Role of Carbohydrate in Health and Diseases

Presented By: Uttara Singh

L-2008.H.Sc.-46D

Introduction

Carbohydrates are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers having linkages of the acetal type.

They may be classified according to their degree of polymerization and may be divided initially into three principal groups:

sugars oligosaccharides polysaccharides

The major dietary carbohydrates Class (DP*) Sub-Group Components

Sugars (1-2)

Monosaccharides Glucose, galactose, fructose

Disaccharides Sucrose, lactose, trehalose

Polyols Sorbitol, mannitol

Oligosaccharides (3-9)

Malto-oligosaccharides Maltodextrins

Other oligosaccharides Raffinose, stachyose, fructo-oligosaccharides

Polisaccharides (>9)

Starch Amylose, amylopectin, modified starches

Non-starch polisaccharides

Cellulose, hemicellulose, pectins, hydrocolloids

DP * = Degree of polymerization

Terminology Related to Carbohydrates

Sugars • The term "sugars" is conventionally used to describe the

mono and disaccharides. • "Sugar", by contrast, is used to describe purified sucrose as

are the terms "refined sugar" and "added sugar".

Intrinsic and extrinsic sugars • Intrinsic sugars occur within the cell walls of plants.• Extrinsic sugars were those which were usually added to

foods.

Complex carbohydrates

• Complex carbohydrate has encompassed, starch, dietary fibre and non-digestible oligosaccharides.

Resistant starch • Resistant starch is defined as "starch and starch degradation

products not absorbed in the small intestine of healthy humans".

• The main forms of resistant starch are: Physically enclosed starch, e.g. within intact cell structures (RS1), Raw starch granules (RS2) Retrograded amylose (RS3) Chemically modified RS4

Available and unavailable carbohydrate

• Available carbohydrate are starch and soluble sugars• Unavailable as "mainly hemicellulose and fibre (cellulose)“.• It is misleading to talk of carbohydrate as "unavailable" because some

indigestible carbohydrate is able to provide the body with energy through fermentation.

Dietary fibre • Dietary fibre is "that portion of food which is derived from cellular walls

of plants which is digested very poorly by human beings".• The main components of dietary fibre are derived from the cell walls of

plant material in the diet and comprise cellulose, hemicellulose and pectin.

• Lignin, a non-carbohydrate component of the cell wall is also often included.

Modified starch

• The proportions of amylose and amylopectin in a starchy food can be altered by plant breeding.

• Genetic engineering are used for the production of genetically modify crop. • High amylose corn starch and high amylopectin (waxy) corn starch have been

available for functional as well as nutritional properties. • High amylose starches require higher temperatures for gelatinization and are

more prone to retrograde and to form amylose-lipid complexes. • These properties can be utilized in the formulation of foods with low glycemic

index and/or high resistant starch content. Physical modifications of starches include pregelatinization and dextrinization. Chemical modification is mainly the introduction of side groups and cross-

linking or oxidation. These modifications may be used to decrease viscosity and to improve gel stability, mouthfeel, appearance and texture, and resistance for heat treatment .

Soluble and insoluble fibre

• Those dietary fibre, allowing a simple division and has glucose and lipid absorption from the small intestine known as soluble and those which were slowly and incompletely fermented and has more pronounced effects on bowel habit referred as insoluble.

Digestion and Absorption of Carbohydrates

• Polysaccharides and oligosaccharides must be hydrolyzed to their component monosaccharides before being absorbed.

• The digestion of starch begins with salivary amylase.• Amylase hydrolyzes starch into maltose, maltotriose, and α -dextrins, and

some glucose is also produced. • The products of α-amylase digestion are hydrolyzed into their component

monosaccharides by enzymes like maltase, sucrase, isomaltase and lactase. • Carbohydrate absorption occurs primarily in the upper small intestine due to

the presence of finger-like villi in the mucosa of the upper small intestine.• Carbohydrate digestion and absorption can occur along the entire length of

the small intestine, and is shifted toward the ileum when the diet contains less readily digested carbohydrates.

