Digested wheat gluten inhibits binding between leptin and its receptor

Effects of a Paleolithic diet compared to a diabetes diet on leptin binding inhibition in secondary analysis of a randomised cross-over study

BACKGROUND

Beneficial effects from practising a Paleolithic diet as compared to a diabetes diet on weight, waist circumference, satiety, leptin, HbA1c and glucose control in randomised controlled trial participants with type 2 diabetes could be due to lower leptin resistance. Support for this hypothesis comes from an in vitro experiment that showed that digested wheat gluten, which is excluded from a Paleolithic diet, inhibits leptin from binding to its receptor, thus indicating a possible dietary cause of leptin resistance. However, the clinical relevance of the latter finding is unclear since removal of enzyme activity from the gluten digest by heat treatment also abolished leptin binding inhibition. Assessment of leptin binding inhibition in vivo is possible by comparison of total leptin levels with those of 'biologically active' leptin bound to its receptor (bioLep).

OBJECTIVES

To assess the effects of a Paleolithic diet compared to a diabetes diet on leptin binding inhibition and to replicate our in vitro study.

METHODS

BioLep and total leptin levels were measured in secondary analysis of fasting plasma samples from our open label random order three plus three-month long cross-over trial performed in 2005-2007, that compared a Paleolithic diet with a diabetes diet in participants with type 2 diabetes without insulin treatment (per protocol). BioLep was also measured in vitro for known recombinant leptin concentrations incubated with a series of concentrations of 10 kDa spin-filtered digested wheat gluten, with or without prior heat treatment, at 100ºC for 30 min and centrifugation.

RESULTS

There was no difference between diets when comparing differences between bioLep and total leptin levels and their ratio in the 13 participants, three women and 10 men, aged 52-74 years with a mean BMI of 30 kg/m2 and a mean diabetes duration of eight years. We found no carry-over or period effect for bioLep and total leptin. In vitro, wheat gluten digest inhibited leptin binding in a dose-dependent manner but not after heat treatment.

CONCLUSIONS

We found no leptin binding inhibition after the Paleolithic or diabetes diet, possibly due to its abolishment from cooking-related heat treatment of wheat gluten.

TRIAL REGISTRATION

Registered on 14/02/2007 at ClinicalTrials.gov Identifier: NCT00435240.

Randomised controlled trial of lifestyle interventions for abdominal obesity in primary health care

AIM

Assess effects on waist circumference from diet with or without cereal grains and with or without long-term physical exercise.

BACKGROUND

Elevated waist circumference is an indicator of increased abdominal fat storage and is accordingly associated with increased cardiovascular mortality. This is likely due to the association between lifestyle-induced changes in waist circumference and cardiovascular risk factors. Reductions in waist circumference may be facilitated by diet without cereal grains combined with long-term physical exercise.

METHODS

Two-year randomised controlled trial with factorial trial design in individuals at increased risk of cardiovascular disease with increased waist circumference. Participants were allocated diet based on current Swedish dietary guidelines with or without cereal grains (baseline diet information supported by monthly group sessions) and with or without physical exercise (pedometers and two initial months of weekly structured exercise followed by written prescription of physical activity) or control group. The primary outcome was the change in waist circumference.

FINDINGS

The greatest mean intervention group difference in the change in waist circumference among the 73 participants (47 women and 26 men aged 23-79 years) was at one year between participants allocated a diet without cereal grains and no exercise and participants allocated a diet with cereal grains and no exercise [M = -5.3 cm and -0.9 cm, respectively; mean difference = 4.4 cm, 4.0%, 95% CI (0.0%, 8.0%), P = 0.051, Cohen's d = 0.75]. All group comparisons in the change in waist circumference were non-significant despite the greatest group difference being more than double that estimated in the pre-study power calculation. The non-significance was likely caused by too few participants and a greater than expected variability in the change in waist circumference. The greatest mean intervention group difference strengthens the possibility that dietary exclusion of cereal grains could be related to greater reduction in waist circumference.

