Shotgun Lipidomics Discovered Diurnal Regulation of Lipid Metabolism Linked to Insulin Sensitivity in Nondiabetic Men.

CONTEXT: Meal timing affects metabolic homeostasis and body weight, but how composition and timing of meals affect plasma lipidomics in humans is not well studied. OBJECTIVE: We used high throughput shotgun plasma lipidomics to investigate effects of timing of carbohydrate and fat intake on lipid metabolism and its relation to glycemic control. DESIGN: 29 nondiabetic men consumed (1) a high-carb test meal (MTT-HC) at 09.00 and a high-fat meal (MTT-HF) at 15.40; or (2) MTT-HF at 09.00 and MTT-HC at 15.40. Blood was sampled before and 180 minutes after completion of each MTT. Subcutaneous adipose tissue (SAT) was collected after overnight fast and both MTTs. Prior to each investigation day, participants consumed a 4-week isocaloric diet of the same composition: (1) high-carb meals until 13.30 and high-fat meals between 16.30 and 22:00 or (2) the inverse order. RESULTS: 12 hour daily lipid patterns showed a complex regulation by both the time of day (67.8%) and meal composition (55.4%). A third of lipids showed a diurnal variation in postprandial responses to the same meal with mostly higher responses in the morning than in the afternoon. Triacylglycerols containing shorter and more saturated fatty acids were enriched in the morning. SAT transcripts involved in fatty acid synthesis and desaturation showed no diurnal variation. Diurnal changes of 7 lipid classes were negatively associated with insulin sensitivity, but not with glucose and insulin response or insulin secretion. CONCLUSIONS: This study identified postprandial plasma lipid profiles as being strongly affected by meal timing and associated with insulin sensitivity.

Diurnal distribution of carbohydrates and fat affects substrate oxidation and adipokine secretion in humans.

Background: A diet in which fat is mainly eaten in the morning and carbohydrates mainly in the evening (compared with the reverse order) was recently shown to worsen glycemic control in people with prediabetes. Objective: We investigated the effects of these dietary patterns on energy metabolism, and on the daily profiles of circulating lipids, adipokines, and inflammatory markers. Design: In a randomized controlled crossover trial, 29 nonobese men (with normal glucose tolerance, n = 18; or impaired fasting glucose/glucose tolerance, n = 11) underwent 2 isocaloric 4-wk diets: 1) carbohydrate-rich meals until 1330 and fat-rich meals between 1630 and 2200 (HC/HF); or 2) the inverse sequence of meals (HF/HC). During a 12-h clinical investigation day after each intervention period, 2 meal tolerance tests were performed, at 0900 and 1540, respectively. Substrate oxidation and concentrations of circulating lipids, adipokines, and cytokines were assessed pre- and postprandially. The postprandial inflammatory response in leukocytes was analyzed ex vivo. Results: Fasting carbohydrate oxidation decreased (P = 0.004) and lipid oxidation increased (P = 0.012) after the HC/HF diet. Fasting concentrations of blood markers did not differ between diets. The diets modulated the daily profiles of carbohydrate oxidation, lipid oxidation, and ß-hydroxybutyrate, although the average daily values of these parameters showed no difference between the diets, and no interaction between diet and glucose tolerance status. Diurnal patterns of triglycerides, low-density lipoprotein cholesterol, leptin, visfatin, and of LPS-induced cytokine secretion in blood leukocytes were also modulated by the diets. Average daily concentrations of leptin (P = 0.017) and visfatin (P = 0.041) were lower on the HF/HC diet than on the HC/HF diet. Conclusions: Diurnal distribution of carbohydrates and fat affects the daily profiles of substrate oxidation, circulating lipids, and cytokine secretion, and alters the average daily concentrations of adipokine secretion in nonobese nondiabetic humans. The study was registered at clinicaltrials.gov as NCT02487576.

Odd-chain fatty acids as a biomarker for dietary fiber intake: a novel pathway for endogenous production from propionate.