• The upper small intestine exhibits wide villous structures with leaf-like arrays, while in the ileum the villi become longer and more finger-like.

The Glycemic Index

• The blood glucose responses of carbohydrate foods can be classified by the glycemic index (GI).

• The GI is considered to be a valid index of the biological value of dietary carbohydrates.

• It is defined as the glycemic response elicited by a 50g carbohydrate portion of a food expressed as a percent of that elicited by a 50g carbohydrate portion of a standard food The standard food has been glucose or white bread.

• If glucose is the standard, (ie. GI of glucose = 100) the GI values of foods are lower than if white bread is the standard by a factor of 1.38 because the glycemic response of glucose is 1.38 times that of white bread.

Implications of the Glycemic Index

• GI improves overall blood glucose control in subjects with diabetes and reduces serum triglycerides in subjects with hypertriglyceridemia.

• Low GI foods eaten before prolonged strenuous exercise increased endurance time and provided higher concentrations of plasma fuels toward the end of exercise.

• However, high GI foods led to faster replenishment of muscle glycogen after exercise.

Physiological effect of carbohydrate

• Carbohydrates have a wide range of physiological effects which may be important to health:

Provision of energy Effects on satiety/gastric emptying Control of blood glucose and insulin metabolism Protein glycosylation Cholesterol and triglyceride metabolism Bile acid dehydroxylation Fermentation- Hydrogen/methane production Short-chain fatty acids production Control of colonic epithelial cell function Bowel habit/laxation/motor activity Effects on large bowel microflora

Carbohydrate as an energy source• Dietary carbohydrates gives an energy value of 4 kcal/g (17 kJ/g), although

where carbohydrates are expressed as monosaccharides, the value of 3.75 kcal/g (15.7 kJ/g) is used.

Satiety • The possibility of controlling hunger, satiety and food intake by altering the

type of carbohydrate in food. • A better approach to controlling hunger and increasing satiety is associated

with changes in the composition of the total diet.

Energy balance• It is important that the amount of energy ingested be matched to the amount

of energy expended.• Maintenance of energy balance is important in order to avoid obesity and its

associated co-morbidities such as diabetes and cardiovascular disease.

Protein glycosylation

• Proteins glycation is dependent on the concentration of glucose and fructose in blood and the half-life of the protein.

• The reaction is between the monosaccharide and the amino group of an amino acid, usually lysine, to form a Shiff base which undergoes rearrangement and formation of Amadori products.

• As the reaction progresses, increasingly complex Maillard products are formed with the eventual production of Advanced Glycation End-products or AGEs which are associated with irreversible loss of protein function.

• The extent of glycation of specific proteins, such as Haemoglobin in diabetics serves as an indication of medium term control of blood glucose.

Fermentation • Fermentation is the colonic phase of the digestive process and breakdown of

carbohydrates in the large intestine.• This process involves gut microflora and is unique to the colon of humans because

it occurs without the availability of oxygen.• It results in the formation of the gases hydrogen, methane and carbon dioxide, as

well as short chain fatty acids (SCFA) (acetate, propionate and butyrate), and stimulates bacterial growth (biomass).

• The gases are either absorbed and excreted in breath, or passed out via the rectum.• SCFA which are rapidly absorbed and metabolized by the body.• Acetate passes primarily into the blood and is taken up by liver, muscle and other

tissues.• Propionate is a major glucose precursor in ruminant animals such as the cow and

sheep, but this is not an important pathway in humans. • Butyrate is metabolized primarily by colonocytes and regulate cell growth, and to

induce differentiation .

Bowel habit • Non-starch polysaccharides are the principal dietary component affecting

laxation through increases in bowel content bulk and a speeding up of intestinal transit time.

