Carbohydrates

ByZahraa Esmat Sayed Mahmoud

Under supervision of

Prof.Dr.Sonia Saleh ZakyProfessor of nutrition

Nutrition and Food Science Department.

Faculty of Home Economic.

Helwan University.

Prof.Dr.Ashraf Abd El-Aziz Abd El-MegeidProfessor of nutrition

Nutrition and Food Science Department.

Faculty of Home Economic.

Helwan University.

Food affects almost everything we do. It affects how we look, feel, and act. It even affects our abilities – how well we function every day.

Food has an impact on life because it supplies nutrients, which are substances in food that body needs to function properly such as in growing, in repairing itself, and in having supply of energy.

Nutrition is both a pure science and a social science. As a pure science it looks at how the body uses nutrients. As a social science it looks at the relationship between food and human behavior and the environment, or how and why people eat.

Introduction

Nutrition and NutrientsThere are six types of nutrients:

Carbohydrates Fats Proteins Vitamins Minerals Water

Carbohydrates

General characteristics

The term carbohydrate is derived from the French: hydrate de carbone.

compounds composed of C, H, and O

empirical formula: (CH2O)n

Carbohydrates, a group of molecules that include sugars and starches, provide energy to the body when the molecules are broken down. All carbohydrates contain carbon, hydrogen, and oxygen.

What are carbohydrates?

Classification

Monosaccharide :

A carbohydrate with one unit of sugar such as glucose, fructose, and galactose, are simple sugars. Usually, the ratio of each of carbon to hydrogen and oxygen is 1:2:1 such that there is one carbon to two hydrogens to one oxygen. Most of the sugars used in the body are six-carbon sugars, so their formula is written as: C6H12O6.

Two monosaccharides make a disaccharide.

There are three types of disaccharides: Sucrose, which is made of glucose and fructose, is common table sugar.

Lactose, made of glucose and galactose, is the sugar found in dairy products.

Maltose, made of two glucose molecules, is found in anything “malted” .Because disaccharides are too large to pass through the cell membranes, they must be broken down into monosaccharides first.

Disaccharide

Polysaccharides

Polysaccharides are several monosaccharides linked in a chain. There are two types of polysaccharides of importance to the body: starches and glycogen.

Polysaccharides must be digested to their individual glucose units for the body to be able to use the energy.

Cellulose, another type of polysaccharide, is a major component of wood. It cannot be broken down into smallerunits, so it is not digestible. When we ingest cellulose, it isconsidered roughage or fiber. Although we get no nutritionalvalue from cellulose, it binds cholesterol in the intestine andhelps us eliminate this chemical. Fiber also helps to regulatethe digestive tract and keep people “regular.”

How do we get carbohydrates from the diet?

The main sources of carbohydrates in our diet are:

Foods made from cereal grains (e.g. bread, flour, rice, pasta, and breakfast cereal). These foods give us mainly complex or starchy carbohydrate.

Fruit and vegetables especially potatoes, root vegetables (e.g. carrots) and pulses (beans and lentils) contain a mix of starches and sugars.

Lactose which is found in milk.Table sugar, honey and soft drinks.We break down most carbohydrates in the gut andabsorb them into our blood stream as individual sugar units.

What is the function of carbohydrates? Carbohydrates have five major functions within the body:

Energy supply, particularly for the brain in the form of glucose

Avoiding the breakdown of amino acids for energy.Avoiding ketosis from the breakdown of fatty acids.Cellular , protein recognition, activation of growth factors and modulation of the immune system.Some carbohydrates are high in fiber, which helps prevent constipation and lowers the risk for certain diseases such as cancer, heart disease and diabetes.

What happens if we don't get enough carbohydrate?

Eating too little carbohydrate may lead to low blood sugar levels (hypoglycaemia) .

Hypoglycaemia is a particular risk for some people with diabetes who are on tablets or insulin. It can also affect very active sports people, who may feel exhausted when their blood sugar and muscle glycogen stores run low.

If we eat too little carbohydrate, over time our body will begin to use up some stored fat but quickly moves on to burning its own protein tissue such as in the heart and muscles. A low intake of wholegrain cereals, fruit and vegetables rich in indigestible carbohydrate can also lead to bowel problems such as constipation.

Different carbohydrate-containing foods are digested and absorbed at different rates.

The Glycaemic Index (GI) is the classification used to identify which carbohydrates are quickly broken down to glucose (high GI) and which are slowly broken down(low GI).

What does the Glycaemic Index of carbohydrates mean?

Glyceamic index

Glyceamic index is defined as the area under the blood glucose curves seen after ingestion of a meal with carbohydrate-rich food, compared with the area under the blood glucose curve observed after a meal consisting of the same amount of carbohydrate in the form of glucose or

white bread.

Examples of medium and low GI carbohydrate foodsinclude:

Wholegrain and seeded bread Pasta, basmati rice Oats and muesliBeans and pulses Most fruit and vegetables including sweet

potatoes and new boiled potatoes in their skins Milk and yogurt.