Background: The risk of type 2 diabetes is inversely correlated with plasma concentrations of odd-chain fatty acids [OCFAs; pentadecanoic acid (15:0) and heptadecanoic acid (17:0)], which are considered as biomarkers for dairy fat intake in humans. However, rodent studies suggest that OCFAs are synthesized endogenously from gut-derived propionate. Propionate increases with dietary fiber consumption and has been shown to improve insulin sensitivity.Objective: We hypothesized that OCFAs are produced in humans from dietary fibers by a novel endogenous pathway.Design: In a randomized, double-blind crossover study, 16 healthy individuals were supplemented with cellulose (30 g/d), inulin (30 g/d), or propionate (6 g/d) for 7 d. In addition, human hepatoma cells were incubated with different propionate concentrations. OCFAs were determined in plasma phospholipids and hepatoma cells by gas chromatography.Results: Cellulose did not affect plasma OCFA levels, whereas inulin and propionate increased pentadecanoic acid by ∼17% (P < 0.05) and 13% (P = 0.05), respectively. The effect on heptadecanoic acid was even more pronounced, because it was elevated in almost all participants by inulin (11%; P < 0.01) and propionate (13%; P < 0.001). Furthermore, cell culture experiments showed a positive association between propionate and OCFA levels (R2 = 0.99, P < 0.0001), whereas palmitate (16:0) was negatively correlated (R2 = 0.83, P = 0.004).Conclusions: Our data show that gut-derived propionate is used for the hepatic synthesis of OCFAs in humans. The association of OCFAs with a decreased risk of type 2 diabetes may therefore also relate to dietary fiber intake and not only dairy fat. This trial was registered at www.germanctr.de as DRKS00010121.

The effect of diurnal distribution of carbohydrates and fat on glycaemic control in humans: a randomized controlled trial.

Diurnal carbohydrate and fat distribution modulates glycaemic control in rodents. In humans, the optimal timing of both macronutrients and its effects on glycaemic control after prolonged consumption are not studied in detail. In this cross-over trial, 29 non-obese men were randomized to two four-week diets: (1) carbohydrate-rich meals until 13.30 and fat-rich meals between 16.30 and 22.00 (HC/HF) versus (2) inverse sequence of meals (HF/HC). After each trial period two meal tolerance tests were performed, at 09.00 and 15.40, respectively, according to the previous intervention. On the HF/HC diet, whole-day glucose level was increased by 7.9% (p = 0.026) in subjects with impaired fasting glucose and/or impaired glucose tolerance (IFG/IGT, n = 11), and GLP-1 by 10.2% (p = 0.041) in normal glucose-tolerant subjects (NGT, n = 18). Diet effects on fasting GLP-1 (p = 0.009) and PYY (p = 0.034) levels were observed in IFG/IGT, but not in NGT. Afternoon decline of glucose tolerance was more pronounced in IFG/IGT and associated with a stronger decrease of postprandial GLP-1 and PYY levels, but not with changes of cortisol rhythm. In conclusion, the HF/HC diet shows an unfavourable effect on glycaemic control in IFG/IGT, but not in NGT subjects. Consequently, large, carbohydrate-rich dinners should be avoided, primarily by subjects with impaired glucose metabolism.

Correlations between mercury concentration, and stable isotope ratios of carbon and nitrogen of amino acids in scalp hair from whale meat eaters and heavy fish eaters.

