"iDoctor – Medical Blog"

L-Arginine supplementation improves exercise capacity after a heart transplant.

Am J Clin Nutr. 2010 Mar 3;

Authors: Doutreleau S, Rouyer O, Di Marco P, Lonsdorfer E, Richard R, Piquard F, Geny B

BACKGROUND: Endothelial dysfunction is associated with the decreased exercise capacity observed in heart-transplant (HTx) recipients. l-Arginine supplementation (LAS) stimulates the nitric oxide (NO) pathway and restores endothelial function. OBJECTIVE: We compared exercise capacity in healthy subjects and HTx patients and investigated whether chronic LAS might improve exercise capacity and NO/endothelin balance after an HTx. DESIGN: Clinical, echocardiographic, and exercise characteristics were measured in 11 control subjects and 22 HTx recipients. In a prospective, double-blind study, the 22 HTx recipients performed a 6-min exercise [6-min-walk test (6MWT)] and a maximal bicycle exercise test before and after a 6-wk period of placebo intake or LAS. Endothelial function was measured by analyzing blood NO metabolites, endothelin, and the resulting NO/endothelin balance. RESULTS: Exercise capacity decreased after transplantation. Unlike with the placebo intake, a 6-wk LAS improved quality of life in HTx recipients (mean +/- SEM Minnesota Score: from 15.3 +/- 1.3 to 10.6 +/- 1.1; P < 0.001) and their submaximal exercise capacity. The distance walked during the 6MWT increased (from 525 +/- 20 to 580 +/- 20 m; P = 0.002), and the ventilatory threshold during the incremental test was delayed by 1.2 min (P = 0.01). Central factors such as resting stroke volume, systolic pulmonary arterial pressure, cardiac systolodiastolic functions, and heart-rate reserve were not modified, but LAS significantly increased the NO:endothelin ratio (from 2.49 +/- 0.38 to 3.31 +/- 0.39; P = 0.03). CONCLUSION: Oral LAS may be a useful adjuvant therapeutic to improve quality of life and exercise tolerance in HTx recipients.

PMID: 20200265 [PubMed - as supplied by publisher]

Selenium bioavailability: current knowledge and future research requirements.

Am J Clin Nutr. 2010 Mar 3;

Authors: Fairweather-Tait SJ, Collings R, Hurst R

Information on selenium bioavailability is required to derive dietary recommendations and to evaluate and improve the quality of food products. The need for robust data is particularly important in light of recent suggestions of potential health benefits associated with different intakes of selenium. The issue is not straightforward, however, because of large variations in the selenium content of foods (determined by a combination of geologic/environmental factors and selenium supplementation of fertilizers and animal feedstuffs) and the chemical forms of the element, which are absorbed and metabolized differently. Although most dietary selenium is absorbed efficiently, the retention of organic forms is higher than that of inorganic forms. There are also complications in the assessment and quantification of selenium species within foodstuffs. Often, extraction is only partial, and the process can alter the form or forms present in the food. Efforts to improve, standardize, and make more widely available techniques for species quantification are required. Similarly, reliable and sensitive functional biomarkers of selenium status are required, together with improvements in current biomarker methods. This requirement is particularly important for the assessment of bioavailability, because some functional biomarkers respond differently to the various selenium species. The effect of genotype adds a potential further dimension to the process of deriving bioavailability estimates and underlines the need for further research to facilitate the process of deriving dietary recommendations in the future.

PMID: 20200264 [PubMed - as supplied by publisher]

Iron bioavailability and dietary reference values.

Am J Clin Nutr. 2010 Mar 3;

