Unit 4: Carbohydrates; Sugar, Starch, Fibre Flashcards
What is the principal building block of Carbohydrates
Glucose
What are the most abundant forms of Carbohydrates
Starch, simple sugars and cellulose
Carbohydrates are found in most plant foods; but the only6 animal product that is a significant source of carbohydrates is?
Milk
What are the 3 main categories of carbohydrates?
- Simple carbohydrates
- Complex carbohydrates
- Dietary fibre
What are the simple carbohydrates?
Monosaccharides-single sugars: glucose, fructose, and galactose
Disaccharides-sugars composed of pairs of monosaccharides: sucrose, maltose and lactose
What is a complex carbohydrate?
Polysaccharides-large molecules composed of chains of monosaccharides: glycogen, starches, and dietary fibre
Explain Carbohydrates
Contain carbon, hydrogen and oxygen [C(H2O)].
General chemical formula is glucose: C6H12O6
Carbon bonds with 4 atoms
Hydrogen bonds with 1 atom
Nitrogen bonds with 3 atoms
Oxygen bonds with 2 atoms
Glucose
Monosaccharide
C6H12O6
Serves as essential energy source for the body’s activities. (Also known as blood sugar)
One of 2 sugars in every disaccharide and unit that forms polysaccharides
Fructose
Monosaccharide
C6H12O6
Sweetest of sugars
Same formula as glucose but different arrangement
Galactose
Monosaccharide
C6H12O6
Same formula as glucose and fructose but different arrangement
Occurs naturally as a single sugar in only a few foods
Condensation Reaction
Links 2 monosaccharides
A hydroxyl group (OH) from one monosaccharide and a hydrogen atom (H) from the other combine to from (H2O). The 2 monosaccharides link with a single oxygen (O).
Hydrolysis Reaction
To break a disaccharide in two.
A molecule of water (H2O) splits to from and H and an H needed to complete the monosaccharides. Mainly occurs during digestion
Maltose
Glucose + Glucose
Produced whenever starch breaks down during carbohydrate digestion. Also during the fermentation process that yields alcohol.
Sucrose
Fructose + Glucose
Accounts for the sweetness in fruits, vegetables and grains. Used to make table sugar by refining.
Lactose
Galactose + Glucose
Principal carbohydrate of milk. Contributes to half the energy provided by skim milk.
Define Polysaccharides
Contain many glucose units (in some cases other monosaccharides). 3 important types: glycogen, starches, fibres
Glycogen
Food is not a significant source (limited in meats, not in plants)
Important role: glucose storage in the body (energy storage)
Made of many glucose molecules linked in branched chains. When the hormonal message arrives in the glycogen storage sites in a liver or muscle cell enzymes respond by attacking the branches of glycogen making a surge of glucose available.
Starches
Plant cells store glucose as starches (long branched or unbranched chains of glucose molecules (hundreds to thousands). Once you eat the plant (grain, vegetable, legumes) your body hydrolysis the starch to glucose for energy
Resistant starch
Less digestible starch
Technically a kind of fibre (ex. Raw potato, seeds)
May be digested slowly or remains intact until the bacteria of the colon break it done. Rate of digestion may affect the body’s handling of glucose
Dextrose
Term commonly used in food labels; refers to glucose
Dextrin
Short chain of glucose units resulting from the partial hydrolysis of starch. Used as a thickening agent.
Refined cereals
Grains that have been milled to remove the bran and leave only the endosperm. (White flour, cornstarch etc.). Lower content of dietary fibre, vitamins and minerals
Only monosaccharides can be digested by the intestinal mucosal cells. TRUE OR FALSE?