Preview of Carbohydrate Metabolism

Storing glucose as glycogen

• 1/3rd of total glycogen is stored in liver and 2/3rd in muscle.

• When blood glucose falls liver cells break down glycogen into single molecules of glucose, which becomes available to supply energy to central nervous system and other organs .

• During exercise the muscle cell themselves use up the glycogen they store.

Using glucose as energy

Glycolysis (“glucose-splitting”)

Glucose (6C) is split into two pyruvate/pyruvic acid (3C) molecules.

– It does not require oxygen (gas O2).– Amount of energy harvested from 1 glucose:

2 ATP2 NADH (actively transported into

mitochondria of eukaryotic cells)

Making glucose from proteins

Glycogen stores only last for some hours , if a person does not replenish the depleted glycogen stores, body protein are broken down to make glucose by a process called

“gluconeogenesis”Taking adequate amount of carbohydrate

prevents the use of protein for energy, this role of carbohydrate is called protein sparing action.

Making ketone bodies from fat fragments

Inadequate supply of carbohydrates causes break down of body fat reserves. This not only supplies energy but also produces ketone bodies.

Some ketone bodies are used by muscle and other tissues for energy, but when produced in excess they accumulate in blood and cause ketosis (disturbance of bodies normal acis-base balance)

Converting glucose to fats

Excess carbohydrates can be converted to fats when glycogen stores are filled to capacity.

However storing carbohydrates as fats is an energetically expensive process. So, body fats mainly come from dietary fats.

Maintaining glucose homeostasis

• Blood glucose homeostasis is regulated mainly by two hormones:

(i)Insulin- secreted when blood glucose is high. Controls transport of glucose from blood to muscle and fat cells

(ii) Glugagon- secreted when blood glucose is low. Helps in release of glucose from storage.

Overview of Carbohydrate Metabolism

Requirements for carbohydrate

Carbohydrates are not essential nutrients, because the carbon skeletons of amino acids can be converted into glucose .

However, the absence of dietary carbohydrate leads to ketone body production ,and degradation of body protein whose constituent amino acids provide carbon skeletons for gluconeogenesis .

The RDA for carbohydrate is set at 130 g/day for adults and children, based on the amount of glucose used by carbohydrate-dependent tissues, such as the brain and erythrocytes.

Adults should consume 45–65 percent of their total calories from carbohydrates.

Requirements for carbohydrate

It is recommended that added sugar represent no more than 25% of total energy because of concerns that sugar may displace nutrient-rich foods from the diet, potentially leading to deficiencies of certain micronutrients.

Factors affecting requirements of carbohydrate

The minimal amount of carbohydrate required, either from endogenous or exogenous sources, is determined by the brain’s requirement for glucose .

The requirement for glucose has been reported to be approximately 110 to 140 g/day in adults. When glucose production or availability decreases below that required for the complete energy requirements of the brain, there is a rise in ketoacid production in the

liver in order to provide the brain with an alternative fuel This has been referred to as a ketosis .Generally this occurs in a starving person only after glycogen stores in the liver are reduced to a low concentration and the contribution of hepatic glycogenolysis is greatly reduced or absent .

The available evidence based on the majority of studies on the relationship dietary fiber to gastrointestinal health, several chronic diseases (colon cancer, breast cancer), glucose tolerance, insulin response as well as weight control and maintenance, indicated that the beneficial effects of fiber in humans are most likely related to the amount of food consumed but not the individual’s age or body weight .

Health effects of starch and fiber

Weight control: Food rich in complex carbohydrates provides less energy per bite and also provides satiety.

Heart disease: diets high in soluble fibers and low in animal fats and cholesterol is associated with lower risk of heart disease.

Cancer: high carbohydrate diet protects against some types of cancer (eg. Colon cancer).

Diabetes: High carbohydrate low fat diet helps in weight control , and this is the most effective way to prevent diabetes type 2.

GI health: dietary fibers enhance health of GI tract and hence blocks absorption of unwanted constituents of food. Insoluble fibers (cellulose) enlarge stool and prevents constipation.

Glucose is the only fuel normally used by brain cells. Because neurons cannot store glucose, they depend on the bloodstream to deliver a constant supply of this precious fuel.

Glucose and the nervous system

Lactose intolerance

Lactose intolerance It also called lactasdeficiency and hypolactasia.

classified as one of three types:

Primary lactase deficiency

 is genetic, only affects adults and is caused by the absence of a lactase persistence allele. It is the most common cause of lactose intolerance as a majority of the world's population lacks these alleles. Secondary acquired or transient lactase deficiency 

is caused by an injury to the small intestine, usually during infancyfromacute gastroenteritis, diarrhea, chemotherapy, intestinal parasites or other environmental causes.

Congenital lactase deficiency 

is a very rare, autosomal recessive genetic disorder that prevents lactase expression from birth. It is particularly common in Finland. People with congenital lactase deficiency are thus unable to digest lactose from birth, and they are unable to digest breast milk .