Effects of Wheat Bran Micronization on the Quality of Reconstituted Whole-Wheat Flour and Its Cooked Noodles

The particle size of wheat bran plays an important role in the quality of reconstituted whole-wheat flour and its products. The effects of wheat bran particle size on the quality of reconstituted whole-wheat flour and its cooked noodles were analyzed; the mean particle size (D50) of wheat bran ranged from 26.05 to 46.08 μm. Results show that the decreases in D50 of wheat bran induced the changes in the quality of whole-wheat flour and its noodles. Specifically, the damaged starch content, water absorption, and the solvent retention capacity of sodium carbonate and sucrose of whole-wheat flour increased at various degrees, while pasting viscosity decreased, and the gluten index and SDS-sedimentation volume increased first and then decreased. The cooking yield, cooking loss, and break rate of fresh noodles decreased first and reached a trough at D50 of 26.05 μm, and then increased. The adhesiveness of cooked noodles increased, the score of smoothness, taste, appearance, and color increased to a stable value, but the hardness, springiness, cohesiveness, resilience, firmness score, and elasticity score increased first and then decreased. These turning points of changing trends of indexes mostly occurred when the D50 of wheat bran was 26.51 μm. In conclusion, whole-wheat noodles with wheat bran of D50 of 26.51 μm addition exhibit better cooking, textural, and sensory properties than those with smaller or larger wheat bran. Excessive crushing of wheat bran not only costs highly in terms of energy, but also has a negative impact on the quality of the noodles.

Gluten consumption may contribute to worldwide obesity prevalence

Gluten consumption has been controversially associated with obesity in previous studies. We sought to examine this association at the worldwide level.

Country specific data were obtained from 168 countries. Scatter plots, bivariate, partial correlation and multiple linear regression models were used to explore and compare the coincidence between obesity prevalence and consumption of gluten, non-gluten cereal protein and total cereal protein respectively. The established risk factors of obesity: caloric intake, sedentary lifestyle, urbanization, socioeconomic status, meat protein intake and sugar consumption were included in analyses as potential confounders. The 168 countries were also stratified into developing and developed country groupings for further examination of the relationships.

Worldwide, bivariate correlation analyses revealed that the strength and direction of correlations between all variables (independent, dependent and potential confounders) were at similar levels. Obesity prevalence was positively correlated to gluten consumption but was negatively correlated to consumption of non-gluten cereal protein, and was in almost nil correlation to total cereal protein consumption. These relationships were similar across all countries (n= 168), developed country grouping (N=44) and developing country grouping (n=124). When caloric intake, Gross Domestic Product at Purchasing Power Parity, sedentary lifestyle and urbanization were kept statistically constant in the partial correlation analysis, obesity was significantly correlated to gluten consumption in all countries, developed country grouping and developing country grouping, and was significantly but inversely and weakly correlated to non-gluten cereal protein in all countries and developing countries, and was in almost nil correlation to total cereal protein in all country groupings. Globally, stepwise multiple regression analysis, when all the independent variables and potential confounding factors were included, selected consumption of sugar as the variable having the greatest influence on obesity with R2 = 0.510, while gluten was placed second increasing R2 to 0.596. Gluten consumption may have been emerging as an inconspicuous, but significant cause of obesity. While Westernization has driven the diet patterns worldwide to incorporate more gluten crops, obesity prevalence projection methods may estimate future obesity rates poorly if gluten consumption is not considered.

Possible Prevention of Diabetes with a Gluten-Free Diet

Gluten seems a potentially important determinant in type 1 diabetes (T1D) and type 2 diabetes (T2D). Intake of gluten, a major component of wheat, rye, and barley, affects the microbiota and increases the intestinal permeability. Moreover, studies have demonstrated that gluten peptides, after crossing the intestinal barrier, lead to a more inflammatory milieu. Gluten peptides enter the pancreas where they affect the morphology and might induce beta-cell stress by enhancing glucose- and palmitate-stimulated insulin secretion. Interestingly, animal studies and a human study have demonstrated that a gluten-free (GF) diet during pregnancy reduces the risk of T1D. Evidence regarding the role of a GF diet in T2D is less clear. Some studies have linked intake of a GF diet to reduced obesity and T2D and suggested a role in reducing leptin- and insulin-resistance and increasing beta-cell volume. The current knowledge indicates that gluten, among many environmental factors, may be an aetiopathogenic factors for development of T1D and T2D. However, human intervention trials are needed to confirm this and the proposed mechanisms.

The Effect of Gluten Free Diet on Components of Metabolic Syndrome: A Randomized Clinical Trial

Background: This study aimed to assess the effects of Gluten free diet (GFD) on components of metabolic syndrome (MES). Materials and Methods: In this randomized clinical trial, 50 subjects diagnosed with MES were randomly divided into two groups (n=25). The first group received a GFD and the second group continued their regular diet. Biochemical markers of MES and blood pressure were measured before and after 8-week intervention. Results: Forty five subjects completed the study. A post-hoc comparison of the groups showed no effects of the GFD and control diet on LDL cholesterol, total cholesterol, fasting insulin, HOMA-IR, systolic and diastolic blood pressure levels. The GFD reduced fasting blood glucose, waist circumference (WC) and serum triglyceride concentration significantly compared with the control diet (p<0.05). Conclusion: Short-term GFD reduced WC and improved glycemic control and Triglyceride level in subjects with the metabolic syndrome.