Authors: Hurrell R, Egli I

Iron differs from other minerals because iron balance in the human body is regulated by absorption only because there is no physiologic mechanism for excretion. On the basis of intake data and isotope studies, iron bioavailability has been estimated to be in the range of 14-18% for mixed diets and 5-12% for vegetarian diets in subjects with no iron stores, and these values have been used to generate dietary reference values for all population groups. Dietary factors that influence iron absorption, such as phytate, polyphenols, calcium, ascorbic acid, and muscle tissue, have been shown repeatedly to influence iron absorption in single-meal isotope studies, whereas in multimeal studies with a varied diet and multiple inhibitors and enhancers, the effect of single components has been, as expected, more modest. The importance of fortification iron and food additives such as erythorbic acid on iron bioavailability from a mixed diet needs clarification. The influence of vitamin A, carotenoids, and nondigestible carbohydrates on iron absorption and the nature of the “meat factor” remain unresolved. The iron status of the individual and other host factors, such as obesity, play a key role in iron bioavailability, and iron status generally has a greater effect than diet composition. It would therefore be timely to develop a range of iron bioavailability factors based not only on diet composition but also on subject characteristics, such as iron status and prevalence of obesity.

PMID: 20200263 [PubMed - as supplied by publisher]

Bioconversion of dietary provitamin A carotenoids to vitamin A in humans.

Am J Clin Nutr. 2010 Mar 3;

Authors: Tang G

Recent progress in the measurement of the bioconversion of dietary provitamin A carotenoids to vitamin A is reviewed in this article. Methods to assess the bioavailability and bioconversion of provitamin A carotenoids have advanced significantly in the past 10 y, specifically through the use of stable isotope methodology, which includes the use of labeled plant foods. The effects of the food matrix on the bioconversion of provitamin A carotenoids to vitamin A, dietary fat effects, and the effect of genotype on the absorption and metabolism of beta-carotene have been reported recently. A summary of the major human studies that determined conversion factors for dietary beta-carotene to retinol is presented here, and these data show that the conversion efficiency of dietary beta-carotene to retinol is in the range of 3.6-28:1 by weight. There is a wide variation in conversion factors reported not only between different studies but also between individuals in a particular study. These findings show that the vitamin A value of individual plant foods rich in provitamin A carotenoids may vary significantly and need further investigation.

PMID: 20200262 [PubMed - as supplied by publisher]

Micronutrient bioavailability: Dietary Reference Intakes and a future perspective.

Am J Clin Nutr. 2010 Mar 3;

Authors: Hambidge KM

This article provides a review of how the challenge of bioavailability was approached in establishing the Dietary Reference Intakes (DRIs), with a special focus on folic acid, vitamin B-12, beta-carotene, iron, selenium, and zinc, the targeted micronutrients for this workshop. In a future perspective, the necessity of having a clear working definition of bioavailability is emphasized. The bioavailability of micronutrients should be considered, with advantage, under subheadings determined by the broad factors that affect bioavailability. Special emphasis is given to giving greater and specific attention to factors involved in the maintenance of homeostasis. These factors, it is argued, are best considered separately from even a broad definition of bioavailability and have the potential to provide new insights into some micronutrient requirements.

PMID: 20200261 [PubMed - as supplied by publisher]

Setting Dietary Reference Intakes with the use of bioavailability data: calcium.

Am J Clin Nutr. 2010 Mar 3;

Authors: Abrams SA

The determination of Dietary Reference Intakes (DRIs) for calcium, especially in children, has relied in significant part on the evaluation of the relation between calcium intake and calcium absorption and retention. At present, most of these studies are conducted with the use of dual-tracer stable isotope, although mass balance or other isotope methods are still used occasionally. Studies carried out to evaluate DRI values need to be conducted under the most controlled conditions possible. However, the achievement of such conditions can be difficult, especially in studies in small children, because strict, long-term dietary monitoring and sample collections are not well tolerated. Other dietary factors, which include vitamin D status and the presence of enhancers and inhibitors of calcium absorption, may have to be considered. However, for most healthy populations who do not have very low calcium intakes or serum 25-hydroxyvitamin D concentrations, other dietary factors will not be major determinants of the net calcium absorption or retention that will be used for the establishment of DRI values. Ultimately, DRI values must be chosen based on an attempt to achieve some targeted value for calcium absorption/retention or to maximize, within constraints, the overall calcium absorbed and retained. In children, it is important to use data obtained at the age and pubertal status being evaluated rather than to interpolate from data performed in other age groups.

PMID: 20200260 [PubMed - as supplied by publisher]

Dietary glycemic index and load in relation to risk of uterine leiomyomata in the Black Women’s Health Study.