TRUE
Define Dextrins (in terms of carbohydrate digestion)
Short chains of glucose resulting from the breakdown of starch
Digestion of starch in the mouth
Salivary enzyme amylase begins to hydrolyze starch into small polysaccharides and the the disaccharide maltose
Digestion of fibre in the mouth
The mechanical action of the mouth crushes and tears fibre and mixes it with saliva for swallowing
Digestion of starch in the stomach
Stomach acids inactivate salivary enzymes, halting starch digestion
Digestion of fibre in the stomach
Fibre is not digested and it delays gastric emptying
Digestion of starch in the small intestine and pancreas
The pancreas produces an amylase that is released through the pancreatic duct to the small intestine
Starch–> Pancreatic amylase –> small polysaccharides, maltose
Then Disaccharidase enzymes on the surface of the intestinal cells hydrolyze the disaccharides into monosaccharides
Maltose –> maltase –> glucose + glucose
Sucrose –> sucrase –> fructose + glucose
Lactose –> lactase –> galactose + glucose
Intestinal cells absorb these monosaccharides
Digestion of fibre in the small intestine
Fibre is not digested and delays the absorption of other nutrients
Digestion of fibre in the Large intestine
Most fibre passes through intact to the large intestine where bacterial enzymes digest fibre.
Some fibre –> bacterial enzymes –> short-chained fatty acids, gas
Fibre holds water, regulates bowel activity and binds substances such as bile, cholesterol, and some minerals carrying them out of the body
Available carbohydrates
Starches and sugars; because the digestive enzymes break them down for use
Unavailable carbohydrates
Fibres; because the digestive enzymes cannot break their bonds
Carbohydrate absorption
- to some extent through the lining of the mouth
- Glucose and galactose enter cells lining the small intestine through active transport
- Fructose absorbed through facilitated diffusion (slows entry and produces smaller rise in blood sugar)
- Unbranched chains of starch are digested slowly (smaller rise in blood sugar) compared to branched chains (many places for enzymes to attack to release glucose)
- Blood from small intestine circulates through liver, cells take fructose and galactose and convert them to other compounds (mainly glucose)
All disaccharides provide one glucose directly and one indirectly. How?
Through conversion of fructose and galactose in the liver
Lactase activity is highest when?
After birth (benefits an infant). Only about 30% of adults retain enough lactase to digest and absorb lactose efficiently
Lactose Intolerance
Decline of lactase due to age or deficiency developed in the intestinal villi from disease, medication, malnutrition etc. Extremely rare cases an infant can be born with lactase deficiency
Define Satiety
The feeling or state of being sated
Most people with lactose intolerance can tolerate some lactose without symptoms. This includes:
Cheese: little lactose
Yogurt: contains lactose but most degrades to lactic acid during fermentation by bacterial cultures.
What is the primary function of carbohydrates?
Supply glucose. Glucose is distributed to the body cells via the bloodstream and used for energy. Optimal functioning requires glucose to be in the normal range
Carbohydrates are essential to the normal functioning of specialized body cells:
Nerve tissue of the brain
Central nervous system
Lungs
Red blood cells
These require glucose as their sole energy source.
In prolonged fasting some brain cells can adapt to use small amounts of ketones (Intermediate products in the breakdown of fats) to fuel the brain. However other brain cells rely exclusively on glucose (~50%)
Carbohydrates “spare” protein.
Energy needs take precedence over all others
Body proteins can be converted to glucose (gluconeogenesis) to provide energy when their is insufficient carbohydrate. However, proteins are needed for synthesis ad maintenance of body tissues and fluids. For optimal functioning of proteins enough carbohydrates are needed.
Carbohydrates prevent ketosis
When there is insufficient carbohydrates, larger amounts of fats are broken down for energy–more than the body can handle–fats are incompletely oxidized producing ketones. When ketone bodies are not excreted fast enough ketosis occurs.
Carbohydrates help maintain normal balance of water and sodium
When ketone bodies are excreted so is sodium (sodium binds with acidic ketones) and since sodium and water are excreted together – results in loss of bodily fluid. Dehydration and sodium imbalance.