RATIONALE: As mercury (Hg) accumulation in marine animals generally increases with increased trophic level (δ15 N values) through the food web, predators accumulate higher levels of Hg. The main source of human Hg intake is the consumption of fish and other marine animals, and Hg concentration in scalp hair is the preferred marker for evaluating consumption of marine animals. Difference in δ15 N values between trophic and source amino acids of human consumers could enable us to estimate the trophic level of the consumer without knowing the bulk δ15 N value of their prey. METHODS: We measured the δ15 N values of 15 amino acids in scalp hair from heavy fish eaters and whale meat eaters using isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS), and investigated the correlations between Hg concentrations in the hair and the δ15 N values of the individual constituent amino acids. RESULTS: The δ15 N values for all trophic amino acids (Ala, Val, Leu, Ile, Pro, Asx and Glx) increased with increases in Hg concentration (p < 0.01), with the highest correlation being with Glx (R2  = 0.725). In contrast, the δ15 N value for Thr decreased with increases in Hg concentration (R2  = 0.663, p < 0.01). The difference in δ15 N values between Glx and Thr was positively correlated with Hg concentration, showing the highest correlation coefficient (R2  = 0.773, p < 0.01) among the various combinations for amino acids. CONCLUSIONS: The difference in δ15 N values between Glx and Thr appears to be the best proxy for the estimation of Hg concentration in scalp hair. Copyright © 2017 John Wiley & Sons, Ltd.

The dietary protein paradox and threonine 15 N-depletion: Pyridoxal-5'-phosphate enzyme activity as a mechanism for the δ15 N trophic level effect.

RATIONALE: Nitrogen stable isotope ratios (δ15 N values) are used to reconstruct dietary patterns, but the biochemical mechanism(s) responsible for the diet to tissue trophic level effect and its variability are not fully understood. Here δ15 N amino acid (AA) values and physiological measurements (nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates) are used to investigate increased dietary protein consumption and oxidative stress (vitamin E deficiency) in rat total plasma protein. METHODS: Using gas chromatography/combustion/isotope ratio mass spectrometry, the δ15 N values from N-pivaloyl-i-propyl esters of 15 AAs are reported for rats (n = 40) fed casein-based diets with: adequate protein (AP, 13.8%; n = 10), medium protein (MP, 25.7%; n = 10), high protein (HP, 51.3%; n = 10) or HP without vitamin E (HP-E; n = 10) for 18 weeks. RESULTS: Between the HP and AP groups, the δ15 NAA values of threonine (-4.0‰), serine (+1.4‰) and glycine (+1.2‰) display the largest differences and show significant correlations with: nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates. This indicates increased AA catabolism by the dietary induction of shared common metabolic pathways involving the enzymes threonine ammonia-lyase (EC 4.3.1.19), serine hydroxymethyltransferase (EC 2.1.2.1) and the glycine cleavage system (EC 2.1.2.10). The δ15 NAA values of the HP-E and HP groups were not found to be significantly different. CONCLUSIONS: The 15 N-depleted results of threonine are linked to increased activity of threonine ammonia-lyase, and show potential as a possible biomarker for protein intake and/or gluconeogenesis. We hypothesize that the inverse nitrogen equilibrium isotope effects of Schiff base formation, between AAs and pyridoxal-5'-phosphate cofactor enzymes, play a key role in the bioaccumulation and depletion of 15 N in the biomolecules of living organisms and contributes to the variability in the nitrogen trophic level effect. Copyright © 2017 John Wiley & Sons, Ltd.

A Slow- Compared with a Fast-Release Form of Oral Arginine Increases Its Utilization for Nitric Oxide Synthesis in Overweight Adults with Cardiometabolic Risk Factors in a Randomized Controlled Study.

