European Journal of Nutrition (v.53, #6)

Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials by Saman Khalesi; Jing Sun; Nicholas Buys; Arash Jamshidi; Elham Nikbakht-Nasrabadi; Hossein Khosravi-Boroujeni (1299-1311).
Although previous literature has reported that regular green tea consumption may improve blood pressure, the evidence from these studies is not consistent. The present study systematically reviewed randomised controlled trials and examined the effect of green tea consumption on blood pressure using meta-analysis.Search of ProQuest, PubMed, Scopus and Cochrane Library (CENTERAL) was conducted, to identify eligible articles. Articles from 1995 to 2013 were included. A random-effect model was chosen to calculate the effect of combined trials.Thirteen studies were included in the meta-analysis. Green tea consumption significantly changed systolic blood pressure, by −2.08 mm Hg (95 % CI −3.06, −1.05), and diastolic blood pressure, by −1.71 mm Hg (95 % CI −2.86, −0.56), compared to the control. Changes in lipid profile, blood glucose and body mass index were also assessed in the meta-analysis. A significant reduction was found in total cholesterol (−0.15 mmol/L [95 % CI −0.27, −0.02]) and low-density lipoprotein cholesterol (−0.16 mmol/L [95 % CI −0.22, −0.09]). Changes in other parameters did not reach statistical significance. Subgroup analysis suggested a greater reduction in both systolic and diastolic blood pressure in studies that included participants with a baseline mean systolic blood pressure of ≥130 mm Hg, and studies involving consuming green tea as an extract.The present meta-analysis suggests that green tea and its catechins may improve blood pressure, and the effect may be greater in those with systolic blood pressure ≥130 mm Hg. The meta-analysis also suggests that green tea catechins may improve total and low-density lipoprotein cholesterol.
Keywords: Green tea; Blood Pressure; Lipid profile; Systematic review; Meta-analysis

Effect of carnitine, acetyl-, and propionylcarnitine supplementation on the body carnitine pool, skeletal muscle composition, and physical performance in mice by Réjane Morand; Jamal Bouitbir; Andrea Felser; Jürgen Hench; Christoph Handschin; Stephan Frank; Stephan Krähenbühl (1313-1325).
Pharmacokinetics and effects on skeletal muscle and physical performance of oral acetylcarnitine and propionylcarnitine are not well characterized. We therefore investigated the influence of oral acetylcarnitine, propionylcarnitine, and carnitine on body carnitine homeostasis, energy metabolism, and physical performance in mice and compared the findings to non-supplemented control animals. Mice were supplemented orally with 2 mmol/kg/day carnitine, acetylcarnitine, or propionylcarnitine for 4 weeks and studied either at rest or after exhaustive exercise.In the supplemented groups, total plasma and urine carnitine concentrations were significantly higher than in the control group receiving no carnitine, whereas the skeletal muscle carnitine content remained unchanged. The supplemented acylcarnitines were hydrolyzed in intestine and liver and reached the systemic circulation as carnitine. Bioavailability of carnitine and acylcarnitines, determined as the urinary excretion of total carnitine, was in the range of 19 %. Skeletal muscle morphology, including fiber-type composition, was not affected, and oxygen consumption by soleus or gastrocnemius fibers was not different between the groups. Supplementation with carnitine or acylcarnitines had no significant impact on the running capacity, but was associated with lower plasma lactate levels and a higher glycogen content in white skeletal muscle after exhaustive exercise.Oral supplementation of carnitine, acetylcarnitine, or propionylcarnitine in mice is associated with increased plasma and urine total carnitine concentrations, but does not affect the skeletal muscle carnitine content. Despite better preservation of skeletal muscle glycogen and lower plasma lactate levels, physical performance was not improved by carnitine or acylcarnitine supplementation.
Keywords: Carnitine and short-chain acylcarnitines; Bioavailability; Muscle composition and metabolism; Physical performance

