Nutrition Chapter 4: Carbohydrates

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.

Dietary Carbohydrates

Are obtained almost exclusively from plant sources; milk is the exception.

Photosynthesis

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

Simple Carbohydrates

Contain one or two molecules, commonly referred to as sugars, monosaccharides contain only one molecule; glucose, fructose, and galactose.

Complex Carbohydrates

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.

Starch

Plants store carbohydrates as this, we digest it to glucose, and a good source of grains, legumes, and tubers.

Glycogen

Animals store carbohydrates as glycogen, stored in liver and muscle, and not found in food and therefore not a source of dietary carbohydrate.

Dietary Fiber

Is the non-digestible part of plants; grains, rice, seeds, legumes, and fruits.

Functional Fiber

Is carbohydrate extracted from plants and added to food; cellulose, gugar gum, pectin, and psyllium.

Total Fiber

Dietary + functional fiber.

Soluble Fibers

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.

Insoluble Fibers

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.

Fiber

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.

Monosaccharides

Glucose, Fructose, and Galactose.

Disaccharides

Maltose, Sucrose, and Lactose.

Glucose

(Dextrose)-"Blood sugar," used to supply cellular energy (fuel). The most abundant carbohydrate.

Fructose

"Fruit sugar," Sweetest of all. Abundant in fruits, honey sap (maple syrup). Used to sweeten a variety of food products.

Galactose

Not found free in nature, component of lactose "milk sugar" and some polysaccharides.

Maltose

Found primarily in germinating seeds. Product of polysaccharides digestion in the GI tract. Composed of two glucose units.

Sucrose

"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.

Lactose

"Milk sugar." Composed of glucose and galactose.

Lactose Intolerance

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.

Milk Allergy

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.

Salivary Amylase

Enzyme that begins carbohydrate digestion in the mouth, and breaks it down to maltose.

Carbohydrate Digestion

Most chemical digestion of carbohydrates occurs in the small intestine.

Pancreatic Amylase

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.

Liver

All monosaccharides are converted to glucose by this. Excess glucose is converted to glycogen.

Glucose circulating in the blood

Is our primary energy source.

Hyperglycemia

High blood sugar.

Hypoglycemia

Low blood sugar.

Insulin

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.

Pancreas

Releases insulin when glucose is high and releases glucagon when glucose is low.

Liver

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.

Glucagon

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.

Cortisol

Increases gluconeogensis and decreases the use of glucose by muscles.

Growth Hormone

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.

Energy

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.