VISUALIZING NUTRITIONCANADIAN EDITION

Mary B. Grosvenor • Lori A. Smolin • Diana Bedoya

Chapter 4: Sugars, Starches and Fibres

CHAPTER 4: SUGARS, STARCHES AND FIBRES

At the end of this chapter, you should be able to:• Distinguish whole grains from refined sugars• Compare types of carbohydrates• Describe digestion and absorption of carbohydrates• Understand carbohydrate function• Describe the role of carbohydrates in health and

disease• Plan a diet to meet carbohydrate recommendations

LEARNING OBJECTIVES

THINK about this – then share within a PAIR – then SHARE with the class

• What do you know about sugars, starches, and fibre?

• What are whole grains and refined sugars?

• How are whole grains and refined sugars important for your health?

Whole grains vs. refined grains

• Whole grains: contain the whole kernel, including the germ, the bran, and the endosperm

• Refined grains: food processed to remove course parts• Removed parts contain fibre, some vitamins, minerals and

phytochemicals

Whole grains vs. refined grains

The endosperm is the largest part of the kernel. It is made up of primarily starch, but it also contains most of the kernel’s protein, along with some vitamins and minerals. The outermost bran layers contain most of the fibre and are a good source of many vitamins and minerals.The germ, located at the base of the kernel, is the embryo where spouting occurs. It is a source of oil and is rich in vitamin E.

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Enrichment

• Refined grains sold in Canada are enriched

• Enrichment is a type of fortification

• Adds back some of the nutrients lost in processing

• Includes specific amounts of thiamin, riboflavin, niacin, and iron and folic acid

Empty calories

• Empty calories: foods that contain energy but few additional nutrients

• Refined sugars contain calories but lack fibre, phytochemicals and other nutrients

• Foods containing natural sugars (fruits, milk, etc.) - higher nutrient density than foods with added refined sugars

Concept check

• What is the difference between a whole-grain product and a product made with a refined grain?

• Why are foods high in added refined sugars said to contribute empty calories?

Concept check

In a refined grain, which part remains?

a) Germb) Branc) Endospermd) All of the above

Types of carbohydrates

• Carbohydrates are made up of one or more sugar units that contain carbon, hydrogen, and oxygen

• Monosaccharides are made up of a single sugar unit

• Disaccharides are made up of two sugar units

• Polysaccharides are made up of two or more sugar units linked together

Simple carbohydrates

• Monosaccharides and disaccharides are classified as simple carbohydrates

• The most common monosaccharides in our diet are glucose, fructose and galactose

• The most common disaccharides in our diet are maltose, sucrose and galactose

Disaccharides vs. Monosaccharides

Disaccharides vs. Monosaccharides

Disaccharides vs. Monosaccharides

1. Obtain one sticky note2. Pair up with another student to form a disaccharide

Which disaccharide did you make?

Galactose Glucose Lactose

Complex carbohydrates

Complex carbohydrates are polysaccharides that include:• Glycogen, made up of glucose; branched; stored in

animal liver and muscles; not present in our diet

• Starch, made up of glucose; branched or straight chains; found in plants

• Fibre, made up of glucose with bonds that cannot be digested and absorbed by humans

Complex carbohydrates

The polysaccharide glycogen is made of highly branched chains of glucose. This branched structure allows glycogen, which is found in muscle and liver, to be broken down quickly when the body needs glucose.

Different types of starch consist of either straight chains or branched chains of glucose. We consume a mixture of starches in grain products, legumes, and other starchy vegetables.

Most fibre is made of either straight or branched chains of monosaccharides, but the bonds that link the sugar units cannot be broken by human digestive enzymes. For example, cellulose, shown here, is a fibre made up of straight chains of glucose molecules. It is found in wheat bran and broccoli.

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Photosynthesis

Glucose is produced in plants through the process of photosynthesis, which uses energy from the sun to convert carbon dioxide and water to glucose.

Plants most often convert glucose to starch. When a human eats plants, digestion converts the starch back to glucose.

Excess glucose is stored as glycogen in skeletal muscle and liver, the rest – as fat

Soluble fibre vs. insoluble fibre

Soluble fibre: • Dissolves in water• Partially digested by bacteria in large intestine• Helps lower cholesterol, prevents type 2 diabetes

• Examples: pectins, gums, & some hemicelluloses

Insoluble fibre:• Does not dissolve in water• Not digested by bacteria in large intestine• Promotes regular bowel movements, binds toxins, etc.

• Examples: cellulose, some hemicelluloses, & lignin

Soluble fibre vs. insoluble fibre

• Jams and jellies are thickened with pectin, which is a soluble fibre found in fruits and vegetables.

