Thursday, 14 July 2016

Digestion and Absorption of Carbohydrates

Sweetness is one of the five basic taste sensations of foods and beverages and is sensed by protein receptors in cells of the taste buds. Fast-releasing carbohydrates stimulate the sweetness taste sensation, which is the most sensitive of all taste sensations. Even extremely low concentrations of sugars in foods will stimulate the sweetness taste sensation. Sweetness varies between the different carbohydrate types—some are much sweeter than others. Fructose is the top naturally occurring sugar in sweetness value. See Table 4.1 "Sweetness Comparison of Carbohydrates" for sweetness comparisons among different naturally-occurring carbohydrates. Sweetness is a pleasurable sensation and some people enjoy the taste more than others. In a colloquial sense we identify such people as having a “sweet tooth.” This does not mean that the less-sweet whole grains containing more starches and fiber are less satisfying. Whole grains take longer to chew and get sweeter the more you chew them. Additionally, once in the stomach, whole-grain foods take longer to digest, and keep you full longer. Remember too that they contain fiber which makes elimination much smoother. Whole-grain foods satisfy the body the entire way through the digestive tract and provide the nutrients that also better satisfy the body’s functional needs.
Table 4.1 Sweetness Comparison of Carbohydrates
Carbohydrate Sweetness (percentage of sucrose)
Sucrose 100
Glucose 74
Galactose 33
Fructose 173
Maltose 33
Lactose 16
Starch 0
Fiber 0

From the Mouth to the Stomach

The mechanical and chemical digestion of carbohydrates begins in the mouth. Chewing, also known as mastication, crumbles the carbohydrate foods into smaller and smaller pieces. The salivary glands in the oral cavity secrete saliva that coats the food particles. Saliva contains the enzyme, salivary amylase. This enzyme breaks the bonds between the monomeric sugar units of disaccharides, oligosaccharides, and starches. The salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose. The increased concentration of maltose in the mouth that results from the mechanical and chemical breakdown of starches in whole grains is what enhances their sweetness. Only about five percent of starches are broken down in the mouth. (This is a good thing as more glucose in the mouth would lead to more tooth decay.) When carbohydrates reach the stomach no further chemical breakdown occurs because the amylase enzyme does not function in the acidic conditions of the stomach. But mechanical breakdown is ongoing—the strong peristaltic contractions of the stomach mix the carbohydrates into the more uniform mixture of chyme.
Salivary glands secrete salivary amylase, which begins the chemical breakdown of carbohydrates by breaking the bonds between monomeric sugar units.

From the Stomach to the Small Intestine

The chyme is gradually expelled into the upper part of the small intestine. Upon entry of the chyme into the small intestine, the pancreas releases pancreatic juice through a duct. This pancreatic juice contains the enzyme, pancreatic amylase, which starts again the breakdown of dextrins into shorter and shorter carbohydrate chains. Additionally, enzymes are secreted by the intestinal cells that line the villi. These enzymes, known collectively as disaccharides, are sucrase, maltase, and lactase. Sucrase breaks sucrose into glucose and fructose molecules. Maltase breaks the bond between the two glucose units of maltose, and lactase breaks the bond between galactose and glucose. Once carbohydrates are chemically broken down into single sugar units they are then transported into the inside of intestinal cells.
When people do not have enough of the enzyme lactase, lactose is not sufficiently broken down resulting in a condition called lactose intolerance. The undigested lactose moves to the large intestine where bacteria are able to digest it. The bacterial digestion of lactose produces gases leading to symptoms of diarrhea, bloating, and abdominal cramps. Lactose intolerance usually occurs in adults and is associated with race. The National Digestive Diseases Information Clearing House states that African Americans, Hispanic Americans, American Indians, and Asian Americans have much higher incidences of lactose intolerance while those of northern European descent have the least.National Digestive Diseases Information Clearing House. “Lactose Intolerance.” Last updated April 23, 2012. Most people with lactose intolerance can tolerate some amount of dairy products in their diet. The severity of the symptoms depends on how much lactose is consumed and the degree of lactase deficiency.

