Advances in Nutrition: An International Review Journal current issue

Diet, Gut Microbiota, and Obesity: Links with Host Genetics and Epigenetics and Potential Applications

ABSTRACTDiverse evidence suggests that the gut microbiota is involved in the development of obesity and associated comorbidities. It has been reported that the composition of the gut microbiota differs in obese and lean subjects, suggesting that microbiota dysbiosis can contribute to changes in body weight. However, the mechanisms by which the gut microbiota participates in energy homeostasis are unclear. Gut microbiota can be modulated positively or negatively by different lifestyle and dietary factors. Interestingly, complex interactions between genetic background, gut microbiota, and diet have also been reported concerning the risk of developing obesity and metabolic syndrome features. Moreover, microbial metabolites can induce epigenetic modifications (i.e., changes in DNA methylation and micro-RNA expression), with potential implications for health status and susceptibility to obesity. Also, microbial products, such as short-chain fatty acids or membrane proteins, may affect host metabolism by regulating appetite, lipogenesis, gluconeogenesis, inflammation, and other functions. Metabolomic approaches are being used to identify new postbiotics with biological activity in the host, allowing discovery of new targets and tools for incorporation into personalized therapies. This review summarizes the current understanding of the relations between the human gut microbiota and the onset and development of obesity. These scientific insights are paving the way to understanding the complex relation between obesity and microbiota. Among novel approaches, prebiotics, probiotics, postbiotics, and fecal microbiome transplantation could be useful to restore gut dysbiosis.

Mechanisms of Action of Probiotics

ABSTRACTProbiotics are living microorganisms that confer health benefits to the host when administered in adequate amounts; however, dead bacteria and their components can also exhibit probiotic properties. Bifidobacterium and strains of lactic acid bacteria are the most widely used bacteria that exhibit probiotic properties and are included in many functional foods and dietary supplements. Probiotics have been shown to prevent and ameliorate the course of digestive disorders such as acute, nosocomial, and antibiotic-associated diarrhea; allergic disorders such as atopic dermatitis (eczema) and allergic rhinitis in infants; and Clostridium difficile–associated diarrhea and some inflammatory bowel disorders in adults. In addition, probiotics may be of interest as coadjuvants in the treatment of metabolic disorders, including obesity, metabolic syndrome, nonalcoholic fatty liver disease, and type 2 diabetes. However, the mechanisms of action of probiotics, which are diverse, heterogeneous, and strain specific, have received little attention. Thus, the aim of the present work was to review the main mechanisms of action of probiotics, including colonization and normalization of perturbed intestinal microbial communities in children and adults; competitive exclusion of pathogens and bacteriocin production; modulation of fecal enzymatic activities associated with the metabolization of biliary salts and inactivation of carcinogens and other xenobiotics; production of short-chain and branched-chain fatty acids, which, in turn, have wide effects not only in the intestine but also in peripheral tissues via interactions with short-chain fatty acid receptors, modulating mainly tissue insulin sensitivity; cell adhesion and mucin production; modulation of the immune system, which results mainly in the differentiation of T-regulatory cells and upregulation of anti-inflammatory cytokines and growth factors, i.e., interleukin-10 and transforming growth factor; and interaction with the brain-gut axis by regulation of endocrine and neurologic functions. Further research to elucidate the precise molecular mechanisms of action of probiotics is warranted.

