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Short-Term Isocaloric Intake of a Fructose- but not Glucose-Rich Diet Affects Bacterial Endotoxin Concentrations and Markers of Metabolic Health in Normal Weight Healthy Subjects

Mol Nutr Food Res, 2019; //doi: 10.1002/mnfr.201800868

Nier A, Brandt A, Rajcic D, et al.

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Objective

  • To
    determine if an isocaloric exchange of complex carbohydrates with fructose
    or glucose affects surrogate markers of liver health and vascular endothelial
    function in healthy normal weight young male and female adults. If so, the
    goal is to whether these effects are related to changes in markers of
    intestinal permeability like bacterial endotoxin and lipopolysaccharide
    binding protein (LBP).

Background

  • Dietary pattern and impairments of intestinal
    barrier function are thought to be critical in the development of
    metabolic impairments.
  • Results of animal studies employing
    pair-feeding models also suggest that consumption of fructose, particularly
    in combination with saturated fat, may be critical in the development of
    NAFLD, vascular dysfunction and hypertension.
  • However, results of short-term intervention
    studies in healthy humans show contradictory results regarding the effects
    of fructose on liver, which may be due marked differences in study design
    and duration. Further, data on the effects on vascular endothelium in
    humans to our knowledge are lacking. 

Methods

  • A total of 15 normal weight healthy subjects
    were enrolled in the study, and after three participants dropped out, only
    12 subjects were included in the final analysis.
  • All participants received a standardized diet
    for 4 days, which was based their individual caloric needs and the
    recommendations of the German Society of Nutrition. This was followed by a
    diet in which complex carbohydrates were either exchanged with fructose or
    glucose (25% of total energy intake) for 3 days.
  • All participants analyzed consumed both sugar-enriched
    diets after being dietary standardized for 4 days starting with the
    fructose intervention. Sugar interventions were separated by a washout
    period of at least 3 weeks during which all participants consumed their
    usual diet.
  • Nutritional intake was assessed using two independent
    24-h recalls conducted by an experienced nutritionist before the study.  Physical activity level was assessed
    using the World Health Organization’s Global Physical Activity Questionnaire.  Nutritional data and total energy
    expenditure were analyzed using the computer software EBISpro.
  • Fasting blood samples, anthropometric data and
    blood pressure were assessed at the beginning of the study, after
    consuming the standard diets and after the intervention periods.
  • Peripheral blood mononuclear cells (PBMCs), plasma
    endotoxin, liver transaminase and blood lipid concentrations were
    analyzed.

Findings

  • Following diet standardization, serum triglycerides and insulin levels increased significantly, while alanine aminotransferase (ALT) serum activity and bacterial endotoxin levels decreased.
  • Fasting insulin, glucose and triglyceride levels were not affected by either intervention diet.  Uric acid levels significantly decreased following the high glucose diet.
  • Plasma NOx levels, which are indicative of vascular endothelial dysfunction, were significantly lower after subjects had consumed the fructose-enriched diet for 3 days. This effect was not seen after subjects consumed the glucose-enriched diet.
  • ALT activity significantly increased after subjects consumed the fructose-enriched diet, as compared to the diet standardization phase. This effect was not seen after subjects consumed the glucose-enriched diet, and Aspartate aminotransferase (AST) activity was not altered by any of the dietary interventions.
  • Leptin and adiponection plasma concentrations were not affected by any of the diets, and non-significant increases in PAI-1 were noted following the consumption of the fructose-rich diet compared to the standard diet.
  • Plasma endotoxin concentrations increased significantly when subjects consumed the fructose-enriched diet for 3 days compared to the respective standard diet.  This effect was not seen after subjects consumed the glucose-enriched diet.  Plasma concentrations of LBP, d-lactate and l-citrulline levels were not changed after the consumption of either diet.
  • Expressions of TLR4, TLR2 and MYD88 mRNA in PBMCs were significantly increased after subjects had consumed the fructose-enriched diet but not after subjects received the glucose-enriched diets as compared to standard diet.

Conclusions

  • According to the authors, the results of this
    study may provide additional support of the  hypothesis that dietary fructose may be
    critical in the development of NAFLD and vascular endothelial dysfunction
    in humans and that, similar to the findings in animal studies, impairments
    of intestinal barrier function and an increased translocation of bacterial
    endotoxin may be critical.
  • Results of the present study suggest that at short-term
    glucose may not have these effects on parameters related to liver and
    vascular endothelial as well as intestinal barrier function.
  • Results of the present study also suggest that
    changing dietary pattern only for a few days may markedly impact liver,
    vascular endothelial and intestinal barrier function. However, molecular
    mechanisms involved and especially those underlying the effects of
    fructose on intestinal barrier function need to be determined in future
    studies.

Points to Consider

  • The small study sample and the inclusion of only
    young, healthy adults limits the generalization of this study’s findings.
  • Direct measurement of intestinal permeability
    and liver health was not included in the present study, as each was assessed
    via surrogate markers.
  • All study food and beverages were provided,
    mostly prepared and consumed in the study center. This does not reflect
    real-world experience and results would likely differ in a more realistic
    setting.

The post Short-Term Isocaloric Intake of a Fructose- but not Glucose-Rich Diet Affects Bacterial Endotoxin Concentrations and Markers of Metabolic Health in Normal Weight Healthy Subjects appeared first on FructoseFacts.

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