Carbohydrates Flashcards
Carbohydrates
Carbon, Hydrogen, Oxygen (CHO)
Energy Cycles
- Through photosynthesis, plants combine carbon dioxide, water and the sun’s energy to form glucose
- When humans metabolize glucose, energy and carbon dioxide are released
Types of carbohydrates
- Simple CHO (sugars)
- Complex CHO or polysaccharides (starch and fibre)
Simple Carbohydrates
- Monosaccharides
- Glucose
- Galactose
- Fructose
- Disaccharides
- Sucrose (glucose + fructose)
- Maltose (Glucose + Glucose)
- Lactose (Glucose + Galactose)
Glucose (Monosaccharides)
Brain is completely dependent on glucose as its energy source
Galactose (Monosaccharides)
Differs from glucose only in that hydroxyl group faces in a different direction on the number four carbon
Fructose (Monosaccharides)
- Same chemical formula as glucose but different structure
- Natural sources: fruits, honey, sugarcane
- Also found in soft drinks, cereals, and products sweetened with high fructose corn syrup
Disaccharides
Pairs of two monosaccharides linked together
Sucrose (glucose + fructose) (Disaccharides)
Table sugar, also found in many F&V, especially sugar beets and sugarcane
Maltose (Glucose + Glucose)
(Disaccharides)
- Common breakdown product of plant starches, rarely found in foods
- Associated with sweet taste in mouth when chewing bread
Lactose (Glucose + Galactose)
(Disaccharides)
Milk sugar, found in dairy products like milk, yogurt, cheese
Polysaccharides
Long chains of monosaccharides that may be branched or not branched
Plant forms: Starch and fibre (Polysaccharides)
Human digestive enzymes can break the bonds between glucose units in starch but not in fibre (e.g., cellulose)
Animal form: glycogen (more branched)
(Polysaccharides)
- Human digestive enzymes can break the bonds
- Found in liver and muscle (meat)
Recommendations
- DRI
- 45-65% of energy from carbohydrates, emphasis on complex and whole grain
- Minimum 130 grams per day
- <25% of energy from added sugars
Food Sources
- Pasta
- Rice
- Beans
- Cereals
- Breads
- Milk/milk products
- Fruits
- Starchy Vegetables (Potatoes, Peas, Corn, Squash)
Dietary Fibre
- Suggested intake:
- WHO: >25 g per day
- DRI:
- <50 yrs: males 38g/d; females 25 g/d
- > 50 yrs: males 30 g/d; females 21 g/d
Water Soluble Fibre (Types & Sources)
- Types:
- gums, mucilages, pectins, psyllium, some hemicellulose
- Sources:
- Oats, oat bran, barley, rye, seeds, fruits, vegetables,legumes
Water Soluble Fibre (Benefits)
- Lower blood cholesterol
- Slow glucose absorption
- Slow transit of food through upper digestive tract
- Hold moisture in stools, softening them
- Yield small, fat-like molecules after fermentation that the colon can use for energy
- Lower risk of heart disease and diabetes
Insoluble Fibre (Types & Sources)
- Types:
- Cellulose, lignin, and some hemicellulose
- Sources:
- Brown rice, wheat bran, whole grains, seeds, fruits, vegetables, legumes
Water Insoluble Fibre (Benefits)
- Increase fecal weight
- Increase colonic transit
- Alleviate constipation
- Reduce risk for diverticular disease, hemorrhoids and appendicitis
- Provide bulk and feeling of fullness
- Weight management
Consumer Corner
- If a bread contains a refined flour, the husk, germ and bran have been removed lower in nutrients and fibre
- If a bread contains an enriched flour, some or all of the nutrients lost when the flour was processed have been added back
How Carbohydrates in Food Become Glucose in the Body
- Mouth
- Stomach
- Small Intestine
- Fibre travels unchanged to the colon
- Absorption of glucose, fructose and galactose into bloodstream
- Liver
- All digestible CHO becomes glucose in the body and is used for:
- Energy (Directly, or from glycogen stores)
- Glycoproteins (CHO attached to proteins) e.g. mucus, cell membranes
Mouth (Glucose in the Body)
Minor digestion by salivary amylase (5%)
Stomach (Glucose in the Body)
Mechanical digestion, turns bolus to chyme
Small Intestine (Glucose in the Body)
Digestion by pancreatic amylase (starch disaccharides) and enzymes on intestinal wall (disaccharides monosaccharides)
Liver (Glucose in the Body)
Liver converts galactose and fructose to glucose
Postprandial CHO Metabolism
- Blood glucose rises after eating CHO
- Amount of increase reflects:
- Amount of CHO consumed
- Rate of digestion and rate of entry into bloodstream
- Rate of uptake by the cells
Blood Glucose (1)
- Under homeostasis
- Is tightly regulated
- Normal fasting blood glucose level is 4 - 6 mmol/L
- Hypoglycemia
- Low blood glucose
- Hyperglycemia
- High blood glucose
Blood Glucose (2)
- When blood glucose is low, the pancreas releases glucagon (hormone)
- Breakdown of liver glycogen → glucose → blood → tissues for energy
- Glucose is produced from protein (gluconeogenesis)
- If this occurs on a long-term basis (e.g. disease states) then result is muscle wasting
Ketosis
- Need minimum 130 g CHO/day to prevent ketosis and spare protein (muscle)
- Usually consume 200-400 g CHO/d
- Liver glycogen lasts 4-6 hrs depending on CHO intake, exercise , etc.