Fluid loss explains why low-carb diets result in rapid weight loss. However, most weight returns when carbohydrate intake is normalized
Carbohydrates combine with protein and lipid molecules to produce vital body components
Glycoproteins: in mucous secretions and connective tissues
Glycolipids: in brain and nerve tissues
Glucose is precursor to penthouses (5-carbon sugar) required for the synthesis of nucleic acids, DNA and RNA
Maintaining Blood Glucose Homeostasis
- Person eats; blood glucose rises
- High blood glucose stimulates the pancreas to release insulin into the blood stream
- Insulin stimulates the uptake of glucose into some tissues (muscle cells) and storage of glycogen in the liver and muscles. Stimulates the conversion of excess glucose into fat for storage
- Body cells use glucose; blood levels decline
- Low blood glucose stimulates the pancreas to release glucagon into the blood stream
- Glucagon stimulates liver cells to break down glycogen and release glucose into the blood
- Blood glucose begins to rise
Explain Diabetes
Blood glucose rises after a meal and remains above normal levels because insulin is inadequate/ineffective
Type 1: less common-pancreas fails to produce insulin
Type 2: cells fail to respond effectively to insulin (consequence of obesity)
Explain Hypoglycemia
Blood glucose drops below normal.
Weakness, rapid heartbeat, sweating, etc.
Caused by certain medications, pancreatic tumours, overuse of insulin, alcohol abuse, uncontrolled diabetes
Rare in healthy people
Define Glycemic response
How quickly glucose is absorbed after a person eats, how high blood glucose rises and how quickly it returns to normal. Slow absorption, a modest rise and a smooth return to normal are desirable
Ideal Range of Glucose
Fasting (before breakfast): 3.3-5 Before meals: 3.3-5.8 After meals (1 hour): 7.7 or less After meals ( 2 hours): 6.6 or less
Explain Insulin
The pancreas (beta cells of islets of Langerhans) secretes insultin to reduce the blood glucose level. Also stimulates fat cells to take up and store fat. Insulin reduces blood glucose by:
- increasing permeability of cell membranes: allowing glucose to enter cells
- stimulating production of energy from glucose
- facilitating conversion of glucose to glycogen in muscle and liver cells
- facilitating the conversion of glucose to fat in liver cells
Explain Glucagon
Between meals blood glucose levels drop. The pancreas (beta cells of the islets of Langerhans) secretes glucagon to increase blood glucose levels by:
- facilitating the conversion of glycogen stored in the liver to glucose (enters the bloodstream and circulates the body)
- stimulating the conversion of body protein to glucose (gluconeogenesis) and energy if the glycogen stores in liver are exhausted
Explain Epinephrine (Adrenaline)
During ‘flight or fight” situations epinephrine is secreted to ensure that sufficient energy is available. It stimulates the conversion of liver and muscle glycogen to glucose and energy. (Similar to glucagon but different circumstances)
Consumption of nutrients in a country is often measured as amount of nutrient that disappears from the marketplace per person per year
Per capita disappearance per year= (total production + imports - exports)/ (total population)
Overestimates by ~25-30%
Canadians consume what percentage of their energy from carbohydrates?
49%
Since the 1950s Canadians have had more disposable income and so…
More food is consumed away from home and more confidence foods are eaten
Since the 1970s the sources of carbohydrates have changed. We are consuming more…
Rice and legumes
Small increase in consumption of wheat flour
Little change in amount of potatoes consumed
Modest increase in fruits and vegetables
Consumption of fruit juice has doubled
Major increase in consumption of soft drinks
~0.5 of total carbohydrate intake is in the form of complex carbohydrates (starch from vegetables and cereal)
Sugar consumption per capita in Canada is?
41 kg (91 lb) per person per year. Since figures of actual consumption ate usually 25-30% lower. Estimated the average person consumes 30 kg (67 lb) of sugar per year (14% of food energy supply)
Sucrose and HFSCS (High-fructose-corn-syrup) are the dominant sweeteners in Canada. TRUE OR FALSE?
TRUE
Is HFCS more harmful than Sucrose?
NO.
It is sugar extracted from corn and its fructose content is usually 42-55% with the remainder being glucose. This small difference compared to sucrose appears to have minimal effects on risk f obesity and other health conditions
Because sugar is devoid of vitamins and minerals, excessive intake of sugar may…
Lower the intake of these nutrients in the diet overall
Sugar can contribute to tooth decay and has the poor ability to satisfy the appetite. Hence…
Encourages overeating and excess weight gain
Studies have shown a direct link to the consumption of sugar and:
- Type 2 diabetes
- Heart disease
- Causative factor of obesity
The intake of sugar should be limited to what percentage of energy intake per day?