• Some foods are thickened with gums, which combine with water to keep solutions from separating. They include

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arabic, karaya, guar, locust bean, xanthan, and tragacanth gums, which are extracted from shrubs, trees, and seedpods. Other gums are derived from seaweed, including agar, carrageenan, and alginates.

Soluble fibre vs. insoluble fibre

Beans contain soluble fibre and small polysaccharides that cannot be broken down by human digestive enzymes. Bothof these pass into the large intestine, where their digestion by bacteria creates gas. Over-the-counter enzyme tablets andsolutions (such as Beano®) can be taken to digest the small polysaccharides and thus reduce the amount of gas produced.

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Starch

1. Galactose or lactose students return to seats2. If you were glucose, come to the front of the room and

form a polysaccharide

Which polysaccharide did you make?

GlucoseGlucose GlucoseGlucose

Starch digestion

1. Break apart into pairs to form disaccharides Which disaccharide did you make?

GlucoseGlucose GlucoseGlucose

GlucoseGlucose GlucoseGlucose

What are similarities and differences between:

• Glucose and maltose?

• Maltose and starch?

• Starch and fibre?

• Starch and glycogen?

• Glucose and glycogen?

Concept check

Amylase breaks down starch into which disaccharide?

a) Glycogen

b) Maltose

c) Glucose

d) Sucrose

Carbohydrate digestion

Lactose intolerance

• Low levels of small intestine enzyme lactase• The disaccharide lactose cannot be broken down

into monosaccharides• Lactose passes into the large intestine where it is

digested by bacteria• Symptoms: gas, abdominal distension, cramping,

diarrhea• Obtain calcium from: tofu, legumes, dark green

vegetables, canned salmon and sardines, calcium-fortified foods, calcium supplements, lactase-treated milk

Indigestible carbohydrates

• Fibre: not broken down by human enzymes• Oligosaccharides: 3–10 sugar units; some are not

broken down by human enzymes• Resistant starch: the structure of the grain prevents

breakdown of the starch it contains• Resistant structure can occur naturally or be the result of

cooking and processing• Examples: legumes, unripe bananas, and cold cooked

potatoes, rice, and pasta

Indigestible carbohydrates

Stool weights are greater and transit times shorter for Ugandan villagers, who consume a diet high in fibre, than for British subjects, who consume a more refined, low-fibre diet.

(Source: Adapted from Burkitt, D.P., Walker, A.R.P., and Painter, N.S. Dietary fibre and disease. JAMA 229:1068–1074, 1974.)

Indigestible carbohydrates

Indigestible carbohydrates: converted by colon to fatty acids. The acidic conditions inhibit the growth of undesirable bacteria and favour the growth of healthy bacteria, such as the Bifidobacteria shown here.

Fatty acids may also protect against colon cancer and may prevent and treat inflammation in the bowel, which causes diarrhea.

Glycemic index vs. load vs. response

• Glycemic response: measure of how quickly, how high and for how long blood glucose levels rise after carbohydrate consumption

• Glycemic index: ranking of how a food affects blood glucose relative to an equivalent amount of carbohydrate from a reference food, such as white bread or pure glucose

• Examples: white bread = 100, kidney beans = 25

• Glycemic load: compares the effect of typical portions (servings) of food on blood glucose

Glycemic index (GI)

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Carbohydrate functions

• Provide energy! • Other functions:

• Monosaccharides: • Galactose: used by nerve cells and to make milk in

breastfeeding women• Ribose & deoxyribose: components of DNA & RNA• Ribose: also a component of B vitamin riboflavin

• Oligosaccharides:• Cell membrane signaling

• Polysaccharides• Cushioning and lubrication

Insulin vs. glucagon

• During and after a meal: rising blood glucose levels promote release of the pancreatic hormone insulin

• Insulin stimulates:• glucose uptake by the cells• glucose use for energy• conversion of glucose to glycogen and fat

Insulin vs. glucagon

• Several hours after a meal: glucacon, another pancreatic hormone, glucagon is released

• Glucagon stimulates:• breakdown of liver glycogen• release of glucose to blood• gluconeogenesis

Insulin vs. glucagon

Increased

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Insulin secretion

Glucose taken

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Decreased

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Decreased

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Glucagon secretion

Glucose released from liver

Increased

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Insulin vs. glucagon

Glucose as a source of energy

Cellular respiration of glucose• Glycolysis: splitting glucose into two three-carbon

pyruvate molecules; no oxygen required• Anaerobic metabolism: metabolism in the absence of

oxygen• Produces 2 molecules of ATP per glucose molecule• Lactic acid is a by-product