Effects of Sweeteners on the Gut Microbiota: A Review of Experimental Studies and Clinical Trials

ABSTRACTThe consumption of sugar-free foods is growing because of their low-calorie content and the health concerns about products with high sugar content. Sweeteners that are frequently several hundred thousand times sweeter than sucrose are being consumed as sugar substitutes. Although nonnutritive sweeteners (NNSs) are considered safe and well tolerated, their effects on glucose intolerance, the activation of sweet taste receptors, and alterations to the composition of the intestinal microbiota are controversial. This review critically discusses the evidence supporting the effects of NNSs, both synthetic sweeteners (acesulfame K, aspartame, cyclamate, saccharin, neotame, advantame, and sucralose) and natural sweeteners (NSs; thaumatin, steviol glucosides, monellin, neohesperidin dihydrochalcone, and glycyrrhizin) and nutritive sweeteners (polyols or sugar alcohols) on the composition of microbiota in the human gut. So far, only saccharin and sucralose (NNSs) and stevia (NS) change the composition of the gut microbiota. By definition, a prebiotic is a nondigestible food ingredient, but some polyols can be absorbed, at least partially, in the small intestine by passive diffusion: however, a number of them, such as isomaltose, maltitol, lactitol, and xylitol, can reach the large bowel and increase the numbers of bifidobacteria in humans. Further research on the effects of sweeteners on the composition of the human gut microbiome is necessary.

Perspective: Are We Ready to Measure Child Nutritional Status with Lasers?

ABSTRACTThe continued use of basic, manual anthropometric tools (e.g., boards and tapes) leaves anthropometry susceptible to human error. A potential solution, 3-dimensional (3D) imaging systems for anthropometry, has been around since the 1950s. In the 1980s, 3D imaging technology advanced from photographs to the use of lasers for body digitization; and by the 2000s, the falling price of 3D scanners made commercial application feasible. The garment sector quickly adopted imaging technology for surveys because of the need for numerous measurements and large sample sizes. In the health sector, 3D imaging for anthropometry was not widely adopted; its use was limited to research and specialized purposes. The different cost and logistical requirements for measurement in the garment and health sectors help to explain why the technology was adopted in one sector and not the other. Despite reductions, the price of 3D imaging systems remained a barrier to the use of 3D imaging for regular nutritional assessment in the health sector. Additional barriers in the health sector were that imaging systems required dedicated space and were not designed for capturing measurements in young children. In recent years, the development of light-coding technology may have removed these barriers, and a handheld imaging system was developed specifically for young children. There are not yet recommendations to replace manual equipment with 3D imaging for nutritional assessment, and there is a need for more research on low-cost, handheld imaging systems—particularly research that evaluates the ability of 3D imaging to improve the quality of anthropometric data and indicators.

Humans against Obesity: Who Will Win?

ABSTRACTThe global obesity epidemic continues its relentless advance, currently affecting >2 billion people. This paper explores alternative ways to assess the potential disease impact of the epidemic, which is currently based almost exclusively on body mass index (BMI) data. It also argues in favor of concerted efforts to modify the built ecosystem that is driving the obesity epidemic. Most of the epidemiologic data on obesity are based on BMI (in kg/m2) and use the ranges of 18.5–24.9 for normality, 25–29.9 for overweight, and ≥30 for obesity. But the gap between the median of the “normal” BMI distribution (∼22) and the current population BMI of, for example, the United States (27.7) has become so wide that it is unlikely that we will be able to close that gap in the near future. Furthermore, the correlation between BMI and disease risk is not linear. Over 60% of the global disease burden of obesity affects individuals with a BMI ≥30, who comprise only ∼10% of the global population of overweight/obese persons. Furthermore, BMI accounts for only ∼17% of the risk of insulin resistance and subsequent type 2 diabetes in the BMI ≥25 population. Epigenetics, specifically DNA methylation, appears to play a far more important role than BMI in determining the risk of obesity's comorbidities, such as diabetes. Similarly, socioeconomic status carries a higher risk than BMI level for the development of obesity-related noncommunicable diseases. Finally, the built environment that sustains our species’ lifestyle is a major driver of the obesity epidemic. Modifying that ecosystem will require no less than a social movement, one able to promote and sustain the necessary coordinated action of virtually all sectors of society.