Serum Concentrations of Insulin, Ghrelin, Adiponectin, Leptin, Leptin Receptor and Lipocalin-2 in Children with Celiac Disease Who Do and Do Not Adhere to a Gluten-Free Diet

Background/Aims

The roles of the many bioactive peptides in the pathogenesis of celiac disease remain unclear. To evaluate the serum concentrations of insulin, ghrelin, adiponectin, leptin, leptin receptor, and lipocalin-2 in children with celiac disease who do and do not adhere to a gluten-free diet (GFD, intermittent adherence).

Methods

Prepubertal, pubertal, and adolescent celiac children were included in this study (74 girls and 53 boys on a GFD and 80 girls and 40 boys off of a GFD).

Results

Insulin levels in prepubertal (9.01±4.43 μIU/mL), pubertal (10.3±3.62 μIU/mL), and adolescent (10.8±4.73 μIU/mL) girls were higher than those in boys (5.88±2.02, 8.81±2.88, and 8.81±2.26 μIU/mL, respectively) and were neither age-dependent nor influenced by a GFD. Prepubertal children off of a GFD exhibited higher ghrelin levels than prepubertal children on a GFD. Adiponectin levels were not age-, sex- nor GFD-dependent. Adherence to a GFD had no effect on the expression of leptin, leptin receptor, and lipocalin-2.

Conclusions

Adherence to a GFD had no influence on the adiponectin, leptin, leptin receptor, and lipocalin-2 concentrations in celiac children, but a GFD decreased highly elevated ghrelin levels in prepubertal children. Further studies are required to determine whether increased insulin concentrations in girls with celiac disease is suggestive of an increased risk for hyperinsulinemia.

Palaeolithic diet decreases fasting plasma leptin concentrations more than a diabetes diet in patients with type 2 diabetes: a randomised cross-over trial

Background

We have previously shown that a Palaeolithic diet consisting of the typical food groups that our ancestors ate during the Palaeolithic era, improves cardiovascular disease risk factors and glucose control compared to the currently recommended diabetes diet in patients with type 2 diabetes. To elucidate the mechanisms behind these effects, we evaluated fasting plasma concentrations of glucagon, insulin, incretins, ghrelin, C-peptide and adipokines from the same study.

Methods

In a randomised, open-label, cross-over study, 13 patients with type 2 diabetes were randomly assigned to eat a Palaeolithic diet based on lean meat, fish, fruits, vegetables, root vegetables, eggs and nuts, or a diabetes diet designed in accordance with current diabetes dietary guidelines during two consecutive 3-month periods. The patients were recruited from primary health-care units and included three women and 10 men [age (mean ± SD) 64 ± 6 years; BMI 30 ± 7 kg/m²; diabetes duration 8 ± 5 years; glycated haemoglobin 6.6 ± 0.6 % (57.3 ± 6 mmol/mol)] with unaltered diabetes treatment and stable body weight for 3 months prior to the start of the study. Outcome variables included fasting plasma concentrations of leptin, adiponectin, adipsin, visfatin, resistin, glucagon, insulin, C-peptide, glucose-dependent insulinotropic polypeptide, glucagon-like peptide-1 and ghrelin. Dietary intake was evaluated by use of 4-day weighed food records.

Results

Seven participants started with the Palaeolithic diet and six with the diabetes diet. The Palaeolithic diet resulted in a large effect size (Cohen’s d = −1.26) at lowering fasting plasma leptin levels compared to the diabetes diet [mean difference (95 % CI), −2.3 (−5.1 to 0.4) ng/ml, p = 0.023]. No statistically significant differences between the diets for the other variables, analysed in this study, were observed.

Conclusions

Over a 3-month study period, a Palaeolithic diet resulted in reduced fasting plasma leptin levels, but did not change fasting levels of insulin, C-peptide, glucagon, incretins, ghrelin and adipokines compared to the currently recommended diabetes diet.

Trial registration: ClinicalTrials.gov NCT00435240

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0398-1) contains supplementary material, which is available to authorized users.