Vitamin B12 as a potential compliance marker for fish intake by Nathalie Scheers; Helen Lindqvist; Anna Maria Langkilde; Ingrid Undeland; Ann-Sofie Sandberg (1327-1333).
The aim of the present study was to investigate whether the following four markers: vitamin B12, selenium, vitamin D, and parvalbumin may be used as compliance markers for fish intake.Blood samples from a randomized cross-over herring intervention study (n = 32) were analysed by HPLC and immunochemistry. The criteria were that plasma or serum concentrations of candidate compliance markers after the herring diet should increase significantly compared to starting concentrations. In addition, the reference meat diet should not yield an increase in plasma concentration of the candidate marker.Vitamin B12 and selenium met the set criteria for indicating a correlation between the marker and fish intake with significant increases in serum concentrations at 8.9 % (p = 0.008) and 4.6 % (p = 0.02), respectively, after a 6-week herring intervention (5 meals a week). Parvalbumin and 25-hydroxy vitamin D3 levels did not increase significantly after the herring interventions.Vitamin B12 may be suitable as a compliance marker for fish intake. Although selenium also met the criteria, the change in selenium serum concentrations was small compared to the change in vitamin B12 levels.
Keywords: Biomarker; Marker; Compliance; Fish; Intake; Vitamin B12

Frequencies and demographic determinants of breastfeeding and DHA supplementation in a nationwide sample of mothers in Germany by Lars Libuda; Madlen Stimming; Christina Mesch; Petra Warschburger; Hermann Kalhoff; Berthold Viktor Koletzko; Mathilde Kersting (1335-1344).
German guidelines recommend breast milk as ideal for infant’s nutrition, supporting exclusive breastfeeding for at least 4 months. Moreover, in mothers with insufficient fish intake, DHA status may be improved by supplementation during pregnancy and lactation. However, little is known on current rates of breastfeeding and DHA supplementation in Germany. The objective of this study was to analyse frequencies and demographic determinants of breastfeeding and DHA supplementation in Germany. Data derived from a nationwide consumer survey of 986 mothers with children between 5 and 36 months of age in Germany.78.3 % reported that they ever breastfed their children, and 55.6 % of the mothers exclusively breastfed for at least 4 months. Mothers who did not breastfeed were less likely to be informed by their paediatrician or midwife and were more often not informed at all; 27.8 % of mothers used DHA supplements during pregnancy, 16.8 % postnatal. DHA supplementation was more common in women with a high versus a low fish intake. The social status was the major determinant of breastfeeding initiation and exclusivity and also DHA supplementation.Breastfeeding initiation and duration of exclusive breastfeeding in Germany need to be improved. Professional counselling and support, with a focus on mothers from lower social classes, appears necessary to increase current rates of breastfeeding initiation, duration, and exclusiveness, but also to ensure a sufficient supply with DHA in pregnant and lactating women, particularly in women with low fish consumption.
Keywords: Breastfeeding; Initiation; Exclusiveness; DHA supplements; Determinants

Determinants of the transition from a cardiometabolic normal to abnormal overweight/obese phenotype in a Spanish population by Helmut Schröder; Rafel Ramos; José M. Baena-Díez; Michelle A. Mendez; Dolors Juvinyà Canal; Montserrat Fíto; Joan Sala; Roberto Elosua (1345-1353).
There is limited prospective evidence at population scale of the impacts of lifestyle and surrogate measures of general and abdominal adiposity on the transition of a metabolically healthy (absence of a metabolic disorder) overweight/obese (MHOO) phenotype to a metabolically abnormal overweight/obese (MAOO) phenotype. Therefore, we determined the relationship between 10-year body mass index (BMI), waist circumferences (WC), waist to height ratio (WHtR), and lifestyle changes and the transition of the MHOO phenotype.We conducted a prospective population-based study of 3,052 male and female Spaniards aged 25–74 years who were followed from 2000 through 2009. Diet and leisure-time physical activity were recorded on validated questionnaires. Weight, height, WC, blood lipids, glycemia, and blood pressure were measured. All variables were obtained at baseline (BL) and follow-up (FL). Participants with a BMI ≥ 25 kg/m2 and free from hypercholesterolemia, hypertriglyceridemia, diabetes, hypertension, and low HDL and high LDL cholesterol levels were characterized as the MHOO phenotype. A composite healthy lifestyle index (HLI) was constructed by including temporary changes in 3 lifestyle variables (diet, leisure-time physical activity, and smoking).Initially, 20.8 % of subjects had the MHOO phenotype; 49.2 % of these shifted to MAOO phenotype. In multivariate analysis, changes in BMI, WC, WHtR were positively associated (p = 0.004, p = 0.018, and p = 0.016, respectively) with this transition. One unit increase in the HLI was associated with a 33 % lower risk (p = 0.025) to the MAOO phenotype transition after adjusting for age, sex, educational level, and baseline energy intake, BMI, WC, and WHtR.The presence of metabolic disorders in the MHOO phenotype is predicted by an increase in anthropometric surrogate measures of general and abdominal adiposity. In contrast, a healthy lifestyle protects against a transition to the MAOO phenotype.
Keywords: Lifestyle; Diet; Prospective study; Metabolically healthy obese phenotype