BACKGROUND: Oral l-arginine supplements can have a beneficial effect on nitric oxide (NO)-related functions when subjects have cardiovascular disease risk factors. OBJECTIVE: The study was designed to determine the utilization for NO synthesis of oral l-arginine as a function of the cardiometabolic risk and the speed of absorption by comparing immediate-release arginine (IR-Arg), as in supplements, and sustained-release arginine (SR-Arg), which mimics the slow release of dietary arginine. METHODS: In a randomized, single-blind, 2-period crossover, controlled trial (1 wk of treatment, >2 wk of washout), using [(15)N-(15)N-(guanidino)]-arginine for the first morning dose, we compared the bioavailability (secondary outcome) and utilization for NO synthesis (primary outcome) of 1.5 g IR- and SR-Arg 3 times/d in 12 healthy overweight [body mass index (BMI; in kg/m(2)): 25-30] adults with the hypertriglyceridemic waist phenotype [HTW; plasma triglycerides (TGs): >150 mg/dL; waist circumference: >94 cm (men) or >80 cm (women)] and 15 healthy control adults (CON; BMI: 18.5-25; no elevated TGs and waist circumference). RESULTS: Plasma oral arginine areas under the curve were lower after supplementation with SR-Arg than with IR-Arg (112 ± 52.3 and 142 ± 50.8 µmol ⋅ h/L; P < 0.01). The utilization of oral arginine for NO synthesis was 58% higher in HTW subjects than in CON subjects and higher with SR-Arg than with IR-Arg (P < 0.05 both), particularly in HTW subjects (group-by-treatment interaction, P < 0.05). In HTW subjects administered the SR form, utilization for NO synthesis was 32% higher than with the IR form and 87% higher than in CON subjects who were administered the SR form. CONCLUSION: In overweight adults with the HTW phenotype, a slow- compared with a fast-release form of oral arginine markedly favors the utilization of arginine for NO synthesis. The utilization of low-dose, slow-release arginine for NO synthesis is higher in overweight adults with the HTW phenotype than in healthy controls, suggesting that the sensitivity of NO synthesis to the dietary arginine supply increases with cardiometabolic risk. The trial was registered at clinicaltrials.gov as NCT02352740.

Beyond the role of dietary protein and amino acids in the prevention of diet-induced obesity.

High-protein diets have been shown to prevent the development of diet-induced obesity and can improve associated metabolic disorders in mice. Dietary leucine supplementation can partially mimic this effect. However, the molecular mechanisms triggering these preventive effects remain to be satisfactorily explained. Here we review studies showing a connection between high protein or total amino nitrogen intake and obligatory water intake. High amino nitrogen intake may possibly lower lipid storage, and prevent insulin resistance. Suggestions are made for further systematical studies to explore the relationship between water consumption, satiety, and energy expenditure. Moreover, these examinations should better distinguish between leucine-specific and unspecific effects. Research in this field can provide important information to justify dietary recommendations and strategies in promoting long-term weight loss and may help to reduce health problems associated with the comorbidities of obesity.

Kinetics of the utilization of dietary arginine for nitric oxide and urea synthesis: insight into the arginine-nitric oxide metabolic system in humans.

BACKGROUND: The systemic availability of oral/dietary arginine and its utilization for nitric oxide (NO) synthesis remains unknown and may be related to a competitive hydrolysis of arginine into urea in the splanchnic area and systemic circulation. OBJECTIVES: We investigated the kinetics and dose-dependency of dietary arginine utilization for NO compared with urea synthesis and studied the characteristics of the arginine-NO metabolic system in healthy humans. DESIGN: We traced the metabolic fate and analyzed the utilization dynamics of dietary arginine after its ingestion at 2 nutritional amounts in healthy humans (n = 9) in a crossover design by using [(15)N-(15)N-(guanido)]-arginine, isotope ratio mass spectrometry techniques, and data analysis with a compartmental modeling approach. RESULTS: Whatever the amount of dietary arginine, 60 ± 3% (±SEM) was converted to urea, with kinetics indicative of a first-pass splanchnic phenomenon. Despite this dramatic extraction, intact dietary arginine made a major contribution to the postprandial increase in plasma arginine. However, the model identified that the plasma compartment was a very minor (~2%) precursor for the conversion of dietary arginine into NO, which, in any case, was small (<0.1% of the dose). The whole-body and plasma kinetics of arginine metabolism were consistent with the suggested competitive metabolism by the arginase and NO synthase pathways. CONCLUSIONS: The conversion of oral/dietary arginine into NO is not limited by the systemic availability of arginine but by a tight metabolic compartmentation at the systemic level. We propose an organization of the arginine metabolic system that explains the daily maintenance of NO homeostasis in healthy humans.

Dietary L-leucine and L-alanine supplementation have similar acute effects in the prevention of high-fat diet-induced obesity.

