Addition of Soluble Fiber in Low-Fat Purified Diets Maintains Cecal and Colonic Morphology, Modulates Bacterial Populations and Predicted Functions, and Improves Glucose Tolerance Compared with Traditional AIN Diets in Male Mice.

Background: Purified diets (PDs) contain refined ingredients with one main nutrient, allowing for greater control relative to grain-based diets (GBDs), which contain unrefined grains and animal byproducts. Traditional PDs like the American Institute of Nutrition (AIN)-76A (76A) and AIN-93G (93G) can negatively impact metabolic and gut health when fed long term, in part due to lower total fiber, no soluble fiber, and higher sucrose content. Objective: Two studies were conducted to determine how PDs with reduced sucrose and increased fiber (soluble and insoluble) influence metabolic and gut health in mice compared with traditional AIN PDs or GBDs. Methods: In study 1, C57Bl/6N mice (n = 75) consumed a GBD [LabDiet 5002 (5002)], 76A, 93G, or 2 PDs with reduced sucrose and higher fiber for 88 d. Body composition and metabolic parameters were assessed. In study 2, C57Bl/6N mice (n = 54) consumed either 2 GBDs (LabDiet 5001 or 5002) or PDs with different types/levels of fiber for 14 d. Microbiome alterations and predicted functional metagenomic changes were measured. Results: The PD with 75 g cellulose and 25 g inulin per 4084 kcals marginally influenced body weight and adiposity, but improved glucose tolerance relative to 93G (P = 0.0131) and 76A (P = 0.0014). Cecal and colonic weights were lower in mice fed cellulose-based PDs compared with those fed GBDs and soluble-fiber PDs. Soluble-fiber PDs reduced alpha diversity and showed similar beta diversity, which differed from cellulose-based PDs and GBDs. Certain genera associated with improved gut health such as Bifidobacteria and Akkermansia were significantly elevated by soluble-fiber PDs (P ≤ 0.01). Metabolic pathways related to carbohydrate and fatty acid metabolism were affected by PDs. Conclusions: PDs formulated with lower sucrose and increased fiber content, particularly soluble fiber, blunted elevations in metabolic parameters and favorably impacted the microbiota and metagenome in C57BL/6N mice.

Considerations When Choosing High-Fat, High-Fructose, and High-Cholesterol Diets to Induce Experimental Nonalcoholic Fatty Liver Disease in Laboratory Animal Models.

Nonalcoholic fatty liver disease (NAFLD) is intricately linked to metabolic disease (including obesity, glucose intolerance, and insulin resistance) and encompasses a spectrum of disorders including steatosis, nonalcoholic steatohepatitis (NASH), and fibrosis. Rodents consuming high-fat (HF; ∼40 kcal% fat including fats containing higher concentrations of saturated and trans fats), high-fructose (HFr), and high-cholesterol (HC) diets display many clinically relevant characteristics of NASH, along with other metabolic disorders. C57BL/6 mice are the most commonly used animal model because they can develop significant metabolic disorders including severe NASH with fibrosis after months of feeding, but other models also are susceptible. The significant number of diets that contain these different factors (i.e., HF, HFr, and HC), either alone or in combination, makes the choice of diet difficult. This methodology review describes the efficacy of these nutrient manipulations on the NAFLD phenotype in mice, rats, guinea pigs, hamsters, and nonhuman primates.

Stearidonic-Enriched Soybean Oil Modulates Obesity, Glucose Metabolism, and Fatty Acid Profiles Independently of Akkermansia muciniphila.

SCOPE: Previous studies have suggested that diets rich in omega-3 and low in omega-6 long-chain polyunsaturated fatty acids (PUFAs) can limit the development of metabolic syndrome (MetS). Transgenic soybeans yielding oils enriched for omega-3 PUFAs represent a new and readily-available option for incorporating omega-3 PUFAs into diets to provide health benefits. METHODS AND RESULTS: Transgenic soybean oils, enriched for either stearidonic acid (SDA) or eicosapentaenoic acid (EPA), are incorporated into diets to test their effects on limiting the development of MetS in a mouse model of diet-induced obesity. Supplementation with SDA- but not EPA-enriched oils improved features of MetS compared to feeding a control wild-type oil. Because previous studies have linked the gut microorganism Akkermansia muciniphila to the metabolic effects of feeding omega-3 PUFAs, the causal contribution of A. muciniphila to mediating the metabolic benefits provided by SDA-enriched diets is investigated. Although A. muciniphila is not required for SDA-induced metabolic improvements, this microorganism does modulate levels of saturated and mono-unsaturated fatty acids in host adipose tissues. CONCLUSION: Together, these findings support the utilization of SDA-enriched diets to modulate weight gain, glucose metabolism, and fatty acid profiles of liver and adipose tissue.

