6: Carbohydrates Flashcards
What are the three main types of carbohydrates?
Sugars, starches, and fibre
Why is fibre unlike other carbohydrates?
fibre has monosaccharides bonded together in a way that humans cannot digest
Define intrinsic sugars and give examples
Sugars naturally found in many foods
- Fruits and milk
Define extrinsic sugars (added sugars)
Sugars added to foods by the food industry to enhance the flavour of processed foods
What are the three main monosaccharides (single sugars) found found in food
Glucose (most common), fructose, galactose
Monosaccharides (Single Sugars):
Define Glucose
- building block of most other longer carbohydrates like starch and fibre
- main monosaccharide found in the blood (blood sugar)
Monosaccharides (Single Sugars):
Functions of Glucose
- fuel the needs of all cells in body, (brain cells, red blood cells), both have an absolute requirement for glucose
- Glucose can be metabolized into ATP, the body’s main energy currency
Monosaccharides (Single Sugars):
Where is Fructose found
- fruit sugar, found in many fruits as well as some vegetables and honey
- significantly sweeter than glucose and other sugars. Therefore added to processed foods to increase perceived sweetness
Monosaccharides (Single Sugars):
Where is Galactose found
- milk sugar because it’s found in milk
- similar in sweetness to glucose
Disaccharides (Double Sugars):
What are the three most common disaccharide in the diet?
sucrose, maltose and lactose
How are Disaccharides (Double Sugars) made, what is its structure
sugars with two monosaccharide units
Disaccharides (Double Sugars):
Sucrose (Table Sugar)
Glucose + Fructose = Sucrose
- typically white or brown
Disaccharides (Double Sugars):
What enzyme breaks down sucrose
Enzyme Sucrase
- breaks down sucrose into its respective two sugars, then absorbed at the villi of the small intestine
T/F: brown sugar is healthier than white sugar
False, no clear advantage to consuming brown sugar over white.
- Brown sugar is white sugar mixed with molasses
- very similar nutritionally
Disaccharides (Double Sugars):
Maltose (Malt Sugar)
- Starch, formed from a long chain of glucose molecules
- Mouth enzymes break down longer starch chains, forming glucose-glucose disaccharide maltose
Disaccharides (Double Sugars):
What enzyme breaks down Maltose
Enzyme Maltase
- in the small intestine, enzyme maltase breaks down maltose into glucose molecules, which can then be absorbed
Disaccharides (Double Sugars):
Lactose (Milk Sugar)
Glucose + Galactose = Lactose
- main sugar found in milk
- enzyme lactase breaks it down
What is Lactose Intolerance
Condition where people lack the enzyme lactase that helps separate glucose and galactose molecules in lactose
What are Extrinsic Sugars
- added sugars into food by manufacturers to increase sweetness
What are Intrinsic Sugars
Naturally found in foods
Both brown and white sugar are sucrose that originates from what foods
Sugar cane or beets
T/F: Both Intrinsic and Extrinsic Sugars Must be Grouped Together on an Ingredients List
False, only extrinsic sugars are grouped together on an ingredients list
Oligosaccharides (Few Sugars)
- between 3 and 10 monosaccharides in their chain
- considered fibres, because humans lack enzymes needed to digest them
- Most common oligos = fructooligosaccharides (FOSs) and galactooligosaccharides (GOSs)
Why are Oligosaccharides prebiotic
- cannot be broken down by enzymes in small intestine, bacteria in the large intestine can ferment them
- prebiotics because bacteria use them for food and growth
What are Polysaccharides (Many Sugars)
- chains of monosaccharides greater than 10 units in length
- composed of long glucose chains
- 2 types of polysaccharides (starches and fibre)
Polysaccharides (Many Sugars):
Starch
- long glucose chain, either straight (amylose) or branched (amylopectin)
- get starch from eating plant foods
- Amylopectin, most common carb in the human diet
How are Polysaccharides: Starch, digested
- broken down into oligosaccharides
- then into disaccharides
- eventually into monosaccharide glucose
- then absorbed
Polysaccharides (Many Sugars):
What is Fibre
Composed of long chains of glucose molecules like starch
- Fibre = PLANT substances such as cellulose, dextrin and inulin that human enzymes cannot break down
T/F: No chemical digestion of fibre in the small intestine
True, fibres reach the large intestine predominantly undigested.
