The effects of galactooligosaccharide (GOS) on peripheral insulin sensitivity and body weight control in obese adults with impaired glucose homeostasis

Gut microbiota is being increasingly recognized as an important factor in fat
distribution, insulin sensitivity, and glucose and lipid metabolism.
Accordingly, the intestinal microbiota could play an important role in the
development and treatment of obesity and type 2 diabetes mellitus.
One of the important activities of the intestinal microbiota is to break down
dietary components such as dietary fiber, which are not or not completely
hydrolyzed by host enzymes in the small intestine. In this study we will
supplement our human volunteers with the soluble dietary fiber
galactooligosaccharide (GOS) produced from lactose. Soluble fibers are
fermented in the colon to yield short chain fatty acids (SCFAs), primarily
acetate, butyrate and propionate. Data derived from the TIM-2 model (TNO,
Delft, the Netherlands) showed that fermentation of GOS resulted in a shift in
the colonic SCFA ratio (normally ca. 60 % acetate, 20 % butyrate, 20 %
propionate) towards an increase in acetate (ca. 75 %) (confidential data TNO
Delft).

There is little known about the metabolic effects of a long-term human
intervention with GOS. A study by Vulevic et al (2013) found that a 12-week
supplementation of a GOS mixture in 45 overweight subjects altered fecal
microbiota, plasma inflammatory markers, insulin, cholesterol and triglyceride
concentrations, thereby improving the metabolic status of these patients. Next
to this, the same group assessed this mixture in healthy elderly volunteers and
showed positive effects on both the microflora composition and the immune
response. However, mechanisms explaining these improved metabolic status are
not elucidated in these studies, we hypothesize that the supplemented GOS will
be fermented into a SCFAs, mainly acetate, which may have beneficial metabolic
effects.

In one of our previous studies (METC 11-3-079) we have shown that acute colonic
acetate infusions have beneficial effects on human substrate and energy
metabolism. We found that colonic acetate administration increased fat
oxidation, increased circulating concentrations of the incretin and satiety
stimulating hormone PYY and reduced the pro-inflammatory marker TNF-* within 2
hours after administration in overweight males. In addition, in another study
(METC 13-3-022), we rectally administered three different SCFA combinations in
overweight men. In this study, we confirmed these effects of SCFAs on fat
oxidation and metabolic plasma markers. Therefore, we hypothesize that a
long-term manipulation of the colonic SCFA ratio towards an increase in
acetate, reached by the oral intake of GOS, will have beneficial effects on
human metabolism.
This hypothesis is supported by a study showing that acetate supplementation in
mice protects against diet-related obesity and this was related to production
of anorexic hormones and enhanced energy expenditure. In addition, in vitro
studies showed that acetate affects adipose tissue lipolysis, decreases the
production of pro-inflammatory markers and stimulates adipogenesis.

However, at the present time, our understanding of the effects of SCFA and GOS
specifically on human metabolism (in gut or systemically) is still limited.
Yet, in light of the health claims of certain dietary fibers, a detailed
picture of the physiology of human SCFA metabolism and its interaction with the
microbiome is of pivotal importance. Therefore, we will investigate the effects
of a 12-week supplementation of GOS on peripheral insulin sensitivity and body
weight control in obese adults with impaired glucose homeostasis.
This study is an important part of a Gastrointestinal Health TIFN project
(GH003 WP 1.2), which will provide important insight in how increased
availability of soluble dietary fiber-derived SCFA might serve as a strategy in
the prevention and treatment of obesity and type 2 diabetes mellitus.

Based on our hypothesis that orally administered GOS will be fermented into a
SCFA pattern high in acetate and that this will lead to beneficial effects on
human substrate and energy metabolism, we aim to address the following primary
objective:
To investigate the effects of a 12-week supplementation of GOS on peripheral
insulin sensitivity and body weight control in obese adults with impaired
glucose homeostasis.

Placebo controlled, double-blind, randomized parallel design.

The subjects will be divided in 2 intervention groups:
1. 1. GOS: Domo® Vivinal® galacto-oligosaccharide rich whey product
5g 3x per day (269.6kjoule/day)
2. Placebo: Maltodextrin
5.65g 3xper day (269.6kjoule/day), isocaloric

Intervention period will be 12 weeks (minimal 84 days, maximal 89 days
intervention period). The products will be consumed with a low-fat milk drink
during the breakfast, lunch and dinner.
The type of treatment will be blinded for both the volunteers and the
researchers.

All subjects will be screened before participation and thereby receive
information about their health status. In the future there can be general
health benefits for the public, but the volunteers receiving placebo will not
have a personal benefits by participating in the study. Subjects receiving the
dietary fibers may have personal health benefits if intervention effects are
according to expectations. The general interest of this study is to investigate
how manipulating the gut microbiota, increasing SCFA production and shifting
colonic SCFA ratios by the intake of dietary fibers will influence human
substrate and energy metabolism.
Burdens that volunteers can experience, such as the time spent with the
study (subjects will have to invest approximately 16 hours in the study,
divided among 3 test days and a screening visit (see for an overview table 1
and figure 1)) and the dietary and healthy regimen they have to follow. Also
the collection of faecal samples can be experienced as a burden, because they
have to handle them themselves and have to store them at home. Also the 12 week
intake of the dietary fiber can be seen as a burden for the subjects.
During the test days, blood will be collected via a venous catheter.
Venepunctures can occasionally cause a local hematoma or bruise to occur. Some
participants report pain during venepuncture. During visit 2, 15 ml blood will
be taken. During visit 1 and 3 the total amount of blood sampled is 170ml per
test day, totalling 315ml (screening 20ml) during the whole test period. During
visit 1 and 3, adipose tissue and skeletal muscle biopsies will be taken. The
adipose tissue biopsy might cause local hematoma as well. After the muscle
biopsy, some participants report pain, which is experienced as muscle pain.
More often the muscle feels stiff for a couple of days after the biopsy. To
minimize the risk for a hematoma, the biopsy place will be compressed for
approximately 5 minutes after biopsy. The place of incision will leave a small
scar (* 3 mm for adipose tissue biopsy and * 8 mm for skeletal muscle biopsy).
To promote good wound healing, the incision will be sealed with sterile
steristrips and a waterproof band-aid. The site of the muscle biopsy will, in
addition, be sealed with a compression bandage. During the
hyperinsulinaemic-euglycemic clamp there is a small risk of hypo- or
hyperglycemia. However, from our own extensive experience, these conditions do
not occur very often and can be reversed immediately. A medical doctor is
always available during the clamp. Concerning the other study procedures (OGTT
(screening), and indirect calorimetry (visit 1 and visit 3)), there are no
known risks (in literature and own extensive experience), and these
measurements are routinely applied in human biology research. SOPs for each
measurement are available in the Human Biology Department*s database.
GOS has been used before in metabolic studies in overweight to obese subjects
and in elderly persons. In both groups, no side-effects were reported. Together
with SCFA, H2 and CO2 are produced after fermentation of GOS, therefore it is
possible that bloating and flatulence can occur in high dosages. Most of the
studies with GOS to date have used a recommended dosage of 8 to 20 g day.