100 lines
5.2 KiB
Markdown
100 lines
5.2 KiB
Markdown
- Carbohydrates are a class of nutrients that is a major source of energy for the body
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- Can also server as a glue that holds cells together
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- Classified as simple or complex
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- Plants are rich sources of carbohydrates
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There are 3 categories of carbs.
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# Sugars
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- A **monosaccharide** is a simple sugar that is the basic molecule of carbohydrates:
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- Glucose: Primary fuel for muscles, nerves, and other cells, the most common.
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- Fructose: In **fruits**, honey, and certain vegetables
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- Galactose: Component of lactose
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- A **disaccharide** is a simple sugar comprised of two monosaccharides.
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- Maltose: Disaccharide composed of two glucose molecules "malt sugar"
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- Sucrose: Disaccharide composed of a glucose and fructose molecule "table sugar"
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- Lactose: Disaccharide composed of a glucose and a galactose molecule "milk sugar"
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- High fructose corn syrup is a syrup obtained from the processing of corn
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- No conclusive evidence that the use of HFCS causes poor health and disease
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- Excessive calories from beverages sweetened with HFCS contributes to increased risk for diabetes and heart disease
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- Nutritive sweeteners are substances that sweeten and contribute energy to foods
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- Each gram of mono or disaccharide supplies 4 kcal
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- Added sugars are sugars added to foods during processing or prep
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- The main source of added sugars in the American diet is sugar sweetened beverages.
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- Alternative sweeteners are substances that sweeten foods while providing few or no calories
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- Sugar alcohols are alternative sweeteners use to replace sucrose in some some sugar free foods:
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- Sorbitol, xylitol, mannitol
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- Not fully absorbed by the intestinal tract
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- Supply 2kcal/g
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- Can cause diarrhea when consumed
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- Non-nutritive sweeteners are a group of synthetic compounds that are intensely sweet tasting compared to sugar
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- Examples include Aspertame, Saccharin, Acesulfame-K, Neotame, and Sucralose
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- Glycogen = storage form of glucose
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- A highly branched storage polysaccharide in animals
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- Muscles and liver are major storage sites
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# Starches
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Complex carbs have 3 or more monosaccharides bonded together
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- Starch is a storage polysaccharide in plants.
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- Composed of amylose and amylopectin
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- Rich sources include:
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- Bread and cereal products made from wheat, rice, barley, and oats
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# Fiber
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- Plants also use complex carbohydrates to make supportive and protective structures
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- Dietary fiber is non-digestible plant material
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- Most types are polysaccharides
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- Soluble fiber
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- Forms of dietary fiber that dissolve or swell in water. includes pectins, gums, mucilages, and some hemicelluloses
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- Delays stomach emptying, slows glucose absorption and lowers blood cholesterol
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- Insoluble fiber
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- Forms of dietary fiber that generally do not dissolve in water: Includes cellulose, hemicelluloses, and lignin
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- Helps with bowel movements and fecal bulk
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# Consumption
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- In developing nations, diets supply 70% or more of energy from unprocessed carbs
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- In industrialized nations, people tend to eat more highly refined starches and added sugars
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- Americans consume about 30% of energy from added sugars (600 kcal/day)
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- Regular soft drinks and energy drinks are major sources of added sugars in Americans' diets
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- According to the dietary guidelines, people should limit their added sugar to
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# Digestion
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- Salivary amylase is an enzyme secreted by salivary glands that begins work in the mouth, stops working soon after food enters the stomach
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- The small intestine is the main site for carbohydrate digestion and absorption
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- Pancreatic amylase
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- Enzyme secreted by the pancreas that breaks down starch into maltose molecules
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- Maltase
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- Enzyme that splits maltose molecules
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- Sucrase
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- Enzyme that splits sucrose molecules
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- Lactase
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- Enzyme that splits lactose molecules
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- Only monosaccharides are absorbed
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1. Dietary carbohydrates from stomach are delivered to small intestine
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2. Glucose and other monosaccharides are transported to liver
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3. Blood levels of glucose maintained for brain and other body cells
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4. Glucose transported to muscle
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- Fructose and galactose are converted to **glucose** in the liver.
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- Absorption of monosaccharides mainly occurs in the small intestine
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- Galactose and glucose are absorbed by active transport
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- Fructose is absorbed by facilitated diffusion
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- Monosaccharides enter the capillary network
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- Transported to the lever by the hepatic portal vein
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- Simple sugars are:
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- Made into glycogen or fat by the liver
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- Released into bloodstream for energy use
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- Fiber is not digested
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- Eventually enters large intestine
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- Bacteria ferment soluble fiber (producing gas)
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- Used for energy
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- Insoluble fiber contributes to softer fees
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- Any fiber Present in food would delay rate at which chyme enters from the stomach
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- Promotes satiety
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- Refined grain products are generally low in fiber
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# Glucose
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- Insulin is the hormone secreted from the beta cells of the pancreas that helps regulate blood glucose levels by helping glucose enter cells
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- Released when blood glucose levels are **HIGH**
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- Glucagon is a hormone secreted from the alpha cells of the pancreas that helps regulate blood glucose levels
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- Released when blood glucose levels are **LOW**
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- Glyconeogenisis: Creates glucose
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- Glycogenolysis: Glycogen stores are broken down
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