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The metabolic syndrome (MetS) was defined as a condition characterized by disturbed glucose and insulin metabolism, central obesity, mild dyslipidemia, and hy-pertension. These conditions are important risk factors for diabetes, cardiovascular disease, and other chronic diseases. It etiology is a complex interaction between genetic , metabolic, and dietetic factors. To overcome the epidemic values of obesity and MetS currently registered, nutritional interventions are needed and the substitution of diet components may be a good strategy. Usually, metabolic disorders that are present in MetS are associated to high consumption of fat; however, as well as fat, carbohydrates have an important influence in MetS components. Taking into account that carbohydrates may be converted to glucose or fermented, producing fatty acids or short-chain fatty acids respectively, is essential consider its influence in lipids bioavailability for the human metabolism. The impact of carbohydrates consumption on human metabolism continues to be a controversial topic and several metabolic characteristics should be considered. Thus, this chapter focuses on the role of carbohydrates in the MetS and associated complication.
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Metabolic Syndrome
Chapter 1
The Role of Carbohydrates in Metabolic
Syndrome
Igor Otavio Minatel1,2,*, Jessica Leite Garcia3, Giusep-
pina Pace Pereira Lima1 and Camila Renata Correa3
1Department of Chemistry and Biochemistry, Institute of
Bioscience, São Paulo State University (UNESP), Botucatu,
Brazil
2Faculdade Sudoeste Paulista - FSP, Avaré, São Paulo, Brazil
3Department of Pathology, São Paulo State University (UN-
ESP), Medical School, Botucatu, Brazil
*Corresponding Author: Igor Otavio Minatel, Department of
Chemistry and Biochemistry, Institute of Bioscience, UNESP,
Botucatu, 18618-689, São Paulo, Brazil, Tel/Fax: +55 14 3880-
0573; Email: igorminatel@hotmail.com
First Published July 28, 2017
Copyright: © 2017 Igor Otavio Minatel, et al.
This article is distributed under the terms of the Creative Com-
mons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which permits
unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s)
and the source.
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Abstract
e metabolic syndrome (MetS) was dened as a
condition characterized by disturbed glucose and insulin
metabolism, central obesity, mild dyslipidemia, and hy-
pertension. ese conditions are important risk factors
for diabetes, cardiovascular disease, and other chronic
diseases. It etiology is a complex interaction between ge-
netic, metabolic, and dietetic factors. To overcome the
epidemic values of obesity and MetS currently registered,
nutritional interventions are needed and the substitution
of diet components may be a good strategy. Usually, meta-
bolic disorders that are present in MetS are associated to
high consumption of fat; however, as well as fat, carbohy-
drates have an important inuence in MetS components.
Taking into account that carbohydrates may be converted
to glucose or fermented, producing fatty acids or short-
chain fatty acids respectively, is essential consider its inu-
ence in lipids bioavailability for the human metabolism.
e impact of carbohydrates consumption on human me-
tabolism continues to be a controversial topic and several
metabolic characteristics should be considered. us, this
chapter focuses on the role of carbohydrates in the MetS
and associated complication.
Introduction
Epidemic values of obesity and MetS are currently
registered, and nutritional strategies have been proposed
to overcome these health problems. e MetS was dened
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Metabolic Syndrome
as a condition characterized by disturbed glucose and in-
sulin metabolism, central obesity, mild dyslipidemia, and
hypertension [1]. ese conditions are important risk fac-
tors for diabetes, cardiovascular disease, and other chron-
ic diseases. It etiology is a complex interaction between
genetic, metabolic, and dietetic factors. Usually, the meta-
bolic disorders present in MetS are associated to high con-
sumption of fat. However, the role of carbohydrates has
been shown by reducing total and low-density lipoprotein
(LDL) cholesterol, weight loss, and improving insulin sen-
sitivity [2–6].
e European and American dietary guidelines have
established dietary reference values for the intake of car-
bohydrates, dietary bre, and fats [7, 8]. ese dietary
guidelines recommend a decrease in saturated fat to 7–
10% of the total energy intake, that represents an fat in-
take range between 20 to 35% of the total energy intake;
whereas the total carbohydrates intake, including complex
or simple molecules, should range from 45 to 60% of the
total energy intake. It is important to consider that dif-
ferent values are given for infants, young children, and
adults. However, changes in dietary patterns results in dif-
ferent responses, since the metabolic state may vary from
person-to-person. Another important situation to consid-
er is the presence of dietary bre when examining carbo-
hydrate intake and metabolic disorders. Extensive studies
have suggested that whole grains (which are rich in bers)
help to prevent chronic diseases and MetS [3, 9–11]. Nev-
ertheless, more information should be produced before
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change daily ingestion of fat or carbohydrates. In a study
conducted in Korean individuals, population with a high
intake of rened carbohydrates, authors showed that di-
etary carbohydrate intakes were positively related to the
prevalence of MetS [12]. In addition, elevated triglycer-
ide and blood glucose levels in combination with reduced
HDL-cholesterol levels were associated with high dietary
carbohydrate intake in men and women [12].