Absorption: Going to the Blood Stream

The cells in the small intestine have membranes that contain many transport proteins in order to get the monosaccharides and other nutrients into the blood where they can be distributed to the rest of the body. The first organ to receive glucose, fructose, and galactose is the liver. The liver takes them up and converts galactose to glucose, breaks fructose into even smaller carbon-containing units, and either stores glucose as glycogen or exports it back to the blood. How much glucose the liver exports to the blood is under hormonal control and you will soon discover that even the glucose itself regulates its concentrations in the blood.
Carbohydrate digestion begins in the mouth and is most extensive in the small intestine. The resultant monosaccharides are absorbed into the bloodstream and transported to the liver.

Maintaining Blood Glucose Levels: The Pancreas and Liver

Glucose levels in the blood are tightly controlled, as having either too much or too little glucose in the blood can have health consequences. Glucose regulates its levels in the blood via a process called negative feedback. An everyday example of negative feedback is in your oven because it contains a thermostat. When you set the temperature to cook a delicious homemade noodle casserole at 375°F the thermostat senses the temperature and sends an electrical signal to turn the elements on and heat up the oven. When the temperature reaches 375°F the thermostat senses the temperature and sends a signal to turn the element off. Similarly, your body senses blood glucose levels and maintains the glucose “temperature” in the target range. The glucose thermostat is located within the cells of the pancreas. After eating a meal containing carbohydrates glucose levels rise in the blood.
Insulin-secreting cells in the pancreas sense the increase in blood glucose and release the hormonal message, insulin, into the blood. Insulin sends a signal to the body’s cells to remove glucose from the blood by transporting to the insides of cells and to use it to make energy or for building macromolecules. In the case of muscle tissue and the liver, insulin sends the biological message to store glucose away as glycogen. The presence of insulin in the blood signifies to the body that it has just been fed and to use the fuel. Insulin has an opposing hormone called glucagon. As the time after a meal increases, glucose levels decrease in the blood. Glucagon-secreting cells in the pancreas sense the drop in glucose and, in response, release glucagon into the blood. Glucagon communicates to the cells in the body to stop using all the glucose. More specifically, it signals the liver to break down glycogen and release the stored glucose into the blood, so that glucose levels stay within the target range and all cells get the needed fuel to function properly.

Leftover Carbohydrates: The Large Intestine

Almost all of the carbohydrates, except for dietary fiber and resistant starches, are efficiently digested and absorbed into the body. Some of the remaining indigestible carbohydrates are broken down by enzymes released by bacteria in the large intestine. The products of bacterial digestion of these slow-releasing carbohydrates are short-chain fatty acids and some gases. The short-chain fatty acids are either used by the bacteria to make energy and grow, are eliminated in the feces, or are absorbed into cells of the colon, with a small amount being transported to the liver. Colonic cells use the short-chain fatty acids to support some of their functions. The liver can also metabolize the short-chain fatty acids into cellular energy. The yield of energy from dietary fiber is about 2 kilocalories per gram for humans, but is highly dependent upon the fiber type, with soluble fibers and resistant starches yielding more energy than insoluble fibers. Since dietary fiber is digested much less in the gastrointestinal tract than other carbohydrate types (simple sugars, many starches) the rise in blood glucose after eating them is less, and slower. These physiological attributes of high-fiber foods (i.e. whole grains) are linked to a decrease in weight gain and reduced risk of chronic diseases, such as Type 2 diabetes and cardiovascular disease.

A Carbohydrate Feast

Thanksgiving dinner: A feast of high-carbohydrate foods.
It’s Thanksgiving and you have just consumed turkey with mashed potatoes, stuffing smothered in gravy, green beans topped with crispy fried onions, a hot roll dripping with butter, and cranberry sauce. Less than an hour later you top it all off with a slice of pumpkin pie and then lie down on the couch to watch the football game. What happens in your body after digesting and absorbing the whopping amount of nutrients in this Thanksgiving feast? The “hormone of plenty,” insulin, answers the nutrient call. Insulin sends out the physiological message that glucose and everything else is in abundant supply in the blood, so cells absorb and then use or store it. The result of this hormone message is maximization of glycogen stores and all the excess glucose, protein, and lipids are stored as fat.
Figure 4.4
The glycemic index measures the effects of foods on blood-glucose levels.
A typical American Thanksgiving meal contains many foods that are dense in carbohydrates, with the majority of those being simple sugars and starches. These types of carbohydrate foods are rapidly digested and absorbed. Blood glucose levels rise quickly causing a spike in insulin levels. Contrastingly, foods containing high amounts of fiber are like time-release capsules of sugar. A measurement of the effects of a carbohydrate-containing food on blood-glucose levels is called the glycemic response (Figure 4.4).

