters; and (4) increased or decreased corticosterone levels on day 7 and 14 post-infection, respectively. No contribution of liver IgA was observed at the intestinal level. Apparently, the changes following metabolic stress induced by intermittent fasting during food deprivation days increased the resistance to S. typhimurium infection by triggering intestinal IgA production and presumably, pathogen elimination by phagocytic inflammatory cells.

Shrinkage of the human core microbiome and a proposal for launching microbiome biobanks

ABSTRACT: 

The Human Microbiome Project (HMP) revealed the significance of the gut microbiome in promoting health. Disruptions in microbiome composition are associated with the pathogenesis of numerous diseases. The indigenous microflora has co-evolved with humans for millions of years and humans have preserved the inherited microbiomes through consumption of fermented foods and interactions with environmental microbes. Through modernization, traditional foods were abandoned, native food starters were substituted with industrial products, vaccines and antibiotics were used, extreme hygiene measures were taken, the rate of cesarean section increased, and breast feeding changed into formula. These factors have reduced human exposure to microbial symbionts and led to shrinkage of the core microbiome. Reduction in microbiome biodiversity can compromise the human immune system and predispose individuals to several modern diseases. This article suggests launching microbiome biobanks for archiving native microbiomes, supervising antibiotic use, probiotic design and native starter production, as well as advertising a revisit to native lifestyles.

Integrating nutrition and immunology: a new frontier

Nutrition is critical to immune defence and parasite resistance, which not only affects individual organisms, but also has profound ecological and evolutionary consequences. Nutrition and immunity are complex traits that interact via multiple direct and indirect pathways, including the direct effects of nutrition on host immunity but also indirect effects mediated by the host's microbiota and pathogen populations. The challenge remains, however, to capture the complexity of the network of interactions that defines nutritional immunology. The aim of this paper is to discuss the recent findings in nutritional research in the context of immunological studies. By taking examples from the entomological literature, we argue that insects provide a powerful tool for examining the network of interactions between nutrition and immunity due to their tractability, short lifespan and ethical considerations. We describe the relationships between dietary composition, immunity, disease and microbiota in insects, and highlight the importance of adopting an integrative and multi-dimensional approach to nutritional immunology.

Resource competition and within-host disease dynamics

The host organism is a complex mosaic of cell populations that requires adequate supplies of nutrients for maintenance, growth and proliferation. Because many nutrient requirements may be shared by host cells, pathogens and indigenous microflora, all these cells may potentially compete for growth-limiting resources. Ecological theory can explain some of the dynamics commonly seen in host-pathogen interactions; and mechanistic resource-consumer theory provides an instructive framework for viewing the disease process.

Dietary protein restriction impairs growth, immunity, and disease resistance in southern leopard frog tadpoles

The immune system is a necessary, but potentially costly, defense against infectious diseases. When nutrition is limited, immune activity may consume a significant amount of an organism's energy budget. Levels of dietary protein affect immune system function; high levels can enhance disease resistance. We exposed southern leopard frog [Lithobates sphenocephalus (=Rana sphenocephala)] tadpoles to high and low protein diets crossed with the presence or absence of the pathogenic amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) and quantified: (1) tadpole resistance to Bd; (2) tadpole skin-swelling in response to phytohaemagglutinin (PHA) injection (a measure of the T cell-mediated response of the immune system); (3) bacterial killing ability (BKA) of tadpole blood (a measure of the complement-mediated cytotoxicity of the innate immune system); and (4) tadpole growth and development. Tadpoles raised on a low-protein diet were smaller and less developed than tadpoles on a high-protein diet. When controlled for developmental stage, tadpoles raised on a low-protein diet had reduced PHA and BKA responses relative to tadpoles on a high-protein diet, but these immune responses were independent of Bd exposure. High dietary protein significantly increased resistance to Bd. Our results support the general hypothesis that host condition can strongly affect disease resistance; in particular, fluctuations in dietary protein availability may change how diseases affect populations in the field.