High-protein diets have been shown to alleviate detrimental effects of high-fat diets and this effect can be partially mimicked by dietary L-leucine supplementation. Here, we aimed to elucidate the early mechanisms and the specificity of leucine effects. We performed a 1-week trial with male C57BL/6 mice fed ad libitum with semisynthetic high-fat diets containing an adequate (10 % w/w, AP) or high (50 % w/w, HP) amount of whey protein, or supplemented with L-leucine corresponding to the leucine content within the HP diet (Leu) or supplemented with equimolar L-alanine (Ala). Food and water intake were monitored continuously using a computer-controlled monitor system and body composition changes were assessed using quantitative NMR. HP completely prevented the AP-induced accumulation of body fat. Leu and Ala resulted in a similar reduction of body fat accumulation which was intermediate between AP and HP. There were no significant effects on plasma glucose or insulin. Triacylglycerol content and gene expression of lipogenesis enzymes in liver as well as plasma cholesterol were reduced by HP compared to AP with Leu and Ala again showing intermediate effects. Body fat gain and liver triacylglycerols were strongly correlated with total energy intake. Water intake was rapidly increased by HP feeding and total water intake correlated strongly with total amino nitrogen intake. We concluded that the positive effects of high-protein diets on metabolic syndrome associated traits are acutely due to effects on satiety possibly linked to amino nitrogen intake and on the subsequent suppression of liver lipogenesis without evidence for a specific leucine effect.

Comparison of high-protein diets and leucine supplementation in the prevention of metabolic syndrome and related disorders in mice.

High-protein diets have been shown to promote weight loss, to improve glucose homeostasis and to increase energy expenditure and fat oxidation. We aimed to study whether leucine supplementation is able to mimic the alleviating effects of high-protein diets on metabolic syndrome parameters in mice fed high-fat diet. Male C57BL/6 mice were fed for 20 weeks with semisynthetic high-fat diets (20% w/w of fat) containing either an adequate (10% protein, AP) or high (50% protein, HP) amount of whey protein, or an AP diet supplemented with L-leucine corresponding to the leucine content of the HP diet (6% leucine, AP+L). Body weight and composition, energy expenditure, glucose tolerance, hepatic triacylglycerols (TG), plasma parameters as well as expression levels of mRNA and proteins in different tissues were measured. HP feeding resulted in decreased body weight, body fat and hepatic TG accumulation, as well as increased insulin sensitivity compared to AP. This was linked to an increased total and resting energy expenditure (REE), decreased feed energy efficiency, increased skeletal muscle (SM) protein synthesis, reduced hepatic lipogenesis and increased white fat lipolysis. Leucine supplementation had effects that were intermediate between HP and AP with regard to body composition, liver TG content, insulin sensitivity, REE and feed energy efficiency, and similar effects as HP on SM protein synthesis. However, neither HP nor AP+L showed an activation of the mammalian target of rapamycin pathway in SM. Leucine supplementation had no effect on liver lipogenesis and white fat lipolysis compared to AP. It is concluded that the essential amino acid leucine is able to mimic part but not all beneficial metabolic effects of HP diets.

Practical recommendations for the reduction of memory effects in compound-specific 15N/14N-ratio analysis of enriched amino acids by gas chromatography/combustion/isotope ratio mass spectrometry.

Gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) is a highly sensitive approach which allows the analysis of the (13)C/(12)C and (15)N/(14)N isotope composition of amino acids in the range of natural abundance or in slightly (13)C- and (15)N-enriched samples. However, the accuracy of measurements remains a permanent challenge. Here we show the effect of the presence of slightly (15)N-enriched compounds in physiological samples on the accuracy and reproducibility of (15)N-abundances of amino acids within or between analytical runs. We spiked several individual amino acids with the respective (15)N-labelled isotopomer and measured the (15)N/(14)N ratios of other amino acids in the same sample or in the following analytical runs. Intra- and inter-run memory effects can be observed in (15)N/(14)N ratios of amino acids. Sample throughput is reduced when cleaning runs using standard mixtures are required to restore initial conditions after runs of samples with (15)N-enriched analytes. Possible reasons for the observed phenomenon and its implications for work in the lower (15)N-enrichment range (<0.5 APE) are discussed and include different aspects of gas chromatography, derivatisation, and hot catalytic metal surface effects. Results need to be interpreted with caution if complex physiological samples contain (15)N-enriched amino acids beyond 500‰ δ(15)N (~0.18 APE).