Associations between Phytoestrogens, Glucose Homeostasis, and Risk of Diabetes in Women: A Systematic Review and Meta-Analysis

ABSTRACTPhytoestrogens might have advantageous effects on diabetes in women. We performed a systematic review and meta-analysis to determine the effect of phytoestrogens on glucose homeostasis and the risk of type 2 diabetes (T2D) among women. Randomized controlled trials (RCTs) and prospective observational studies that assessed associations of phytoestrogens (supplementation, dietary intake, or biomarkers) with fasting glucose or insulin, homeostatic model assessment of insulin resistance (HOMA-IR), or with the risk of T2D were included. We identified 18 RCTs (n = 1687 individuals) investigating the effect of phytoestrogen supplementation on glucose homeostasis and 9 prospective population-based studies (n = 212,796 individuals) examining the association between phytoestrogen intake and the risk of T2D. Compared with placebo, phytoestrogen supplementation resulted in improvements in fasting glucose and HOMA-IR: the pooled mean differences of changes were –0.12 mmol/L (95% CI: –0.20, –0.03 mmol/L) and –0.24 mmol/L (95% CI: –0.45, –0.03 mmol/L), respectively. Although there was no significant decrease in insulin concentrations with overall phytoestrogen supplementation, the pooled mean difference in changes was –0.99 pmol/L (95% CI: –4.65, 2.68 pmol/L). However, the results of RCTs varied by type of phytoestrogens: soy-derived isoflavones and genistein improved glucose homeostasis, whereas isoflavone mix and daidzein had no effect or were associated with an adverse glycemic profile. Higher dietary phytoestrogen intake was associated with a 10% lower risk of developing T2D in observational studies (pooled RR: 0.90; 95% CI: 0.85, 0.96; for the highest compared with the lowest quantiles). Results were similar when the analyses were restricted to only medium- and high-quality studies. Overall, phytoestrogens may have a positive influence on glycemia and could be used for diabetes prevention in women. However, for some individual types of phytoestrogens, such as mixed isoflavones, caution is needed in recommending their use in women, because their use could lead to an adverse glycemic profile in women.

Nutrient Profile Models with Applications in Government-Led Nutrition Policies Aimed at Health Promotion and Noncommunicable Disease Prevention: A Systematic Review

ABSTRACTNutrient profile (NP) models, tools used to rate or evaluate the nutritional quality of foods, are increasingly used by government bodies worldwide to underpin nutrition-related policies. An up-to-date and accessible list of existing NP models is currently unavailable to support their adoption or adaptation in different jurisdictions. This study used a systematic approach to develop a global resource that summarizes key characteristics of NP models with applications in government-led nutrition policies. NP models were identified from an unpublished WHO catalog of NP models last updated in 2012 and from searches conducted in different databases of the peer-reviewed (n = 3; e.g., PubMed) and gray literature (n = 15). Included models had to meet the following inclusion criteria (selected) as of 22 December 2016: 1) developed or endorsed by governmental or intergovernmental organizations, 2) allow for the evaluation of individual food items, and 3) have publicly available nutritional criteria. A total of 387 potential NP models were identified, including n = 361 from the full-text assessment of >600 publications and n = 26 exclusively from the catalog. Seventy-eight models were included. Most (73%) were introduced within the past 10 y, and 44% represent adaptations of ≥1 previously built model. Models were primarily built for school food standards or guidelines (n = 27), food labeling (e.g., front-of-pack; n = 12), and restriction of the marketing of food products to children (n = 10). All models consider nutrients to limit, with sodium, saturated fatty acids, and total sugars being included most frequently; and 86% also consider ≥1 nutrient to encourage (e.g., fiber). No information on validity testing could be identified for 58% of the models. Given the proliferation of NP models worldwide, this new resource will be highly valuable for assisting health professionals and policymakers in the selection of an appropriate model when the establishment of nutrition-related policies requires the use of nutrient profiling.