Targeted Nutrient Modifications in Purified Diets Differentially Affect Nonalcoholic Fatty Liver Disease and Metabolic Disease Development in Rodent Models.

Nonalcoholic fatty liver disease (NAFLD) is a complex spectrum of disorders ranging from simple benign steatosis to more aggressive forms of nonalcoholic steatohepatitis (NASH) and fibrosis. Although not every patient with NAFLD/NASH develops liver complications, if left untreated it may eventually lead to cirrhosis and hepatocellular carcinoma. Purified diets formulated with specific nutritional components can drive the entire spectrum of NAFLD in rodent models. Although they may not perfectly replicate the clinical and histological features of human NAFLD, they provide a model to gain further understanding of disease progression in humans. Owing to the growing demand of diets for NAFLD research, and for our further understanding of how manipulation of dietary components can alter disease development, we outlined several commonly used dietary approaches for rodent models, including mice, rats, and hamsters, time frames required for disease development and whether other metabolic diseases commonly associated with NAFLD in humans occur.

Choice of Laboratory Rodent Diet May Confound Data Interpretation and Reproducibility.

The reproducibility of experimental data is challenged by many factors in both clinical and preclinical research. In preclinical studies, several factors may be responsible, and diet is one variable that is commonly overlooked, especially by those not trained in nutrition. In particular, grain-based diets contain complex ingredients, each of which can provide multiple nutrients, non-nutrients, and contaminants, which may vary from batch to batch. Thus, even when choosing the same grain-based diet used in the past by others, its composition will likely differ. In contrast, purified diets contain refined ingredients that offer the ability to control the composition much more closely and maintain consistency from one batch to the next, while minimizing the presence of non-nutrients and contaminants. In this article, we provide several different examples or scenarios showing how the diet choice can alter data interpretation, potentially affecting reproducibility and knowledge gained within any given field of study.

Effects of Rodent Diet Choice and Fiber Type on Data Interpretation of Gut Microbiome and Metabolic Disease Research.

Poor diet reporting and improperly controlling laboratory animal diet continues to reduce our ability to interpret data effectively in animal studies. In order to make the best use of our resources and improve research transparency, proper reporting methods that include a diet design are essential to improving our understanding of the links between gut health and metabolic disease onset. This unit will focus on the importance of diet choice in laboratory animal studies, specifically as it relates to gut health, microbiome, and metabolic disease development. The two most commonly used diet types, grain-based (GB) diets, and purified ingredient diets, will each be described, with particular emphasis on their differences in dietary fiber. A further description of how these diet types and fiber can affect gut morphology and microbiota will be provided as well as how purified ingredient diets may be improved upon. © 2018 by John Wiley & Sons, Inc.

Correction to: The common use of improper control diets in diet-induced metabolic disease research confounds data interpretation: the fiber factor.

[This corrects the article DOI: 10.1186/s12986-018-0243-5.].

The common use of improper control diets in diet-induced metabolic disease research confounds data interpretation: the fiber factor.

Diets used to induce metabolic disease are generally high in fat and refined carbohydrates and importantly, are usually made with refined, purified ingredients. However, researchers will often use a low fat grain-based (GB) diet containing unrefined ingredients as the control diet. Such a comparison between two completely different diet types makes it impossible to draw conclusions regarding the phenotypic differences driven by diet. While many compositional differences can account for this, one major difference that could have the greatest impact between GB and purified diets is the fiber content, both in terms of the level and composition. We will review recent data showing how fiber differences between GB diets and purified diets can significantly influence gut health and microbiota, which itself can affect metabolic disease development. Researchers need to consider the control diet carefully in order to make the best use of precious experimental resources.

Improving Metabolic Health Through Precision Dietetics in Mice.

