Carbohydrates: Sugars and Starches

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What mechanism does soluble fiber use to help lower blood cholesterol?

Binds with cholesterol-containing bile for excretion (correct)

Stimulates cholesterol synthesis in the liver

Reduces fiber fermentation in the gut

Increases cholesterol absorption in the intestine

How does fiber contribute to blood glucose control?

Increases nutrient absorption speed

Promotes immediate glucose absorption

Increases insulin sensitivity

Traps nutrients and delays intestinal transit (correct)

Which type of carbohydrate is typically found in foods that promote healthy weight management?

Complex carbohydrates (correct)

Simple sugars

Saturated fats

Refined carbohydrates

What is one way that increased dietary fiber intake may protect against colon cancer?

Speeds the removal of potential cancer-causing agents Signup and view all the answers

What role does cellulose play in digestive health?

Softens and enlarges stools for easier bowel movements Signup and view all the answers

Which type of carbohydrate is referred to as the body's first choice for energy?

Monosaccharides Signup and view all the answers

What is the primary role of starch in the body?

Excellent source of glucose Signup and view all the answers

Which of the following is a disaccharide?

Sucrose Signup and view all the answers

What distinguishes soluble fibre from insoluble fibre?

Soluble fibre dissolves in water Signup and view all the answers

Which of the following is NOT a monosaccharide?

Sucrose Signup and view all the answers

Which type of fibre is known for its cholesterol-lowering effect?

Soluble fibre Signup and view all the answers

What is the storage form of glucose in animals?

Glycogen Signup and view all the answers

Which carbohydrate is referred to as milk sugar?

Lactose Signup and view all the answers

What role does water play in relation to dietary fibre?

Enhances the gelling ability of soluble fibre Signup and view all the answers

Which component of a grain is considered the protective fibrous coating that is rich in fibre?

Bran Signup and view all the answers

Study Notes

Carbohydrates: Sugars, Starches, and Fibres

Carbohydrates are the body's primary energy source.
They're used as glucose or stored as glycogen.
Dietary sources include grains (bread, cereals, pasta), beans, legumes, milk, alternatives, fruits, and starchy vegetables (potatoes, turnips, corn, carrots).

Types of Carbohydrates

Monosaccharides: Single sugar units (glucose, galactose, fructose).
Disaccharides: Two monosaccharides joined (sucrose, lactose, maltose).
Polysaccharides: Many monosaccharides linked (starch, fiber, glycogen).

The Sugars (Simple Carbohydrates)

Monosaccharides (single sugars):
- Glucose (blood sugar, dextrose): Main energy source for brain and nerves; excreted in urine by diabetics.
- Fructose: Found in fruit and honey; sweeter than regular sugar.
- Galactose: Part of lactose (milk sugar); freed during digestion.
Disaccharides (pairs of monosaccharides):
- Sucrose (glucose + fructose): Table sugar (beet or cane).
- Lactose (glucose + galactose): Sugar in milk; poorly digested by some (lactose intolerance).
- Maltose (glucose + glucose): Produced during starch breakdown; important in brewing.

Polysaccharides (Complex Carbohydrates)

Starch: Excellent glucose source in plants; long branched and unbranched chains.
Fiber: Structural part of plants; indigestible, contributes little energy (e.g., cellulose, hemicellulose).
Glycogen: Storage form of glucose in the liver and muscles in humans and animals.

Fibre

Polysaccharides: Sugar units held together by bonds indigestible by human enzymes.
Whole grains, fruits, vegetables, and legumes contain fiber.
Two types: soluble (viscous) and insoluble (non-viscous).
Functional fiber is extracted from plants and added to foods/supplements.
Important to drink enough water when consuming fiber.

Soluble Fibre (Viscous Fibre)

Dissolves in water, forming gummy gels.
Fermentable.
Adds thickness to foods (e.g., pectin).
Found in apples, barley, carrots, legumes, oats, and psyllium.
Promotes stool formation, significant cholesterol-lowering effect, and helps regulate blood glucose.

Insoluble Fibre (Non-Viscous Fibre)

Does not dissolve in water, does not form gels.
Less readily fermented.
Found in bran, tough, stringy parts of foods (cellulose and hemicellulose in wheat bran, skin on fruits, vegetables and hulls of seeds).
Helps move stool through the large intestine.

Carbohydrate Digestion in the Mouth

Initiated by salivary amylase.
Splits starch into maltose (sweet taste).

Carbohydrate Digestion in the Stomach

Enzymes are deactivated by stomach acid.
No further starch digestion occurs.
Fiber is not digested.
Delays gastric emptying, contributing to satiety.

Carbohydrate Digestion in the Small Intestine

Majority of carbohydrate digestion occurs here.
Pancreatic amylase digests starch into shorter glucose chains and maltose.
Intestinal cells secrete enzymes (lactase, sucrase, maltase) to break down disaccharides.
Fiber is not digested.
Slows glucose absorption, preventing spikes in blood glucose.

Carbohydrate Digestion in the Large Intestine

Fiber and resistant starch travel unchanged to the colon.
Fiber attracts water to soften stool.
Bacterial fermentation occurs, possibly producing odorous gases.
Resistant starches may help prevent chronic diseases.
Oligosaccharides and polyols are indigestible components.

