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P1 Spring 2024 > biochem - nutrition exam 1 > Flashcards

biochem - nutrition exam 1 Flashcards

1
Q

Carbohydrates – Quick Review

A

Monosaccharides:
– Glucose (glc)
– Fructose (fru) – the sweetest of the sugars
– Galactose (gal)

  • Disaccharides:
    – Maltose (glc-glc) – minor food constituent
    – Sucrose (glc-fru)
    – Lactose (glc-gal)
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2
Q

Polysaccharides

A

Glycogen
– Poly-glucose
– Highly branched
– Not a significant food source

Starch

Fiber

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3
Q

Starch

A

Poly-glucose

  • Amylose: linear
  • Amylopectin: branched
  • Found in grains: rice, wheat, corn, etc.

two components:
- Amylose
- Amylopectin

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4
Q

Fiber

A

Structural parts of plants

  • Polysaccharides other than starch (next slide) – Cellulose, hemicellulose, etc.
  • Some non-polysaccharides
  • Cannot be broken down by the human digestive system (missing enzymes)
    – Not a source of monosaccharides
    – Bacteria in GI tract may digest some
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5
Q

Polysaccharides other than starch

A

Cellulose (plant cell walls)
– Vegetables, fruits, legumes
– Linear and non-digestible, because of (β1→4) linkage

Hemicellulose(cereal fibers)
– Branched
– Some soluble, some not

long chain and linear

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6
Q

Carbohydrate Digestion of starch

A

mouth and salivary glands
- the salivary glands secrete saliva into the mouth to moisten the food. The salivary enzyme amylase begins digestion
- starch + amylase = small polysaccharide

stomach
- stomach acid inactivates salivary enzymes, halting starch digestion

small intestine and pancreas
- the pancreas produces an amylase that is released through the pancreatic duct into the small intestine
- starch + pancreatic amylase = small polysaccharide and disaccharides

not finished

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7
Q

Carbohydrate Digestion of fiber

A
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8
Q

Notes on Carbohydrate Metabolism

A

Catabolism:
– Branched chains: digested more rapidly
– Linear chains: digested more slowly

  • Glucose, galactose and fructose:
    – Glc and gal: move quickly into the blood (active transport); fru transport slower (passive)
    – Fru and gal metabolized primarily in the liver; glc metabolized in many cells, as needed.
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9
Q

Fructose

A
  • Recall that fructose is metabolized by the glycolytic pathway.
    – Liver (major): converted to glyceraldehyde 3- phosphate, bypassing steps #1-5
    – Muscle & kidneys (minor): converted to fructose 6-phosphate, bypassing steps #1-2
  • Compared to glucose, fructose catabolism is less stringently regulated (steps #1 & 3 – chapter 15) and may lead to more fat- formation in the liver.
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10
Q

Fructose (continued)

A

Unlike glucose, fructose does not induce insulin secretion and does not reduce appetite as much as glucose.

  • Same true of high-fructose corn syrup.
    – HFCS is made by enzymatically converting some of the glucose in corn syrup to fructose, typically resulting in mix of ~55% fru. Because fru is much sweeter than glc, this is sweeter than a mix with 50% fru and 50% glc.
    more sweeter due to fru so they can use less of it
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11
Q

Lactose Intolerance

A

Little/No lactase → lactose reaches the large intestine and is converted into toxic products by bacteria [→ cramps, diarrhea])

  • Solution: reduce lactose, and add lactase
  • Soy milk contains sucrose, not lactose.
  • Caution: milk products contain many important nutrients (e.g., riboflavin, Vitamin D, calcium)
  • Note: 20% of prescription meds and 5% of
    OTC meds use lactose as a filler/sweetener.
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12
Q

Glycemic Effect/Response

A

Food containing carbohydrates leads to an increase in blood [glucose], which elicits an insulin response (secretion)

  • Foods are classified according to how rapidly they lead to this increase.
  • Classification of food: Glycemic Index
    – Low: slow absorption., modest rise, smooth return, slow spikes
    – High: rapid absorption., surge in [glc], dramatic drop, quick spikes

