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VOLUME 8 NUMBER 4 • NOVEMBER 2011
JOURNAL UPDATE
SA JOURNAL OF DIABETES & VASCULAR DISEASE
Of several sugar alcohols widely used as
sugar substitutes, xylitol has been considered
a safer sweetener, lacking the gastrointesti-
nal side effects of the other sugar alcohols.
Numerous studies have confirmed the effect
of xylitol in the prevention of dental caries,
plaque and oral biofilm production. The
effects of xylitol on glycaemic control has
also been reported. Compared with sucrose,
xylitol has similar sweetness but relatively
lower caloric value. Xylitol has a significantly
lower glycaemic index (13) compared with
sucrose (65), with the potential for reduction
of diabetic hyperglycaemia.
The overall antidiabetic effects of xylitol as
a sugar replacement on diabetes-associated
parameters have not yet been investigated.
Data from this University of KwaZulu/Natal
Department of Biochemistry study suggests
that xylitol not only reduces the blood glucose
concentration but also significantly improves
the glucose tolerance level compared with
sucrose in non-diabetic rats.
Seventeen Sprague-Dawley rats were ran-
domly divided into three groups, supplied for
three weeks with drinking water
ad libitum
(control group), 10% sucrose solution (sucrose
group) or 10% xylitol solution (xylitol group),
respectively. Between the sucrose and xylitol
groups, food intake was not significantly dif-
ferent, but drink intake and body weight were
signifcantly increased in the sucrose group.
Blood glucose data suggested that xylitol
could maintain both the non-fasting and fast-
ing blood glucose levels in a physiologically
safer and more stable condition compared
with sucrose. The significantly better glucose
tolerance ability of the xylitol group confirmed
that it has better effects in blood glucose
and diabetes management compared with
sucrose. The xylitol group also had signifi-
cantly higher liver glycogen concentrations.
Key take-home message:
Xylitol can be a
better sweetener than sucrose to maintain
diabetes-related parameters at a physiologi-
cally safer and more stable condition.
Source: Shahidul Islam M. Effects of xylitol as a sugar
substitute on diabetes-related parameters in nondiabetic
rats.
J Medicinal Food
2011;
14
(5), 505-511. DOI:
10.1089/jmf.2010.0015.
GENETIC STUDIES
Increased obesity-related insulin
resistance in black South African
women has genetic basis
Adipogenesis is controlled by a sequential
activation of transcription factors. Peroxisome
proliferator-activated receptor
γ
(PPAR
γ
) and
CCAAT/enhancer-binding protein
α
(C/EBP
α
)
function with other adipogenic transcription
factors to regulate the expression of lipogenic
genes. The adipogenic capacity of subcu-
taneous adipose tissue (SAT) has been pro-
posed as a potential mechanism underlying
the link between adiposity and insulin resist-
ance. Reduced adipogenic capacity of SAT is
typically associated with increased adipose cell
size, apoptosis, inflammation, reduced vascu-
larisation and insulin signalling within adipose
tissue, and peripheral insulin resistance.
Despite a high prevalence of insulin resist-
ance, black South African women have
less visceral adipose tissue (VAT) and more
peripheral (gluteal–femoral) SAT than their
white counterparts. Although increased VAT
is considered a major determinant of insu-
lin resistance, peripheral SAT deposition has
been shown to be protective, being inversely
associated with fasting insulin levels in over-
weight and obese pre-menopausal white
women. The mechanisms underlying this
apparent paradox are unkown.
The authors hypothesised that a reduc-
tion in the expression of lipogenic genes may
be associated with insulin resistance in black
South African women. This study sought to
measure expression of the genes involved in
adipogenesis and lipogenesis in abdominal
VAT and gluteal SAT depots and determine
their relationships with insulin sensitivity in
normal-weight and obese black and white
South African women.
The black and white women were well
matched for percentage of body fat and waist
circumference, whereas obese black women
had less VAT and more superficial SAT (SSAT)
than white women, but similar deep SAT
(DSAT). Obese black women had greater
gynoid fat mass. Fasting glucose levels were
not different between ethnic groups, but
black women had higher fasting insulin levels
than white women. Circulating adiponectin
levels did not differ by ethnicity, nor did aver-
age abdominal and gluteal adipocyte size.
Novel findings of the study were that the
expression of PPAR
γ
and PPAR
γ
-responsive
genes were down-regulated to a greater
extent with obesity in black compared with
white women. Furthermore, expression of
these genes, mainly in the gluteal and DSAT
depots, was associated with insulin sensitiv-
ity in black but not white women. An ethnic-
specific adaptation is suggested from the
observation that expression of PPAR
γ
and
PPAR
γ
-responsive genes was down-regulated
to a greater extent with obesity in black com-
pared with white women. The expression of
the major adipogenic transcription factors
and PPAR
γ
-responsive genes was correlated
with insulin sensitivity in black but not white
women. These gene associations with insulin
sensitivity were significant only in the gluteal
and, to a lesser extent, the DSAT depot.
Novel findings of this study indicated that
gynoid fat mass was negatively correlated
with insulin sensitivity in black but not white
women, contrasting with the prevailing
hypothesis that peripheral (gluteal–femoral)
SAT deposition is protective.The findings of
this study add to the weight of evidence refut-
ing the hypothesis that black women display
healthy obesity due to their greater periph-
eral fat distribution, but instead suggest
that obesity in black South African women
impairs gluteal SAT adipogenesis and stor-
age, potentially leading to insulin resistance
and an increased risk of type 2 diabetes.
Key take-home message:
Gluteal fat
depositon in black women is related to insu-
lin resistance, while visceral fat depostion in
white women is the determinant of risk of
type 2 diabetes.
Source: Goedecke JH, Evans J,
et al
. Reduced gluteal
expression of adipogenic and lipogenic genes in black
South African women is associated with obesity-related
insulin resistance.
J Clin Endocrinol Metab
2011;
96
(12).
DOI: 10.1210/jc.2011-1576.
EVIDENCE FOR CLINICAL PRACTICE
Simple anthropometric measures
suitable for determination of meta-
bolic risk – a South African study
Central obesity, specifically the accumula-
tion of VAT, is linked to the development of
several metabolic diseases, including hyper-
tension, dyslipidaemia and insulin resistance.
Waist circumference (WC) is used as a proxy
measure for VAT; however, ethnic differences
exist in the relationship between WC and
VAT. Few studies have looked at the ability of
central obesity measures to identify metabolic
risk factors in southern African populations.
Recent studies in Europeans and Asians
have shown thatwaist-to-height ratio (WHtR)
and waist-to-hip ratio (WHR) have a greater
ability than WC alone to identify patients
with hypertension, dyslipidaemia and type
2 diabetes. Black South African women are
on average shorter and have more periph-
eral fat than white South African women.
With increasing WC, black women accumu-
late less VAT than white women, yet black
women are more insulin resistant and para-
doxically, present with lower TG and total
cholesterol (TC) levels than white women.
Similarly to WC and VAT, the ethnic-specific