Increased fat-free body mass and no adverse effects on blood lipid concentrations 4 weeks after additional meat consumption in comparison with an exclusion of meat in the diet of young healthy women.

Aims. To investigate whether changes of meat consumption can affect body composition and laboratory parameters in healthy, normal weight, young women without the aim to reduce body weight. Research Design and Methods. Women volunteered to eat low-fat meat in addition to their habitual diet (M) or to exclude meat products from their diet (NOM). After 4 weeks M and NOM were crossed over between subjects. Changes in nutrient intake, morphometrics and plasma parameters were compared during M and NOM. Results. Daily protein intake (means ± SD) was 2.25 ± 0.35 (25.2% of energy) and 1.15 ± 0.26 g/kg (14.0% of energy) during M and NOM, respectively. Fat-free body mass (FFM) increased during M (0.7 ± 1.0 kg, P = .02) and decreased during NOM (-0.8 ± 0.8 kg, P = .003). Body fat mass was unchanged. Concentrations of total cholesterol (-7%), LDL-cholesterol (-8%), and glucose (-4%) deceased significantly after M. Fasting glutamine concentrations were decreased by M and increased by NOM. Conclusions. Additional meat intake can increase FFM without adverse effects on blood lipid concentrations. Long-term studies are required. Urinary excretion of 3-methylhistidine could represent a biomarker for meat protein consumption.

Effects of supplemented isoenergetic diets differing in cereal fiber and protein content on insulin sensitivity in overweight humans.

BACKGROUND: Despite their beneficial effects on weight loss and blood lipids, high-protein (HP) diets have been shown to increase insulin resistance and diabetes risk, whereas high-cereal-fiber (HCF) diets have shown the opposite effects on these outcomes. OBJECTIVE: We compared the effects of isoenergetic HP and HCF diets and a diet with moderate increases in both cereal fibers and dietary protein (Mix diet) on insulin sensitivity, as measured by using euglycemic-hyperinsulinemic clamps with infusion of [6,6-(2)H(2)]glucose. DESIGN: We randomly assigned 111 overweight adults with features of the metabolic syndrome to 1 of 4 two-phased, 18-wk isoenergetic diets by group-matching. Per 3-d food protocols, the percentages of energy derived from protein and carbohydrates and the intake of cereal fiber per day, respectively, were as follows-after 6 wk: 17%, 52%, and 14 g (control); 17%, 52%, and 43 g (HCF); 28%, 43%, and 13 g (HP); 23%, 44%, and 26 g (Mix); after 18 wk: 17%, 51%, and 15 g (control); 17%, 51%, and 41 g (HCF); 26%, 45%, and 14 g (HP); and 22%, 46%, and 26 g (Mix). Eighty-four participants completed the study successfully and were included in the final analyses. Adherence was supported by the provision of tailored dietary supplements twice daily in all groups. RESULTS: Insulin sensitivity expressed as an M value was 25% higher after 6 wk of the HCF diet than after 6 wk of the HP diet (subgroup analysis: 4.61 ± 0.38 compared with 3.71 ± 0.36 mg · kg(-1) · min(-1), P = 0.008; treatment × time interaction: P = 0.005). Effects were attenuated after 18 wk (treatment × time interaction: P = 0.054), which was likely explained by lower adherence to the HP diet. HP intake was associated with a tendency to increased protein expression in adipose tissue of the translation initiation factor serine-kinase-6-1, which is known to mediate amino acid-induced insulin resistance. Biomarkers of protein intake indicated interference of cereal fibers with dietary protein absorption. CONCLUSION: Greater changes in insulin sensitivity after intake of an isoenergetic HCF than after intake of an HP diet might help to explain the diverse effects of these diets on diabetes risk. This trial is registered at clinicaltrials.gov as NCT00579657.

