Yvonne Schwarz

A low-glycemic load diet reduces serum C-reactive protein and modestly increases adiponectin in overweight and obese adults.

Low-glycemic load (GL) diets improve insulin resistance and glucose homeostasis in individuals with diabetes. Less is known about whether low-GL diets, independent of weight loss, improve the health profile for persons without diabetes or other preexisting conditions. We conducted a randomized, cross-over feeding study testing low- compared to High-GL diets on biomarkers of inflammation and adiposity in healthy adults. Eighty participants (n = 40 with BMI 18.5-24.9 kg/m²; n = 40 with BMI 28.0-40.0 kg/m²) completed two 28-d feeding periods in random order where one period was a high-GL diet (mean GL/d = 250) and the other a low-GL diet (mean GL/d = 125). Diets were isocaloric with identical macronutrient content (as percent energy). All food was provided and participants maintained weight and usual physical activity. Height, weight, and DXA were measured at study entry and weight assessed again thrice per week. Blood was drawn from fasting participants at the beginning and end of each feeding period and serum concentrations of high-sensitivity CRP, serum amyloid A, IL-6, leptin, and adiponectin were measured. Linear mixed models tested the intervention effect on the biomarkers; models were adjusted for baseline biomarker concentrations, diet sequence, feeding period, age, sex, and body fat mass. Among participants with high-body fat mass (>32.0% for males and >25.0% for females), the low-GL diet reduced CRP (P = 0.02) and marginally increased adiponectin (P = 0.06). In conclusion, carbohydrate quality, independent of energy, is important. Dietary patterns emphasizing low-GL foods may improve the inflammatory and adipokine profiles of overweight and obese individuals.

Cruciferous Vegetable Feeding Alters UGT1A1 Activity : Diet-and Genotype-Dependent Changes in Serum Bilirubin in a Controlled Feeding Trial

Chemoprevention by isothiocyanates from cruciferous vegetables occurs partly through up-regulation of phase II conjugating enzymes, such as UDP-glucuronosyltransferases (UGT). UGT1A1 glucuronidates bilirubin, estrogens, and several dietary carcinogens. The UGT1A1*28 polymorphism reduces transcription compared with the wild-type, resulting in decreased enzyme activity. Isothiocyanates are metabolized by glutathione S-transferases (GST); variants may alter isothiocyanate clearance such that response to crucifers may vary by genotype. We evaluated, in a randomized, controlled, crossover feeding trial in humans (n = 70), three test diets (single- and double-“dose” cruciferous and cruciferous plus apiaceous) compared with a fruit and vegetable–free basal diet. We measured serum bilirubin concentrations on days 0, 7, 11, and 14 of each 2-week feeding period to monitor UGT1A1 activity and determined effects of UGT1A1*28 and GSTM1/GSTT1-null variants on response. Aggregate bilirubin response to all vegetable-containing diets was statistically significantly lower compared with the basal diet (P < 0.03 for all). Within each UGT1A1 genotype, lower bilirubin concentrations were seen in *1/*1 in both single- and double-dose cruciferous diets compared with basal (P < 0.03 for both); *1/*28 in double-dose cruciferous and cruciferous plus apiaceous compared with basal, and cruciferous plus apiaceous compared with single-dose cruciferous (P < 0.02 for all); and *28/*28 in all vegetable-containing diets compared with basal (P < 0.02 for all). Evaluation of the effects of diet stratified by GST genotype revealed some statistically significant genotypic differences; however, the magnitude was similar and not statistically significant between genotypes. These results may have implications for altering carcinogen metabolism through dietary intervention, particularly among UGT1A1*28/*28 individuals.

Metabolomic profiling of urine: response to a randomised, controlled feeding study of select fruits and vegetables, and application to an observational study.

Metabolomic profiles were used to characterise the effects of consuming a high-phytochemical diet compared with a diet devoid of fruits and vegetables (F&V) in a randomised trial and cross-sectional study. In the trial, 8 h fasting urine from healthy men (n 5) and women (n 5) was collected after a 2-week randomised, controlled trial of two diet periods: a diet rich in cruciferous vegetables, citrus and soya (F&V), and a fruit- and vegetable-free (basal) diet. Among the ions found to differentiate the diets, 176 were putatively annotated with compound identifications, with forty-six supported by MS/MS fragment evidence. Metabolites more abundant in the F&V diet included markers of the dietary intervention (e.g. crucifers, citrus and soya), fatty acids and niacin metabolites. Ions more abundant in the basal diet included riboflavin, several acylcarnitines and amino acid metabolites. In the cross-sectional study, we compared the participants based on the tertiles of crucifers, citrus and soya from 3 d food records (n 36) and FFQ (n 57); intake was separately divided into the tertiles of total fruit and vegetable intake for FFQ. As a group, ions individually differential between the experimental diets differentiated the observational study participants. However, only four ions were significant individually, differentiating the third v. first tertile of crucifer, citrus and soya intake based on 3 d food records. One of these ions was putatively annotated: proline betaine, a marker of citrus consumption. There were no ions significantly distinguishing tertiles by FFQ. The metabolomic assessment of controlled dietary interventions provides a more accurate and stronger characterisation of the diet than observational data.