Systematic Review of Tools and Methods to Measure Appetite in Undernourished Children in the Context of Low- and Middle-Income Countries

ABSTRACTChild undernutrition has multifactorial causes, ranging from food insecurity to etiologies refractory to conventional nutritional approaches, such as infections, environmental enteric dysfunction, and other conditions that lead to systemic inflammation. Poor appetite may be an important symptom of these causes and may be a useful marker of an undernourished child's ability to recover. We conducted a systematic review to characterize the methods and tools to measure appetite among children <5 y old in low- and middle-income countries. A systematic search of 8 databases identified 23 eligible studies published since 1995. Thirteen described methods based on direct feeding observation or quantification of nutrient intake from caregiver report, 16 described tools that assessed caregiver perceptions of appetite, and 6 reported assessments in both categories. Four studies that gauged caregiver perceptions assessed multiple appetite domains, whereas 12 assessed 1 domain—often with a single question. Only 6 studies reported validation processes, the most common of which compared an observed test meal with daily energy intake. No studies reported the use of a method or tool that was validated in multiple cultural or linguistic contexts. Although dietary intake measures and observed feeding tests have shown validity in some contexts, they are resource intensive. Subjective caregiver questionnaires may offer a more efficient appetite evaluation method, but they have been evaluated less consistently. A rigorously developed and validated tool to rapidly assess child appetite is needed and could be best addressed by a questionnaire that leverages the multiple domains of appetite. The application of interventions that target causes of undernutrition that are not amenable to food-based interventions in clinical or research contexts could be facilitated by an efficient appetite screening tool to identify appetite-related causes of undernutrition and to monitor children's response to such interventions.

The Effect of Nutrients and Dietary Supplements on Sperm Quality Parameters: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

ABSTRACTInfertility, which affects ∼15% of the world's population, is a global public health issue recognized by the WHO. Therefore, it is of major clinical and public health importance to investigate whether modifiable lifestyle factors—such as stress, drug use, smoking, alcohol intake, and diet—may influence human fertility. A systematic review and meta-analysis of randomized clinical trials (RCTs) from the MEDLINE-PubMed database was conducted to assess the effect of nutrients, dietary supplements, or food on sperm quality parameters. In total, 28 articles were included for qualitative analysis and 15 for quantitative meta-analysis. Total sperm concentrations [expressed as mean differences (MDs); 95% CIs, in spermatozoa (spz)/mL] were increased by selenium (3.91 × 106 spz/mL; 3.08, 4.73 spz/mL), zinc (1.48 × 106 spz/mL; 0.69, 2.27 spz/mL), omega-3 (n–3) fatty acids (10.98 × 106 spz/mL; 10.25, 11.72 spz/mL), and coenzyme Q10 (CoQ10) (5.93 × 106 spz/mL; 5.36, 6.51 spz/mL). Sperm counts were increased by ω-3 fatty acids (18.70 × 106 spz/mL; 16.89, 20.51 spz/mL) and CoQ10 supplementation (10.15 × 106 spz/mL; 8.34, 11.97 spz/mL). Sperm total motility was increased by selenium (3.30%; 2.95%, 3.65%), zinc (7.03%; 6.03%, 8.03%), ω-3 fatty acids (7.55%; 7.09%, 8.01%), CoQ10 (5.30%; 4.98%, 5.62%), and carnitines (7.84%; 6.54%, 9.13%), whereas sperm progressive motility was increased only after supplementation with carnitines (7.45%; 6.24%, 8.67%). Finally, sperm morphology was enhanced by selenium (1.87%; 1.50%, 2.24%), ω-3 fatty acid (0.91%; 0.69%, 1.13%), CoQ10 (1.06%; 0.72%, 1.41%), and carnitine (4.91%; 3.68%, 6.15%) supplementation. This meta-analysis of RCTs suggests that some dietary supplements could beneficially modulate sperm quality parameters and affect male fertility. However, results must be cautiously interpreted due to the limited sample size of the meta-analyzed studies and the considerable observed interstudy heterogeneity.The present study and the corresponding search protocol were registered at the PROSPERO registry at http://www.crd.york.ac.uk/PROSPERO as CRD42017058380.