Am J Clin Nutr. 2010 Mar 3;

Authors: Radin RG, Palmer JR, Rosenberg L, Kumanyika SK, Wise LA

BACKGROUND: High dietary glycemic index (GI) and glycemic load (GL) may promote tumorigenesis by increasing endogenous concentrations of insulin-like growth factor I (IGF-I) or the bioavailability of estradiol. In vitro studies have shown that uterine leiomyoma (UL) cells proliferate in response to IGF-I and display increased IGF-I gene expression and protein synthesis. Previous epidemiologic studies suggest that a high GL is a risk factor for endometrial and ovarian cancers, which, like UL, are hormone-responsive tumors. OBJECTIVE: We investigated the relation of dietary GI and GL with UL risk in the Black Women’s Health Study. DESIGN: In this prospective cohort study, we followed 21,861 premenopausal women for incident UL from 1997 to 2007. Diet was assessed in 1995 and 2001 with food-frequency questionnaires. We used Cox regression to estimate incidence rate ratios (IRRs) and 95% CIs, controlled for potential confounders. RESULTS: During 162,604 person-years of follow-up, there were 5800 cases of UL diagnosed by ultrasound or surgery. Dietary GI was weakly associated with UL risk overall (IRR for highest compared with lowest quintile: 1.09; 95% CI: 0.99, 1.19; P for trend = 0.04). Positive associations were observed between GL and UL in women aged <35 y (IRR for highest compared with lowest quintile: 1.18; 95% CI: 1.02, 1.37; P for trend = 0.15) and between GI and UL in college-educated women (IRR for highest compared with lowest quintile: 1.17; 95% CI: 1.03, 1.34; P for trend = 0.004). CONCLUSIONS: Our results suggest that high dietary GI and GL may be associated with an increased UL risk in some women. The observed associations warrant investigation in future studies.

PMID: 20200259 [PubMed - as supplied by publisher]

The effect of home-delivered Dietary Approach to Stop Hypertension (DASH) meals on the diets of older adults with cardiovascular disease.

Am J Clin Nutr. 2010 Mar 3;

Authors: Troyer JL, Racine EF, Ngugi GW, McAuley WJ

BACKGROUND: Many older adults with hyperlipidemia or hypertension participate in the Older Americans Act Nutrition Program, which serves meals in community settings and delivers meals to homes. However, there is little information regarding whether therapeutic meals designed around Dietary Approach to Stop Hypertension (DASH) principles have a beneficial effect on the diets of these older adults. OBJECTIVE: The objective of this study was to determine the degree to which dietary change is influenced by providing 7 home-delivered therapeutic meals weekly to adults aged >/=60 y. DESIGN: We conducted a 1-y randomized controlled trial in 298 persons with hyperlipidemia or hypertension, in which 50% of participants received 7 therapeutic meals per week for 12 mo. Those in need of dietary change at baseline (n = 210) were examined. Changes in intermediate DASH accordance, DASH accordance, and the nutrients that make up the DASH diet were measured by using 24-h food recalls at baseline, 6 mo, and 12 mo. Chi-square tests, t tests, and multiple regression were used to examine the association between receipt of meals and dietary change over time. RESULTS: Participants who received meals were 20% (P = 0.001) more likely to reach intermediate DASH accordance at 6 mo and were 18% (P = 0.007) more likely to meet saturated fat accordance at 12 mo than were those who did not receive meals. When stratified by race and income, gains were marginally larger for whites and higher-income individuals. CONCLUSION: Delivery of 7 DASH meals per week was found to increase compliance with dietary recommendations among noncompliant older adults with cardiovascular disease.

PMID: 20200258 [PubMed - as supplied by publisher]

Effect of conjugated linoleic acid on body fat accretion in overweight or obese children.