• The extent of the effect depends on the chemical and physical nature of the polysaccharides and the extent to which they are fermented in the colon.

• Fermentable polysaccharides stimulate increases in microbial biomass in the colon, resulting in some increase in fecal weight.

• More transit time ,less feacal weight and vice-versa.

Microflora• Carbohydrate which is fermented stimulates the growth of bacteria in the

large gut.• The efficiency of conversion of carbohydrate to biomass is determined by: the type of substrate, the rate of breakdown and the transit time through the large intestine .

The role of carbohydrates in maintenance of health

Carbohydrates in the diet• Amount of carbohydrate required to avoid ketosis is very small (about 50

g/day).• carbohydrate provides the majority of energy in the diets of most people. • carbohydrate-containing foods are vehicles for important micronutrients

and phytochemicals. • Dietary carbohydrate is important to maintain glycemic homeostasis and

for gastrointestinal integrity and function.• Diets high in carbohydrate as compared to those high in fat, reduce the

obesity and its co-morbid conditions.• A diet should consist of at least 55% of total energy coming from

carbohydrate.

Physical activity• Maintenance of energy balance is dependent both on energy intake and

energy expenditure. • The combination of a high carbohydrate diet and regular physical activity is

the optimal arrangement to avoid positive energy balance and obesity. • The increased energy needs of physical activity can be supplied by

carbohydrate or fat.• The importance of carbohydrate in the diet becomes more critical as the

amount and intensity of physical activity increases.

Carbohydrate and behaviour• It has been suggested that providing breakfast to children who do not

typically eat breakfast can increase cognitive performance. • It has been suggested that sugar consumption leads to hyperactivity in

children.

Beneficial effect of carbohydrate in disorders/diseases

• Carbohydrates may directly influence human diseases by affecting physiological and metabolic processes by reducing risk factors for the disease.

• Carbohydrates may also have indirect effects on diseases, for example, by displacing other nutrients or facilitating increased intakes of a wide range of other substances frequently found in carbohydrate-containing foods.

• Thus the nutrient-disease or food-disease associations discussed below must be considered in terms of the strength of evidence from a range of observational studies and clinical experiments and the existence of plausible hypotheses.

Obesity• The frequency of obesity has increased in many developed and developing

countries. • This is public health importance because of negative effect of obesity in

relation to diabetes, coronary heart disease and other chronic diseases of lifestyle.

• Genetic ,environmental factorsand lack of physical activity is believed to contribute to the increasing rates of obesity.

• As fat is stored more efficiently than excess carbohydrate, use of high carbohydrate foods is likely to reduce the risk of obesity in the long term.

• Excess energy in any form will promote body fat accumulation.

Non-insulin dependent diabetes mellitus (NIDDM)

• High rates of NIDDM in all population groups are associated with rapid cultural changes in populations consuming traditional diets, and also with increasing obesity.

• Foods rich in non-starch polysaccharides and carbohydrate-containing foods with a low glycemic index appear to protect against diabetes.

• Some epidemiological evidence suggests particular benefit of appropriately processed cereal foods, while other epidemiological and clinical studies suggest benefits of non-starch polysaccharide from legumes and pectin-rich foods.

• Avoid obesity and increase intakes of foods rich in non-starch polysaccharide and carbohydrate-containing foods with a low glycemic index offers the best means of reducing the rapidly increasing rates of NIDDM.

Cardiovascular disease• Genetic , lifestyle factors , dietary factors ,obesity and high intakes of saturated

fatty acids are involved in the etiology of coronary heart disease and influence both the atherosclerotic and thrombotic processes.

• On the other hand, there is strong protective effect by a range of antioxidant nutrients found in fruits and vegetables ,increasing carbohydrate intake can assist in the reduction of saturated fat.

• Among those who are overweight or obese it is more important to reduce total fat intake and to encourage the consumption of the carbohydrate-containing foods.