Body weight and energy homeostasis was not affected in C57BL/6 mice fed high whey protein or leucine-supplemented low-fat diets.

BACKGROUND: Leucine is suggested to act as nutrient signal of high-protein diets regulating pathways associated with an alleviation of metabolic syndrome parameters. However, the subject remains controversial. AIM OF THE STUDY: The aim of this study was to assess and to compare the effects of high-protein diets with dietary leucine supplementation in mice, particularly on energy homeostasis, body composition, and expression of uncoupling protein (UCP), which are suggested to decrease food energy efficiency. METHODS: Male C57BL/6 mice were exposed for 14 weeks to semi-synthetic diets containing either 20% (adequate protein content, AP) or 50% whey protein (high-protein content, HP). A third group was fed the AP diet supplemented with L-leucine (AP + L) corresponding to the leucine content of the HP diet. The total fat content was 5% (w/w). RESULTS: Body weight gain, body composition, energy expenditure, and protein expression of UCP1 in brown adipose tissue, and UCP3 in skeletal muscle were not different between groups. In HP-fed mice, a stronger increase in blood glucose levels was detected during glucose tolerance tests compared to AP and AP + L, whereas plasma insulin was similar in all groups. Leucine supplementation did not affect glucose tolerance. Plasma cholesterol was significantly decreased in HP and AP + L when compared to AP. Plasma triglyceride concentrations were increased twofold in HP-fed mice when compared to AP + L and AP groups. Liver and skeletal muscle triglyceride and glycogen concentrations were similar in all groups. Postabsorptive plasma concentrations of branched-chain amino acids were not significantly increased after exposure to HP and AP + L diets, whereas those of lysine were decreased in HP and AP + L mice when compared to AP (P < 0.001). Plasma methionine concentrations were lower after HP intake when compared to AP and AP + L (P < 0.05). CONCLUSIONS: We suggest that an exposure of mice to HP diets or a corresponding leucine supplementation has no significant effect on energy homeostasis and UCP expression compared with AP diets when feeding a low-fat diet. The use of high-quality whey protein might at least in part explain the results obtained.

Telomerase deficiency impairs glucose metabolism and insulin secretion.

Reduced telomere length and impaired telomerase activity have been linked to several diseases associated with senescence and aging. However, a causal link to metabolic disorders and in particular diabetes mellitus is pending. We here show that young adult mice which are deficient for the Terc subunit of telomerase exhibit impaired glucose tolerance. This is caused by impaired glucose-stimulated insulin secretion (GSIS) from pancreatic islets, while body fat content, energy expenditure and insulin sensitivity were found to be unaltered. The impaired secretion capacity for insulin is due to reduced islet size which is linked to an impaired replication capacity of insulin-producing beta-cells in Terc-deficient mice. Taken together, telomerase deficiency and hence short telomeres impair replicative capacity of pancreatic beta-cells to cause impaired insulin secretion and glucose intolerance, mechanistically defining diabetes mellitus as an aging-associated disorder.

Advances in natural stable isotope ratio analysis of human hair to determine nutritional and metabolic status.

PURPOSE OF REVIEW: We review the literature on the use of stable isotope ratios at natural abundance to reveal information about dietary habits and specific nutrient intakes in human hair protein (keratin) and amino acids. In particular, we examine whether hair isotopic compositions can be used as unbiased biomarkers to provide information about nutritional status, metabolism, and diseases. RECENT FINDINGS: Although the majority of research on the stable isotope ratio analysis of hair has focused on bulk protein, methods have been recently employed to examine amino acid-specific isotope ratios using gas chromatography or liquid chromatography coupled to an isotope ratio mass spectrometer. The isotopic measurement of amino acids has the potential to answer research questions on amino acid nutrition, metabolism, and disease processes and can contribute to a better understanding of the variations in bulk protein isotope ratio values. First results suggest that stable isotope ratios are promising as unbiased nutritional biomarkers in epidemiological research. However, variations in stable isotope ratios of human hair are also influenced by nutrition-dependent nitrogen balance, and more controlled clinical research is needed to examine these effects in human hair. SUMMARY: Stable isotope ratio analysis at natural abundance in human hair protein offers a noninvasive method to reveal information about long-term nutritional exposure to specific nutrients, nutritional habits, and in the diagnostics of diseases leading to nutritional stress and impaired nitrogen balance.