- bacteria ferment certain fibres into short-chain fatty acids. Short-chain fatty acids are then absorbed and contribute to our energy intake
T/F: Fibres are predominantly composed of glucose, and is a source of glucose to the body
False. Even though fibres are predominantly composed of glucose, fibre is not a source of glucose to the body. Instead, it is potentially a source of short chain fatty acids
Whether fibre can or cannot be fermented into short chain fatty acids primarily depends on what
whether it is soluble or insoluble fibre
Soluble Fibre
Dissolves in water to form a gelatinous solution
- Bacteria in large intestine can ferment soluble fibre to produce short-chain fatty acids
- provides 2-3 kcal/g
Foods that have Soluble Fibre
Oats, apples, beans, peas, citrus fruits, barley and psyllium
Soluble fibre has what health benefits
- may improve cardiovascular health
- regulate blood glucose
- lower blood cholesterol
Insoluble fibre
- Does not dissolve readily in water
- Passes through digestive tract virtually unchanged, not fermented by bacteria in large intestine
Health benefits of Insoluble fibre
May promote digestive health
High sources of Insoluble fibre in food
Wheat, bran, beans, potatoes, cauliflower
Glycogen
- synthesizing long chains of glucose mlcs with the aim of storing them
- glycogen stored in our muscles and around our liver
- only store so much carbohydrate – typically around 0.5-2 kg
Unrefined Carbohydrates
Unrefined sources of carbs are consumed in their entire form; entire grain is used
Ex: whole grain wheat, whole grain oats
Refined Carbohydrates
Refined sources of carbohydrates have part of the grain removed, typically the bran and germ layer
- lowers nutrient density of plant
T/F: whole wheat is the same as whole grain wheat
False, whole wheat is not the same as whole grain wheat; not fully a whole grain but contains more fibre than a refined grain
Carbohydrate Digestion
- Mouth, salivary amylase begins digestion of starch
- Stomach, HCl inactivates salivary amylase, no carb digestion here
- Pancreatic amylase secret into small intestine to continue digestion
- Microvilli of small intestine also secrete carb digesting enzymes
- Undigested carb pass onto large intestine; further broken by bacteria
- Any remaining undigested carb is excreted
Digestion and Absorption of Carbohydrates at the Villi
- Brush border intestinal cells release carb digesting enzymes to finish digesting job of amylase
- Small intestine villi absorbs carbs digested into monosaccharides
- Glucose, fructose, galactose absorb across small intestine wall into blood capillaries
- Liver metabolizes fructose/galactose, live stores glucose as glycogen
Lactose Intolerance
- insufficient secretion of enzyme lactase
- lactose cannot be digested in small intestine, bacteria in large intestine ferment it
- Leads to production of methane gas
What is Glycemic Response and its association with diets
spike in blood glucose that follows a meal once glucose enters the general circulation
- Diets that produce a lower GR associated with a lower risk of type 2 diabetes, CVD and obesity
Glycemic index
relative ranking of a food’s potential to spike blood sugar on a 100-point scale
Glycemic load (GL)
more accurate assessment of blood glucose will spike since it considers the food’s GI plus the actual amount of carbohydrate within the food
What are the glycemic index of common foods
Low GI (< 55): non-starchy veggie, soy milk, less sweet fruit, 100% whole wheat
Med GI (56-69): ice cream, rice, sweeter fruits, bread, whole grain wheat
High GI (>70): candy, watermelon, chips, white rice/bread, muffins
Blood Sugar Regulation –
Role of Insulin and Glucagon
bodies try to establish glucose homeostasis
- Insulin and glucagon are blood glucose-regulating hormones (secreted by pancreas)
Blood Sugar Regulation:
Hypoglycemia
- Low blood glucose levels
- tiredness, lethargy and irritability
Blood Sugar Regulation:
Hyperglycemia
- elevated blood sugar levels
- damage blood vessels, kidneys and promote diabetes
Endocrine Pancreas
secretion of hormones insulin and glucagon into blood to regulate blood glucose
Exocrine Pancreas
- secretes pancreatic juice into the small intestine
- Pancreatic amylase, lipase and protease promote digestion of carbs, lipids and proteins
Insulin lowers blood glucose levels - process
- Normal blood glucose
- After meal, blood glucose concentration increases
- Pancreas secretes insulin into blood due to increase in blood glucose