Short-term creatine supplementation does not reduce increased homocysteine concentration induced by acute exercise in humans by Rafael Deminice; Flávia Troncon Rosa; Gabriel Silveira Franco; Selma Freirede Carvalho da Cunha; Ellen Cristini de Freitas; Alceu Afonso Jordao (1355-1361).
The purpose of the study is to evaluate the effects of creatine supplementation on homocysteine (Hcy) plasma levels after acute exercise in humans.Twenty-three young (under-20) soccer players were divided into 2 groups: creatine (Cr)- and placebo (Pla)-supplemented groups. The supplementation was performed in double-blind controlled manner using creatine or placebo tablets with 0.3 g/kg during 7 days. Before and after 7 days of supplementation, the athletes performed an acute high-intensity sprint exercise (two consecutive running-based anaerobic sprint test protocol consisted in 6 × 35 m sprint with 10 s between them). Blood samples were collected before and after 7 days of supplementation as well as 0 and 1 h after exercise protocol.Homocysteine concentration significant increased (P < 0.05) 1 h after acute exercise (18 %). Acute exercise also decreased red blood cell S-adenosylmethionine (SAM) 30 % with no changes in SAM/SAH ratio. Seven days of creatine supplementation were able to increase (P < 0.05) plasma creatine concentration (Pla 130.1 ± 21.7 vs Cr 1,557.2 ± 220.3 μmol/L) as well as decrease (P < 0.05) plasma guanidinoacetic acid (33 %). Controversially, creatine supplementation did not change Hcy plasma level after 7-day supplementation (Pla 6.9 ± 0.2 vs Cr 7.2 ± 0.2 μmol/L) or after acute exercise (Pla 8.2 ± 0.3 vs Cr 8.4 ± 0.3 μmol/L). No changes in plasma vitamin B12 and folate as well as cysteine and methionine were found.Seven days of creatine supplementation does not avoid increased plasma Hcy induced by acute sprint exercise in humans.
Keywords: Creatine supplementation; Homocysteine; Acute exercise; Humans

Diets high in total antioxidant capacity improve risk biomarkers of cardiovascular disease: a 9-month observational study among overweight/obese postmenopausal women by Ying Wang; Meng Yang; Sang-Gil Lee; Catherine G. Davis; Sung I. Koo; Maria Luz Fernandez; Jeff S. Volek; Ock K. Chun (1363-1369).
Previous studies have shown that total antioxidant capacity (TAC) of typical diets is associated with higher plasma TAC and antioxidant enzyme activities. At present, however, little is known for the association between dietary TAC and inflammatory biomarkers.The present study was designed to examine the association between dietary TAC and inflammatory biomarkers in a group of overweight/obese postmenopausal women, a population with high cardiovascular disease (CVD) risk, during a 9-month period.Thirty-five postmenopausal, overweight or obese, but apparently healthy women aged 40–70 years were recruited for a 9-month observational study. Seven-day food records and 12-h fasting blood samples were collected at baseline and at the end of the study for dietary and plasma biomarker assessments. Dietary TAC was calculated theoretically for taking account of both diet and dietary supplements, and energy-adjusted values were obtained using residual method.At baseline, subjects consuming diets with high dietary TAC had lower levels of plasma C-reactive protein (CRP) and monocyte chemoattractant protein-1 (p < 0.05) compared with those with low dietary TAC. Over the 9-month period, change in dietary TAC had a negative partial correlation with plasma CRP levels (p < 0.01) when age, ethnicity, and changes in BMI, blood total cholesterol and triglyceride were adjusted.Findings suggest that consumption of diets high in TAC are inversely associated with plasma CRP levels cross-sectionally and dynamically and may contribute to CVD protection.
Keywords: Dietary total antioxidant capacity (TAC); Cardiovascular disease; Inflammation; C-reactive protein (CRP); Postmenopausal women

