Fructose metabolism in humans - what isotopic tracer studies tell us.

Fructose consumption and its implications on public health are currently under study. This work reviewed the metabolic fate of dietary fructose based on isotope tracer studies in humans. The mean oxidation rate of dietary fructose was 45.0% ± 10.7 (mean ± SD) in non-exercising subjects within 3-6 hours and 45.8% ± 7.3 in exercising subjects within 2-3 hours. When fructose was ingested together with glucose, the mean oxidation rate of the mixed sugars increased to 66.0% ± 8.2 in exercising subjects. The mean conversion rate from fructose to glucose was 41% ± 10.5 (mean ± SD) in 3-6 hours after ingestion. The conversion amount from fructose to glycogen remains to be further clarified. A small percentage of ingested fructose (<1%) appears to be directly converted to plasma TG. However, hyperlipidemic effects of larger amounts of fructose consumption are observed in studies using infused labeled acetate to quantify longer term de novo lipogenesis. While the mechanisms for the hyperlipidemic effect remain controversial, energy source shifting and lipid sparing may play a role in the effect, in addition to de novo lipogenesis. Finally, approximately a quarter of ingested fructose can be converted into lactate within a few of hours. The reviewed data provides a profile of how dietary fructose is utilized in humans.

Fructose and non-fructose sugar intakes in the US population and their associations with indicators of metabolic syndrome.

BACKGROUND: Relationships of sugar intakes with indicators of metabolic syndrome are important concerns for public health and safety. For individuals, dietary intake data for fructose and other sugars are limited. METHOD: Descriptive statistics. The data from 25,506 subjects, aged 12-80 yr, contained in the NHANES 1999-2006 databases were analyzed for sugar intakes and health parameters. RESULTS: Dietary fructose was almost always consumed with other sugars. On average, fructose provided 37% of total simple sugar intake and 9% of energy intake. In more than 97% of individuals studied, fructose caloric contribution was lower than that of non-fructose sugars. Fructose and non-fructose sugar intakes had no positive association with blood concentrations of TG, HDL cholesterol, glycohemoglobin, uric acid, blood pressure, waist circumference, and BMI in the adults studied (aged 19 to 80 yr, n=17,749). CONCLUSION: Daily fructose intakes with the American diet averaged approximately 37% of total sugars and 9% of daily energy. Fructose was rarely consumed solely or in excess over non-fructose sugars. Fructose and non-fructose sugar ordinary consumption was not positively associated with indicators of metabolic syndrome, uric acid and BMI.

Lack of association between dietary fructose and hyperuricemia risk in adults.

BACKGROUND: High serum uric acid concentration (hyperuricemia) has been studied for its relationship with multiple adverse health outcomes, such as metabolic syndrome. Intervention studies have produced inconsistent outcomes for the relationship between fructose intake and serum uric acid concentration. METHODS: The association of dietary fructose intake with hyperuricemia risk in adults was examined using logistic regression and U.S. NHANES 1999-2004 databases. A total of 9,384 subjects, between the ages 20 and 80 years, without diabetes, cancer, or heart disease, were included. RESULTS: The highest added or total fructose intake (quartiles by grams or % energy) was not associated with an increase of hyperuricemia risk compared to the lowest intake with or without adjustment (odds ratios = 0.515-0.992). The associations of alcohol and fiber intakes with the risk were also determined. Compared to the lowest intake, the highest alcohol intake was associated with increased mean serum uric acid concentration (up to 16%, P < 0.001) and hyperuricemia risk (odds ratios = 1.658-1.829, P = 0.057- < 0.001); the highest fiber intake was correlated with decreases of uric acid concentration (up to 7.5%, P < 0.002) and lower risk (odds ratios = 0.448-0.478, P = 0.001- < 0.001). Adults who were over 50 y old, male, or obese had significantly greater risk. CONCLUSIONS: The data show that increased dietary fructose intake was not associated with increased hyperuricemia risk; while increased dietary alcohol intake was significantly associated with increased hyperuricemia risk; and increased fiber intake was significantly associated with decreased hyperuricemia risk. These data further suggest a potential effect of fructose consumption in an ordinary diet on serum uric acid differs from results found in some short-term studies using atypical exposure and/or levels of fructose administration.

A 13-week dietary toxicity study in rats of a Napin-Rich Canola Protein Isolate.