Reliability of serum biomarkers of inflammation from repeated measures in healthy individuals.

Background: Biomarkers of low-grade systemic inflammation are used to study the associations of inflammation with chronic diseases, including cancer. However, relatively little is known about the intraindividual variability of most of these measures. Methods: Fasting serum samples, collected at baseline and the end of ≥3-week washout periods in a four-diet crossover feeding trial, were used to measure the inflammatory markers high sensitivity C-reactive protein (hsCRP), interleukin (IL)-6, tumor necrosis factor (TNF)-α, IL-8, and soluble TNF receptor (sTNFR) I and II. Participants included 62 men and women for analyses of IL-6 and CRP and 56 for analyses of IL-8, TNF-α, and sTNFRs, aged 20 to 40, who were free of factors known to influence inflammation, for example, chronic disease, medication use, heavy alcohol use, smoking, and obesity (body mass index >30 kg/m2). Intraclass correlations (ICC) were estimated using random effects ANOVA, across all four time points (∼6 weeks apart). Results: ICCs for TNF-α and sTNFR I and II were very high: ICC = 0.92 [95% confidence interval (CI), 0.89–0.96], 0.92 (95% CI, 0.88–0.95), and 0.90 (95% CI, 0.85–0.94), respectively. ICCs for IL-8 and hsCRP were 0.73 (95% CI, 0.63–0.83) and 0.62 (95% CI, 0.49–0.75), respectively. The ICC for IL-6 was considerably lower, ICC = 0.48 (95% CI, 0.36–0.62). Three measures of IL-6 would be needed to achieve a reliability coefficient (Cronbach α) of 0.75. Conclusions: With the exception of IL-6, reliability of all inflammatory markers in our panel was high. Impact: This suggests that a single measure accurately captures the short-term (e.g., 4–6 months) variability within an individual. Cancer Epidemiol Biomarkers Prev; 21(7); 1167–70. ©2012 AACR.

UGT1A6 and UGT2B15 Polymorphisms and Acetaminophen Conjugation in Response to a Randomized, Controlled Diet of Select Fruits and Vegetables

Acetaminophen (APAP) glucuronidation is thought to occur mainly by UDP-glucuronosyltransferases (UGT) in the UGT1A family. Interindividual variation in APAP glucuronidation is attributed in part to polymorphisms in UGT1As. However, evidence suggests that UGT2B15 may also be important. We evaluated, in a controlled feeding trial, whether APAP conjugation differed by UGT1A6 and UGT2B15 genotypes and whether supplementation of known dietary inducers of UGT (crucifers, soy, and citrus) modulated APAP glucuronidation compared with a diet devoid of fruits and vegetables (F&V). Healthy adults (n = 66) received 1000 mg of APAP orally on days 7 and 14 of each 2-week feeding period and collected saliva and urine over 12 h. Urinary recovery of the percentage of the APAP dose as free APAP was higher (P = 0.02), and the percentage as APAP glucuronide (APAPG) was lower (P = 0.004) in women. The percentage of APAP was higher among UGT1A6*1/*1 genotypes, relative to *1/*2 and *2/*2 genotypes (P = 0.045). For UGT2B15, the percentage of APAPG decreased (P < 0.0001) and that of APAP sulfate increased (P = 0.002) in an allelic dose-dependent manner across genotypes from *1/*1 to *2/*2. There was a significant diet × UGT2B15 genotype interaction for the APAPG ratio (APAPG/total metabolites × 100) (P = 0.03), with *1/*1 genotypes having an approximately 2-fold higher F&V to basal diet difference in response compared with *1/*2 and *2/*2 genotypes. Salivary APAP maximum concentration (Cmax) was significantly higher in women (P = 0.0003), with F&V (P = 0.003), and among UGT1A6*2/*2 and UGT2B15*1/*2 genotypes (P = 0.02 and 0.002, respectively). APAP half-life was longer in UGT2B15*2/*2 genotypes with F&V (P = 0.009). APAP glucuronidation was significantly influenced by the UGT2B15*2 polymorphism, supporting a role in vivo for UGT2B15 in APAP glucuronidation, whereas the contribution of UGT1A6*2 was modest. Selected F&V known to affect UGT activity led to greater glucuronidation and less sulfation.

