Carbohydrates: Structure, Digestion, and Health Implications, Lecture notes of Nutrition

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Diet and Nutrition:

Carbohydrates

Dr. Sorensen

Disclosure: some carbs were used in the creation of this presentation

Objectives

• Identify and classify various types of carbohydrates
• Monosaccharides, disaccharides, and types
• Oligosaccharides, Polysaccharides, amylose, amylopectin, beta glycans
• Look for bold font
• Identify and summarize health effect of fiber
  • Be able to describe 2 different types in your own words
• Identify negative health effects from high carb intake
• Demonstrate knowledge of diets for hyperglycemia
• Review from wk 1: Bristol stool chart, bile, incretin,

Carbohydrates

Carbohydrates

• Basic fuel for human energy needs
  • Provides 4 kcal/g
• protein sparing=body uses carbs before protein to protect muscles
• Can only be stored in limited quantities, so the body is eager to use them for energy. - can only store a ~ day or two of carbs - - > turns into fat

Carbohydrates

• Disaccharide s- two sugars, simple
  • Sucrose - glucose+fructose
    • Table sugar, honey, molasses. 100/100 sweetness
  • Maltose - glucose+glucose
    • Malt sugar, in beer and malt liquor
    • 32/100 sweetness
  • Lactose - glucose+galactose
    • Milk sugar. 7.5% of human milk, 4.5% of cows milk. 16/100 sweetness

Carbohydrates

• Oligosaccharides – less abundant in diet
• Polysaccharides
  • complex carbs and starches
  • glycogen, cellulose, fungal glucans
    • amylose, amylopectin
• Fiber ( soluble & insoluble ), nondigestible carbohydrates, fermentable vs nonfermentable - glycosidic bond in linkages of oligo and polysaccharides determines if broken down by human or bacteria enzymes ‘prebiotic’ (alpha vs beta link. 1-4 or 1-6) - Some broken down to SCFA by gut flora, feeds colonic cells

Fructose

• ‘Fruit sugar’
• highly soluble
• sweetest carbohydrate
  • fruits, vegetables, honey (which is about 50% fructose and 50% glucose)
  • high fructose corn syrup
• High intakes of fructose (↑HFCS) is associated with hepatic insulin resistance, non-alcoholic fatty liver disease (NAFLD), metabolic syndrome, and maybe with small intestine epithelial barrier deterioration* *PMID: 34619076

Sucrose

• Contains equal proportions of fructose and glucose - found naturally in honey
• White sugar: purified sucrose, no other nutrients
• Brown Sugar: white sugar with molasses added back in, less calories
  • Molasses adds some calcium, iron, potassium
  • When packed in a cup has more calories than white sugar
• Invert sugar a mixture of glucose and fructose obtained by the hydrolysis of sucrose

Human milk oligosaccharides (HMOs) PMC

Glycemic Index & Load

• Glycemic index (GI) a score out of 100 on how significant the food will make blood sugar increase - Sugar is 100
• Glycemic load includes portion of food, amount of carb with GI
  • Thought to be more reliable
  • Must know GI
• Use chart or calculator

Polysaccharides

• Polysaccharides: >10 monosaccharides linked by various linkages similar to oligosaccharide - Tasteless and mostly insoluble, but absorb water - Most are high-molecular-weight (HMW) polymers
• Two types
  • Homopolysaccharides
  • only one type of monosaccharide usually glucose
    • Starch
    • Cellulose (b 1 - 4 linkages, nonfermentable)
  • Heteropolysaccharides
    • Different types of monosaccharides subunits, e.g. Gums, Pectins, Mucilages, Hemicellulose

Starches

• If these chains are straight, they’re called amylose
• if they’re branched, they’re called amylopectin
• Found in grains, potatoes, legumes, tapioca, banana, arrowroot and anything made from these → breads
• Was considered to be broken down slower, stabilizing blood sugar but if refined are high glycemic (raise blood sugar) Starch is made up of long chains of glucose linked with alpha 1-4 linkages

Resistant starches

• Resist digestion functions like soluble, fermentable fiber
  • green bananas, various legumes, cashews and raw oats
• Some starchy foods form large amounts of resistant starch when cooled down after cooking - white potatoes and white rice - Some named RS type 1- 4

Cellulose

• Major component of cell walls in plants ~33%
  • Whole grains (bran), legumes, leafy/root veg, apple/pear skin
• Provides structure in plants (building blocks?)
• Like the starches, made of glucose
  • but with beta 1-4 bonds
  • resistant to the digestive enzyme alpha amylase
  • a potential energy source for intestinal bacteria that can digest it
• defined as insoluble fiber, considered not to provide energy, insoluble fiber
• Used as bulk-forming laxative - draws water into stool, help make them softer and easier to pass