The objective was to study the safety of a Napin-Rich Canola Protein Isolate (NRCPI) fed to rats at various levels for 13-weeks. The study included four groups (20 animals/sex/group) of young Sprague Dawley rats. They were fed ad libitum with an AIN-93G based protein-free diet containing, respectively, 5%, 10% and 20% (w/w) NRCPI (test article) or 20% (w/w) vitamin-free casein (control article). Protein levels were adjusted at 18% in all groups with vitamin-free casein. Body weights, food consumption, locomotor activity and behavioral and clinical pathology parameters were recorded at various points in the study, followed by macroscopic examination, determination of organ weights and microscopic examination at termination. There were no test article-related effects on ophthalmology, functional observations, hematology, serum chemistry, urinalysis, organ weights and macroscopic or microscopic findings. Lower body weight gains were observed in the 10% NRCPI-treated males and the 20% NRCPI-treated males and females. The lower body weight gains were associated with significantly lower food consumption. Therefore, for NRCPI the No Observed Adversed Effect Level (NOAEL) was considered to be 20% (the highest fed level); equivalent to 12.46 g/kg BW/day for males and 14.95 g/kg BW/day for females. The NRCPI was considered safe under the tested conditions.

A 13-week sub-chronic dietary toxicity study of a cruciferin-rich canola protein isolate in rats.

The objective was to evaluate the safety of a cruciferin-rich canola protein isolate (Puratein) when fed as a protein source at various dietary levels to rats for 13-weeks. The study included four groups (20 animals/sex/group) of young Sprague Dawley rats. They were fed ad libitum with an AIN-93 G based protein-free diet added respectively with 5%, 10% and 20% (w/w) Puratein (test article) or 20% (w/w) vitamin-free casein (control article). Protein levels were adjusted in all groups at 18% using vitamin-free casein. Body weights, food consumption, locomotor activity and behavioral and clinical pathology parameters were recorded at various points of the study, followed by macroscopic examination, determination of organ weights and microscopic tissue examination. There were no test article-related effects on body weight, food consumption, clinical observations, functional observational battery, motor activity, clinical pathology, or ophthalmic examinations. A slightly higher thyroid/parathyroid weight (g/100g BW) noted in the 20% Puratein group was not correlated with histopathological changes. The no-observed-effect-level (NOEL) was 10%, whereas the no-observed-adverse-effect-level (NOAEL) was the highest fed level of 20%, equivalent to 11.24 g/kg BW/day for males and 14.11 g/kg BW/day for females. The cruciferin-rich canola protein isolate (Puratein) was considered safe under the conditions tested.

Effects of dietary flaxseed lignan extract on symptoms of benign prostatic hyperplasia.

A flaxseed lignan extract containing 33% secoisolariciresinol diglucoside (SDG) was evaluated for its ability to alleviate lower urinary tract symptoms (LUTS) in 87 subjects with benign prostatic hyperplasia (BPH). A randomized, double-blind, placebo-controlled clinical trial with repeated measurements was conducted over a 4-month period using treatment dosages of 0 (placebo), 300, or 600 mg/day SDG. After 4 months of treatment, 78 of the 87 subjects completed the study. For the 0, 300, and 600 mg/day SDG groups, respectively, the International Prostate Symptom Score (IPSS) decreased -3.67 +/- 1.56, -7.33 +/- 1.18, and -6.88 +/- 1.43 (mean +/- SE, P = .100, < .001, and < .001 compared to baseline), the Quality of Life score (QOL score) improved by -0.71 +/- 0.23, -1.48 +/- 0.24, and -1.75 +/- 0.25 (mean +/- SE, P = .163 and .012 compared to placebo and P = .103, < .001, and < .001 compared to baseline), and the number of subjects whose LUTS grade changed from "moderate/severe" to "mild" increased by three, six, and 10 (P = .188, .032, and .012 compared to baseline). Maximum urinary flows insignificantly increased 0.43 +/- 1.57, 1.86 +/- 1.08, and 2.7 +/- 1.93 mL/second (mean +/- SE, no statistical significance reached), and postvoiding urine volume decreased insignificantly by -29.4 +/- 20.46, -19.2 +/- 16.91, and -55.62 +/- 36.45 mL (mean +/- SE, no statistical significance reached). Plasma concentrations of secoisolariciresinol (SECO), enterodiol (ED), and enterolactone (EL) were significantly raised after the supplementation. The observed decreases in IPSS and QOL score were correlated with the concentrations of plasma total lignans, SECO, ED, and EL. In conclusion, dietary flaxseed lignan extract appreciably improves LUTS in BPH subjects, and the therapeutic efficacy appeared comparable to that of commonly used intervention agents of alpha1A-adrenoceptor blockers and 5alpha-reductase inhibitors.

Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects.