The association between urinary phytoestrogen excretion and components of the metabolic syndrome in NHANES by Tristan Struja; Aline Richard; Jakob Linseisen; Monika Eichholzer; Sabine Rohrmann (1371-1381).
Metabolic syndrome is a major risk factor for cardiovascular diseases, which are still the major cause of death in developed countries.We cross-sectionally studied the association between urinary phytoestrogen excretion and metabolic cardiovascular risk factors. Hence, we used data from the National Health and Nutrition Examination Survey from 1999 to 2004 with 1,748 participants, who had urine levels of isoflavones and lignans measured. Geometric means of waist circumference, blood pressure, fasting glucose, HDL cholesterol, and triglyceride levels were computed by quartiles of isoflavone or lignan urinary excretion. Outcome was assessed as the presence of metabolic syndrome according to NCEP-ATP III criteria. The association between phytoestrogen concentration and the metabolic syndrome was calculated using logistic regression analyses.Plasma triglyceride and HDL cholesterol levels were lower in participants in the highest quartile of lignan excretion compared with the lowest (both P < 0.01). However, blood pressure, waist circumference, and plasma glucose levels did not differ significantly between extreme quartiles. The presence of metabolic syndrome was lower with increasing levels of urinary lignans (OR 0.48, 95 % CI 0.28; 0.80 top vs. bottom quartile), especially when separately computed for the excretion of enterolactone (OR 0.47, 95 % CI 0.28; 0.78). There was no significant association between isoflavone excretion and any component of the metabolic syndrome.Our study shows that an increasing excretion of lignans, especially enterolactone, might be associated with a decreased presence of the metabolic syndrome.
Keywords: Metabolic syndrome; Phytoestrogens; Isoflavones; Lignans; NHANES

Effect of white tea (Camellia sinensis (L.)) extract in the glycolytic profile of Sertoli cell by A. D. Martins; M. G. Alves; R. L. Bernardino; T. R. Dias; B. M. Silva; P. F. Oliveira (1383-1391).
Many health benefits have been attributed to tea (Camellia sinensis (L.)), and tea infusions are used as dietary agent and included in food supplements. Herein, we report the effect of a white tea (WTEA) extract in Sertoli cell (SC) metabolism. The SC is responsible for the nutritional support of the developing germ cells.An aqueous WTEA extract was prepared and analyzed by 1H-NMR. Rat SCs were cultured with or without the WTEA extract. mRNA and protein levels of glucose transporters (GLUT1 and GLUT3), phosphofructokinase, lactate dehydrogenase (LDH) and monocarboxylate transporter 4 were determined by qPCR and western blot. LDH activity was assessed and metabolite production/consumption determined by 1H-NMR.WTEA-exposed SCs presented decreased protein and mRNA levels of GLUT1 and decreased glucose uptake. However, intracellular LDH activity was increased and SC lactate production was stimulated by the presence of the WTEA extract. Interestingly, alanine production was also found to be stimulated in WTEA extract-exposed SCs.WTEA extract altered the glycolytic profile of cultured SCs, stimulating lactate production. Since lactate is used as metabolic substrate and has an anti-apoptotic effect in the developing germ cells, the supplementation with WTEA extract may be advantageous to improve male reproductive health.
Keywords: White tea; Camellia sinensis (L.); Sertoli; Metabolism; Lactate

Hepatic inflammation induced by high-fructose diet is associated with altered 11βHSD1 expression in the liver of Wistar rats by Ana Vasiljević; Biljana Bursać; Ana Djordjevic; Danijela Vojnović Milutinović; Marina Nikolić; Gordana Matić; Nataša Veličković (1393-1402).
High fructose consumption provokes metabolic perturbations that result in chronic low-grade inflammation and insulin resistance. Glucocorticoids, potent anti-inflammatory hormones, have important role in pathogenesis of diet-induced metabolic disturbances. The aim of this study was to examine the link between glucocorticoid metabolism and inflammation in the liver of fructose-fed rats. Fructose-fed male Wistar rats consumed 60 % fructose solution for 9 weeks. Glucocorticoid prereceptor metabolism and signaling were analyzed by measuring the level of 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and hexose-6-phosphate dehydrogenase expression, as well as via determination of intracellular corticosterone concentration, glucocorticoid receptor subcellular distribution and expression of its target gene, phosphoenolpyruvate carboxykinase. Nuclear factor kappa B (NFκB), tumor necrosis factor alpha (TNFα) and the level of inhibitory phosphorylation of insulin receptor substrate-1 (IRS-1) on Ser307 were analyzed as markers of hepatic inflammation. The protein and/or mRNA levels of all examined molecules were assessed by Western blot and/or qPCR.Fructose-rich diet led to an enhancement of 11βHSD1 protein level in the liver, without affecting intracellular level of corticosterone and downstream glucocorticoid signaling. On the other hand, proinflammatory state was achieved through NFκB activation and increased TNFα expression, while elevated level of inhibitory phosphorylation of IRS-1 was observed as an early hallmark of insulin resistance.High-fructose diet does not influence hepatic glucocorticoid signaling downstream of the receptor, permitting development of NFκB-driven inflammation. The alteration in 11βHSD1 expression is most likely the consequence of enhanced inflammation, finally leading to disruption of insulin signaling in the rat liver.
Keywords: 11βHSD1; Glucocorticoids; Inflammation; Fructose; Liver