Glycemic Index

The glycemic responses of various foods have been measured and then ranked in comparison to a reference food, usually a slice of white bread or just straight glucose, to create a numeric value called the glycemic index (GI). Foods that have a low GI do not raise blood-glucose levels neither as much nor as fast as foods that have a higher GI. A diet of low-GI foods has been shown in epidemiological and clinical trial studies to increase weight loss and reduce the risk of obesity, Type 2 diabetes, and cardiovascular disease.Brand-Miller, J., PhD, et al. “Dietary Glycemic Index: Health Implications.” J Am Coll Nutr 28, no. 4, supplement (2009): 446S–49S.
Table 4.2 The Glycemic Index: Foods in Comparison to Glucose
Foods GI Value
Low GI Foods (< 55)
Apple 44
Pear 38
Banana (under-ripe) 51
Grapefruit 25
Barley 25
Navy beans 38
Green peas 48
Oat bran (Quaker Oats) 50
Spaghetti (whole wheat) 37
Mashed sweet potatoes 54
Baked beans 48
Butter beans 44
Banana bread 47
Bread (sourdough) 52
Soy milk 31
Skim milk 32
Whole milk 27
Yogurt (sweetened) 33
Yogurt (plain, artificial sweetener) 14
Medium GI Foods (56–69)
Apricots 57
Cantaloupe 65
Mashed potatoes 70
Whole-wheat pita bread 57
Whole-wheat bread 69
Couscous 65
Brown rice 55
Cheese pizza 60
Rye bread 65
Hamburger bun 61
Black bean soup 64
Macaroni and cheese 64
Coca-Cola 63
High GI Foods (70 and higher)
Dates 103
Banana (over-ripe) 82
Parsnips 97
Corn chips 72
Pretzels 83
White bread 70
White rice 72
Spaghetti (durum flour) 78
White rice (instant) 87
French baguette 95
Bagel 72
Bread stuffing 74
Cheerios 74
Cream of wheat 71
Raisin Bran 73
Fruit roll-up 99
Gatorade 78
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Monday, 11 July 2016


DEFINITION : Food preservation is defined as a means of keeping foods for longer periods than would naturally be possible without destroying it's nutrients.

 • Rodents, Insects, Monkey, Microorganisms e.g bacteria, yeast and moulds and spoilage.


 • Destroy the agent responsible for food spoilage
 • Arrest enzymatic activities on food
• Prevents entry of new microorganisms during storage .

 • It make foods available all the year round.
 • Food is not wasted due to spoilage.
 • Food poisoning is prevented.

 • Food wastage.
 • Food poisoning
 • Scarcity of food.

 (1)  Application of heat

     e.g. -Boiling and frying for meat and fish
             -Pasteurization for canned food.
             -Sterilization for canned food.

 The food in these methods are subjected to a high temperature and held at this temperature for varying methods. The enzymes are destroyed and micro-organisms are killed. Also excluding air and sealing of containers in canned foods prevents re-contamination.

(2) Dehydration (Removal of water content) 

e.g. - Sun drying for fruits and Vegetables
        - Smoking for meat and fish. In this method, the water content in food is reduced And consequently made unavailable for micro organism to grow and cause spoilage.

(3) Pickling (Addition of salt or Sugar) 
 Sugar or salt are added to give a concentrated solution in which micro organism become dehydrated and die. Examples of foods preserved in this method are meat, jams, etc.

(4) Refrigeration and Freezing In this method n micro organisms cease to grow or grow only very slowly at low temperature E.g. refrigerators temperature at 5-7C can store daires, fruits and vegetables for short periods only and deep freezers at 18 degrees centigrade or below will store meat and fish for long periods.

