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.
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: 1. 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 2. determine the types of bacteria in the stools of lean and overweight subjects 3. 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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
25
75g glucose dissolved in 300ml water
75g glucose plus 24g inulin dissolved in 300ml water
75g glucose plus 28g resistant starch in 300ml water
Glycemic Index Laboratories
Toronto, Ontario, Canada
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)
Time frame: 0 to 6 hours after the intervention
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)
Time frame: 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)
Time frame: 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)
Time frame: 0 to 6 hours after the intervention
Energy intake
From 3-day diet record, mean energy intake.
Time frame: 3 days
Fat intake
From 3-day diet record, mean total fat intake.
Time frame: 3 days
Protein intake
From 3-day diet record, mean protein intake.
Time frame: 3 days
Carbohydrate intake
From 3-day diet record, mean available carbohydrate intake.
Time frame: 3 days
Dietary fiber intake
From 3-day diet record, mean dietary fiber intake.
Time frame: 3 days
Fecal microbiota
Ion Torrent V6 16S-rRNA sequencing for comparison of phyla
Time frame: 1 day
0-2 hour Glucose response
Incremental area under the curve of the serum glucose response from fasting to 2 hours.
Time frame: 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.
Time frame: 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.
Time frame: 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
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 0 to 2 hours after consuming lunch
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