Opposing effects of dietary sugar and saturated fat on cardiovascular risk factors and glucose metabolism in mitochondrially impaired mice.

PURPOSE: Both dietary fat and dietary sucrose are major components of Western diets that may differentially affect the risk for body mass gain, diabetes mellitus, and cardiovascular disease. METHODS: We have phenotypically analyzed mice with ubiquitously impaired expression of mitochondrial frataxin protein that were challenged with diets differing in macronutrient content, namely high-sucrose/low-fat and high-saturated fat/low-sugar diets. RESULTS: We find here that a high-sucrose/low-fat diet has especially detrimental effects in mice with impaired mitochondrial metabolism promoting several independent cardiovascular risk factors, including impaired glucose metabolism, fasting hyperinsulinemia, reduced glucose-stimulated insulin secretion, increased serum triglycerides, and elevated cholesterol levels due to increased expression of HMG-CoA reductase. In contrast, a high-saturated fat/low-sugar diet protects mice with impaired mitochondrial metabolism from diet-induced obesity by increasing total energy expenditure and increasing expression of ACAA2, a rate-limiting enzyme of mitochondrial beta-oxidation, whereas no concomitant improvement of glucose metabolism was observed. CONCLUSIONS: Taken together, our results suggest that mitochondrial dysfunction may cause sucrose to become a multifunctional cardiovascular risk factor, whereas low-sugar diets high in saturated fat may prevent weight gain without improving glucose metabolism.

Hair protein and amino acid 13C and 15N abundances take more than 4 weeks to clearly prove influences of animal protein intake in young women with a habitual daily protein consumption of more than 1 g per kg body weight.

A high protein or meat intake might be a risk factor for metabolic disorders. Stable isotopic abundances (SIA) of hair can be used as biomarkers for animal protein intake due to characteristic isotopic patterns of food proteins. We investigated if an additional meat intake (M, 200 g pork fillet/day) or an omission of meat and meat products (NOM) can influence the natural (15)N and (13)C SIA within 4 weeks in hair and plasma of young women. The daily protein intake (means +/- SD) was 1.40 +/- 0.29, 2.25 +/- 0.35, and 1.15 +/- 0.26 g/kg at baseline, during M, and during NOM, respectively. At baseline the animal protein intake correlated with bulk SIA of hair ((15)N: R(2) = 0.416; (13)C: R(2) = 0.664; n = 14). However, isotope ratio mass spectrometry (IRMS) analyses have not shown that hair and plasma SIA were changed significantly after M or NOM. Possible reasons were discussed. Urinary SIA were significantly lower after M than after NOM ((15)N: p = 0.039; (13)C: p = 0.006) and close to those of pork fillet. Characteristic patterns of SIA were measured in individual amino acids (AA) by gas chromatography/combustion isotope ratio mass spectrometry (GC/C/IRMS). The results confirmed considerable differences in SIA between AA (delta(15)N, up to 22 per thousand; delta(13)C, up to 31 per thousand). Plots of (15)N versus (13)C abundances in hair revealed characteristic differences between indispensable and dispensable AA. The intervention-dependent changes of AA-specific SIA were not as clear as expected. Although the AA-specific SIA may reveal more detailed characteristics of physiological conditions, further methodological research is required. We suggest that the SIA of leucine can be potential markers of protein intake. The reliability of SIA as biomarkers of protein intake still have to be tested in longer lasting intervention studies in humans. The results may have implications in the assessment for possible benefits and risks of protein consumption.