- If liver glycogen is depleted, then ketosis occurs
Diabetes (1)
- Type 1 (early or mid-life, <10% cases)
- Hyperglycemia due to little or no insulin produced by the pancreas
- Auto-immune response
- Untreated: glucose wasting (urine) and weight loss
- Treatment: insulin is injected to match food intake and physical activity
Diabetes (2)
- Type 2 (T2D)
- Formerly adult, now children/teens = >90% cases
- Hyperglycemia due to insulin resistance (associated with overweight and obesity)
- Pancreas produces lots of insulin, but cells respond poorly
- Chronic hyperglycemia increases risk of cardiovascular disease, kidney disease, cataracts/blindness, amputations, etc.
Risk Factors for T2D
- Family history
- Sedentary lifestyle
- Overweight / obese
- Moderate weight gain in adulthood
- History of gestational diabetes
- Genes: Aboriginal, African American, Hispanic, Asian, Pacific Islander descent
Warning Signs of T2D (1)
- Excessive urination and thirst
- Glucosuria (glucose in urine)
- Weight loss, nausea, weakness, irritability
- Cravings for food, especially sweets
- Drowsiness, tire easily
- Vision disturbances
Warning Signs of T2D (2)
- Frequent infections (e.g. skin, gums, urinary tract, yeast)
- Slow healing of cuts and bruises
- Pain in legs, feet, or fingers
- Usually with tingling due to nerve damage
- Abnormally high glucose tolerance test results
Management of T2D
- Diet and physical activity
- 10% weight loss is beneficial
- Oral agents
- Sometimes insulin injections
Glycemic Effect of Food (1)
- Extent to which foods elevate blood glucose compared to a glucose solution or white bread
- Low number considered best: legumes, peas
- High number: white bread, juice
Glycemic Effect of Food (2)
- Factors to consider:
- Type of food:
- Apple < apple juice
- Cooking method:
- Baked potato < mashed
- Eaten alone or part of a mixed meal
- Type of food:
Glycemic Effect of Food (3)
- Limitation
- Does not consider amount of carbohydrate, only type
- Combining different high and low GI foods changes the GI for the overall meal (glycemic load)
- Some nutrient dense foods have higher GIs than less nutritious foods
- EX: oatmeal has higher GI than chocolate because chocolate has higher fat content
Carbohydrate Counting
- Simple, flexible meal planning tool
- Want consistent CHO intake at meals
- Grains, fruits, milk, sweets, all CHO choices
- 1 grains & Starch choice = 15 g CHO
- 1 Fruits choice = 15 g CHO
- 1 Milk & Alternatives choice = 15 g CHO
- Meat & Alternatives and Fat choices do not contain CHO
Lactose Intolerance (1)
- In sufficient lactose enzyme activity to digest lactose → glucose + galactose
- Develops in adults of non-Northern European background
- Signs: nausea, pain, diarrhea, and gas
- More osmotic particles draws water
- Bacterial fermentation in intestine
Lactose Intolerance (2)
- Management:
- Consume milk in small amounts (1/2 - 1 cup) with meals
- Yogurt, aged cheeses
- Products treated with lactase (e.g. Lactaid milk, ice cream)
- Add enzyme drops to milk-based foods
- Lactaid pills
Milk Allergy
- Need non-dairy sources of calcium:
- Calcium-fortified soy milk and orange juice
- Canned sardines or salmon with bones
- Vegetables (e.g. broccoli, bok choy)
- Consider a calcium supplement
Controversy 4: Sugars and Health (1 Do sugars play a role in)
- Obensity?
- Aggravating diabetes?
- Increasing risk for heart disease?
- Behavioral problems?
- Dental problems
Controversy 4: Sugars and Health (2 Use sugar in moderation)
- WHO: <10% Calories from added sugars [DRI: <25%]
- IOM: no more than 25% of total calories from added sugars
Controversy 4: Sugars and Health (3 Added vs natural Sugars)
- Added
- Sugars and syrups added to foods during processing or preparation
- EX: brown sugar, corn syrup, dextrose, fructose, fruit juice concentrates, maple syrup, sucrose, and raw sugar that are added to foods
- Sugars and syrups added to foods during processing or preparation
- Natural
- Naturally occurring in foods and have not been added
- Includes the above natural sources
- Naturally occurring in foods and have not been added
Controversy 4: Sugars and Health (4 Sugar Alcohols)
- members of chemical alcohol family (structure)
- Sorbitol, mannitol, xylitol, isomalt, maltitol, lactitol
- Not readily used by mouth bacteria
- All have 3-5 Calories/g but poorly absorbed
Controversy 4: Sugars and Health (5 Artificial Sweeteners (1))
- Aspartame (200 x sweeter than sucrose),
acesulfame-K (200 x), sucralose (600 x)
[cyclamate and saccharin have restricted
uses in Canada] - Calorie-free because so little is used
- Aspartame = phenylalanine + aspartic acid, 4 cal/g from the amino acids but calorie-free; product warning for
people with PKU (phenylketonuria)
Controversy 4: Sugars and Health (6 Artificial Sweeteners (2))
- Acceptable daily intake (ADI) is the estimated amount of sweetener that can be consumed daily over a person’s lifetime
without any adverse effects - ADI = 40 mg/kg body weight for aspartame in Canada
- 150 lb (68 kg) person: ~72 packets of Equal or ~13 diet soft drinks
