食品营养学 碳水化合物（英文）Carbohydrates

食品营养学 碳水化合物（英文）Carbohydrates知识总结，包括总体介绍、它的营养功能等内容。

Carbohydrates

• General Introduction
  • Definition
    • Compounds composed of single or multiple sugars.
    • This name means "Carbon and water". There's a chemical shorthand for carbohydrate: "CHO", signifying "carbon", "hydrogen", "oxygen".This means it is composed of these 3 elements, with the hydrogen/oxygen ratio usually "C+H2O".
    • Chemically, carbohydrates refer to the polyhydroxy aldehydes and ketones found in foods.
  • Simple and complex
    • Complex carbo (Polysaccharides) : Long chains of sugar units arranged to form starch or fiber.
    • Simple carbo: including both single units and linked pairs of sugar units.
• Subgroups
  • -saccharides
    • Monosaccharides
      • Glucose/Dextrose
        • created in body mainly from starch digestion
        • all other types sugar are converted into glucose
        • the sugar circulates in the blood stream is in the form of glucose
          • blood glucose
            • hyperglycemia, refers to an elevated blood glucose level
            • hypoglycemia, refers to a lower blood glucose level
      • Fructose
        • The sweetest of the simple sugars
      • Galactose
        • It is not found free in foods but is produced in human digestion from lactose
        • Galactosemia: the enzyme for changing galactose to glucose is missing
    • Disaccharides
      • Sucrose
        • it consists of one unit of glucose and one units of fructose.
        • it is a common disaccharides in nature from sugar cane and sugar beets
        • Limited use of refined sugar: no more than 5%EER (<=25g)
      • Maltose
        • it consists of two units of glucose
        • occurs in commercial malt products of starch breakdown & germinating cereal grains
        • In human bodies, it occurs during the digestion of starch
      • Lactose
        • it consists of one glucose and one unit of galactose
        • the least sweet of disaccharides
        • Lactose intolerance: a problem stems from a deficiency in lactase. and it can result in abnormal cramps, nausea, bloating, or diarrhea when milk is consumed. How to address: fermented milk products, such as cheese, buttermilk, yogurt very well.
        • Lactase: a digestive enzyme in the microvilli of small intestine that by hydrolysis converts marginal milk sugar (lactase) into glucose and galactose.
    • Oligosaccharides
      • definition: short-chain carbo comprising 3-9 units of monocaccharides
      • category
        • digestible oligosaccharides
        • indigestible oligosaccharides
    • Polysaccharides
      • definition: complex carbo composed of numerous monosaccharides (>=10 units) linked by glycosidic bonds in a linear or branched manner.
      • The number of units is the degree of polymerization (DP)
      • category
        • Homo-polysaccharides: same type of monosaccharides
        • Hetero-polysaccharides: have to or more different monosaccharides
      • subgroups
        • Starch
          • the storage form of glucose in plants.
          • a relatively complex compound made up of coiled and branching chains of glucose units
          • food source: cereal grains, tubers, legumes, potatoes, roots, etc.
          • category 1 (the glycosidic bonds)
            • digestible starches (Alpha-glycosidic bonds)
              • RDS (Rapid digestible starch): be digested in 20 mins
              • SDS (Slow digestible starch): 20-120 mins
            • undigestible starches (Beta-glycosidic bonds) ,also called RS (resistant starch)
              • RS1: plant cell walls. (whole grains, partially milled grains)
              • RS2: uncooked potatoes and unripe bananas
              • RS3: retrograded starches formed by heating and cooking pastes (corn starch , sorghum flour)
              • RS4: chemically modifies to be undigestible, including starch esters and cross-bonded starches.
          • category 2
            • RAG (Rapid available glucose): sugar and RDS
            • SAG (Slow available glucose): SDS, RS
        • Dextrins (淀粉的部分水解产物)
          • intermediate products in breakdown of starch
        • Glycogen
          • stored in the liver and muscle, formed during cell metabolism
          • longer and highly branched
        • Dietary fibers
          • Definition
            • total amount of naturally occurring material in foods, mostly plants, that is not digested.
            • Broadly:
              • plant dietary fiber from...
              • undigested animal tissue polysaccharides
              • undigested pharmaceutical products
              • undigested biosynthetic polysaccharides
          • includes:
            • Cellulose: all glucose, indigestible beta-bonds
            • Noncellulose: hemicellulose(), pectins(), gums(), mucilages(), algal substances(), lignin
          • category (soluble or not)
            • Insoluble Fibers
              • do not dissolve in water
              • do not form gels, not viscous, resist fermentation in colin
              • such as cellulose, outer layers of whole grains, strings of celery, hulls of seeds, skins of corn kernels