Am J Clin Nutr. 2010 Mar 3;

Authors: Racine NM, Watras AC, Carrel AL, Allen DB, McVean JJ, Clark RR, O’Brien AR, O’Shea M, Scott CE, Schoeller DA

BACKGROUND: Conjugated linoleic acid (CLA) is a supplemental dietary fatty acid that decreases fat mass accretion in young animals. OBJECTIVE: The aim of this study was to determine CLA’s efficacy with regard to change in fat and body mass index (BMI) in children. DESIGN: We conducted a 7- +/- 0.5-mo randomized, double-blind, placebo-controlled trial of CLA in 62 prepubertal children aged 6-10 y who were overweight or obese but otherwise healthy. The subjects were randomly assigned to receive 3 g/d of 80% CLA (50:50 cis-9,trans-11 and trans-10,cis-12 isomers) or placebo in chocolate milk. RESULTS: Fifty-three subjects completed the trial (n = 28 in the CLA group, n = 25 in the placebo group). CLA attenuated the increase in BMI (0.5 +/- 0.8) compared with placebo (1.1 +/- 1.1) (P = 0.05). The percentage change in body fat measured by dual-energy X-ray absorptiometry was smaller (P = 0.001) in the CLA group (-0.5 +/- 2.1%) than in the placebo group (1.3 +/- 1.8%). The change in abdominal body fat as a percentage of total body weight was smaller (P = 0.02) in the CLA group (-0.09 +/- 0.9%) than in the placebo group (0.43 +/- 0.6%). There were no significant changes in plasma glucose, insulin, or LDL cholesterol between groups. Plasma HDL cholesterol decreased significantly more (P = 0.05) in the CLA group (-5.1 +/- 7.3 mg/dL) than in the placebo group (-0.7 +/- 8 mg/dL). Bone mineral accretion was lower (P = 0.04) in the CLA group (0.05 +/- 0.03 kg) than in the placebo group (0.07 +/- 0.03 kg). Reported gastrointestinal symptoms did not differ significantly between groups. CONCLUSIONS: CLA supplementation for 7 +/- 0.5 mo decreased body fatness in 6-10-y-old children who were overweight or obese but did not improve plasma lipids or glucose and decreased HDL more than in the placebo group. Long-term investigation of the safety and efficacy of CLA supplementation in children is recommended.

PMID: 20200257 [PubMed - as supplied by publisher]

Orange juice neutralizes the proinflammatory effect of a high-fat, high-carbohydrate meal and prevents endotoxin increase and Toll-like receptor expression.

Am J Clin Nutr. 2010 Mar 3;

Authors: Ghanim H, Sia CL, Upadhyay M, Korzeniewski K, Viswanathan P, Abuaysheh S, Mohanty P, Dandona P

BACKGROUND: The intake of glucose or a high-fat, high-carbohydrate (HFHC) meal, but not orange juice, induces an increase in inflammation and oxidative stress in circulating mononuclear cells (MNCs) of normal-weight subjects. OBJECTIVE: We investigated the effect of orange juice on HFHC meal-induced inflammation and oxidative stress and the expression of plasma endotoxin and Toll-like receptors (TLRs). DESIGN: Three groups (10 subjects in each group) of normal, healthy subjects were asked to drink water or 300 kcal glucose or orange juice in combination with a 900-kcal HFHC meal. Blood samples were obtained before and 1, 3, and 5 h after the drinks and meal combinations were consumed. RESULTS: Protein expression of the NADPH oxidase subunit p47(phox), phosphorylated and total p38 mitogen-activated protein kinase, and suppressor of cytokine signaling-3; TLR2 and TLR4 messenger RNA (mRNA) and protein expression; mRNA expression of matrix metalloproteinase (MMP)-9 in MNCs; and plasma concentrations of endotoxin and MMP-9 increased significantly after glucose or water were consumed with the meal but not when orange juice was consumed with the meal. The generation of reactive oxygen species by polymorphonuclear cells was significantly lower when orange juice was added to the meal than when water or glucose was added to the meal. CONCLUSIONS: The combination of glucose or water and the HFHC meal induced oxidative and inflammatory stress and an increase in TLR expression and plasma endotoxin concentrations. In contrast, orange juice intake with the HFHC meal prevented meal-induced oxidative and inflammatory stress, including the increase in endotoxin and TLR expression. These observations may help explain the mechanisms underlying postprandial oxidative stress and inflammation, pathogenesis of insulin resistance, and atherosclerosis.

PMID: 20200256 [PubMed - as supplied by publisher]