Acute Effects of Dietary Fiber on Postprandial Responses in Lean and Overweight Subjects

Study Overview
=================
Brief Summary
-----------------
It has been suggested that obesity occurs because the colonic microbes in obese individuals, compared to those who are lean, produce more short chain fatty acids during the fermentation of dietary fiber; this means that obese individuals obtain more energy from dietary fiber than lean. On the other hand, it is possible that the ability of colonic short chain fatty acids to improve glycemic control and suppress appetite may be reduced in obese subjects. The aim of this study was to determine the acute effects of 2 fibers commonly used as food ingredients, inulin and resistant starch, on postprandial serum responses of short chain fatty acids, glucose, insulin, free-fatty acids and selected gut hormones in lean and overweight or obese subjects.

Detailed Description
-----------------
The human colon (large intestine) contains hundreds of species of bacteria which exist in a symbiotic (mutually beneficial) relationship with their human host. The number and type of colonic bacteria varies in different people. Recent studies show that overweight individuals have different types of bacteria in their colons than lean subjects, and that as overweight subjects lose weight their colonic bacteria change to resemble those in lean subjects. It was suggested that this was because the bacteria in overweight people more efficiently ferment dietary fiber thus producing more SCFAs and providing more energy to the body. However, this is not consistent with other studies showing that high fiber intakes are associated with reduced risk of obesity. Some studies have shown that overweight people have higher concentrations of SCFA in their stool samples. But the reasons for the difference in stool concentrations of SCFA have not been studied. Stool concentrations of SCFA may differ in lean and overweight people because of differences in type of bacteria in their colons, differences in dietary intakes or maybe because lean and overweight people absorb SCFA produced by bacteria differently. Therefore, the objectives of this study were to: determine the relationship between SCFA production and the acute effects of consuming an unabsorbed carbohydrate on blood SCFA, FFA, glucose, insulin, c-peptide and gut hormone responses in lean and overweight subjects determine the types of bacteria in the stools of lean and overweight subjects to see if the types of bacteria are correlated with body weight, the composition of the diet, breath gases, fecal SCFA and other demographic and lifestyle factors. Healthy subjects with a BMI <25 (lean) or between 25 and 35 (overweight or obese; OWO) took part in a 2 phase study. In phase 1 subjects recorded their dietary intake for 3 days and then provided a stool sample for analysis of micro-organisms and short chain fatty acids. In phase 2 overnight fasted subjects were studied on 3 occasions separated by about a week. On each occasion subjects consumed a control test meal of dextrose, or dextrose plus inulin or dextrose plus resistant start and had breath and blood samples taken at intervals over 4 hours. Subjects were then given a standardized lunch and had more blood and breath samples taken over the next 2 hours.

Official Title
-----------------
Role of Colonic Short Chain Fatty Acids in Obesity: Acute Effects of Inulin and Resistant Starch on Postprandial Short Chain Fatty Acid, Glucose, Insulin, Free-fatty Acid and Gut Hormone Responses

Conditions
-----------------
Obesity, Diabetes

Intervention / Treatment
-----------------
* Other: Glucose
* Other: Inulin
* Other: Resistant starch


Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria: over 18 years of age Exclusion Criteria: Pregnant BMI<18 or >39.9 diabetes anaemia use of diuretics of beta-blockers regular user of antibiotics (≥1 course per year over the last 5 years) any use of antibiotics within 3 months use of laxatives, weight reducing agents, pre/probiotics or supplements known to influence gastrointestinal function within 3 months presence of inflammatory bowel disease, malabsorption, motility disorder, gastrointestinal infection, short bowel, or other condition affecting gastrointestinal function liver or kidney disease or major medical or surgical event (within the last 6 months) requiring hospitalization high fibre intake (>30g/day) or other abnormal dietary pattern on a weight-loss diet or not on their habitual diet in the two months prior to the study unwilling or unable to give informed consent and/or comply with study protocol

Ages Eligible for Study
-----------------
Minimum Age: 18 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
Accepts Healthy Volunteers

Study Plan
=================
How is the study designed?
-----------------

Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Other: Lean<br>Subjects within the range of desirable body weight (BMI<25) | Other: Glucose<br>* 75g glucose dissolved in 300ml water<br>Other: Inulin<br>* 75g glucose plus 24g inulin dissolved in 300ml water<br>Other: Resistant starch<br>* 75g glucose plus 28g resistant starch in 300ml water<br>|
| Other: OWO<br>Subjects who are overweight or obese (BMI between 25 and 40) | Other: Glucose<br>* 75g glucose dissolved in 300ml water<br>Other: Inulin<br>* 75g glucose plus 24g inulin dissolved in 300ml water<br>Other: Resistant starch<br>* 75g glucose plus 28g resistant starch in 300ml water<br>|

