Diet-induced alteration of microbiota and development of obesity, nonalcoholic fatty liver disease and diabetes

Gut microbiota play an important part in the development of obesity-related
type 2 diabetes. The composition, localisation and translocation of intestinal
bacteria is greatly influenced by antimicrobial proteins which are secreted by
Paneth cells in the small intestine, as well as mucin components secreted by
goblet cells in the small intestine.

The exact mechanism behind these dietary influenced modulations of the
composition of gut microbiota is unknown. Our hypothesis is that dietary fat
intake indirectly causes alteration of the gut microbiota composition, by
affecting the function of Paneth cells and goblet cells.

The objective of this study is to prove a causal relation between dietary fat
intake en alterations in gut microbiota composition, by focussing on diet
induced alterations in Paneth cell function and the impact of diet induced
alterations in goblet cell function and mucin composition.

Patients will be approached for participation while they are on the waiting
list for a laparoscopic gastric bypass. After obtaining informed consent,
patients will take a oral glucose toleration test and will be asked to provide
a stool sample. As a part of the standard pre-operative screening by the
anesthesiologist, blood will be drawn with some additional samples for
research. All participants in the obese group will have a sampling of the
exhailed air. During the operation a biopsy will be performed of liver tissue,
subcutaneous fat, visceral fat, rectus abdominis muscle tissue and jejunal
tissue.
The control group will receive the same interventions, but the jejunal tissue
will be obtained in a different population. We will be using jejunal biopsies
obtained during endoscopy in patients with dysfagia of dyspepsia.

The duration of follow-up is one year, comprising of five routine visits to the
outpatient department at 3-6 weeks, 3 months, 6 months, 9 months and 12
months). During these visits, some extra blood will be drawn for research
purposes simultaneously to the standard blood sample protocol. After 12 months
a new stool sample will be requested and new glucose tolerance test will be
performed.

For the glucose tolerance test the patient will be asked to come to the
hospital without breakfast of any other food intake prior to the test. A
baseline bloodsample will be drawn. The patient will be asked to drink a
solution of 75 grams of glucose in 200 ml of water. Two hours after ingestion
another bloodsample will be drawn. Patients will be asked to provide a stool
sample at baseline and at 12 months postoperatively, which will be used for
analysis of microbiota composition.

During every routine blood sample drawal about 6ml of blood will be drawn and
processed to plasma. The blood necessary for research will be drawn
simultaneously to the routine collection. This adds up to two times 6 ml extra
per patient.

The sampling of exhailed air takes about 5 minutes and is risk free.

The biopsies of liver, fat, muscle and jejunum tissue will be performed by the
surgeon during laparoscopy. A biopsy of about 0.5cm3 will be taken from the
outside of the liver and rectum abdominis muscle. The site of biopsy will be
checked for possible bleeding and if necessary cauterisation will be perforemd.
Likewise, a biopsy of the omentum majus and subcutaneous fat of the abdominal
wall will be performed. These biopsies do not cause inconvenience to the
patient, because they will be performed during the gastric bypass surgery. A
possible complication could be bleeding from the biopsy site, but previous
studies have shown this possible complication to occur very rarely.

The jejunal biopsies of the control population willl be obtained via endoscopy
and might cause a slight inconvenience for the patient due to a possible more
lengthy procedure. The biopsy itself is not painful and a possible complication
might be bleeding of the biopsy site or a perforation, but previous experience
has shown that these complications occur very rarely.