- Insulin bines to receptors on cells
- Finding of insulin to receptors bring glucose channels to sell surface
- Glucose leaves blood and enters cells through glucose channels
- Blood glucose returns to normal
Glucagon and blood glucose
When blood glucose levels drop, pancreas releases glucagon
- Glucagon increases blood glucose by promoting three main processes (glycogenolysis, gluconeogenesis, lipolysis)
Glucagon and blood glucose:
Glycogenolysis
Conversion of glycogen to glucose
Glucagon and blood glucose:
Gluconeogenesis
Conversion of certain amino acids into glucose
Glucagon and blood glucose:
Lipolysis
Breakdown of stored lipids
- glycerol from triglycerides can then be used to make glucose
Carbohydrate functions:
Energy provision
Carbs main role is to provide energy
- glucose is main carb and used as source of energy by all body tissues
- Cells metabolize glucose to capture its energy as ATP
Carbohydrate functions:
Protein sparing
If body does not consume enough carbs in diet, certain amino acids are used to make glucose through gluconeogenesis
- leads to breakdown of body protein
- Getting enough carbs in diet, prevent this from happening and helps maintain protein and tissues (muscles)
Carbohydrate functions:
Fat burns in a carbohydrate flame
- Sufficient dietary carbs are needed to maintain the citric acid cycle
- diet very low in carbs, products of lipid metabolism cannot enter citric acid cycle and will instead form ketones bodies to fuel body needs
Carbohydrates and health:
Diabetes
- chronically elevated blood glucose levels, due to bodies,inability to regulate (both acute/chronic symptoms)
Carbohydrates and health:
Acute diabetes symptoms
Increased thirst, tiredness/lack of energy, slow healing infections, frequent urination, weight loss
Carbohydrates and health:
Chronic diabetes symptoms
Neuropathy/numbness, cardiovascular disease, blindness, kidney disease, amputation
Carbohydrates and health:
Type one diabetes
- Approximately 10% of cases
- immune system attacks, insulin secreting cells of pancreas = no insulin to promote glucose uptake into cells and out of blood
Carbohydrates and health:
Type two diabetes
- approximately 90% of cases
- Pancreas still secrete insulin but cells lose sensitivity to it (insulin resistance)
Carbohydrates and health:
Gestational diabetes
- Elevated blood glucose and impaired glucose management that first occurs during pregnancy
- Approximately 5% of pregnant women develop it
- Increases future risk for type two diabetes and mother
Carbohydrates and health:
Risk factors for type 1 diabetes
Unknown
Carbohydrates and health:
Risk factors for type 2 diabetes
Obesity, physical inactivity, genetics, family history, gestational diabetes, diets high in processed foods sugars, fat
Carbohydrates and health:
Prevention of type 1 diabetes
No preventative measures have been established
Carbohydrates and health:
Prevention of type 2 diabetes
- Lifestyle changes: weight balance (loss), reduction in caloric intake (fat), physical activity
- Medication
Carbohydrates and health:
Management of type 1 diabetes
No cure
- Insulin injection
- Lifestyle
Carbohydrates and health:
Management for type 2 diabetes
No cure
- lifestyle, blood sugar monitoring, medication, insulin injections, bariatric surgery (shrink size of stomach)
Sir Frederick Banting
Discovered insulin
Carbohydrates and health:
Hypoglycemia
- Low blood glucose
- Dizziness, hunger, headache, irritability, tiredness, mental confusion
- 2 types of chronic hypoglycemia (reactive, and non-reactive)
Carbohydrates and health:
Reactive hypoglycemia
Low blood glucose due to excessively high release of insulin
- Occurs 2 to 5 hours after meal
Carbohydrates and health:
Non-reactive hypoglycemia
“Fasting hypoglycemia”
- May or may not be related to meals
- May occur due to fasting medications, pregnancy, alcohol abuse, liver, heart, kidney disorders
Carbohydrates and health:
Sugar and health
- Sugar is not inherently bad or good
- Foods high in extrinsic sugars are often energy dense and nutrient poor
- Diet high in extrinsic sugars, increase risk of CVD, diabetes and obesity
Carbohydrates and health:
Non-nutritive sweeteners (NNSs)
“Sugar substitutes, artificial sweeteners”
- negligible number of calories and nutrients but sweet tasting flavour
- 30-1300 x sweeter than sugar
- Effects on weight and disease are still being studied
Carbohydrates and health:
Is Aspartame Safe?