• Aerobic metabolism: metabolism in the presence of oxygen

• Produces 30 molecules of ATP• Carbon dioxide and water are by-products

Protein and fat breakdown

• Glucose is the primary source of energy for the brain and red blood cells

• If blood glucose is low or absent:

• Glucose can be synthesized via gluconeogenesis from amino acids released during protein breakdown

• Ketone bodies are produced from fatty acids

Ketones

• Ketones or ketone bodies: acidic molecules produced by fat breakdown when carbohydrates are not available to cells

• Heart, muscle and kidneys use for energy• Brain adapts after 3 days to use ketones• Produced with starvation, low-carb diets, diabetes

• Ketosis: increased ketones in blood

• Ketoacidosis: acidic blood from increased ketones

Ketone formation

Fatty acids are broken down into two-carbon units that form acetyl CoA. To proceed through aerobic metabolism, acetyl CoA must combine with oxaloacetate, a molecule derived primarily from carbohydrate. When carbohydrate is in short supply, molecules of acetyl CoA react with each other to form ketones. The presence of carbohydrate allows fatty acids to be completely broken down to yield ATP.

Concept check

Which hormone is secreted when blood glucose is low?

a) Insulinb) Glycogenc) Ketonesd) Glucagon

• What do you know about diabetes mellitus?

Diabetes mellitus

• Disease characterized by high blood glucose

• Type 1: elevated blood glucose; absolute insulin deficiency

• Autoimmune destruction of insulin-secreting cells in the pancreas

• Type 2: insulin resistance; relative insulin deficiency

• Gestational: first observed during pregnancy; increased risk of type 2 diabetes later in life

Diabetes mellitus

• Normal blood glucose is >6 mmol/L bloodafter an eight-hour fast; a fasting blood level of 6.1–6.9 mmol/L is defined as prediabetes; a fasting level ≥7 mmol/L is defined as diabetes.

• Two hours after consuming 75 g of glucose, normal blood levels are <7.8 mmol/L; prediabetes levels are 7.8-11 mmol/L; and diabetes levels are ≥ 11.1 mmol/L

Incidence of diabetes mellitus in Canada

The incidence of diabetes in Canada is rising. Newfoundland and Labrador, Nova Scotia, Manitoba, Ontario, and New Brunswick have the highest rates of diabetes, while Alberta, British Columbia, and Quebec have the lowest rates. In most provinces, rates in men are higher than in women, but rates are higher in women in Yukon and the Northwest Territories.

Diabetes mellitus signs & symptoms

• High blood glucose because insulin does not signal cells to take up glucose

• Causes weight loss resulting from break down of fat and protein and loss of water

• Causes increased hunger because cells are starved for glucose

• Increased glucose in urine• Water tries to dilute glucose leading to increased excretion of

water causing dehydration and thirst

Diabetes mellitus complications

Diabetes mellitus management

• Control blood sugar levels• Limit carbohydrate intake

• Increase whole grains and vegetables, decrease refined sugars; limit saturated fats, trans fats, and cholesterol

• Insulin injections for type 1 & some type 2 patients; type 2 patients often take oral drugs

• Manage weight

• Exercise• Exercise and weight loss in type 2 helps prevent, reverse, and

manage the disease

What are similarities and differences between:

• Insulin and glucagon?

• Type 1 and type 2 diabetes mellitus?

Hypoglycemia

• Abnormally low blood glucose levels

• Caused by:• Overmedication with insulin• Abnormal secretion of or response to insulin or other

hormones

• Fasting hypoglycemia: when a person has not eaten and usually has some other condition

• Reactive hypoglycemia: insulin response to a high-carbohydrate meal

Dental caries (cavities)

• Bacteria in mouth digest carbohydrates and produce acid which damages tooth enamel

• Increased risk:• Increased intake of sucrose and starch• Frequent and prolonged exposure

Carbohydrates & calorie intake

• The fat added to high-carbohydrate foods increases calorie count. A medium baked potato = about 160 kcal. Adding 30 mL (2 tablespoons) of sour cream brings the total to > 200 kcal; adding 30 mL (2 tablespoons) of butter more than doubles the total kcal.

• A diet high in sugar-sweetened beverages may increase caloric intake because they do not induce satiety to the same extent as solid carbohydrates.

• A diet high in unrefined, fiber-rich whole-grain carbohydrates may help reduce food intake by adding bulk (feeling of fullness) and slowing digestion.

