Chapter 4. Carbohydrates
Chapter Review
IMPORTANT: Key Takeaways
- Fast-releasing simple carbohydrates, known as “sugars,” can be classified as monosaccharides (glucose, fructose, and galactose) or disaccharides (lactose, maltose, and sucrose).
- Slow-releasing complex carbohydrates include oligosaccharides (ie. stachyose and raffinose) and polysaccharides (starches, fibres, and glycogen).
- Soluble fibres dissolve in water, are fermentable, and can form gels that serve to trap nutrients and slow down absorption. These fibres are associated with a reduced risk of cardiovascular disease and type 2 diabetes. Insoluble fibres do not typically dissolve in water and are not typically fermented by bacteria in the colon, but help with regular bowel movements, constipation, and diverticulosis.
- Carbohydrate digestion begins in the mouth with salivary amylase breaking down starch into smaller polysaccharides. In the stomach, no further chemical breakdown occurs due to the acidic environment. However, mechanical digestion continues through peristaltic contractions. In the small intestine, pancreatic amylase breaks down starch into shorter carbohydrate chains, while brush border enzymes break down disaccharides and oligosaccharides into monosaccharides. These monosaccharides are then absorbed into the bloodstream for distribution or storage. In the large intestine, bacteria partially break down fibre and indigestible carbohydrates, with the remaining fibre excreted in feces.
- Carbohydrates primarily serve as an energy source, particularly during higher exercise intensities, providing 4 kcal of energy per gram. Excess glucose can be stored as glycogen in the liver or muscles. Maintaining adequate dietary carbohydrate intake is crucial, as synthesizing glucose from amino acids leads to protein breakdown, primarily from muscle tissue.
- Carbohydrates are found in all five food groups: grains, fruits, vegetables, meats, beans, and dairy products. Optimal carbohydrate sources are nutrient-dense and minimally processed, such as whole-grain bread and cereals, fruits, vegetables, and low-fat dairy products.
- The Recommended Dietary Allowance (RDA) for carbohydrates is 130 grams per day for children and adults, which is the minimum amount required for proper brain function. The Acceptable Macronutrient Distribution Range (AMDR) suggests that carbohydrates should make up between 45 and 65 percent of total caloric intake. However, individual choices and food variety contribute to specific health benefits, with preferences for whole grains and reduced consumption of sugary beverages leading to more favorable outcomes.
Practice Questions
- What is the difference between monosaccharides and disaccharides? Provide a few examples of each.
- What is the difference between soluble and insoluble fibres? Provide examples of each.
- Which enzymes are involved in the chemical digestion of carbohydrates and what are their respective roles?
- Which condition does a lactase enzyme deficiency lead to? How does this health condition influence one’s digestive process and dietary choices?
- How does the pancreas regulate blood glucose levels in the body?
- What is the difference between type I and type II diabetes? What are the complications associated with uncontrolled diabetes?
- What happens to any remaining indigestible carbohydrates in the large intestine?
- How can the glycemic index be used to make healthier carbohydrate choices? What are some of the limitations of using the glycemic index?
- Under which circumstances can carbohydrate loading optimize athlete performance and how? HINT: Think about muscle glycogen reserves and how long they typically last.
- Explain the “fat-sparing” effect of glucose and how it relates to fat metabolism.
- Discuss the claims made by low-carbohydrate diets concerning weight loss and their associated challenges.
- What are some of the potential benefits and side effects of consuming foods and beverages made with sugar substitutes?
- Provide examples of personal dietary choices that can assist individuals in meeting the Health Canada recommendations of eating more unrefined carbohydrates and fibres.