• There has been concern that a substantial increase in carbohydrate-containing food at the expense of fat, might result in a decrease in high-density lipoprotein and an increase in very low-density lipoprotein and triglycerides in the blood.

• Non-starch polysaccharides (NSP) have an appreciable effect in lowering serum cholesterol when consumed in naturally occurring foods and it may be used in the management hypercholesterolemia.

• Plant foods are good sources of potassium and reducing the sodium to potassium ratio may help to reduce the risk of hypertension as well as cerebrovascular disease.

Cancer• Cancer is a disease associated with well-recognized genetic abnormalities. • Gene defects in somatic cells is thought to be through DNA damage and failure of

the DNA repair system ( apoptosis).• Dietary carbohydrate is thought to be protective through mechanisms involving

arrest of cell growth, differentiation and selection of damaged cells for cell death (apoptosis).

• Butyric acid which is formed in the colon from fermentation of carbohydrates fight against the abnormalities..

• The process of fermentation may protect the colorectal area against the genetic damage that leads to colorectal cancer through other mechanisms which include:

the dilution of potential carcinogens; the reduction of products of protein fermentation through stimulation of bacterial

growth; pH effects; maintenance of the gut mucosal barrier; and, effects on bile acid degradation. • Carbohydrate staple foods are a source of phytoestrogens which may be protective

for breast cancer.

Gastrointestinal diseases • Intakes of non-starch polysaccharides(NSP) and resistant starch (RS)are

the most important contributors to stool weight.

• Therefore, increasing consumption of foods rich in these carbohydrates like bran and cereals are very effective means of preventing and treating constipation, diverticular disease as well as haemorrhoids and anal fissures.

The Role of Carbohydrates in Exercise and Physical Performance

Some general dietary considerations • Health professionals argue that a healthy diet is one which provides us

with at least 50% of our daily energy intake in the form of carbohydrates,35% or less from fats and the remainder from proteins.

• The common message is that we should move from high fat meat-based diets to those that are made up of more carbohydrates and fresh fruits and vegetables.

• Diet for athletes and active people should include more carbohydrate-containing foods.

• Their diets should be such that about 60% of their daily energy intake is obtained from carbohydrates,30% or less from fat and 10 to 15 % from proteins.

Carbohydrate diets and endurance capacity :Studies

• A study exploring the link between diet and exercise capacity found that after a period on a high carbohydrate diet, endurance capacity on a cycle ergometer doubled in comparison with the exercise times achieved after consuming a normal mixed diet.

• In contrast, a fat and protein diet reduced exercise capacity to almost half that achieved after normal mixed diets.

• This clearly showed the benefits of eating a high-carbohydrate diet before prolonged exercise have been shown mainly during cycling and establish importance of the carbohydrate content in the diets of athletes preparing for competition.

• The importance of muscle glycogen during prolonged exercise was confirmed in studies which showed that fatigue occurs when muscle glycogen concentrations are reduced to low values.

Carbohydrate diets and endurance capacity :Studies

• One study examined the influence of different nutritional states on the resynthesis of glycogen during recovery from prolonged exhaustive exercise.

• It found that a diet low in carbohydrate, and high in fat and protein for 2 to 3 days after prolonged submaximal exercise, produced a delayed muscle glycogen resynthesis, but when this was followed by a high carbohydrate diet for the same period of time, glycogen supercompensation occurred ( Figure 1).

• This dietary manipulation not only increased the pre-exercise muscle glycogen concentration but also resulted in a significant improvement in endurance capacity (Figure 2).

• It was found that a carbohydrate-rich diet consumed for 3 days prior to competition, accompanied by a decrease in training intensity, resulted in increased muscle glycogen concentrations.

Carbohydrate diets and endurance capacity :Studies

• Studies on the influence of carbohydrate loading and endurance capacity during running.

• The runner’s normal mixed diets were modified by providing either additional protein, complex carbohydrates or simple carbohydrates.