The incidence of diet-induced metabolic disease has soared over the last half-century, despite national efforts to improve health through universal dietary recommendations. Studies comparing dietary patterns of populations with health outcomes have historically provided the basis for healthy diet recommendations. However, evidence that population-level diet responses are reliable indicators of responses across individuals is lacking. This study investigated how genetic differences influence health responses to several popular diets in mice, which are similar to humans in genetic composition and the propensity to develop metabolic disease, but enable precise genetic and environmental control. We designed four human-comparable mouse diets that are representative of those eaten by historical human populations. Across four genetically distinct inbred mouse strains, we compared the American diet's impact on metabolic health to three alternative diets (Mediterranean, Japanese, and Maasai/ketogenic). Furthermore, we investigated metabolomic and epigenetic alterations associated with diet response. Health effects of the diets were highly dependent on genetic background, demonstrating that individualized diet strategies improve health outcomes in mice. If similar genetic-dependent diet responses exist in humans, then a personalized, or "precision dietetics," approach to dietary recommendations may yield better health outcomes than the traditional one-size-fits-all approach.

Endogenous and diet-induced hypercholesterolemia in nonhuman primates: effects of age, adiposity, and diabetes on lipoprotein profiles.

Nonhuman primates (NHPs) share with humans many features of lipid metabolism and often develop all features of the metabolic syndrome, including hypertriglyceridemia and low high-density lipoprotein cholesterol, and have been used in many studies of potential therapeutics during the preclinical phase. Here we identify for the first time in middle-aged and older rhesus the natural occurrence of hypercholesterolemia, and this hypercholesterolemia develops despite maintenance on a low-cholesterol diet. The aims of this study were to (a) define normal and hypercholesterolemia in rhesus monkeys, (b) determine the factors associated with the development of hypercholesterolemia, (c) compare the lipoprotein profiles in adult rhesus monkeys fed a low-fat/low-cholesterol diet (LFLC) with the profiles of human subjects, and (d) determine the effect of a 16-week high-fat/high-cholesterol (HFHC) diet feeding on total cholesterol and lipoprotein profiles in middle-aged and older monkeys. In our colony, maintained on a constant diet with negligible cholesterol, the mean total cholesterol level in healthy nondiabetic monkeys was 3.7 ± 0.02 mmol/L, with hypercholesterolemia identified as the 95th percentile of the normal cholesterol distribution (≥5.2 mmol/L). Severe hypercholesterolemia developed in the HFHC-fed group; however, despite the high-fat diet composition, unexpectedly, no weight gain occurred in these NHPs. The diet-induced hypercholesterolemia differed significantly in lipoprotein pattern from that of the spontaneous hypercholesterolemia. In summary, despite ingesting only a LFLC, NHPs frequently develop hypercholesterolemia, reflecting lipoprotein patterns similar to human subjects; and this lipid profile of spontaneous hypercholesterolemia differs significantly from the hypercholesterolemia induced by an HFHC diet.

Fish oil promotes macrophage reverse cholesterol transport in mice.

OBJECTIVE: Fish oil (FO), and specifically omega 3 fatty acids, has favorable effects on cardiovascular outcomes. The aim of this study was to investigate the effects of FO on the process of macrophage reverse cholesterol transport (RCT) in an in vivo mouse model. METHODS AND RESULTS: C57BL/6J mice were fed a FO diet, whereas control mice were fed diets containing alternative sources of fats, soybean oil (SO), and coconut oil (CO) for 4 weeks. Macrophage RCT was assessed by injecting [(3)H]cholesterol-labeled J774 macrophages intraperitoneally into mice. After 48 hours, tissues were harvested and feces were collected. An increase in the excretion of macrophage-derived [(3)H]-tracer recovered in fecal neutral sterols for FO-fed mice was observed (273% versus SO and 182% versus CO). FO also decreased [(3)H]-tracer in hepatic cholesteryl ester compared to SO and CO by 76% and 56%, respectively. To specifically determine the effect of FO on the fate of HDL-derived cholesterol, mice fed FO or SO diets were injected with HDL labeled with [(3)H]cholesteryl oleate, and the disappearance of [(3)H]-tracer from blood and its excretion in feces was measured. There was no significant difference in the fractional catabolic rate of [(3)H]cholesteryl oleate-HDL between the 2 groups. However, there was a 242% increase in the excretion of HDL-derived [(3)H]-tracer recovered in fecal neutral sterols in FO-fed mice, concordant with significantly increased expression of hepatic Abcg5 and Abcg8 mRNA. CONCLUSIONS: As measured by this tracer-based assay, FO promoted reverse cholesterol transport, primarily by enhancement of the hepatic excretion of macrophage-derived and HDL-derived cholesterol.