5-10% of energy intake
(1 can of cola is the upper limit of daily intake for most people)
Refers to added sugar not sugar naturally present in food
How many grams of carbohydrate is needed to permit complete oxidation of fats and to avoid production of ketone bodies
About 180 grams of carbohydrate. About 130 grams can be supplied through gluconeogenesis and therefore an intake of at least 50 grams of carbohydrate per day is required.
The RDA for carbohydrate is 130 grams per day based on the minimum about of glucose needed by the brain.
The Acceptable Macronutrient Distribution Range (AMDR) for carbohydrate is 45-65% of total kilocalories, with most coming from complex carbohydrates.
A diet high in complex carbohydrates is generally:
Low in fats and high in dietary fibre; associated with low incidence of heart disease, obesity, colon cancer
Data has indicated a correlation between high-fibre foods and:
Low incidence of disease: -cardiovascular -colon cancer -diverticular disease -appendicitis -haemorrhoids -obesity However, data cannot prove that low intake of fibre causes these disease. Other dietary/lifestyle choices may contribute: smoking, sedentary lifestyle etc.
Data can confirm that fibre prevents what?
Constipation
The DRI for fibre, based on dietary intake is:
14 grams per 1000 kilocalories (~ 21-28 grams per day)
Canada’s fibre intake is low
17-21 grams-men
10-18 grams-women
Health Effects of Soluble, viscous, more fermentable fibres (Gums and mucilage, Pectins, Psyllium, some hemicelluloses)
Major food sources: whole grain products (barley, oats, rye), fruits (apple, citrus), legumes, seeds and husks, vegetables; also extracted and used as food additives
Actions in the body:
-lower blood cholesterol by binding to bile
-slow glucose absorption
-slow transit of food through upper GI tract
-hold moisture in stools (softening them)
-yield small fat molecules after fermentation that the colon can use for energy
Health Benefits:
-lower risk of heart disease
-lower risk of diabetes
Health Effects of Insoluble, nonviscous, less fermentable fibres (Cellulose, Ligins, Psylliuma, Resistant Starch, many hemicelluloses)
Major food sources: Brown rice, fruits, legumes, seeds, vegetables (cabbage, carrots, brussel sprouts), wheat bran, whole grains; also extracted and used as food additives
Actions in the Body:
-Increase fecal weight and speed fecal passage
-provide bulk and feelings of fullness
Health Benefits:
-alleviate constipation
-lower risks off diverticulosis, haemorrhoids and appendicitis
-may help with weight management
Resistant starch are potentially significant for colonic health
Inhibit growth of cancer cells and reduce inflammation. Legumes are a particularly good source
Define Microbiome
Overall microbial ecosystem in the human body and is found mainly in the GI tract. Includes hundreds of species of bacteria, yeast, fungi and viruses. Includes health benefits such as protecting the GI tract, aiding in digestion and the production of short-chain fatty acids and some vitamins. Indirectly/directly influences other organ systems through modulation of hormones, immunity and even brain function
A healthy diet is vital to maintaining a healthy microbiome. A substance that enhances the growth of beneficial microorganisms is known as a:
Prebiotic
Many types of dietary fibre can act as a prebiotic.
Can also be obtained from fermented foods, particularly diary products such as yogurt
A healthy microbiome can be disrupted by:
Antibiotics
Stress
Diet
Can result in damage to mucin layers, which protect epithelial cells, and can allow pathogenic microorganisms to cross the mucosal barrier and cause illness or disease
Define Phytic Acid
Phosphate ester of inositol.
Contains 6 phosphate groups.
Significant nutritional role as the principal storage from of phosphorus in many plant tissues, especially bran and seeds
Absorption of carbohydrates takes place…
Mainly in the intestinal mucosa of the jejunum and ileum, although some can be absorbed through the lining of the mouth.