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Weight management

• Low carbohydrate diets

• Diets height in fibre

• Replacement of refined sugar with non-nutritive sweeteners; pros and cons:

+Decrease dental caries+Control blood sugar−Associated with weight gain−Present in low nutrient density foods−Toxic at high doses

Non-nutritive sweeteners

Aspartame, the sweetener in NutraSweet and Equal, is 200 times sweeter than sucrose. The ADI is 50 mg/kg of body weight/day, and one packet contains 37 mg of aspartame. To exceed the ADI, a 70-kg (154-lb.) person would have to consume 95 packets or 16 355-mL (12-oz.) aspartame-sweetened beverages.

Sucralose, the sweetener in Splenda, is 600 times sweeter than sucrose. The ADI is 5 mg/kg of body weight/day, and one packet contains about 12 mg of sucralose. A 70-kg (154-lb.) person could consume 29 packets without exceeding the ADI.

In the United States, Sweet’n Low is primarily composed of saccharine, which is 300 times sweeter than sucrose. In Canada, since saccharin is still not approved for use, Sweet’n Low’s main ingredient is cyclamate, which is 30-50 times sweeter than sugar. Its ADI is approximately 5 mg/kg of body weight/day. It is not recommended for pregnant women.

Andy Washnik

Carbohydrate and heart disease

• High sugar diets:• increase blood glucose levels; damage blood vessels • increase lipid levels, which accumulate in arteries

• High fibre diets:• Soluble fibre: decrease cholesterol absorption; may decrease

cholesterol synthesis in the liver• Insoluble fibre: may decrease blood pressure, body weight,

blood glucose, obesity and other heart disease risks

Soluble fibre & cholesterol

Bowel health

• High-fibre diets decrease:• Constipation (if adequate water is consumed)• Hemorrhoids (varicose veins in the anus and rectum)• Diverticula (outpouching of the large intestines)

• May reduce risk of colon cancer

Diverticulosis

Diverticula (the singular is diverticulum): outpouches in the wall of the colon that form at weak points due to pressure exerted when the colon contracts.

Diverticulitis: inflammation caused by fecal matter accumulation in these pouches

High-fibre diet is recommended to prevent diverticulitis.

Carbohydrate recommendations

• Enough carbohydrate to meet glucose needs

• Choosing the right types for health & disease prevention 

• RDA for carbohydrate = 130 g/day

• Acceptable Macronutrient Distribution Range for carbohydrate = 45–65% of total calorie intake

• AI for fibre = 38 g/day for men & 25 g for women/day

How much carbohydrate do you eat?

Determine the number of grams of carbohydrate and multiply this value by 4 kilocalories per gram. For example, this vegetarian diet provides about 300 grams of carbohydrate:300 g × 4 kcalories/g = 1,200 kilocalories from carbohydrate

Next divide the number of kilocalories fromcarbohydrate by the total number of kilocalories in the diet and multiply by 100 to convert it to a percentage. In this example, the diet contains 2,000 total kilocalories, and so it provides:(1,200 kilocalories from carbohydrate/2,000 kilocalories total) × 100 = 60% of kilocalories from carbohydrate. This value is between the AMDR of 45–65% daily energy from carbohydrates.

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Calculate

• Total calories = 3,000

• Total carbohydrates = 500 grams

• Carbohydrates = 4 calories/gram

• Fibre = 20 grams

Put it together

What is the percentage of calories from carbohydrate in a diet that provides 240 grams of carbohydrate and 2400 Calories?

a) 10b) 40c) 50d) 60

Thinking it through

Choose a combination of fruits and vegetables from this list that will add at least 13 grams of fibre to the diet.

Choosing carbohydrate wisely

• Eating Well with Canada’s Food Guide recommends:• increasing consumption of whole grains, vegetables, and

fruits• limiting bakery products, candy, soft drinks, and other foods

high in added sugars

• For a 2,000-kilocalorie diet, the food guide recommends that:

• adult females consume six to seven servings of grain products

• adult males consume eight servings of grain products a day• at least half of the grain servings should be whole grains

Healthy Canada’s Food Guide carbohydrate choices

Interpreting food labels

Interpreting food labels

• Food labeled “source of fibre,” “high source of fibre,” and “very high source of fibre” must respectively contain at least 2, 4, and 6 grams of fibre per serving

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Interpreting food labels

Nutrition in the news

• Low-carb diets

• High-fructose corn syrup

• Vending machines in schools

• Artificial sweeteners

• Taxes on sugar-sweetened beverages

Checking student learning outcomes

• How are whole grains and refined sugars similar and different? How do they contribute to health and disease?

• How are types of carbohydrates similar and different?

• What advice would you give to a loved one about carbohydrate consumption?

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