What are carbohydrates?
One of the three macronutrients, preferred energy source for the brain, important source of energy for all cells, composed of C, H, and O, and good sources of fruits, vegetables, and grains.
Are obtained almost exclusively from plant sources; milk is the exception.
Plants convert water and carbon dioxide to sugar through this and light energy is trapped as chemical energy in the sugar molecules.
Two Major Groups
Simple Carbohydrates: Monosaccharides
Complex Carbohydrates: Polysaccharides
Contain one or two molecules, commonly referred to as sugars, monosaccharides contain only one molecule; glucose, fructose, and galactose.
Long chains of glucose molecules, commonly called polysaccharides, hundreds to thousands of molecules long, the storage forms of glucose, digestible is starch and glycogen, and indigestible are most fibers.
Plants store carbohydrates as this, we digest it to glucose, and a good source of grains, legumes, and tubers.
Animals store carbohydrates as glycogen, stored in liver and muscle, and not found in food and therefore not a source of dietary carbohydrate.
Is the non-digestible part of plants; grains, rice, seeds, legumes, and fruits.
Is carbohydrate extracted from plants and added to food; cellulose, gugar gum, pectin, and psyllium.
Dietary + functional fiber.
Dissolve in water, are viscous and gel-forming, associated with risk reduction of cardiovascular disease and Type 2 Diabetes, found in citrus fruits, berries, oats, and bean. Ex: Pectin, gum, mucilage.
Do not dissolve in water, are non-viscous, promote regular bowel movements, good source of whole grains, seeds, legumes, fruits, and vegetables. EX: Lignins, cellulose, and hemicellulose.
Physical Characteristics of Fiber
Water-holding capacity, viscosity, cation-exchange capacity, bile binding capacity, and fermentable.
Effect of Fiber on the Digestive Tract
Stimulates the flow of saliva, delays gastric emptying, delays the absorption of CHO & fat, binds heavy metals and minerals in the intestines, attracts water in the colon, and stimulate bacterial fermentation.
Positive Effects of Fiber on Diet
Moderates nutrient absorption, reduces the absorption of cholesterol and other sterols, stimulates growth of a healthy bacterial population in the colon, and increases softness and volume of stools.
May reduce the risk of colon cancer, help prevent hemorrhoids, constipation, and other intestinal problems, may reduce the risk of diverticulosis, may reduce the risk of heart disease, may enhance weight loss, and may lower the risk of Type 2 Diabetes.
Adequate Intake (AI) Fiber
Is 25 grams daily or 14g/1000 kcal.
Negative Effects of Fiber on the Diet
Displaces energy and nutrient-dense foods, may cause intestinal discomfort and gas, may interfere with absorption of minerals, and can cause G.I. obstructions if consumed without adequate fluids.
Recommendation of Fiber Intake
Increase fiber gradually so the GI tract can adjust, drink plenty of fluids, and select fiber from a variety of food sources: fruits, vegetables, legumes, and whole grains.
Glucose, Fructose, and Galactose.
Maltose, Sucrose, and Lactose.
(Dextrose)-"Blood sugar," used to supply cellular energy (fuel). The most abundant carbohydrate.
"Fruit sugar," Sweetest of all. Abundant in fruits, honey sap (maple syrup). Used to sweeten a variety of food products.
Not found free in nature, component of lactose "milk sugar" and some polysaccharides.
Found primarily in germinating seeds. Product of polysaccharides digestion in the GI tract. Composed of two glucose units.
"Table sugar." Main energy ingredient of candy and other sweets. Found in sugar cane and sugar beets and in some fruits. Composed of glucose and fructose.
"Milk sugar." Composed of glucose and galactose.
Insufficient enzyme lactase to digest the lactose-containing foods, symptoms: gas, bloating, cramping, diarrhea, extent of intolerance: mild to severe, and persons with lactose intolerance may need to find alternate sources of calcium.
What to do if you are Lactose Intolerance?
Determine amount you can tolerate, eat dairy with fat, cheese and yogurt are usually tolerated well, use of Lact-Aide, and does not require the elimination of milk/milk products.
Inability to hydrolyze lactose is an example of food intolerance, lactase deficiency is not a food allergy, in some individuals, especially young children, the immune system becomes sensitized to milk proteins, these individuals have a food allergy, and symptoms are similar in some cases.
Enzyme that begins carbohydrate digestion in the mouth, and breaks it down to maltose.
Most chemical digestion of carbohydrates occurs in the small intestine.
Enzyme produced in the pancreas and secreted into the small intestine. Digests carbohydrates to maltose.
Additional enzymes in the small intestine digest disaccharides to monosaccharides
Include maltase, sucrase, and lactase.
All monosaccharides are converted to glucose by this. Excess glucose is converted to glycogen.
Glucose circulating in the blood
Is our primary energy source.
High blood sugar.
Low blood sugar.
Produced by beta cells of the pancreas, stimulates glucose transporters (carrier proteins) to help take glucose from the blood across the cell membrane, and stimulates the liver to take up glucose and convert it to glycogen.
Releases insulin when glucose is high and releases glucagon when glucose is low.
Removes glucose from bloodstream: response to insulin, and releases glucose into the bloodstream: response to glucagon.
Functions of Insulin
Promotes glycogen synthesis, increases glucose uptake by the cells, reduces gluconeogenesis, and net effect: lowers the blood glucose.
Produced by alpha cells of the pancreas, stimulates the liver to breakdown glycogen to glucose, making glucose available to body cells, and stimulates the breakdown of body proteins to amino acids to form new glucose- gluconeogenesis.
Functions of Glucagon
Breakdown of glycogen, enhances gluconeogensis, and net effect: raises blog glucose.
Epinephrine and Norepinephrine
Secreted by the adrenal glands and nerve endings when blood glucose is low, stimulates the liver to breakdown glycogen to glucose, and responsible for our "fight or flight" reactions to danger.
Increases gluconeogensis and decreases the use of glucose by muscles.
Increases fatty acid mobilization and utilization, and increases liver's output of glucose.
Cortisol and Growth Hormone
Secreted by the adrenal glands to act on the liver, muscle, and adipose tissue.
Functions of Carbohydrates
Supplies energy, prevent ketosis, protein sparing, and sweetener.
Each gram of CHO: 4kcal, RBC's rely only on glucose for their energy supply, both CHO and fats supply energy for daily activities, and glucose is especially important for energy during exercise.
How much carbohydrate?
RDA is 130 grams/day just to supply the brains with glucose. AMDR: is 45-65% of daily calorie intake, complex CHO 50% or more, and limit foods with added sugars.
Related Dietary Guidelines
Eat plenty of vegetables, fruits, and whole grain products, and use sugars in moderation.