Types of Carbohydrates

Today's lesson features carbohydrates!

Monosaccharides
-The sweet taste of edible sugars (fructose and sucrose) was an evolutionary advantage because sweetness guided humans to select plants with the highest energy value.
-Reducing Sugars: hydroxyl group can reduce (donate hydrogen); examples are glucose and galactose
-Glucose, Galactose, Fructose

Glucose
-Most widely distributed sugar in nature
-Glucose + Fructose = Sucrose (make up a large content of fruits and vegetables)
-Also referred to as "blood sugar"

Fructose
-Other names: levulose, fruit sugar
-The sweetest
-Fruits are generally 1-7% fructose
-Vegetables have 3% fructose
-Honey is 40% fructose
-As fruit ripens, enzymes cleave sucrose into glucose and fructose resulting in a sweeter taste.

Galactose
-Produced from lactose (milk sugar) by hydrolysis in the digestive process.

Disaccharides
-Monosaccharide units joined by glycosidic linkages.
-Sucrose= fructose + glucose
-Maltose = glucose + glucose
-Lactose = glucose + galactose

Sucrose
-When used in preparation of acidic foods it becomes inverted and sweeter

Honey
-More calorie dense because monosaccharides are packed more closely together than disaccharides
-1 tbsp honey = 64 kcal
-1 tbsp sugar = 46 kcal

HFCS
-Manufactured by changing glucose in cornstarch to fructose
-Added to canned/frozen fruits to preserve

Oligosaccharides
-Polymers containing 2-20 sugar molecules.
-Water soluble and often sweet
-Nondigestible oligosaccharides: resistant to stomach acid and action of amylase, enter intestine intact
-Raffinose: in sugar beets (galactose + glucose + fructose)
-Stachyose: in legumes and squash (2 galactose + glucose + fructose)

Polysaccharides
-Plants store carbohydrates as starch granules in plastids within cellulose walls
-Edible plants make 2 types of starch (amylose, amylopectin)
-In whole foods, starch is poorly digested. Moist cooking will improve digestibility.
-Carbohydrates that cannot be digested are classified as dietary fiber.

Resistant Starch
-Remains intact throughout cooking
-Limited glucose is produced for absorption

Waxy Starch
-Obtained from corn and rice strains bred to increase amylopectin
-When dissolved in water, forms a smooth paste
-Used as a thickener for frozen pies and sauces

Modified Food Starch
-Used for instant puddings, salad dressings, and baby food
-Adds viscosity and gel-like properties

Cellulose
-A nondigestible carbohydrate found in celery, broccoli, carrots, and many other vegetables
-Falls in the category of insoluble fiber

Pectins/Gums
-Contains sugars and sugar alcohols that make them water soluble
-Pectin is found in apples, citrus, strawberries, jams, and jellies
-Gums are galactose units combined with other sugars found in oats, legumes, and barley

Fructooligosaccharides
-Poorly digested in the upper GI tract
-Provide 1kcal/g, half as sweet as sucrose
-Used as a sugar replacement
-Naturally found in onions, garlic, bananas
-Increase colonic bacteria growth and have been added to yogurts marketed as a prebiotic

Lignin
-Woody insoluble fiber found in stems and seeds of fruits and vegetables and flaxseed
-Also found in the bran layer of grains

Carrageenan
-Extracted from macroalgae or seaweed.
-Used to stabilize food mixtures in pudding and infant formula
-Some studies have shown at high doses to increase cancer risk
http://www.webmd.com/vitamins-supplements/ingredientmono-710-carrageenan.aspx?activeIngredientId=710&activeIngredientName=carrageenan

Chitosan
-Sugar extracted from the shells of crabs, lobsters, and shrimp
-Hypocholesterolemic effect
-Positive charge on chitosan binds negatively charged lipids and blocks their absorption
http://www.webmd.com/vitamins-supplements/ingredientmono-625-chitosan.aspx?activeIngredientId=625&activeIngredientName=chitosan

See the next post on how carbohydrates impact health!

Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004. 

Nutrition Basics: Digestion

Today's topic is on the digestion, absorption, transport, and excretion of nutrients! I will incorporate both science, textbook-like information, and fun facts. For health professionals, this may serve as a brush-up on your past knowledge.

The GI Tract
The primary roles of GI tract are to: extract macronutrients from ingested food and drink, absorb micronutrients, and serve as a protective barrier to microorganisms and foreign material. Depending on the diet consumed, about 92-97% of food/drink is digested and absorbed. Since humans lack the enzymes to hydrolyze the chemical bonds of plant fibers, most of unabsorbed material is of plant origin.  The health of the body depends on the health and function of your GI tract. The GI tract is more susceptible to micronutrient deficiencies, drugs, and protein malnutrition. The nutrients passing through the lumen supply energy to both the small intestine and the colon. With a few days of starvation, the GI tract will begin to break down (decrease in absorption and function).

Digestion Overview
Mouth: limited starch and lipid digestion have taken place.
Stomach: protein digestion has just begun.
Small Intestine: macronutrients, vitamins, minerals, trace elements, and most water is absorbed. Most fat digestion takes place.
Colon/Rectum: remaining fluid and electrolytes are absorbed.
Enzymes: HCL, bile, sodium bicarbonate, lipases, etc.
Hormones: peptides, gastrin, secretin, CCK, GIP, GLP-1, GLP-2, motilin, somatostatin

Interesting Facts About Digestion
-Most of a liquid meal will empty the stomach in 1-2 hours.
-Most of a solid meal will empty the stomach in 2-3 hours.
-When eaten alone, carbohydrates leave the stomach the most rapidly, followed by protein, fat, and fibrous food.
-The small intestine is the primary site for digestion of food and nutrients.

Nutrient Absorption
-The small intestine is the primary organ of absorption.
-Fun fact: Each day, the small intestine absorbs 200-300g of monosaccharides, 60-100g of fatty acids, 60-120g amino acids and peptides!
-The large intestine absorbs the remaining of the water and salts.
-Transit time from your mouth to your anus can vary from 18-72 hours (fruits and vegetable rich diet decreases this time).

Fiber
-Valuable for maintaining healthy cells in the colon.
-Prevents excessive intracolonic pressure.
-Prevents constipation.

Carbohydrate Digestion/Absorption
-Glucose ("blood sugar") is transported from the liver to the tissues (some is stored in liver and muscles as glycogen).
-Consuming large amounts of lactose (milk sugar), fructose (fruit sugar), and sugar alcohols can result in them passing unabsorbed in the colon. This can lead to gas and diarrhea.
-Cellulose, pectin, gums, and other fiber forms cannot be digested by humans; thus, they are passed unchanged into the colon.

Just a final note about the processing of food:
-Cooking food at high temperatures for prolonged periods can destroy nutrients (ascorbic acid and folate), but in general, cooked food is more digestible than raw food.
-Cooking food helps to soften dietary fiber. This helps to make the nutrients attached to the fiber more available for digestion.
-During grain refinement for bread and cereal, nutrients, phytochemicals, and fiber are lost. The "enrichment" of the product will replace some nutrients but not the fiber or phytochemicals.





Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004.