Simple Carbohydrates
e obesity and MetS are strongly associated to cardi-
ovascular and kidney disease, diabetes, and other chronic
diseases in industrialized societies [13]. us, prevention
or early intervention to reverse MetS would reduce the in-
cidence of this common disease [13, 14]. Mostly, the obe-
sity, dietetic imbalance and life quality may be a powerful
contributor to the development of the MetS. Our ances-
tors obtained their food from hunting and gathering, but
the transition to modern Western society lifestyle with its
tremendous technological advances in food processing
led to extensive changes in food intake and composition.
e Western-style diet, also called the meat-sweet diet is
characterized by high intakes of processed foods rich in
saturated fat, trans-fatty acids, proteins from red meat,
and sodium, as well as an excessive consumption of sim-
ple carbohydrates, such as sucrose and fructose [15]. Most
carbohydrates occur naturally in foods or can be added
articially as sweeteners, mainly in processed foods and
beverages. However, the addition of these sugars to foods
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has been associated to metabolic impairment in indi-
viduals by inducing weight gain, obesity, and MetS [16].
Comparing overweight and obese individuals consuming
glucose or fructose-sweetened beverages, providing 25%
of energy requirements for 10 weeks, was observed that
subjects consuming fructose-sweetened beverages exhib-
ited increased de novo lipogenesis, dyslipidemia, and cir-
culating uric acid levels and reduced fatty acid oxidation
and insulin sensitivity, while subjects consuming glucose-
sweetened beverages did not, despite comparable body
weight gain [17]. ese results clearly show that simple
carbohydrates are dierently metabolized by human or-
ganism.
e rate of dietary fructose consumption, mostly in
combination with glucose, continued to rise worldwide
over the last y years [18–20]. Fructose, which is found
in fruits, became a major component of the modern diet
by robust intake of sucrose (table sugar, consisting of one
molecule of glucose and one molecule of fructose, which
are cleaved in the intestinal tract) and synthetic high fruc-
tose corn syrup (HFCS, consisting of a mixture of glucose
and fructose) that are currently added to beverages and
foods [21]. e HFCS are produced with various fructose-
to-glucose ratios, although the most commonly sugar con-
centration is 55% fructose and 45% glucose. Compared
with glucose, fructose has a lower glycemic index and does
not generate an insulin response, but has a slightly higher
sweetening power. Glucose and fructose have similar mo-
lecular structures, but its metabolism is markedly dier-
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ent. Fructose is rapidly absorbed by liver and converted
into glucose, glycogen, lactate, and fat. Furthermore, fruc-
tose is a potent lipogenic and adipogenic nutrient. Diets
rich in fructose have promoted an increased adipogenic
potential, on adipocyte precursor cells (APCs), that con-
sequently results in accelerated adipocyte hypertrophy
[22]. ese can be explained by the fact that hepatic me-
tabolism results in the formation of triglycerides that will
be stored in the adipocyte. In addition, a small amount of
fructose is also taken up by adipose tissue, generating tri-
glycerides as well as in the liver, potentiating the stock in
the adipocytes [22]. Unlike fructose, glucose depends on
insulin to enter the cell; aer supplying the cellular energy
requirement part of the glucose is stored as glycogen (i.e.
a limited stock), then the excess will also result in triglyc-
erides accumulation.