Caloric restriction and chronic inflammatory diseases

A reduction in calorie intake [caloric restriction (CR)] appears to consistently decrease the biological rate of aging in a variety of organisms as well as protect against age-associated diseases including chronic inflammatory disorders such as cardiovascular disease and diabetes. Although the mechanisms behind this observation are not fully understood, identification of the main metabolic pathways affected by CR has generated interest in finding molecular targets that could be modulated by CR mimetics. This review describes the general concepts of CR and CR mimetics as well as discusses evidence related to their effects on inflammation and chronic inflammatory disorders. Additionally, emerging evidence related to the effects of CR on periodontal disease in non-human primates is presented. While the implementation of this type of dietary intervention appears to be challenging in our modern society where obesity is a major public health problem, CR mimetics could offer a promising alternative to control and perhaps prevent several chronic inflammatory disorders including periodontal disease.

Caloric restriction increases free radicals and inducible nitric oxide synthase expression in mice infected with Salmonella Typhimurium

It is well known that CR (caloric restriction) reduces oxidative damage to proteins, lipids and DNA, although the underlying mechanism is unclear. However, information concerning the effect of CR on the host response to infection is sparse. In this study, 6-month-old mice that were fed AL (ad libitum) or with a CR diet were infected with Salmonella serovar Typhimurium. EPR (electron paramagnetic resonance; also known as ESR (electron spin resonance)) was used to identify FRs (free radicals). These results were subsequently correlated with SOD (superoxide dismutase) catalytic activity, iNOS [inducible NOS (nitric oxide synthase) or NOSII] expression and NO (nitric oxide) content. EPR analysis of liver samples demonstrated that there was a higher quantity of FRs and iron-nitrosyl complex in infected mice provided with a CR diet as compared with those on an AL diet, indicating that CR was beneficial by increasing the host response to Salmonella Typhimurium. Furthermore, in infected mice on the CR diet, NOSII expression was higher, NO content was greater and spleen colonization was lower, compared with mice on the AL diet. No changes in SOD activity were detected, indicating that the NO produced participated more in the formation of iron-nitrosyl complexes than peroxynitrite. These results suggest that CR exerts a protective effect against Salmonella Typhimurium infection by increasing NO production.

The nature of nutrition: a unifying framework

We present a graphical approach, which we believe can help to integrate nutrition into the broader biological sciences, and introduce generality into the applied nutritional sciences. This ‘Geometric Framework’ takes account of the fact that animals need multiple nutrients in changing amounts and balance, and that nutrients come packaged in foods that are often hard to find, dangerous to subdue and costly to process. We then show how the Geometric Framework has been used to understand the links between nutrition and relevant aspects of the biology of individual animals. These aspects include the physiological mechanisms that direct the nutritional interactions of the animal with its environment, and the fitness consequences of these interactions. Having considered the implications of diet for individuals, we show that these effects can translate into the collective behaviour of groups and societies, and in turn ramify throughout food webs to influence the structure of ecosystems.

Calorie restriction and susceptibility to intact pathogens

Long-term calorie restriction (CR) causes numerous physiological changes that ultimately increase mean and maximum lifespan of most species examined to date. One physiological change that occurs with CR is enhanced immune function, as tested using antigens and mitogens to stimulate an immune response. Fewer studies have used intact pathogen exposure to test whether the enhanced capacity of the immune response during CR actually decreases susceptibility of hosts to their pathogens. So far, studies using intact bacteria, virus, and helminth worm exposure indicate that, despite similar or enhanced immune system function, CR hosts are more susceptible to infection by intact pathogens than their fully fed counterparts. Long-term CR studies that examine susceptibility to a variety of parasite taxa will help determine if direct CR or CR mimetics will be beneficial to people living in pathogen-rich environments.

Feeding critically ill patients: what is the optimal amount of energy?