High
- White Bread
- Baked pot.
- Cornflakes
- Sports dr.
- Donuts

low
- Low
- Peanuts
- Cashews
- Soybeans
- Milk
- Beans

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13
Q

Some Nutrition Guidelines & Recommendations

A
  • American & Canadian standards (1997-): Dietary Reference Intakes (DRI) - being continually updated
  • Recommended Dietary Allowances (RDA): age-, sex- and life-stage-specific
  • Daily Values (DV): Average recommended daily intake for a person on a 2000-kcal. diet (Note: average, not based on age or sex)
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14
Q

Dietary Recommendations: Carbohydrates

A

45-65% of calories from carbohydrates

  • E.g., on a 2000-kcal diet, 900-1300 kcal
  • 1200 kcal/4 kcal/g = 300 g (the Daily Value) - this is the conversion factor
  • Includes sugar, starch, and fiber. – Sugar: slides #17-20
    – Fiber: slides #21-27
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15
Q

Sugar Intake

A

where we get our sugar from:

In the U.S., ~1/2 from milk, fruits, vegetables, grains

  • Other 50% is refined and added by processors (drinks, desserts, candy, cereals) or consumers: sucrose, high-fructose corn syrup, honey, etc.
  • Recommendations below.
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16
Q

Health Effects of Sugar

A

A little is OK

  • Honey (sucrose = glc-fru)
    – Trace amounts of protein, Ca, Fe, Vit. C no need to know these Ca, Fe, etc…
  • The refined (= processed/purified; nothing added) sugar problem: usually means:
    – Too many calories, or …
    – Too few nutrients (low nutrient density)
17
Q

More Sugar Health Effects

A

Dental caries (bacteria in or mouth, bacteria secretes acid onto our teeth)
– Worst case: sugar alone, between meals

  • Obesity
  • Heart disease: sugar is a minor factor (compared to smoking, genetics, lipids)
  • Hyperactivity: connection not supported by research * not on exam *
18
Q

Recommended Intake of Sugar

A

Guidelines: “Reduce intake … from added sugars.”

  • Old recommendation: ≤ 10% of total calories (still a good approximation)
  • E.g., 200 kcal of a 2000 kcal/day diet
  • 1 tsp = 20 kcal
  • Typically, Americans get about 1/6 (16%) of daily energy from simple sugars.
  • Minimize consumption of HFCS (slide #12).
19
Q

Fiber: sources, actions

A

Soluble
- Whole grains (oats, oat bran, barley, rye), fruits, legumes (beans, peas), seeds, vegetables
* *Slow upper GI transit, slow starch hydrolysis, slow glucose absorp., lower blood cholesterol, soften stools

Insoluble
- Brown rice, fruit, legumes, seeds, vegetables, wheat & corn bran, whole grains
* Accelerate colon transit, increase stool weight, relieve constipation, increase feeling of fullness

20
Q

Health Effects: Fiber

A

Makes one feel full, reducing appetite.

  • High-fiber foods help to reduce the risk of
    Type-2 diabetes
    – Soluble fibers slow glucose absorption, moderating glucose surge/rebound (which appears to lead to Type 2 Diabetes)
21
Q

Health Effects: Fiber

A

May decrease risk of heart disease
– Reasons not well understood
– Soluble fiber binds and removes bile acids, lowers blood cholesterol
– Byproducts of bacterial digestion may inhibit cholesterol synthesis in the liver
– Fiber may displace fat in the diet.

22
Q

Health Effects: Fiber

A

High-fiber diet correlated with decreased
risk of cancer, esp. colon cancer
– Esp. green & yellow vegetables, and citrus fruits
* Cause may be fiber, or other chemicals in these foods (antioxidants and phytochemicals: See Chapter 11 and 13 Highlights.)

23
Q

Health Effects: Fiber

A

Intake of dietary fiber is associated with
increased GI health

  • Insoluble fiber often helps to alleviate constipation
24
Q

(Un)Healthy Effects of Excess Fiber

A

For a person who does not eat much (young, elderly, malnourished), consuming a large amount of fiber may mean consuming an inadequate amount of foods high in nutrients such as vitamins, minerals, and proteins.