The 'complex' carbohydrate group supplemented their normal mixed diet with bread, potatoes, rice or pasta.

The 'simple' carbohydrate group ate their normal mixed diet but increased their carbohydrate intake with chocolates.

• The complex carbohydrate group improved their running times by 26%, and the simple carbohydrate group improved by 23%.

• There was no improvement in the performance times of the protein group.

Fig.1Muscle glycogen concentrations before and after constant load cycling to exhaustion, following three dietary conditions

Source: Adapted from Bergstrom, J.Hermansen,L., Hultman, E.,Saltin, B.

1 = Mixed diet for 3 days2 = Low carbohydrate diet for 3 days3 = High carbohydrate diet for 3 days

Fig.2Cycling time to exhaustion at constant load under three dietary conditions

1 = Mixed diet for 3 days2 = Low carbohydrate diet for 3 days3 = High carbohydrate for 3 days

Carbohydrate diets and high intensity exercise

• Multiple-sprint sports involve a mixture of brief periods of exercise of maximum intensity followed by recovery periods of rest or light activity, and last up to 90 minutes.

• There is rapid utilization of muscle glycogen during several brief periods of maximal exercise, the rate of glycogenolysis decreases as exercise continues.

• Sports which demand that their participants perform a combination of submaximal running and brief periods of sprinting, such as soccer, reduces muscle glycogen values.

• Performance is impaired when glycogen value lowered, so carbohydrate loading would be necessary for participants in multiple-sprint sports.

Composition of pre-exercise meals

• The low glycemic index carbohydrate appeared to improve endurance capacity to a greater extent than the high glycemic index food .

• Lentils as the low glycemic index food, with potatoes and glucose as the high glycemic index foods, and compared the responses to these after drinking a glucose solution or plain water.

• Eating a high fat meal before exercise is not recommended as a nutritional preparation for endurance competitions because these meals take a longer time to digest.

• From animal studies to suggest that increased fat intake will result in a lower oxidation of carbohydrate during exercise.

• If this glycogen sparing did occur following a high fat meal then it would be expected to delay the onset of fatigue in a similar manner to consuming carbohydrate-rich meals before exercise.

• A recent study has attempted to answer this question by comparing the endurance performances of subjects following isocaloric high fat or high carbohydrate meals, four hours before submaximal exercise.

• The pre-exercise meals contained approximately 280g of carbohydrate in the high carbohydrate meal and 84g in the high fat meal.

Recovery from exercise

• Recovery from exercise is not a passive process. • Tissues undergo repair and reproduction, fluid balance is restored and

substrate stores are replaced. • Carbohydrate replacement is one of the most important events during

recovery. • Several days participation in sport need a normal mixed diet containing

about 4 to 5 g/kg body weight (BW) of carbohydrate to replace muscle glycogen stores.

• Increasing the carbohydrate intake to 8 g/kg BW per day may not be enough to prevent a significant reduction in muscle glycogen concentrations after 5 successive days of hard training.

• A high carbohydrate diet and adequate fluid intake to avoid dehydration are the two most important elements in the formula for successful participation in sport.

Disorder of carbohydrate metabolism in health Dental caries

• Foods containing sugars may be easily broken down by α-amylase and bacteria in the mouth and can produce acid which increases the risk of caries.

• Starches with a high glycemic index produce more pronounced changes in plaque than low glycemic index starch.

• The impact of these carbohydrates on caries is dependent on the type of food, frequency of consumption, degree of oral hygiene performed, availability of fluoride, salivary function, and genetic factors.

• Prevention programmes to control and eliminate dental caries should focus on fluoridation and adequate oral hygiene, and not on sucrose intake alone.

Glycogen Storage Diseases

• Glycogen storage diseases are caused by lack of an enzyme needed to change glucose into glycogen and break down glycogen into glucose.

• Symptoms include weakness, sweating, confusion, kidney stones, and stunted growth.

