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SA JOURNAL OF DIABETES & VASCULAR DISEASE
CURRENT TOPICS
VOLUME 8 NUMBER 2 • JUNE 2011
77
associated with marked improvement in fitness and diabetes,
hypertension, and dyslipidaemia control.
23
In one randomised
controlled trial that compared laparoscopic adjustable gastric
banding and conventional therapy for type 2 diabetic patients
with BMI between 30 and 40 kg/m
2
, remission of diabetes was
significantly higher in the surgical than in the conventional
therapy group (73 vs 13%;
p
<
0.001) through a greater loss
of weight.
24
•
Reduced caloric intake.
Some gastrointestinal hormones that
have a role in the regulation of energy homeostasis may be
modified after bariatric surgery. An increase in plasma levels
has been observed of the appetite suppressant PYY, which is
secreted in the ileum and colon, following Roux-en-Y gastric
bypass
25
and sleeve gastrectomy.
26
The orexigenic hormone
ghrelin, which is secreted in the gastric fundus, appears to
decrease after sleeve gastrectomy
26
but its evolution after
Roux-en Y gastric bypass is deemed controversial.
27,28
Although
laparoscopic adjustable gastric banding decreases appetite, its
effect on satiety appears to be lower, probably due to a lesser
change in PYY and ghrelin than with other techniques.
29
Post-
surgery changes in gut-derived hormones result in decreased
appetite and increased satiety, which improve patients’
compliance to nutritional guidance.
•
Incretin effect.
Food intake provokes the secretion of several
intestinal peptides, some of which stimulate insulin secretion
from the endocrine pancreas. The observation that the
increase in insulin release is higher by oral (or enteral) glucose
administration than intravenous administration is called the
incretin effect.
30
GLP-1 and GIP exert the incretin effect,
the former being more important in terms of carbohydrate
homeostasis.
31
GLP-1 secretion from the L-cells in the ileum
increases after a meal and enhances insulin biosynthesis and
release by beta-cells, decreases glucagon release by alpha-
cells, improves glucose uptake and glycogen synthesis in liver
and peripheral tissues, slows gastric emptying, and decreases
appetite and increases satiety at the central level. Beta-cell
mass expansion is observed as a long-term effect.
32
GIP, which
is secreted from K-cells in the duodenum, stimulates post-meal
insulin secretion and promotes beta-cell mass expansion.
31
Type 2 diabetic patients show a reduced or lost incretin effect,
leading to impaired insulin secretion.
33
Roux-en-Y gastric bypass
significantly enhances GLP-1 levels and activity in morbidly
obese subjects with or without diabetes,
25,34
and the same is
observed with novel surgical techniques such as the digestive
adaptation.
35
Post-surgical changes in GIP levels after an oral
glucose tolerance test are an early peak and a decreased area
under the curve.
36
The American Diabetes Association established, in 2009, that
bariatric surgery should be considered for diabetic adults with
BMI
≥
35 kg/m
2
if diabetes is difficult to control with lifestyle and
pharmacological therapy. Surgery is not recommended in patients
with BMI
<
35 kg/m
2
outside a research protocol.
37
Metabolic surgery in type 2 diabetes with BMI
<
35 kg/m
2
This could be a major issue in clinical practice, since most diabetic
patients are overweight or mildly obese and have a BMI
<
35 kg/m
2
.
For example, a retrospective cohort study which included nearly
50 000 patients with type 2 diabetes from the UK General Research
Practice Database of 1986–2008, showed that male weight was
approximately 90 kg and female weight was approximately 80
kg.
38
Not withstanding the bias added by inclusion and exclusion
criteria, landmark clinical trials have consistently shown that
diabetic patients have a mean BMI close to 30 kg/m
2
(Table 2).
39-44
This is below the cut off for eligibility for bariatric surgery in current
guidelines, which also disregard the presence of abdominal obesity.
Bariatric surgery is effective not only in reducing obesity but also
in the remission of diabetes and associated metabolic disorders,
which explains the emergence of terms like ‘diabetes surgery’ or
‘metabolic surgery’ as complementary to the concept of bariatric
surgery.
45
In fact, these procedures can cause complete remission
of diabetes within days to weeks of undergoing surgery, before
significant weight loss has occurred.
46
This is due mainly to a rapid
reduction in insulin resistance and minor improvements in beta-cell
Table 1.
Actions of intestinal hormones which affect glycaemic control
17
Hormone
Plasma concentration of
hormone
Effects of hormone
In
T2DM
Bariatric surgery Appetite/
meal size
Insulin
secretion
Glucagon
secretion
Bypass Restricion
CCK
↑
?
?
↓
↑
↓
Gastrin
–
?
?
–
↑
–/
↑
Ghrelin
↓
–/
↓
?
↑
?
↑
↓
?
GIP
–/
↑ ↓
a
–
–
↑
–/
↑
GLP-1
↓
↑
–
↓
↑
↓
PYY
↓
↑
–?
↓
↓
–/
↓
Secretin
–/
↑
?
–?
–/
↓
↑
↑
Somatostatin –
/↓
?
?
↓
?
↓
↓
a
Not in all studies; –
=
no change; ?
=
not dear;
↑
=
increase;
↓
=
decrease;
CCK
=
cholecystokinin; GIP
=
gastric inhibitory polypeptide; GLP-1
=
glucagon-like peptide-1; PYY
=
peptide YY; T2DM
=
type 2 diabetes melliltus
Source:
Reproduced with kind permission from Flatt,
et al
.
Br J Diabetes Vasc Dis
2009;
9
: 103–107.
Figure 1.
Main mechanisms for type 2 diabetes improvement after
bariatric procedures.
GIP
=
glucose-dependent insulinotropic peptide/gastric inhibitory
polypeptide; GLP-1
=
glucagon-like peptide-1; PYY
=
peptide YY
WEIGHT
LOSS
Restriction
Malabsorp-
tion
REDUCED
INTAKE
↑
Ghrelin
↑
PYY
INCRETIN EFFECT
↑
GLP-1
↑
GIP