UGT1A6 polymorphism and salicylic acid glucuronidation following aspirin.

Objectives In vivo, aspirin (acetylsalicylic acid) is rapidly deacetylated to form salicylic acid, which then undergoes primary or secondary glucuronidation catalyzed by UDP-glucuronosyltransferases (UGTs). The variant UGT1A6*2 (T181A, R184S) is associated with altered enzyme function. Our objective was to compare salicylic acid glucuronidation in individuals with different UGT1A6 genotypes. Methods Following orally dosing with 650 mg aspirin, saliva and urine samples were collected over a period of 24 h from healthy individuals with homozygous wild-type UGT1A6 *1/*1 (n=19) and homozygous variant UGT1A6 *2/*2 (T181A, R184S) (n=9) genotypes. Results No statistically significant differences were observed in salivary pharmacokinetic parameters. Urinary excretion of the sum of aspirin and its metabolites (salicyluric acid, salicyluric acid phenolic glucuronide, salicyl phenolic glucuronide, salicyl acyl glucuronide, salicylic acid) during the early period of 2–4 h of collection was significantly lower in UGT1A6 *1/*1 than in UGT1A6 *2/*2 individuals. Further, UGT1A6 *1/*1 individuals excreted a lower percentage of aspirin and its metabolites in the first 12 h and a greater percentage after 12 h than UGT1A6 *2/*2 individuals. Conclusions The variant UGT1A6*2 or polymorphisms in other UGTs that are in linkage disequilibrium with UGT1A6*2 may confer more rapid glucuronidation of salicylic acid than the wild-type UGT1A6 *1/*1.

Modulation of Human Serum Glutathione S-Transferase A1/2 Concentration by Cruciferous Vegetables in a Controlled Feeding Study Is Influenced by GSTM1 and GSTT1 Genotypes

Glutathione S-transferases (GST) detoxify a wide range of carcinogens. Isothiocyanates (ITC), from cruciferous vegetables, are substrates for and inducers of GST. GST variants may alter ITC clearance such that response to crucifers varies by genotype. In a randomized cross-over trial, we tested the hypothesis that changes in serum GSTA1/2 concentration in response to cruciferous vegetable feeding depends on GSTM1/GSTT1 genotype. Thirty-three men and 34 women (age 20-40 years) ate four 14-day controlled diets—basal (vegetable-free), basal supplemented with two different doses of crucifers (“single dose” and “double dose”), and single-dose cruciferous-plus-apiaceous vegetables—fed per kilogram of body weight. Fasting bloods from days 0, 7, 11, and 14 of each diet period were analyzed for serum GSTA1/2 by ELISA. GSTA1/2 increased with single- and double-dose cruciferous compared with basal diet (10% and 13%, respectively; P = 0.02 and 0.004), but cruciferous-plus-apiaceous did not differ from basal (P = 0.59). Overall, GSTA1/2 was higher in GSTM1-null/GSTT1-null than GSTM1+/GSTT1+ individuals (4,198 ± 338 and 3,372 ± 183 pg/mL; P = 0.03). The formal interaction of genotype-by-diet was not statistically significant, but the GSTA1/2 increase during the single-dose cruciferous diet was among GSTM1-null/GSTT1-null individuals (by 28%; P = 0.008), largely explained by GSTM1-null/GSTT1-null men (by 41%; P = 0.01). GSTA1/2 increased during the double-dose cruciferous diet in both GSTM1-null/GSTT1-null men (by 35%; P = 0.04) and GSTM1+/GSTT1+ men (by 26%; P = 0.01) but not in women. In summary, cruciferous vegetable supplementation increased GSTA1/2, but the effect was most marked in GSTM1-null/GSTT1-null men. (Cancer Epidemiol Biomarkers Prev 2009;18(11):2974–8)

CYP1A2, GSTM1, and GSTT1 polymorphisms and diet effects on CYP1A2 activity in a crossover feeding trial.