• The diagnosis is made by examining a piece of tissue under a microscope (biopsy).

• Treatment depends on the type of glycogen storage disease and usually involves regulating the intake of carbohydrates.

• Give uncooked cornstarch every 4 to 6 hours around the clock.

• Give carbohydrate solutions through a stomach tube all night to prevent low blood sugar levels from occurring at night.

Types and Characteristics of Glycogen Storage DiseasesName Affected Organ,Tissues or Cells Symptoms

Type O Liver or muscle Episodes of low blood sugar levels (hypoglycemia) during fasting if the liver is affected

Von Gierke's disease (type IA) Liver and kidney Enlarged liver and kidney, slowed growth, very low blood sugar levels, and abnormally high levels of acid, fats, and uric acid in blood

Type IB Liver and white blood cells 1.Same as in von Gierke's disease but may be less severe2.Low white blood cell count, recurring infections, and inflammatory bowel disease

Pompe's disease (type II) All organs Enlarged liver and heart and muscle weakness

Forbes' disease (type III) Liver, muscle, and heart Enlarged liver or cirrhosis, low blood sugar levels, muscle damage, heart damage, and weak bones in some people

Andersen's disease (type IV) Liver, muscle, and most tissues Cirrhosis, muscle damage, and delayed growth and development

McArdle disease (type V) Muscle Muscle cramps or weakness during physical activity

Hers' disease (type VI) Liver Enlarged liver-Episodes of low blood sugar during fasting-Often no symptoms

Tarui's disease (type VII) Skeletal muscle and red blood cells

Muscle cramps during physical activity and red blood cell destruction (hemolysis)

Galactosemia

• Galactosemia is caused by lack of one of the enzymes needed to metabolize the galactose sugar in milk.

• Symptoms include vomiting, jaundice, diarrhoea, and abnormal growth.

• The diagnosis is based on a blood test. • Treatment involves completely eliminating milk and milk

products from the diet.• Avoid seaweed ,some fruits and vegetables which contain

galactose.• Most common and the most severe form is referred to as

classic galactosemia.

Hereditary Fructose Intolerance

• Hereditary fructose intolerance is caused by lack of the enzyme needed to metabolize fructose.

• A by-product of fructose accumulates in the body, blocking the formation of glycogen and its conversion to glucose for use as energy.

• Symptoms includes sweating, confusion, seizures and coma. • Children who continue to eat foods containing fructose

develop kidney and liver damage, resulting in jaundice, vomiting, mental deterioration, seizures, and death.

• Diagnosis is based on the chemical examination of liver tissue determines that the enzyme is missing.

• Treatment involves excluding fructose ,sucrose, and sorbitol from the diet.

Mucopolysaccharidoses

• Mucopolysaccharidoses are a group of hereditary disorders in which complex sugar molecules are not broken down normally and accumulate in harmful amounts in the body tissues.

• The result is a characteristic facial appearance and abnormalities of the bones, eyes, liver, and spleen, accompanied by intellectual disability.

• Symptoms include short stature, hairiness, stiff finger joints, and coarseness of the face.

• The diagnosis is based on symptoms and a physical examination.

• A bone marrow transplant may help.• Excess mucopolysaccharides enter in the blood and are

deposited in abnormal locations throughout the body.

Disorders of Pyruvate Metabolism• Pyruvate metabolism disorders are caused by lack of the

pyruvate carboxilase and dehydrogenase which are involved in pyruvate metabolism.

• These disorders cause a buildup of lactic acid and a variety of neurologic abnormalities.

• Symptoms include seizures, intellectual disability, muscle weakness, and coordination problems.

• Some children are helped by diets that are either high in fat and low in carbohydrates or high in carbohydrates and low in protein.

• Problems with pyruvate metabolism can limit a cell's ability to produce energy and allow a buildup of lactic acid, a waste product.

• These disorders are diagnosed by measuring enzyme activity in cells from the liver or skin.

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