e accumulation of triacylglycerol in the adipocyte
and resulting hypertrophy leads to a cellular signaling re-
sponse that swi the oxidative metabolism to anaerobic
glycolysis and increases the secretion of several inamma-
tion-related adipokines (leptin, resistin, apelin, visfatin,
monocyte chemoattractant protein-1 (MCP-1), Interleu-
kin-8, Interleukin-6, Interleukin-1, Angiotensin-II, Tu-
moral Necrosis Factor-α, and Interleukin-10, among oth-
ers), which will result in cell damage. is inammatory
response, accompanied from morphological and function-
al changes, increases visceral adiposity and fat accumula-
tion, and insulin signaling impairment [23]. In addition
to the high potential of being stored in the form of triglyc-
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erides, fructose can follow another pathway that also re-
sults in pathological complications. Aer entering the cell
by the glucose-transporter (Glut) 2 and Glut 5 receptors,
both of which are not insulin dependent, they undergo the
action of the enzyme fructokinase and formation of uric
acid occurs, a metabolite that when generated in excess,
may be an independent risk factor for cardiovascular and
kidney disease [24], arterial hypertension, obesity, and di-
abetes [25]. us, its elevation may contribute to some co-
morbidities involving MetS. e ingestion of excess car-
bohydrates is also an oxidative stress modulating factor
that is related to the pathogenesis of the MetS. Derivatives
of glucose and fructose oxidative metabolism lead to the
formation of short chain reactive compounds or carbonyl
products, such as glyoxal (GO) and methylglyoxal (MgO),
which react with amino groups of biological molecules,
generating a large variety of adducts and crosslinks called
(AGEs - Advanced glycation end products) that stimulate
the production of inammatory cytokines and cause tis-
sue damage, especially of the kidney, an organ with a high
level of specic receptors (RAGE - Receptor for advanced
glycation end products) for these molecules (Figure1).
Excessive circulating glucose can also activate the poliol
pathway, another source of oxidative stress, in which it is
converted to sorbitol and subsequently to fructose. is
glucose-fructose conversion induces oxidative stress and
generates derivatives with higher glycation potential than
glucose itself. A cycle is formed in which fructose plays
a central role with its high potential to be converted to
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triglycerides that will be stored inducing inammation
and forming oxidative stress-causing derivatives that feed
back.
Figure 1:Excess of carbohydrate intake and its metabolism lead to
the formation of short-chain reactive compounds or carbonyl prod-
ucts, such as glyoxal (GO) and methylglyoxal (MgO), which generate
a large variety of adducts and crosslinks called AGEs that stimulate
the production of inammatory cytokines via RAGE (Receptor for
advanced glycation end products).
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End Products of Complex Carbohydrates
e human body is unable to digest some foods com-
ponents as complex carbohydrates and dietary bers. Tak-
ing into account that carbohydrates may be converted to
glucose or fermented, producing fatty acids or short-chain
fatty acids (SCFA) respectively, is essential to evaluate its
inuence on lipids bioavailability for the human metabo-
lism. Gut microbiota is directly involved in fermentation
of these components that are incompletely hydrolysed
due to a absence of the appropriate enzymes. ese fer-
mentation products includes the SCFA (Figure 2), which
are represented by acetate, propionate, butyrate, formate,
valerate, and caproate [26]. Acetate, propionate and bu-
tyrate represents 95% from the total SCFA produced in
the human gut, and these molecules have been shown to
exert multiple benecial eects on mammalian energy
metabolism [27]. SCFA might be related to energy me-
tabolism in several tissues, such as adipose tissue, skeletal
muscle, pancreas, intestine, and liver [26, 28]. is regula-
tion is associated with the bidding of SCFA to free fatty
acids receptors (FFARs) expressed in these organs. e
FFARs belongs to G-protein coupled receptors (GPRs)
family, of which, the most studied are GPR41 (also known
as FFAR3) and GPR43 (also known as FFAR2).
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Figure 2: Whole grains and vegetables are rich source of complex car-
bohydrates, and these compounds are undigested or poorly digested
in stomach or by gut enzymes. Undigested carbohydrates are con-
verted by gut microbiota in short-chain fatty acids (SCFA), mainly
acetate, propionate, and butyrate. SCFA are absorbed by enterocytes,
reach the bloodstream and interact with specic organs.
e exactly tissue response induced by FFARs activa-
tion for SCFA remains unclear [28]; whereas, data from
animal studies indicate that SCFA are associated to re-
duction or reversion of MetS components as weight gain,
obesity, and insulin sensitivity. Mice fed a high-fat diet
supplemented with oral acetate, propionate and butyrate
administration shown reduced body weight and improved
insulin sensitivity [29]. In contrast, other investigators
have found that GPR43-decient mice were protected
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from high-fat diet induced obesity and dyslipidemia by
increasing energy expenditure [30].
Dietary bre fermentation dier signicantly in total
and individual SCFA production [31]. However, assum-
ing that 10 g of dietary bre fermentation yields about 100
mmol SCFA, individuals consuming high-bre diet may
produce ~ 400–800 mmol SCFA per day. Data sustaining
these ratio of SCFA production were observed in a human
intervention study, which a four-week supplementation
with resistant starch (30 g per day), increased postpran-
dial systemic acetate and propionate concentrations up to
280 μmol/l and 13 μmol/l, respectively [32]. e recom-
mended amount of bre ingestion per day is 25-38 grams;
whereas, the people are consuming much less than this
recommendation. Fibre intake helps the gut and human
body to prevent a ranging of diseases as heart failure, hy-
pertension [33], and intestinal disorders [34].