Repeated versus single measurement of plasma omega-3 fatty acids and risk of heart failure by Luc Djoussé; Andrew B. Petrone; Natalie L. Weir; Naomi Q. Hanson; Robert J. Glynn; Michael Y. Tsai; J. Michael Gaziano (1403-1408).
Studies have previously examined the relation between a single measure of plasma fatty acids and risk of heart failure. However, it is unclear whether the use of repeated measures of fatty acids over time is required for the assessment of omega-3 fatty acids heart failure relation.Using a nested case–control design, this ancillary study used 421 cases and 421 matched controls from the Physicians’ Health Study to assess the variability of plasma phospholipid fatty acids over time and compare the results of omega-3 fatty acids heart failure associations using a single versus repeated measurements of plasma phospholipid fatty acids. Plasma omega-3 fatty acids were measured at baseline (1982) and approximately 15 years later using gas chromatography.Spearman’s correlation coefficients between baseline and follow-up measures of α-linolenic acid (ALA), EPA, DPA, and DHA were 0.20, 0.45, 0.28, and 0.50, respectively, in the control series. Multivariable adjusted odds ratios for heart failure per standard deviation higher plasma ALA were 0.98 (95 % CI 0.85–1.13) when using baseline ALA and 0.86 (95 % CI 0.74–1.01) when using the average of baseline and follow-up ALA measurements. Corresponding odds ratios for total long chain omega-3 FAs (EPA + DHA + DPA) were 0.87 (0.73–1.03) and 0.88 (0.75–1.04).Our data demonstrate modest correlation between measurements of plasma phospholipid fatty acids spaced by 15 years. A single measurement of plasma phospholipid fatty acids appears reasonable to estimate the risk of heart failure over long-term follow-up.
Keywords: Epidemiology; Omega-3 fatty acids; Methodology; Heart failure

Dietary fructose-related adiposity and glucocorticoid receptor function in visceral adipose tissue of female rats by Sanja Kovačević; Jelena Nestorov; Gordana Matić; Ivana Elaković (1409-1420).
Excessive fructose intake coincides with the growing rate of obesity and metabolic syndrome, with women being more prone to these disorders than men. Findings that detrimental effects of fructose might be mediated by glucocorticoid regeneration in adipose tissue only indirectly implicated glucocorticoid receptor (GR) in the phenomenon. The aim of the present study was to elucidate whether fructose overconsumption induces derangements in GR expression and function that might be associated with fructose-induced adiposity in females.We examined effects of fructose-enriched diet on GR expression and function in visceral adipose tissue of female rats. Additionally, we analyzed the expression of genes involved in glucocorticoid prereceptor metabolism [11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and hexose-6-phosphate dehydrogenase], lipolysis (hormone-sensitive lipase) and lipogenesis (sterol regulatory element binding protein 1 and peroxisomal proliferator-activated receptor γ).Fructose-fed rats had elevated energy intake that resulted in visceral adiposity, as indicated by increased visceral adipose tissue mass and its share in the whole-body weight. GR hormone binding capacity and affinity, as well as the expression of GR gene at both mRNA and protein levels were reduced in visceral adipose tissue of the rats on fructose diet. The glucocorticoid prereceptor metabolism was stimulated, as evidenced by elevated tissue corticosterone, while the key regulators of lipolysis and lipogenesis remained unaffected by fructose diet.The results suggest that the 11βHSD1-mediated elevation of intracellular corticosterone may induce GR downregulation, which may be associated with failure of GR to stimulate lipolysis in fructose-fed female rats.
Keywords: Fructose diet; Glucocorticoid receptor; 11βHSD1; Visceral adipose tissue; Adiposity; Female rats