Absorption

Occurs in the small intestine.
Monosaccharides (glucose, fructose, galactose) enter cells via active or facilitated transport.
Liver converts galactose and fructose to glucose.

Lactose Intolerance

Inadequate lactase to break down lactose in the small intestine.
Intestinal cells produce the highest amount of lactase at birth, declining with age.
Symptoms include bloating, abdominal discomfort, and diarrhea.
Lactose travels undigested to the colon.
Etiology: Primary (genetic) versus secondary (diet-related) lactose intolerance.
Dietary changes/strategies may be needed, including partial elimination of lactose, foods containing live bacteria, or lactase tablets.

Glucose in the Body

Used as energy for cells throughout the body.
Stored as glycogen for later use in the liver and muscles.
Brain relies on glucose for energy.
Glycogen holds water, limiting the total amount stored.

Carbohydrate Storage as Glycogen

Muscle: ~2/3 of body's glycogen - used during high-intensity exercise.
Liver: ~1/3 of body's glycogen - released to maintain blood glucose for the brain and other tissues.
Brain: Small amount of glycogen as an emergency reserve.

Using Glucose for Energy

Glucose fuels most body cells.
Glucose is split into two 3-carbon compounds, yielding energy (and water).
The 3-carbon compounds can be reformed into glucose or converted to other compounds like fatty acids.
Breakdown of glucose compounds to CO2 and water results in energy release in the Krebs cycle and electron transport chain.

Below Healthy Minimum

Minimum 50-100g carbohydrates per day needed for brain and nerve function, to prevent ketosis.
Insufficient carbohydrates can lead to reliance on fat as an energy source, and ketosis and ketone bodies.
Glucose made from fat, or protein through gluconeogenesis is not ideal.

Handling Excess Glucose

Excess glucose is typically converted to fat and stored in fat cells.

Regulation of Blood Glucose

Glucose is regulated by two hormones:
- Glucagon: Released when blood glucose levels fall; triggers the breakdown of liver glycogen to free glucose.
- Insulin: Released when blood glucose levels rise; stimulates the uptake of glucose into cells and the storage of glycogen in the liver.
Maintaining a proper balance relies on a regular schedule of balanced meals containing carbohydrates (starch), fiber, protein, and healthy fat.

Diabetes Mellitus

Chronic disease where the body cannot regulate blood glucose levels normally.
Types include Type 1, Type 2, Gestational, and Prediabetes (less common types: MODY - Maturity Onset Diabetes of the Young, and LADA- Latent Autoimmune Diabetes in Adults).
Type 1 is insulin-dependent (autoimmune attack on pancreas, inadequate insulin produced).
Type 2 is insulin-resistant (body cells do not respond to insulin, or pancreas does not produce enough insulin adequately).
Prediabetes (impaired glucose tolerance - symptoms of increased sugar levels but not meet the criteria for diabetes).

Hypoglycemia

Blood glucose level is below the normal range.
Two types:
- Reactive hypoglycemia: Low blood glucose after a meal (body secretes too much insulin).
- Fasting hypoglycemia: Low blood glucose between meals due to prolonged time between meals or other factors (e.g., pancreatic damage, certain cancers, infection, uncontrolled diabetes).

Symptoms of Hypoglycemia

Fatigue, weakness, dizziness, headache, rapid heartbeat, sweating, trembling, hunger, anxiety, irritability, moodiness, confusion.
Extreme cases: Amnesia, seizures, unconsciousness.

The Glycemic Response

How quickly glucose is absorbed after ingestion.
How high blood glucose rises and how quickly it returns to normal.
Glycemic index reflects the rate of absorption.

Carbohydrate Recommendations

Canada's Food Guide (CFG) and the Dietary Reference Intakes (DRIs) suggest daily values of carbohydrates and dietary fiber.
Minimum daily intake is 130 g of glucose to meet brain/nerve needs.
Adults should aim for 45–65% of total calories from carbohydrates.

Practice Calculation

Determine the grams of carbohydrates to consume based on total calories consumed daily and desired macronutrient distribution.

Guidelines Regarding Sugar

Canada's Food Guide (CFG), the Dietary Reference Intake (DRI), and the World Health Organization (WHO) recommend limiting added sugars in the diet (less than 10% of total energy intake).

Sugar Substitutes

Sugar alcohols: occur naturally, fewer calories than sugar, lead to GI issues in high doses (restricted on low FODMAP diets).
Artificial sweeteners: calorie-free, approved daily intake values, some banned or not best for certain uses - (e.g., sucralose).

Health Effects of Sugar

Sugar intake and obesity, heart disease, diabetes, behavior (in a restricted context).
Excess sugar intake can lead to weight gain, increased risk of heart disease, type 2 diabetes, and dental problems. Food labels for carbohydrate/sugar content are shown on product labels.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the various types of carbohydrates, including sugars, starches, and fibers. Learn about monosaccharides, disaccharides, and polysaccharides, as well as their dietary sources and roles in the body. Test your knowledge on how these carbohydrate types contribute to energy metabolism.