In a previous study, authors followed lean, overweight
and obese subjects, showing that the composition of gut
microbiota is direct associated to SCFA production and
the two major phyla related to SCFA production are Fir-
micutes and Bacteroidetes [35]. In this same study, the total
amount of SCFA was higher in the obese than in the lean
subjects. In addition, in obese and overweight subjects the
proportion of individual SCFA changed in favor of pro-
pionate and Bacteroidetes phyla, when compared to lean
subjects [35]. However, human data about gut microbiota
are inconsistent and have been shown variables bacteria
ratios.
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Human intervention studies, using obese patients,
has demonstrated a positive eect of SCFA consumption
by preventing body weight gain [36] or reducing body
weight, body mass index, visceral fat area, waist circum-
ference, and serum triglycerides [37]. In addition, SCFA
can induce the gut-secretion of satiety hormones as chol-
ecystokinin (CCK), glucagon-like peptide (GLP)-1, pep-
tide tyrosine-tyrosine (PYY), hormones that regulates ap-
petite and satiety. On the other hand, the SCFA itself, as in
case of acetate, can cross the blood-brain barrier and sup-
press food intake by reducing appetite [38]. Furthermore,
several studies have been shown a positive eect of SCFA
in adipose tissue and the consequent release by this tissue
of leptin (satiety regulating hormone).
e eects/interactions of SCFA with body metabo-
lism is very broad, and a interesting study suggested that
these molecules can downregulate peroxisome prolifer-
ator-activated receptor-gamma (PPAR-γ) and shi the
adipose and liver tissue from lipogenesis to fatty acid ox-
idation [29]. In the same study, when SCFA at 5% were
added to high fat diet, a protection against obesity and
improved insulin sensitivity were observed. ese results
lead the authors to suggest the use of SCFA (in especial
acetate, propionate, and butyrate) as selective modulators
of PPAR-γ. Considering that insulin-sensitive organs are
responsible by energy and metabolism in human body,
and the systemic interorgan crosstalk triggered by SCFA,
these molecules are a promising eld of study intending to
prevent obesity and related diseases, such as MetS.
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Eects of Low-Carbohydrate Diets
Versus Low-Fat Diets on Metabolic Risk
Factors
e recommended daily intake of carbohydrates,
based on a 2.000 kcal diet, range between 225 to 300 g/day
[8]. However, minimum ingestion necessary to prevent
the loss of lean muscle tissue or avoid brain tissue glucose
starving is 100 g [39]. Carbohydrates may be divided in
groups, such as sugar, starch, and bers, according to sugar
units and chemical structures. In foods, carbohydrates are
widely used as sweeteners (to improve palatability), food
preservatives, and to improve functional properties such
as viscosity, texture, body, and browning capacity [40].
Dierent types of intervention have been used in the
tentative of prevent or reduce the physiologic markers of
MetS. Diets based on low-fat (LFD) or low-carbohydrate
(LCD) are the most common interventions, non drug-
based, methods employed. ese diets have become a
popular strategy for weight loss and weight management.
Studies have shown that people tend to remove carbohy-
drate without replacement of either fat or protein [41].
Similarly to LFD, carbohydrate-restricted diet (CRD) is
generally accompanied by weight loss [42–44].
Nowadays is still uncertain the benecial eects of
the LCD into possible prevention of MetS. Discordant re-
sults between studies have shown that replacing saturated
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fats from diets with carbohydrates has benecial eects
on human metabolism, but may increases blood levels of
triglycerides and reduces high-density lipoprotein (HDL)
cholesterol. However, these results can reect the incapac-
ity of the organism to lead with the increased amount of
carbohydrate ingested. When carbohydrates are fed in ex-
cess and surpass the metabolic capacity of organism oxi-
dize glucose, starts a de novo lipogenesis that culminates
in saturated fatty-acids (SFA) production. Fatty acids,
coming from dietary fat intake or endogenously synthe-
sized, are important predictors of MetS development [45].