Impact of a very low-energy diet on the fecal microbiota of obese individuals by C. D. Simões; J. Maukonen; K. P. Scott; K. A. Virtanen; K. H. Pietiläinen; M. Saarela (1421-1429).
Study how the dietary intake affects the fecal microbiota of a group of obese individuals after a 6-week very low-energy diet (VLED) and thereafter during a follow-up period of 5, 8, and 12 months. Additionally, we compared two different methods, fluorescent in situ hybridization (FISH) and real-time PCR (qPCR), for the quantification of fecal samples.Sixteen subjects participated in a 12-month dietary intervention which consisted of a VLED high in protein and low in carbohydrates followed by a personalized diet plan, combined with exercise and lifestyle counseling. Fecal samples were analyzed using qPCR, FISH, and denaturing gradient gel electrophoresis.The VLED affected the fecal microbiota, in particular bifidobacteria that decreased approximately two logs compared with the baseline numbers. The change in numbers of the bacterial groups studied followed the dietary intake and not the weight variations during the 12-month intervention. Methanogens were detected in 56 % of the participants at every sampling point, regardless of the dietary intake. Moreover, although absolute numbers of comparable bacterial groups were similar between FISH and qPCR measurements, relative proportions were higher according to FISH results.Changes in the fecal microbial numbers of obese individuals were primarily affected by the dietary intake rather than weight changes.
Keywords: Obesity; Human fecal microbiota; Very low-energy diet; Weight loss

Dietary factors associated with metabolic risk score in Finnish children aged 6–8 years: the PANIC study by A. M. Eloranta; V. Lindi; U. Schwab; S. Kiiskinen; T. Venäläinen; H. M. Lakka; D. E. Laaksonen; T. A. Lakka (1431-1439).
Previous evidence for the associations of eating frequency and food consumption with clustering of metabolic risk factors among children is limited. We therefore investigated association of the daily number of main meals and snacks and food consumption with a metabolic risk score and individual metabolic risk factors in primary school children.The subjects were a population sample of Finnish girls and boys 6–8 years of age. Dietary factors were measured by a four-day food record. Metabolic risk score was calculated summing up the Z-scores of waist circumference, systolic and diastolic blood pressure, and concentrations of fasting serum insulin and fasting plasma glucose, triglycerides and high-density lipoprotein cholesterol, the latest multiplying by −1.Skipping main meals (standardized regression coefficient β = −0.18, P < 0.001), a higher consumption of non-root vegetables (β = 0.18, P < 0.01), low-fat vegetable-oil-based margarine (β = 0.13, P < 0.01) and sugar-sweetened beverages (β = 0.11, P < 0.05) and a lower consumption of vegetable oils (β = −0.10, P < 0.05) were associated with a higher metabolic risk score after adjustment for age, sex, total physical activity, electronic media time, energy intake and other dietary factors. The consumption of red meat was directly related to the metabolic risk score, but the association was not statistically significant after adjustment for energy intake.Eating main meals regularly, decreasing the consumption of sugar-sweetened beverages and low-fat margarine and increasing the consumption of vegetable oils should be emphasized to reduce metabolic risk among children.
Keywords: Metabolic risk score; Diet; Food consumption; Main meals; Children

High-fat feeding increases hepatic vitamin C synthesis and its circulatory mobilization in mice by Britt Tranberg; Axel Kornerup Hansen; Jens Lykkesfeldt (1441-1444).
Vitamin C (vitC) deficiency has been linked to obesity and increased risk of cardiovascular disease and type 2 diabetes. Whereas humans are unable to synthesize vitC and therefore to compensate for increased turnover, we investigated whether mice—independent of dietary vitC—are able to modulate their vitC homeostasis during high-fat (HF) feeding.Twenty-five male 5-week-old C57BL/6 mice were fed high- or low-fat diets for 14 weeks. An oral glucose tolerance test (OGTT) was performed after 12 weeks of intervention. Terminal fasting plasma samples were analyzed for insulin, glucose and vitC concentrations. Hepatic vitC concentration and gulonolactone oxidase (GLO) capacity, as a measure of vitC de novo biosynthesis, were analyzed in liver homogenates.HF diet significantly increased plasma concentrations of vitC compared with a control diet low in fat (P < 0.05). Hepatic de novo biosynthesis of vitC was upregulated (P < 0.05) as measured by GLO capacity, and liver vitC was reduced (P < 0.01) by HF feeding compared with low-fat feeding. Moreover, plasma concentration of vitC was significantly positively correlated with plasma glucose and insulin concentrations as well as glucose intolerance as measured by an OGTT (P < 0.05).Our data suggest that mice have the ability to adapt to increased vitC turnover induced by HF diet by increasing hepatic de novo synthesis and mobilization.
Keywords: Vitamin C; Diet-induced obesity; High-fat diet; Mice