  • Fiber may decrease nutrient absorption.
  • Sudden change to high fiber can lead to GI problems (discomfort, obstruction).
  • Without adequate water: stool problems
  • None of the above should be taken to mean that fiber in the diet is unhealthy.
25
Q

Dietary Recommendations: Fiber

A

11.5 g/1000 kcal
* D.V. (daily value) of Dietary Fiber: 25 g [Know this]
* The average intake in the U.S. is about half of this.
* Good fiber sources: whole grains, vegetables, fruits, legumes

26
Q

Alternative Sweeteners

A
  1. Extracts of natural products (no energy)
  2. Artificial Sweeteners (no energy, with one exception which is aspartame)
  3. Sugar Alcohols (yield energy)
27
Q

FDA regulation

A

FDA may approve as …
– supplements (“Generally Recognized As Safe” [GRAS]) – based on generally available data and consensus of experts
– food additives – based on data and information submitted by sponsor
* FDA sets an Acceptable Daily Intake (ADI) for each (1% of amount found to produce adverse effects in animal studies) – more on slide #33.

28
Q

Extracts of natural products

A

Extracts of Stevia (glycosides): (e.g., Truvia, PureVia)

  • Extracts of Monk Fruit (a.k.a., Swingle Fruit, Luo Han Guo)
  • Thaumatin (a group of intensely sweet basic proteins isolated from the fruit of Thaumatococcus danielli [West African Katemfe fruit])
  • Allulose (epimer of fructose; found in figs & raisins)
  • Tagatose (epimer of fructose; found in dairy foods, fruits)
29
Q

Artificial sweeteners

A

Saccharin(e.g.,Sweet’nLow)

  • Aspartame (a di-peptide of aspartate and phenylalanine; phenylketonurics (PKU) beware; 4 kcal/g) (e.g., Equal, Nutrasweet)

Neotame (Newtame), Advantame (aspartame analogs)

  • Acesulfame-K (e.g.,Sunett)
  • Sucralose(e.g.,Splenda)
30
Q

Sweetness relative to sucrose

A

Acesulfame-K: 200x

  • Aspartame: 200x
  • Monk Fruit: 100-250x
  • Steviol glycosides: 200-400x * Sucralose: 600x
  • Thaumatin: 2,000-3,000x
  • Neotame: 7,000-13,000x
  • Advantame: 20,000x

no need to know the numbers

31
Q

Some Acceptable Daily Intake equivalents for a 132-lb. person

A

Saccharin: 10 packets (3 cans of soda) * Aspartame: 75 packets (24 cans)
* Neotame: 23 packets
* Advantame: 4,920 packets
* Acesulfame-K: 23 packets (18 cans) * Sucralose: 23 packets (5 cans)
* Stevia: 27 packets (4 cans)

no need to know the numbers

32
Q

Changing tastes: FYI

A

The sweetener in Diet Pepsi has changed over the years:
– 1964: saccharin; 1983: aspartame
– 2013: combination of aspartame & acesulfame-K
– 2015: combination of acesulfame-K & sucralose

  • Yale J Biol Med (2010): most commonly used alternative sweeteners:
    – Sucralose (1,500 products)
    – acesulfame-K (1,103 products)
    – aspartame (974 products).
33
Q

Sweet receptors

A

alitame

receptors for different sugars
the same receptors for the natural sugars also accept the signal for the natural sugars

34
Q

aspartame vs

A

just a different stereochemistry, then they are different

35
Q

Sugar Alcohols (Polyols)

A

Erythritol, mannitol, sorbitol, xylitol, maltitol, isomalt, lactitol (in gum, candy, pharmaceutical & oral health products)

  • Erythritol-Stevia is a popular blend.
  • Calories, but fewer than sugars (0.2-2.6 kcal/g)
  • Low glycemic effect (but most ≠ 0)
  • May cause abdominal discomfort, and diarrhea (Food labels must carry advisory notice.)
  • Do not contribute to dental caries
36
Q

General Comments

A

Are the Alternative Sweeteners Toxic?
– Dose is everything. At reasonable levels, approved sweeteners are not toxic.
– Paracelsus: “The dose makes the poison.”

  • Not clear whether they help reduce weight
  • For more information, see RPW, Chapter 4, and documents on Blackboard (relative sweetness, Acceptable Daily Intakes (ADI), etc.).

P1 Spring 2024 (57 decks)

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