Symptoms

The principal symptom of lactose intolerance is an adverse reaction to products containing lactose (primarily milk), including:•Abdominal bloating .• Cramps.• flatulence•Diarrhea.•Nausea.•Borborygmi (rumbling stomach) .•Vomiting (particularly in adolescents).

Diagnosis

Four tests are available:

Hydrogen breath testIn a hydrogen breath test, after an overnight fast, 25 grams of lactose (in a solution with water) is swallowed.

If the lactose cannot be digested, enteric bacteria metabolize it and produce hydrogen, which, along with methane, if produced, can be detected on the patient's breath by a clinical gas chromatograph or compact solid-state detector.

The test takes about 2 to 3 hours to complete.

Blood test

In conjunction, measuring blood glucose level every 10 to 15 minutes after ingestion will show a "flat curve" in individuals with lactose malabsorption, while the lactase persistent will have a significant "top", with a typical elevation of 50% to 100%, within one to two hours. However, due to the need for frequent blood sampling, this approach has been largely replaced by breath testing.

Lactose tolerance test:

In a lactose tolerance test, you will be given a drink of lactose solution, and then a sample of blood will be taken from your arm using a needle. The blood will be tested to see how much glucose (blood sugar) it contains.

Milk tolerance test:

In a milk tolerance test, you will be given a glass of milk (about 500ml) and your blood sugar levels will be tested. If your blood sugar levels do not rise after drinking the milk, you may be lactose intolerant.

After an overnight fast, blood is drawn and then 50 grams of lactose (in aqueous solution) is swallowed. Blood is then drawn again at the 30 minute, 1-hour, 2-hour, and 3-hour mark. If the lactose cannot be digested, blood glucose levels will rise by less than 20 mg/dL .

Stool acidity test

This test can be used to diagnose lactose intolerance in infants, for whom other forms of testing are risky or impractical.

The infant is given lactose to drink. If the individual is tolerant, the lactose is digested and absorbed in the small intestine; otherwise it is not digested and absorbed and it reaches the colon.

The bacteria in the colon, mixed with the lactose, cause acidity in stools. Stools passed after the ingestion of the lactose are tested for level of acidity.

If the stools are acidic, the infant is intolerant to lactose.

Stool pH in lactose intolerance < 5.5.

Management

Lactose intolerance is not usually an absolute condition:

The reduction in lactase production, and the amount of lactose that can therefore be tolerated, varies from person to person. Since lactose intolerance poses no further threat to a person's health, the condition is managed by minimizing the occurrence and severity of symptoms.

Avoiding lactose-containing products:

Dietary control of lactose intolerance depends on people learning through trial and error how much lactose they can handle. Label reading is essential, as commercial terminology varies according to language and region.

Alternative products

Soy milk It has about the same amount of protein as cow's milk, though the amino acid profile differs.

Natural soy milk contains little digestible calcium as it is bound to the bean's pulp, which is insoluble in humans.

To counter this, many manufacturers enrich their products with calcium carbonate available to human digestion.

Unlike cow's milk, it has little saturated fat and no cholesterol.

The American Academy of Pediatrics considers soy milk a suitable alternative for children who cannot tolerate human or cow's milk, or whose parents opt for a vegan diet. They find no medical benefit to using soy milk instead of human or cow's milk.

Rice milkCompared to cow's milk, rice milk contains more carbohydrates, but does not contain significant amounts of calcium or protein, and no cholesterolor lactose.

Commercial brands of rice milk, however, are often fortified with vitamins and minerals, including calcium, vitamin B12, vitamin B3, and iron.

Almond milk Unlike animal milk, almond milk contains no cholesterol or 

lactose. As it does not contain any animal products, it is suitable for vegans and vegetarians who abstain from dairy products.

Commercial almond milk products often come in plain, vanilla or chocolate flavors and are sometimes enriched with vitamins. Almond milk can also be made at home by combining ground almonds with water in a blender. Vanilla flavoring and sweeteners are often added.

Almond milk is not a suitable replacement for breast milk, cow's milk or hydrolyzed formulas in children under two years of age due to the low protein content.

Coconut milk Coconut milk contains a large proportion of lauric acid, a saturated fat that

raises blood cholesterol levels by increasing the amount of high-density lipoprotein cholesterol that is also found in significant amounts in breast milk and sebaceous gland secretions. 

This may create a more favourable blood cholesterol profile, though it is unclear if coconut oil may promote atherosclerosis through other pathways.

Because much of the saturated fat of coconut oil is in the form of lauric acid, coconut oil may be a better alternative to partially hydrogenated vegetable oil when solid fats are required.In addition, virgin coconut oil is composed mainly of medium-chain triglycerides,which may not carry the same risks as other saturated fats.

Early studies on the health effects of coconut oil used partially hydrogenated coconut oil, which creates trans fats, and not virgin coconut oil, which has a different health risk profile.