Cytochrome P-450 1A2 (CYP1A2) is a biotransformation enzyme that activates several procarcinogens. CYP1A2 is induced by cruciferous and inhibited by apiaceous vegetable intake. Using a randomized, crossover feeding trial in humans, we investigated the dose effects of cruciferous vegetables and the effects of any interaction between cruciferous and apiaceous vegetables on CYP1A2 activity. We also investigated whether response varied by CYP1A2*1F, GSTM1, and GSTT1 genotypes (glutathione S-transferases that metabolize crucifer constituents) and whether CYP1A2 activity rebounds after apiaceous vegetables are removed from the diet. Participants (N = 73), recruited based on genotypes, consumed four diets for two weeks each: low-phytochemical diet (basal), basal plus single dose of cruciferous (1C), basal plus double dose of cruciferous (2C), and basal plus single dose of cruciferous and apiaceous vegetables (1C+A). CYP1A2 activity was determined by urine caffeine tests administered at baseline and the end of each feeding period. Compared with basal diet, the 1C diet increased CYP1A2 activity (P < 0.0001) and the 2C diet resulted in further increases (P < 0.0001), with men experiencing greater dose-response than women. The 1C+A diet decreased CYP1A2 activity compared with the 1C and 2C diets (P < 0.0001 for both). Although there was no overall effect of CYP1A2*1F or GSTM1-null/GSTT1-null genotypes or genotype-by-diet interactions, there were significant diet response differences within each genotype. Additionally, CYP1A2 activity recovered modestly one day after the removal of apiaceous vegetables. These results suggest complex interactions among dietary patterns, genetic variation, and modulation of biotransformation that may not be apparent in observational studies. (Cancer Epidemiol Biomarkers Prev 2009;18(11):3118–25)

Glycemic load effect on fasting and post-prandial serum glucose, insulin, IGF-1 and IGFBP-3 in a randomized, controlled feeding study.

Background/objectives:The effect of a low glycemic load (GL) diet on insulin-like growth factor-1 (IGF-1) concentration is still unknown but may contribute to lower chronic disease risk. We aimed to assess the impact of GL on concentrations of IGF-1 and IGF-binding protein-3 (IGFBP-3).Subjects/methods:We conducted a randomized, controlled crossover feeding trial in 84 overweight obese and normal weight healthy individuals using two 28-day weight-maintaining high- and low-GL diets. Measures were fasting and post-prandial concentrations of insulin, glucose, IGF-1 and IGFBP-3. In all 80 participants completed the study and 20 participants completed post-prandial testing by consuming a test breakfast at the end of each feeding period. We used paired t-tests for diet component and linear mixed models for biomarker analyses.Results:The 28-day low-GL diet led to 4% lower fasting concentrations of IGF-1 (10.6 ng/ml, P=0.04) and a 4% lower ratio of IGF-1/IGFBP-3 (0.24, P=0.01) compared with the high-GL diet. The low-GL test breakfast led to 43% and 27% lower mean post-prandial glucose and insulin responses, respectively; mean incremental areas under the curve for glucose and insulin, respectively, were 64.3±21.8 (mmol/l/240 min; P<0.01) and 2253±539 (μU/ml/240 min; P<0.01) lower following the low- compared with the high-GL test meal. There was no effect of GL on mean homeostasis model assessment for insulin resistance or on mean integrated post-prandial concentrations of glucose-adjusted insulin, IGF-1 or IGFBP-3. We did not observe modification of the dietary effect by adiposity.Conclusions:Low-GL diets resulted in 43% and 27% lower post-prandial responses of glucose and insulin, respectively, and modestly lower fasting IGF-1 concentrations. Further intervention studies are needed to weigh the impact of dietary GL on risk for chronic disease.

LOW GLYCEMIC LOAD EXPERIMENTAL DIET MORE SATIATING THAN HIGH GLYCEMIC LOAD DIET

Effective strategies for reducing food intake are needed to reduce risk of obesity-related cancers. We investigated the effect of low and high glycemic load (GL) diets on satiety and whether satiety varied by body mass index (BMI), gender, and serum leptin. Eighty normal weight (BMI = 18.5–24.9 kg/m2) and overweight/ obese (BMI = 28.0–40.0 kg/m2) adults participated in a randomized, crossover controlled feeding study testing low GL vs. high GL diets. The 28-day diets were isocaloric with identical macronutrient distributions, differing only in GL and fiber. Participants completed visual analog satiety surveys and fasting serum leptin after each 28-day period. T-tests compared mean within- and between-person satiety scores and leptin values. Participants reported 7% greater satiation on the low GL vs. the high GL diet (P = 0.03) and fewer food cravings on the low GL vs. the high GL diet (P < 0.001). Compared to males, females reported less hunger (P = 0.05) and more satiety on the low GL vs. the high GL diet (P < 0.01). Participants with low body fat (<25.0% for men; <32.0% for women) and BMI <25.0 kg/m2 reported study food was tastier on the low GL vs. the high GL diet (P = 0.04 and P = 0.05, respectively). In summary, reducing GL, and/or increasing fiber, may be an effective way to lower calories consumed, improve energy balance, and ultimately reduce cancer risk.