(5) Fermentation : Garri, fufu, locust beans are product of fermentation and can be kept in this for a long period of time.

(6) Oil : Can be used to preserve food e.g. fried meat can be covered with oil and kept for a long period of time.

(7) Chemical Preservatives : e.g. Vinegar is used to preserve fruit and vegetable, sulphates for sausages, fruit juices, wine and jams; and benzonic acid for soft drinks.

(8) Spices e.g. pepper is used to store beans in air tight containers.

(9) Burying: Is another method of preserving food e.g. yam, cassava, and potatoes can be hidden under ground and buried till required.

(10) Another method used in preserving food in the greenery (Rhombus) grains are well dried and kept there till needed.
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DEFINITION : Vitamin A can be defined as important organic substance needed in small quantities by the body for proper functioning of the body systems. This is a fat soluble vitamin.

 Fish, liver, oil, egg, milk, Butter, cheese and liver.

Very green vegetables, palm oil, paw paw, carrots, mangoes, water melon, yellow corn, and tomatoes.  

  •  5,000 international units. 
  • Children : 7,500 international units.

 Vitamin A is not affected by normal cooking temperature, although long, slow cooking will destroy carotene which is the plant sources of vitamin A.

 • It controls the general state of the epithelial cell which reduces the risk of infection.
 • It is required for the regeneration of the visual purple in the retina of the eye so that rapid adaptation to dim light is possible.
 • It aids growth and development during childhood.
 • It helps to keep the cornea of the eyes in a healthy condition.

 • Night blindness which is the inability to see a dim light.
 • Keratomalacia which is the softening of the cornea which result in blindness.
 • Xerophthalmia which is drying and hardening of the cornea and conjunctiva .

 Hyervitaminosis of vitamin A might occur if additional vitamin A is taken in a medicine. In early life vitamin A affect skeletal growth and lead to softening and dailiness of the bone, patchy hair loss, drying and ulceration of the skin and sore lips.
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DEFINITION: Protein can be defined as an organic compound composed of carbon , iron, hydrogen, oxygen, nitrogen and other element such as phosphorous and sulfur.

Protein are classified into animal and plant proteins. Animal protein are referred to as complete or first class protein because they contain full range of  the eight essential amino acids.

                          Plant protein or vegetable protein are referred to as partial/incomplete or protein of low biological value because their protein do not contain the full range of the eight essential amino acids. For example, the protein of cereal/grain (e.g. maize) is deficient in essential amino acid Lysine, while the protein found in legumes such as the soya bean is relatively low in methionine. The value of each of these foods is therefore enhanced if eaten as cereal-legume mixture , thereby providing the whole range of essential amino acids.


ANIMAL PROTEIN: Meat , fish , shellfish , eggs, cheese , milk, yogurt, snail, edible insects etc.
PLANT PROTEIN: Groundnut, melon seed , locust bean seed, beans, peas, lentis, soya bean etc.

  • They are needed for the growth and development of tissue cell from birth until growth stops.
  • They are important for the repair and renewal of the tissues cell which constantly undergo wear and tear e.g the sole of the feet , nails , hair and skin.
  • They are needed for the formation of enzyme, hormones, antibodies , hemoglobin and antitoxins.
  • They help to control alkalinity of blood and the osmotic pressure in the blood vessels.
  • They can be used for the production energy if insufficient  energy foods are eaten .
       The daily requirement of protein for an adult is 60-90g while the daily requirement for children up to eighteen years is 20-70g.

         The chemical digestion of protein in the stomach with the conversion of pepsinogen by hydrochloric acid into the enzyme pepsin.
          Caseinogen which is the protein in milk is converted by another enzyme called rennin into casein. Protein then converts all protein and casein into peptones.

          In the intestine, Enterokinase of the intestine juice convert pep tone into peptides and polypeptides. Further down the intestine , peptidase of the intestinal juice convert peptide and polypeptide to amino-acids . The amino-acids are then conveyed via the portal circulation to the liver. For their metabolism , amino acid pass from the liver into the general circulation and in this way reach the various cell which utilize them. Excess amino acids are deaminated, that is the nitrogenous content is removed and converted into urea for elimination in the urine. The remaining part is converted to glucose and use to provide energy and heat.
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Supply Of Carbohydrate to the Body

DEFINITION: Carbohydrates are organic compounds made up of the chemical elements of carbon, hydrogen and oxygen in the same proportion as water.