In some experiments, the reduction of dietary carbohy-
drate results in a decreased level of lipogenic fatty acids,
despite higher saturated fat intake [46, 47]. ese results
reinforce the hypothesis that carbohydrates, as well as fat,
may induce hypercholesterolemia. In contrast, Volk et al.
showed that plasma SFA correlates poorly with dietary
saturated fat and better with carbohydrate, mainly by in-
creasing plasma levels of palmitoleic acid [48].
Low-carbohydrate diets seems as eective as LFD to
weight loss and improve other health markers, showing
that, as well as fat, carbohydrates have an important in-
uence in components of MetS. In a recent meta-analysis
comparing individuals consuming diets (6 months to 2
years of intervention) with reduced amounts of carbo-
hydrates or fat was demonstrated that LCD signicantly
decreased body weight and triacylglycerol, and increased
HDL-cholesterol, when compared to LFD. However, sub-
jects consuming LCD experienced a signicant increase
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in low-density lipoprotein (LDL) cholesterol compared
with their counterparts consuming an LFD [49]. Consid-
ering these results is possible suggest that benecial eects
of LCD may be dierent among individuals and must be
carefully weighted. In general, LFD and LCD have im-
proved body composition, HDL cholesterol level, triglyc-
eride level, total cholesterol; therefore, reducing the risk of
chronic diseases.
Volek et al. (2009) showed that CRD improve a wide
spectrum of lipid markers of cardiovascular disease risk,
including eects on LDL cholesterol particle size. In addi-
tion, the CRD resulted in a decrease in plasma saturated
fatty acids (SFAs) despite higher dietary saturated intake,
and resulted in a signicant decrease in retinol binding
protein 4 (RBP4) [44]. RBP4 is a adipokine that has been
associated to adiposity, insulin resistance, and type 2 dia-
betes [50, 51]. ese ndings lead the authors to suggest
that there are many options for treating obesity or the indi-
vidual components of MetS, but carbohydrate restriction
has the ability to target the range of markers with a single
intervention [44]. In another report, the introduction of
low-fat, high-carbohydrate diets in overweight subjects,
with at least three characteristics of MetS, showed that
weight gain was prevented, and modest weight loss was
achieved [52]. In this study, the high-carbohydrates di-
ets were formulated by replacing one-quarter of dietary
fat for simple or complex carbohydrates. Weight loss and
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cholesterol reduction were greatest in complex carbohy-
drates diets when compared to control and simple carbo-
hydrates diets [52]. Knowing that complex carbohydrates
can be fermented by human gut microbiota to produce
SCFA, we may speculate that these results are induced by
regulatory mechanisms associated to SCFA (as discussed
above in this chapter).
Conclusion
e direct and the indirect eects of carbohydrates
on the development of MetS should be better understood.
ere are several data supporting a direct causal role of
sugar promoting body weight gain and development of as-
sociated diseases. However, there are similar number of
data supporting an inverse role. Diet intervention has be-
came very popular nowadays, especially employing carbo-
hydrates restriction, but before change the dietary habits
individuals should consider several factor that inuences
in metabolism, such as body weight, physical status, and
the presence of metabolic disorders.
Acknowledgments
e authors gratefully acknowledge the nancial
support from the “Faculdade Sudoeste Paulista - FSP,
Fundação de Amparo a Pesquisa do Estado de São Pau-
lo - FAPESP (Project No. 2015/10626-0), and Conselho
Nacional de Desenvolvimento Cientíco e Tecnológico -
CNPq (Project No. 305177/2015-0).
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... The intake of refined carbohydrates, such as bread, pasta, and sweeteners in drinks, increases the risk of obesity and type 2 diabetes mellitus. However, a high-carbohydrate high-fiber diet helps to prevent cardiovascular diseases and MetS [6,7,[13][14][15]. ...
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Recent attention has focused on fructose as having a unique role in the pathogenesis of cardiometabolic diseases. However, because we rarely consume fructose in isolation, the major source of fructose in the diet comes from fructose-containing sugars, sucrose and high fructose corn syrup, in sugar-sweetened beverages and foods. Intake of sugar-sweetened beverages has been consistently linked to increased risk of obesity, type 2 diabetes, and cardiovascular disease in various populations. Putative underlying mechanisms include incomplete compensation for liquid calories, adverse glycemic effects, and increased hepatic metabolism of fructose leading to de novo lipogenesis, production of uric acid, and accumulation of visceral and ectopic fat. In this review we summarize the epidemiological and clinical trial evidence evaluating added sugars, especially sugar-sweetened beverages, and the risk of obesity, diabetes, and cardiovascular disease and address potential biological mechanisms with an emphasis on fructose physiology. We also discuss strategies to reduce intake of fructose-containing beverages.