              • retain shape and rough texture even after hours of cooking
              • Function
                • ease elimination
                • contribute to stools
            • Soluble Fibers
              • readily dissolve in water
              • viscous and gel-forming, can add a pleasing consistency to food
              • food: oats, barley, legume, okra, berries, citrus fruit
              • Function:
                • modulate blood glucose level,
                • lower blood cholesterol,
                • promote the healthy colon: fermented by colonic bacteria to SCFA (短链脂肪酸)
                  • nourish cells of colon and promote resistance to colon cancer
                  • reduce inflammation
                  • support immunity
• Nutritious Function
  • Digestible Carbo
    • Energy Usage
      • critical energy source, especially for CNS
      • red blood cells use glucose exclusively
    • Glycogen Reserve
    • Components of Human
      • dangle from protein molecules, dramatically alter the shape and function
      • watery lubricant: sugar-protein complex is responsible for the slippery of mucus, coats and protect the body's internal linings and membranes
      • bind to outside of cell membranes, for cells communication, nerve and brain cell function, and certain disease processes.
    • Protein-sparing Action
      • it refers to that carbo and fat are used to make energy so that protein can be used for purpose it alone can serve
      • carbohydrate should be kept available precisely to prevent the use of protein for energy
      • fat can regenerate a small amount of glucose, but not enough to brain and nerve tissues
    • Anti-ketogenic Effect
      • ketosis: with too low carbo flowing to brain, so body shifts to another metabolism mode which fat products ketone bodies are used.
      • This shift normally cause an accumulation of scarce acid ketone bodies which may be life-threatening
      • adverse outcomes
        • disturb the acid-base balance in blood
        • deficiencies of vitamins and minerals
        • loss of bone minerals
        • elevated blood cholesterol
        • impaired mood
  • Undigestible Carbo
    • Lower blood cholesterol & Lower heart disease risk
      • soluble, gel-forming fiber can bind bile and carry some of its cholesterol out withe the feces to lower the blood cholesterol
      • Food rich in fibers and other complex carbohydrates are protective against heart disease and stroke
    • Control blood glucose
      • soluble fibers can delay the nutrients digestion, slowing the absorption of glucose in digestive tract; so people with diabetes are urged to eat food with high soluble fibers.
    • Maintain the health of digestive tract
      • Soluble fibers can be fermented to SCFA; help to sustain the intestinal colonies of beneficial bacteria
      • Insoluble and soluble fibers can enlarge and soften stools and ease the elimination, prevent the compaction of intestine contents, lessen the pressure of rectal veins, better for the rectal muscles
      • prevent constipation, hemorrhoids, appendicitis; reduce the risks of colon and rectal cancers
    • Healthy weight management
      • Foods with high fibers are usually low in calories
      • It can create feelings of fullness, especially soluble, control appetite, delay hunger and food intake
• Intake
  • AMDR: 45-65%EER
  • RDA: 130g/day carbohydrate at least
  • AI
    • 19-50man: 38g/day
    • >51man: 30g/day
    • 19-50woman: 25g/day
    • >51woman: 21g/day
• Metabolism
  • Digestion
    • Mouth: chewing stimulates the salivary glands to secrete saliva which has salivary amylase to break down starch into shorter polysaccharides and maltose
    • Stomach: the amylase is destroyed by acids, so no digestion
    • Pancreas: secrete pancreatic amylase to small intestine
    • Small intestine: pancreatic amylase breaks down remaining starch into maltose; specific enzymes (maltase, sucrase, lactase) break disaccharides into monosaccharides which are all absorbed into bloodstream
    • Colon: some carbo undigested
      • bacterias ferment some
      • remaining carbo to feces
    • Liver
      • convert all monosaccharides into glucose
      • excess glucose to glycogen
  • blood glucose
    • 2 hormone
      • insulin
        • secreted by β-cells of pancreas
        • stimulates glycogen synthesis in liver
        • facilitate blood glucose uptake by muscle and adipose tissue
      • glucagon
        • secreted by α-cells of pancreas
        • when blood glucose concentration dips, it stimulates the liver to release glycogen
    • Diabetes
      • typeⅠ: pancreas produce little or no insulin
      • typeⅡ: the body cells fail to respond to insulin
        • Insulin resistance : a condition in which a normal or high concentration of circulating insulin produces a subnormal glucose-uptake response in muscle, liver, and adipose tissue.
    • GI: Glycemic Index
      • a rank of food according to the potential for raising blood glucoce
      • reference dose of pure glucose, same person
      • 55: low; 70: high; mediate
    • GL: Glycemic Load
      • = GI*available carbohydrates (g) / 100