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Serum acetate response | Incremental area under the curve of the serum acetate response from the lowest concentration achieved during the first 3 hours to the end of the study (6hr) | 0 to 6 hours after the intervention | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Serum propionate response | Incremental area under the curve of the serum propionate response from the lowest concentration achieved during the first 3 hours to the end of the study (6hr) | 0 to 6 hours after the intervention | 
| Serum butyrate response | Incremental area under the curve of the serum butyrate response from the lowest concentration achieved during the first 3 hours to the end of the study (6hr) | 0 to 6 hours after the intervention | 
| Breath hydrogen response | Incremental area under the curve of the breath hydrogen response from the lowest concentration achieved during the first 3 hours to the end of the study (6hr) | 0 to 6 hours after the intervention | 
| Energy intake | From 3-day diet record, mean energy intake. | 3 days | 
| Fat intake | From 3-day diet record, mean total fat intake. | 3 days | 
| Protein intake | From 3-day diet record, mean protein intake. | 3 days | 
| Carbohydrate intake | From 3-day diet record, mean available carbohydrate intake. | 3 days | 
| Dietary fiber intake | From 3-day diet record, mean dietary fiber intake. | 3 days | 
| Fecal microbiota | Ion Torrent V6 16S-rRNA sequencing for comparison of phyla | 1 day | 
| 0-2 hour Glucose response | Incremental area under the curve of the serum glucose response from fasting to 2 hours. | 0 to 2 hours after consuming treatment | 
| 2-4 hour Glucose response | Incremental area under the curve of the serum glucose response from 2 to 4 hours. | 2 to 4 hours after consuming treatment | 
| Second-meal glucose response | Total area under the curve of the serum glucose response for 2 hours after lunch. | 0 to 2 hours after lunch | 
| 0-2 hour Insulin response | Incremental area under the curve of the serum insulin response from fasting to 2 hours | 0 to 2 hours after consuming treatment | 
| 2-4 hour Insulin response | Incremental area under the curve of the serum insulin response from 2 to 4 hours. | 2-4 hours after consuming treatment | 
| Second-meal Insulin response | Total area under the curve of the serum insulin response for 2 hours after lunch. | 0-to 2 hours after lunch | 
| 0-2 hour c-peptide response | Incremental area under the curve of the serum c-peptide response from fasting to 2 hours. | 0 to 2 hours after consuming treatment | 
| 2-4 hour c-peptide response | Incremental area under the curve of the serum c-peptide response from 2 to 4 hours. | 2 to 4 hours after consuming treatment | 
| Second-meal c-peptide response | Total area under the curve of the serum c-peptide response for 2 hours after lunch. | 0-2 hours after lunch | 
| Free-fatty acid rebound | Increase in serum free-fatty acid concentration from the lowest to the subsequent highest concentration before consuming lunch | 0 to 4 hours after consuming intervention | 
| Acute total glucagon-like peptide-1 response | Incremental area under the curve of the serum total glucagon-like peptide-1 response from 0 to 4 hours. | 0 to 4 hours after consuming intervention | 
| Post-lunch total glucagon-like peptide-1 response | Incremental area under the curve of the serum total glucagon-like peptide-1 response from 0 to 2 hours after lunch. | 0 to 2 hours after consuming lunch | 
| Acute active glucagon-like peptide-1 response | Incremental area under the curve of the serum active glucagon-like peptide-1 response from 0 to 4 hours. | 0 to 4 hours after consuming intervention | 
| Post-lunch active glucagon-like peptide-1 response | Incremental area under the curve of the serum active glucagon-like peptide-1 response from 0 to 2 hours after lunch. | 0 to 2 hours after consuming lunch | 
| Acute peptide tyrosine tyrosine response | Incremental area under the curve of the serum PYY response from 0 to 4 hours. | 0 to 4 hours after consuming intervention | 
| Post-lunch peptide tyrosine tyrosine response | Incremental area under the curve of the serum PYY response from 0 to 2 hours after lunch. | 0 to 2 hours after consuming lunch | 
| Acute ghrelin response | Incremental area under the curve of the serum ghrelin response from 0 to 4 hours. | 0 to 4 hours after consuming intervention | 
| Post-lunch ghrelin response | Incremental area under the curve of the serum ghrelin response from 0 to 2 hours after lunch. | 0 to 2 hours after consuming lunch | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
Nutrition, Humans, Obesity, Blood glucose, Dietary fiber, Appetite, Short chain fatty acids