Hypermetabolism and malnourishment are common in the intensive care unit. Malnutrition is associated with increased morbidity and mortality, and most intensive care unit patients receive specialized nutrition therapy to attenuate the effects of malnourishment. However, the optimal amount of energy to deliver is unknown, with some studies suggesting that full calorie feeding improves clinical outcomes but other studies concluding that caloric intake may not be important in determining outcome. In this narrative review, we discuss the studies of critically ill patients that examine the relationship between dose of nutrition and clinically important outcomes. Observational studies suggest that achieving targeted caloric intake might not be necessary since provision of approximately 25% to 66% of goal calories may be sufficient. Randomized controlled trials comparing early aggressive use of enteral nutrition compared with delayed, less aggressive use of enteral nutrition suggest that providing increased calories with early, aggressive enteral nutrition is associated with improved clinical outcomes. However, energy provision with parenteral nutrition, either instead of or supplemental to enteral nutrition, does not offer additional benefits. In summary, the optimal amount of calories to provide critically ill patients is unclear given the limitations of the existing data. However, evidence suggests that improving adequacy of enteral nutrition by moving intake closer to goal calories might be associated with a clinical benefit. There is no role for supplemental parenteral nutrition to increase caloric delivery in the early phase of critical illness. Further high-quality evidence from randomized trials investigating the optimal amount of energy intake in intensive care unit patients is needed.

Permissive underfeeding: its appropriateness in patients with obesity, patients on parenteral nutrition, and non-obese patients receiving enteral nutrition

The concept of permissive underfeeding is based on the rationale that higher nutrient intake is detrimental from a metabolic and functional perspective. Animal studies have demonstrated improved morbidity and mortality with energy restriction. Studies with obese patients have demonstrated that a hypocaloric feeding regimen can promote nitrogen equilibrium and minimize negative nitrogen balance without causing weight loss. In critically ill patients, permissive underfeeding with parenteral nutrition has not been well studied, although some benefit is apparent. In enterally fed patients, more research exists but the data are not generated from prospective controlled trials. Studies of enterally supported patients demonstrate an association between higher caloric intake and decreased morbidity and mortality. Despite limited research, provision of reduced energy intake in critically ill patients and obese patients may result in improved metabolic control, reduce the detrimental effects of overfeeding, and promote improved patient outcomes.

Nutritional interventions in critical illness

The metabolism of critical illness is characterised by a combination of starvation and stress. There is increased production of cortisol, catecholamines, glucagon and growth hormone and increased insulin-like growth factor-binding protein-1. Phagocytic, epithelial and endothelial cells elaborate reactive oxygen and nitrogen species, chemokines, pro-inflammatory cytokines and lipid mediators, and antioxidant depletion ensues. There is hyperglycaemia, hyperinsulinaemia, hyperlactataemia, increased gluconeogenesis and decreased glycogen production. Insulin resistance, particularly in relation to the liver, is marked. The purpose of nutritional support is primarily to save life and secondarily to speed recovery by reducing neuropathy and maintaining muscle mass and function. There is debate about the optimal timing of nutritional support for the patient in the intensive care unit. It is generally agreed that the enteral route is preferable if possible, but the dangers of the parenteral route, a route of feeding that remains important in the context of critical illness, may have been over-emphasised. Control of hyperglycaemia is beneficial, and avoidance of overfeeding is emphasised. Growth hormone is harmful. The refeeding syndrome needs to be considered, although it has been little studied in the context of critical illness. Achieving energy balance may not be necessary in the early stages of critical illness, particularly in patients who are overweight or obese. Protein turnover is increased and N balance is often negative in the face of normal nutrient intake; optimal N intakes are the subject of some debate. Supplementation of particular amino acids able to support or regulate the immune response, such as glutamine, may have a role not only for their potential metabolic effect but also for their potential antioxidant role. Doubt remains in relation to arginine supplementation. High-dose mineral and vitamin antioxidant therapy may have a place.

Dietary protein deficiency in pregnant mice and offspring

Previous studies suggest an association between dermal contact hypersensitivity and preterm delivery. We hypothesized that dietary protein deficiency produces cell-mediated immune hypersensitivity in pregnant animals and their offspring akin to those known to produce tissue damage. We compared the effects of feeding a 20% protein diet (controls) to those of feeding a 10% protein (deficient) diet ad libitum to pregnant BALB/c mice. We measured dermal contact sensitivity to 2,4-dinitrofluorobenzene (DNFB) by the increment in ear skin thickness (swelling) 72 h after immunization and parity by the number of viable pups delivered. Dams fed the protein-deficient diet ingested less food, gained less weight and delivered fewer viable pups than the dams fed the control diet. Greater DNFB-stimulated increment in ear skin thickness was found in the protein-deficient mothers and in their offspring than in the control mothers and their offspring. We conclude that dietary protein deficiency limits parity and induces immune hypersensitivity. These findings suggest the potential for dietary protein deficiency to activate a T-cell-mediated branch of the immune response that may put pregnant animals at risk for preterm delivery.