Flaxseed reduces plasma cholesterol levels in hypercholesterolemic mouse models.

OBJECTIVE: We examined the effects of whole ground flaxseed added to a Western diet on plasma and hepatic lipids and hepatic gene expression in male and female human apolipoprotein B-100 transgenic (hApoBtg) mice which have a plasma lipid profile more closely resembling man than wild type mice and in mice lacking the low density lipoprotein receptor (LDLr) and apolipoprotein B mRNA editing enzyme complex 1 (LDLr(-/-)/apobec(-/-)). METHODS: The Westernized control diet containing 0.1% cholesterol and 30% kcal as fat was fed for 10 days to hApoBtg mice and for 14 days to LDLr(-/-)/apobec(-/-) mice. Animals from each genetic background were then divided into 2 groups based on gender and mean plasma total cholesterol (TC). The hApoBtg and LDLr(-/-)/apobec(-/-) mice either continued on the control diet for a total of 31 and 35 days, respectively or were fed 20% w/w whole ground flaxseed (flax) with comparable caloric, macronutrient and fiber content for 21 days. Blood was obtained after a 4 hour fast from all mice prior to feeding both control and flax diets, after 10 days on the flax diet, and after 21 days on the flax at which time all mice were exsanguinated. RESULTS: The control diet increased TC by >100 mg/dl in the hApoBtg with a greater increase observed in males and by 800 mg/dl in mice lacking the LDLr. After 3 weeks, the flax diet significantly reduced plasma TC by 19% and 22% in hApoBtg and LDLr(-/-)/apobec(-/-), respectively and non-high density lipoprotein cholesterol (non-HDL-C) by 24% in both models (p for all <0.05). Flax significantly reduced hepatic cholesterol in hApoBtg by 32% and 47% in males and females, respectively and LDLr(-/-)/apobec(-/-) mice by 66%. Flax had no effect on the expression of the following hepatic genes: LDLr, 3-hydroxy-3-methylglutaryl (HMG) CoA reductase, phospholipid transfer protein, cholesterol 7alpha hydroxylase, fatty acid synthase, and acyl CoA oxidase in either mouse model. CONCLUSIONS: Flaxseed reduces plasma and hepatic cholesterol in hApoBtg mice, but had no effect on hepatic lipogenic genes and was equally effective in mice lacking LDLr. The combined data suggest that the lipid lowering effect of flax is not hepatic mediated and may be at the level of cholesterol absorption and/or bile acid reabsorption.

Calcium and dairy intake and measures of obesity in hyper- and normocholesterolemic children.

OBJECTIVE: Calcium intake has been inversely associated with body weight and body fatness in adults and, to a lesser extent, in children. Dairy intake has been inversely associated with metabolic syndrome in overweight but not normal-weight adults. We assessed whether intakes of calcium and dairy foods were associated with measures of obesity in hypercholesterolemic (HC) and normocholesterolemic (non-HC) children at baseline and over 1 year. RESEARCH METHODS AND PROCEDURES: Non-obese 4- to 10-year-old HC and non-HC children (342) completed three 24-hour dietary recalls and provided measures of relative weight (BMI and BMI z scores) and adiposity (sum of skinfolds, trunk skinfolds) at baseline, 3, 6, and 12 months. Cross-sectional and longitudinal regression analyses, stratified by cholesterol risk status (HC vs. non-HC) and age (4 to 6 years and 7 to 10 years) and adjusted for potential confounders, were conducted. RESULTS: After adjusting for age, sex, energy intake, and percentage energy from fat, calcium intake was inversely associated with BMI, sum of skinfolds, and trunk skinfolds at baseline and over 1 year in the 7- to 10-year-old non-HC children. Results from the regression models also indicated an inverse relation between intake of dairy foods and measures of obesity at baseline in these children. Calcium or dairy intake was not associated with measures of obesity in HC children or in the 4- to 6-year-old non-HC children. DISCUSSION: These results suggest a complex relation among intake of calcium and dairy foods, measures of obesity, age, and serum cholesterol in children. Older children without risk of metabolic syndrome may benefit most from increased calcium intake.