Lignans, derived from flaxseed, are phyto-oestrogens being increasingly studied for their health benefits. An 8-week, randomised, double-blind, placebo-controlled study was conducted in fifty-five hypercholesterolaemic subjects, using treatments of 0 (placebo), 300 or 600 mg/d of dietary secoisolariciresinol diglucoside (SDG) from flaxseed extract to determine the effect on plasma lipids and fasting glucose levels. Significant treatment effects were achieved (P < 0.05 to < 0.001) for the decrease of total cholesterol (TC), LDL-cholesterol (LDL-C) and glucose concentrations, as well as their percentage decrease from baseline. At weeks 6 and 8 in the 600 mg SDG group, the decreases of TC and LDL-C concentrations were in the range from 22.0 to 24.38 % respectively (all P < 0.005 compared with placebo). For the 300 mg SDG group, only significant differences from baseline were observed for decreases of TC and LDL-C. A substantial effect on lowering concentrations of fasting plasma glucose was also noted in the 600 mg SDG group at weeks 6 and 8, especially in the subjects with baseline glucose concentrations > or = 5.83 mmol/l (lowered 25.56 and 24.96 %; P = 0.015 and P = 0.012 compared with placebo, respectively). Plasma concentrations of secoisolariciresinol (SECO), enterodiol (ED) and enterolactone were all significantly raised in the groups supplemented with flaxseed lignan. The observed cholesterol-lowering values were correlated with the concentrations of plasma SECO and ED (r 0.128-0.302; P < 0.05 to < 0.001). In conclusion, dietary flaxseed lignan extract decreased plasma cholesterol and glucose concentrations in a dose-dependent manner.

Lack of findings for the association between obesity risk and usual sugar-sweetened beverage consumption in adults--a primary analysis of databases of CSFII-1989-1991, CSFII-1994-1998, NHANES III, and combined NHANES 1999-2002.

UNLABELLED: The relationship between obesity risk and sugar-sweetened beverage (SSB) consumption was examined together with multiple lifestyle factors. Statistical analysis was performed using population dietary survey databases of USDA CSFII 1989-1991, CSFII 1994-1996, CDC NHANES III, and combined NHANES 1999-2002. Totally, 38,409 individuals, ages 20-74 years, with accompanying data of dietary intake, lifestyle factors, and anthropometrics were included in the descriptive statistics and risk analysis. Analytical results indicate that obesity risk was significantly and positively associated with gender, age, daily TV/screen watching hours and dietary fat content, and negatively associated with smoking habit, education and physical activity; obesity risk was not significantly associated with SSB consumption pattern, dietary saturated fat content and total calorie intake. No elevated BMI values or increased obesity rates were observed in populations frequently consuming SSB compared to populations infrequently consuming SSB. Additionally, one-day food consumption data was found to overestimate SSB usual intake by up to 38.9% compared to the data of multiple survey days. CONCLUSION: multiple lifestyle factors and higher dietary fat intake were significantly associated with obesity risk. Populations who frequently consumed SSB, primarily HFCS sweetened beverages, did not have a higher obesity rate or increased obesity risk than that of populations which consumed SSB infrequently.

Isoflavone supplements containing predominantly genistein reduce hot flash symptoms: a critical review of published studies.

OBJECTIVE: Several reviews have evaluated the clinical evidence relating isoflavone treatment to the relief of menopausal hot flash symptoms. The majority of these reviews included a variety of isoflavone sources, often without discriminating between the identities of individual isoflavones contained in the study product. An evaluation of published studies using well-characterized isoflavone-containing supplements was conducted to determine whether the observed effects, or lack thereof, were attributable to differences in the composition of isoflavones in study products. DESIGN: Eleven studies that met the inclusion criteria were stratified according to specific isoflavone composition. RESULTS: All 11 studies contained similar total isoflavone doses. In five studies, involving a total of 177 treated participants, the study product provided more than 15 mg genistein (calculated as aglycone equivalents) per treatment. Each of these five studies consistently reported a statistically significant decrease in hot flash symptoms. In the six studies involving a total of 201 treated participants that provided less than 15 mg genistein per treatment, only one reported a statistically significant decrease in hot flash symptoms. Thus, the reduction in hot flashes was related to genistein dose, not total isoflavone content of the treatments. CONCLUSION: Reports concluding that isoflavone supplements do not significantly reduce hot flash symptoms may be incorrect. The lack of discrimination between individual isoflavones contained in heterogeneous isoflavone mixtures from differing sources can be misleading when designing studies, interpreting results, and conducting reviews. In light of these observations, evaluation of isoflavone effects should focus greater attention to the specific composition within supplements in future studies.