Dietary restriction modifies fever response in aging rats

Intermittent (every-other-day) feeding initiated at 19 months of age and continued for 12 weeks, led to a moderate decrease in body weight of aging rats, enhanced survival and modified diurnal changes in body temperature and fever response to bacterial endotoxin (E. coli lipopolysaccharide, LPS). Diet-restricted animals which survived LPS administration, displayed reduced febrile response, i.e. (i) a moderate hypothermia in an early phase, and (ii) a delayed onset of body temperature elevation, as compared with their ad libitum-fed controls. However, peak body temperature values were similar in both groups. The rats of both groups which did not develop hyperthermia in response to LPS, died within 24 h of LPS administration. In control, but not in diet-restricted rats, variations in body weight during the 12 weeks prior LPS administration may be predictable in regard to their survival after LPS treatment. It seems that the resistance to bacterial endotoxin in aging rats is associated with their ability to develop hyperthermia.

Morphological plasticity varies with duration of infection: evidence from lactating and virgin wild-derived house mice (Mus musculus) infected with an intestinal parasite (Heligmosomoides polygyrus; Nematoda)

With chronic parasite infection, host response to the parasite may change throughout the duration of the infection as the host progresses from the acute to the chronic phase. We investigated the effects of parasite infection ranging in duration from 30 to 120 days on host morphology both alone and in combination with lactation by using captive wild-derived house mice (Mus musculus) experimentally infected with a naturally occurring intestinal nematode (Heligmosomoides polygyrus). We found that some changes in host morphology were greatest at 30-60 days post-infection (e.g. spleen mass) followed by a decline towards the control state whereas other morphological changes were greatest at 90-120 days post-infection (e.g. small intestine mass) after a relatively steady increase with infection duration. For all infection durations, the morphological responses to parasite infection were similar for virgin and lactating mice (except for lean body mass). After accounting for changes in body mass with lactation, lactating mice increased organs of the gastrointestinal tract as well as liver and kidney but had less body fat than virgin mice. This is the first study to demonstrate that morphological plasticity of mice parasitized by H. polygyrus varies with infection duration and that this variation is generally similar for lactating and virgin mice.

Effect of low-protein diet and protein supplementation on the expressions of TNF-alpha, TNFR-I, and TNFR-II in organs and muscle of LPS-injected rats

Previous studies had shown that increasing energy intake in anorexic TNF-alpha-treated rats increased morbidity due to stabilization of TNF activity by soluble and membrane TNF receptors (TNFR). Although protein supplementation reduces septic morbidity, its effect on TNF and TNFR is unknown. To determine the effect of low protein intake and supplementation on TNF and TNFR, 30 male Wistar rats weighing 250 g were fed a liquid defined-formula diet for 10 days and randomly allocated to 1) controls (C; n = 6), receiving normal energy and protein energy density of 0.047 MJ/60 ml + normal saline (NS); 2) low protein (LP; n = 6), receiving normal energy but a reduced protein-energy density of 0.012 MJ/60 ml + LPS; 3) refeeding (RF; n = 6), initially depleted on low-protein diet (10 days) and then repleted on normal protein (10 days) while receiving LPS; and 4) pair fed (P-F; n = 12), individual P-F rats being paired with individual LP or RF rats receiving NS. Protein and mRNA expression of TNF-alpha, TNFR-I, and TNFR-II in liver, spleen, and gastrocnemius were measured by Western blot and RT-PCR, respectively. In liver, the changes in TNF-alpha, TNFR-I, and TNFR-II were translational, whereas in spleen the effects were due to a combination of transcription and translation. In gastrocnemius, the effects were transcriptional/translational for TNFRs. In contrast, TNF-alpha mRNA was significantly increased, but TNF-alpha protein expression was reduced in LP rats compared with C and RF groups. In conclusion, protein deficiency in endotoxic rats increases the expression of TNFR-I and TNFR-II in all organs studied and TNF-alpha in selected ones. This increase is suppressed by refeeding protein. A differential pattern between translation and transcription of TNF-alpha and its receptors is present. Our data suggest that protein restriction may be deleterious in sepsis.