- most rigorously studied food additive
- Large scale systemic reviews have found no link between aspartame and cancer logical symptoms
Carbohydrates and health:
Carbohydrates and weight management
- Carb intake does not increase caloric intake, weight will not be gained
- Liquid sources of carbs (sugar, sweetened beverages, decrease in fullness), increase caloric consumption
- Fiber is associated with lower BMI due to ability to increase fullness
Carbohydrates and health: carbohydrates and dental caries
Cavities: holes that develop in teeth, promote pain and tooth loss
- Sugars provide food for bacteria to grow and thrive = bacteria release acid when act on sugar damaging tooth enamel
Carbohydrates and health:
Carbohydrates on CVD
- diet high and sugars, refined carbs pose a greater CVD risk
- diet high in fibre associated with lower CBD risk (soluble fiber, lower bad cholesterol, regulates blood sugar)
Carbohydrates and health:
FODMAPs and IBS
- short chain carbs are not fully absorbed in small intestine and are fermented by bacteria in large intestine, producing gas (may promote IBS symptoms)
- Reducing FODMAPs (fermentable oligosaccharides, disaccharide, monosaccharide, and polyols) may improve IBS symptoms
High FODMAP foods that may promote IBS
Vegetables, fruits, carb dense foods, lipid dense foods, protein dense foods
Carbohydrates and health:
Fibre and colon cancer
- dietary fibre intake may reduce risk of developing colon cancer
- individuals who consume more fibre have lower risk of colon cancer
- Fiber made dilute concentrations of cancer causing agents, promote removal or minimize damage they can cause
Recommendations of carbs
- Limit added sugars to no more than 10% of total energy intake, and ideally below 5% of total energy intake
- Consume fibre rich foods aiming for approx 25 g/day woman and 38 g/day men
Recommendations of carbs
- Limit added sugars to no more than 10% of total energy intake, and ideally below 5% of total energy intake
- Consume fibre rich foods aiming for approx 25 g/day woman and 38 g/day men
What is known as milk sugar
Lactose and galactose
Bacteria ferment certain fibres into __________, which can be absorbed and used for energy
Short chain fatty acids
Bacteria ferment certain fibres into __________, which can be absorbed and used for energy
Short chain fatty acids
T/F: body stores about a quarter of its energy as glycogen
False, at most, glycogen storage accounts for a few kilograms of stored energy
Lactase is brush border enzyme, which means it is secreted by the __________, which are collectively known as the brush border
Microvilli
Diabetes Canada recommends that those with diabetes consume foods that produce a lower ____________
Glycemic response
__________ is the conversion of certain amino acids into glucose
Gluconeogenesis
What is the main role of carbs in human body?
Fuelling body needs
T/F: Obesity is an outcome of diabetes
False, obesity is a risk factor, not an outcome