We classify carbohydrate as follows:

----Polysaccharides, disaccharides and monosaccharide. These classifications are based on the complexity.

----Polysaccharides are the most complex forms of carbohydrate. They therefore must undergo a considerable amount of chemical changes during the process of digestion before they can be absorbed into the blood stream. Examples of polysaccharides are starchy foods like yam, rice aand bread. GLYCOGEN is a polysaccharides of animal origin as it is made in liver and muscles, and when extra glucose is needed by the body, it is reconverted into glucose.

CELLULOSE is another polysaccharide and is found in the cell walls of foods such as fruit and vegetables. It becomes tender when cooked but humans cannot digest it. However , it provides the body with roughage, which forms bulk in the intensine and stimulates bowel actions. 
Lack of excess of carbohydrate in the body can be harmful.
-----Disaccharides consist of two sugar units or monosaccride, whereas polysaccharides consist of many monosaccharides, Disaccharides therefore do not need to be broken down as much as polysaccharides before they can be used by the body.

Examples of disaccharides are sucrose found in sugarcane, and lactose which found in milk.
Monosacrides are the simplest forms of carbohydrates digestion, fructose, which is found in some fruit and honey and galactose, which is found together with lactose in milk.

The chief dietary sources of carbohydrates are :
  • Cereals e.g rice, maize, guinea corn, millet , wheat, barley and oats.
  • Starchy roots and fruits e.g yams, cassava, sweet potatoes , plantains and banana
  • Fruit and Honey.
The functions are :
  • They provide energy , which is used by the body for the heat and bases metabolism
  • Carbohydrates satisfy hunger 
  • They are bulky and cheap
  • Carbohydrates maintain the glucose level in the blood 
  • As long as carbohydrate intake is insufficient , protein will not be used to produce energy.
  • Indigestible parts of carbohydrates i.e cellulose , provides bulk in the intestine which aids in the elimination of waste products.

The digestion and absorption of carbohydrates starts in the mouth where the enzymes pryalin begins the conversation of all cooked starches into maltose. The food then passes to the stomach , where hydrochloric acids inactivates ptyalin. When it reaches the upper part of the small intenstine amylase , the enzyme in the pancreatic juice , converts all starches into maltose. Lower down in the small intenstine , the enzymes sucrose , maltase and lactase complete the conversation of the sugars into glucose which is the end product of carbohydrates of digestion.
The glucose is then absorbed into the venous capillaries of the villi in the small intenstine and conveyed via the portal circulation to the liver. In the carbohydrate metabolism , glucose combines with oxygen in the tissue cells and produce energy and heat. Carbon dioxide and water are the end product of this reaction between glucose and oxygen and are removed from the body as waste . Excess glucose is converted int glycogen by the liver and stored in the muscles for the muscles for use in times of need.
        If too much carbohydrate  is eaten frequently, a certain amount will be deposited as fats depots of the body and the individual becomes obese. As we have said , obesity resulting from this poor nutritional habit is a form of malnutrition.


  1. Obesity 
  2. Diabetes Milieus
  3. Inadequate supply of carbohydrate may results to serious underweight 
  4. Inadequate supply of carbohydrate may also leads to disease called hypoglycemia

If there is excess carbohydrates in the body , this is converted to human facts and stored in the adipose tissues which can result in Obesity. The person looks excessively big and lumpish .
Note;The man body fat should be nothing less than 0-15%, while the woman body fat should be nothing less than 15-25%. Anything except this it is called excess fat. It is much in woman because of child bearing because after child bearing the pelvic girdle enlarges.

Excess carbohydrates can results to  diabetes milieus which is when the supply of sugar in the blood is too much. The person may become seriously sick or die.

This may be result to serious underweight . The person will be skinning powerless and easily tired due to lack of adequate energy in the body.

This may also leads to disease called Hypoglycemia
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