Effect of malnutrition and short-term refeeding on peripheral blood mononuclear cell mitochondrial complex I activity in humans

BACKGROUND

Previous investigations in rats have shown that the first enzyme of the mitochondrial electron transport chain (complex I) is altered in peripheral blood mononuclear cells (PBMCs) and muscle by dietary manipulations.

OBJECTIVE

We hypothesized that similar changes would occur in human PBMCs as a result of dietary malnutrition and short-term refeeding irrespective of the presence or absence of active inflammatory bowel disease (IBD).

DESIGN

Fourteen malnourished patients with active IBD, 13 malnourished patients without IBD, and 42 healthy subjects were investigated. Complex I activity, body mass index, body composition, energy and protein intakes, and resting energy expenditure were measured. Five patients without IBD and 6 patients with IBD were investigated after 7 d of refeeding.

RESULTS

In patients without IBD, weight loss was mainly due to a loss of fat mass. In contrast, weight loss in IBD patients was due to a loss of both fat-free mass and fat mass. Complex I activity was reduced to the same degree in both groups of patients and was significantly lower than that observed in healthy subjects. In both groups of patients, complex I activity correlated significantly with body weight, body mass index, percentage weight loss, and fat mass. Complex I activity increased significantly after 1 wk of refeeding in both groups of patients before observed changes of measured nutritional assessment indexes.

CONCLUSION

Our study showed that mitochondrial complex I activity measured in PBMCs seems to be a specific marker of dietary malnutrition and responds rapidly to refeeding.

Effects of calorie restriction on polymicrobial peritonitis induced by cecum ligation and puncture in young C57BL/6 mice

Calorie restriction (CR) is known to prolong the life span and maintain an active immune function in aged mice, but it is still not known if rodents under CR can respond optimally to bacterial infection. We report here on the influence of CR on the response of peritoneal macrophages to lipopolysaccharide, splenic NF-kappaB and NF-interleukin-6 (IL-6) activities, and mortality in polymicrobial sepsis induced by cecal ligation and puncture (CLP). Macrophages from 6-month-old C57BL/6 mice on a calorie-restricted diet were less responsive to lipopolysaccharide, as evidenced by lower levels of IL-12 and IL-6 protein and mRNA expression. Furthermore, in vitro lipopolysaccharide-stimulated macrophages from mice under CR also expressed decreased lipopolysaccharide receptor CD14 levels as well as Toll-like receptor 2 (TLR2) and TLR4 mRNA levels. In addition, the phagocytic capacity and class II (I-A(b)) expression of macrophages were also found to be significantly lower in mice under CR. Mice under CR died earlier (P < 0.005) after sepsis induced by CLP, which appeared to be a result of increased levels in serum of the proinflammatory cytokines tumor necrosis factor alpha and IL-6 and splenic NF-kappaB and NF-IL-6 activation 4 h after CLP. However, mice under CR survived significantly (P < 0.005) longer than mice fed ad libitum when injected with paraquat, a free radical-inducing agent. These data suggest that young mice under CR may be protected against oxidative stress but may have delayed maturation of macrophage function and increased susceptibility to bacterial infection.

Inflammatory responses to lipopolysaccharide are suppressed in 40% energy-restricted mice

To elucidate the suppressive effects of energy restriction on the inflammatory responses to lipopolysaccharide (LPS), mice were divided into a control group (fed 5.0 g diet/d; 71 kJ/d) and a 40% energy-restricted group (fed 3.0 g diet/d; 43 kJ/d) at 8-wk of age. Four weeks later, 25 microg of LPS was intraperitoneally injected. After the LPS injection, interleukin-1beta, interleukin-6 and tumor necrosis factor-alpha were elevated in serums in the 40% energy-restricted mice and in the controls, but the extent of the elevation was significantly lower in the restricted group. The LPS-induced expression of inducible nitric oxide synthase in the liver was significantly suppressed by the energy restriction. In addition, the LPS-induced elevations of serum aspartate and alanine aminotransferase activities, which are indexes of hepatic injury, were also significantly attenuated in the restricted group. Moreover, the extent of LPS-induced alterations in hepatic structure was less in the restricted mice than in controls. Serum corticosterone level in the restricted mice was higher than that in the controls before LPS treatment (P < 0.05). Furthermore, after LPS injection, the significantly higher level of corticosterone was maintained in the restricted mice, although the LPS treatment significantly enhanced the level even in the control group. These results suggest that the extreme inflammatory responses to endotoxin are prevented in the 40% energy-restricted mice, and corticosterone participates in the preventive effects.

Caloric restriction mimetics: metabolic interventions

Caloric restriction (CR) retards diseases and aging in laboratory rodents and is now being tested in nonhuman primates. One way to apply these findings to human health is to identify and test agents that may mimic critical actions of CR. Panel 2 focused on two outcomes of CR, reduction of oxidative stress and improved glucoregulation, for which candidate metabolic mimics exist. It was recommended that studies on oxidative stress should emphasize mitochondrial function and to test the efficacy of nitrone and other antioxidants in mimicking CR's effects. Studies should also focus on the long-term effects of compounds known to lower circulating glucose and insulin concentrations or to increase insulin sensitivity. Also, four other developing areas were identified: intermediary metabolism, response to infection, stress responses, and source of dietary fat. These areas are important because either they hold promise for the discovery of new mimetics or they need to be explored prior to initiation of CR trials in humans. Other recommendations were that transgenic approaches and adult-onset CR should be emphasized in future studies.

Energy restriction and severe zinc deficiency influence growth, survival and reproduction of Heligmosomoides polygyrus (Nematoda) during primary and challenge infections in mice

The objectives of this study were (1) to determine the impact of severe zinc deficiency on the establishment, growth, survival and reproduction of Heligmosomoides polygyrus in the laboratory mouse, during both primary and challenge infection protocols, and (2) to determine whether the observed effects resulted from zinc deficiency per se, or from the accompanying energy restriction. Three diet groups were used: zinc-sufficient (Zn+:60 mg zinc/kg diet), zinc-deficient (Zn-:0.75 mg zinc/kg diet) and energy restricted (ER:60 mg zinc/kg diet pair fed to Zn- mice). Neither Zn- nor ER influenced the establishment of the parasite during a primary infection. However, both significantly influenced the early development of the parasite. The proportion of adult worms recovered 9 days post-infection (p.i.) was highest in Zn- mice, intermediate in ER mice and lowest in Zn+ mice. Worms were also distributed more distally in the intestine of the Zn- mice and worm survival was highest in Zn- mice, intermediate in ER mice and lowest in Zn+ mice at both 4 and 5 weeks p.i. Although the length of female worms was reduced in Zn- mice, neither per capita fecundity nor egg viability was affected by zinc deficiency. Energy restriction, on the other hand, significantly reduced worm fecundity at 5 weeks post-primary infection, but had no effect on egg viability. Zinc concentration of adult H. polygyrus was similar among dietary groups. The effects of zinc deficiency and energy restriction were also investigated 4 and 5 weeks after a challenge infection. Whereas strong host resistance was evident in Zn+ and ER mice, based on comparison of worm numbers between challenged mice and primary infection controls, no evidence of resistance was detected in Zn- mice. As in the primary infection, female worms were shorter in Zn- mice than in ER and Zn+ mice, and energy restriction but not zinc deficiency significantly affected per capita fecundity. However, in contrast to the primary infection, ER mice had elevated rather than reduced fecundity. This study demonstrates a complex interaction between H. polygyrus and zinc and energy restriction, and highlights the importance of controlling for reduced food intake in nutrition-infection studies.