2/3 - 2/5: MACRONUTRIENTS: CARBOHYDRATES

What is the breakdown of carbohydrates?

• monosaccharides

What does carbohydrates = ?

• energy

What is the classification of carbs?

• simple: just one or two sugar units

• complex: contain more than one or two units

What is a monosaccharide? What are the different types of monosaccharide? What is the most abundant one? What are they a key fuel source for?

• monosaccharide is one sugar unit

• glucose, fructose, and galactose

• glucose is the most abundant monosaccharide

  • key fuel source for brain cells, nervous system, and RBCs

What is a disaccharide? What reaction forms them? What are the different combinations, and what do they produce? What is the most abundant disaccharide?

• a disaccharide contain two sugar units

• condensation reaction links the two monosaccharides

  • hydroxyl group (-OH) gains a hydrogen and forms H2O

• glucose + glucose → maltose

• glucose + fructose → sucrose

• galactose + glucose → lactose

• sucrose is the most common disaccharide

What is an oligosaccharide? What do they make up a part of? How do humans digest them? What are the common food sources? Why do these food sources produce gas?

• an oligosaccharise is a short chain of monosaccharides

  • 3 to 10 units

• they make up a part of the plant cell walls

• humans lack enzyme necessary to break down bonds, so they are digested in the large intestine by gut bacteria

• food sources: produce gas because they are undigested until the bacteria in the large intestine ferment them

  • legumes

  • beans

  • cabbage

  • brussels sprouts

  • broccoli

What is a polysaccharide? What is common in plants and what do they do? What are the two types, and what makes them distinctly different?

• long chains of glucose linked together

• starch: storage form of glucose in plants

  • amylose: straight chains

  • amylopectin: branched chains

What is glycogen? Where are they stored? Are they easily broken down and mobilized? What do they increased? Are they stored after death?

• glycogen is the storage form of glucose in animals

• long, branched chains of glucose

• stored in muscle and liver

• easily broken down and mobilized

• increased sites for enzyme action

• not stored after death, so eating meat does not provide glycogen

What is dietary fiber? What is most fiber a form of? How are they arranged, and how does that contribute to our inability to digest? What bonds are humans unable to digest? Why is oatmeal beneficial for heart health?

• dietary fiber is the nondigestable food component of plants

• most fiber is in the form of cellulose (structural)

  • straight chains of glucose units compacted in layers

  • beta-glycosidic bonds that humans lack enzymes to digest

• oatmeal have fiber that sequester and excrete cholesterol

Carbohydrate Digestion

What is the name of the game?

• food broken down into progressively smaller components for absorption by enterocytes in the small intestine

Carbohydrate Digestion

What are disaccharides, starch, and dietary fiber digested into? What is special about fiber?

• disaccharides and starch get digested into monosaccharides

• dietary fiber passes undigested into the large intestine

  • similar to lactose as it will be important for bacteria to feed on

Carbohydrate Digestion

Walk through the steps of digestion and absorption

• mouth

  • mechanical digestion via chewing

  • chemical digestion through salivary glands releasing salivary amylase, which breaks down amylose and amylopectin

• bolus leaves the mouth to go to the stomach

• stomach

  • peristalsis propels food forward in GI tract

  • mechanical digestion via churning with gastric juices HCl to create chyme

• chyme travels to the small intestine

  • pancreas release pancreatic amylase to hydrolyze the bonds of carbohydrates to be broken down into glucose, fructose, and galactose

  • brush border enzymes, sucrase, lactase, and maltase from enterocytes digest/hydrolyze disaccharides into monosaccharides

• carbohydrates are absorbed, except fiber will continue into the large intestine

What pH is ideal for salivary amylase? What is our first layer of defense when eating, and why?

• a pH between 6 and 7 is ideal for salivary amylase

• gastric juice is the first layer of defense for what we are eating

  • a acidic stomach environment denatures some enzymes (while being ideal for others), and also destroys bacteria

What is sucrose, and what does it get broken into during digestion in the small intestine? How about maltose or lactose?

• sucrose (white & brown sugars) → glucose & fructose (abundant in fruits)

• maltose → glucose

• lactose → glucose & galactose

Are all carbohydrates easily digested? Which ones are, and which ones aren’t?

• not all carbohydrates are easily digested

• sucrose and maltose are easier to digest

• lactose and cellulose are harder to digest

What is resistant starch?

• heating in water (cooking) disrupts starch: gelatinization

  • sequences are broken

• cooled starch changes formation slightly: retrogradation

  • reformation of bonds

  • cooled starch is now more resistant to digestion (harder to digest, and less quickly digested & absorbed), increasing blood sugar post digestion and absorption

Carbohydrate Absorption

What are carbohydrates absorbed as? What are they absorbed through?

• absorbed as monosaccharides

• absorbed through the intestinal mucosa cells called enterocytes

Carbohydrate Absorption

How are the carbohydrates absorbed?

• glucose: active transport

• fructose: facilitated diffusion

• galactose: active transport

Carbohydrate Transport

Where are they transported and how?

• transported to the liver via the portal vein

Carbohydrate Absorption

What are the fates of monosaccharides, and what directs their fates?

• metabolic needs direct the fate of monosaccharides

  • galactose and fructose are used for energy or converted to glucose to be released into the bloodstream

  • glucose stored as glycogen via glycogenesis

  • excess glucose is stored as fatty acids & glycerol in adipocytes

Glycemic Index and Glycemic Load

What do they measure?

• they are measures of the effects of carbohydrate-containing foods or meals on blood glucose levels

Glycemic Index and Glycemic Load

What does this chart mean?

• impact or the spike in blood glucose is less for foods under white bread, and higher above white bread

• the ones above are quickly digested and absorbed, while the ones below take longer

Glycemic Index and Glycemic Load

_ adjusts _ for what?

• GL adjusts GI for CHO quantity and cooking/preparation methods

  • basically takes the GI, as well as portion size, to get a sense of the impact of a given food in our post glucose levels

Walk through the steps of carbohydrate digestion

What are the functions of carbohydrates?

• provides energy for the body as the primary source

• regulates blood glucose

• protein-sparing: preferred fuel source

What is glucose the only energy source for? What is it a primary source for?

• only energy source for red blood cells

• primary source for brain cells

How does glucose regulate blood glucose?

• prevents blood glucose from going too high (hyperglycemia) or too low (hypoglycemia)

After 4 hours without eating, what does the body utilize?

• body utilizes glycogen stores

How is glucose protein-sparring?

• there are many other essential functions for proteins, and proteins/amino acids are not stored like glucose/glycogen

Glucose Homeostasis

What is the goal, and ranges?

• managing tight BG regulation in a narrow range

  • generally: 70-110 mg/dL

  • fasting: 70-100mg/dL

Glucose Homeostasis

What are the key hormones to maintaining homeostasis?

• insulin

  • facilitating glucose entry, which lowers BG levels by having cells take in glucose

• glucagon

  • release of glucose via the breakdown of glycogen

• epinephrine/norepinephrine

  • increase BG levels

• cortisol/steroid medications

  • increase BG levels due to increased glucose production in the liver and increased insulin resistance in body tissue (which will decrease uptake)

Glucose Homeostasis

Which organ plays a big role and why?

• liver plays a big role because it acts as a reservoir (of glycogen), and motor (production and release back into the bloodstream)

Glucose Homeostasis

Is there a limit to the liver’s reservoir of glycogen? What will happen to the excess?

• there is a limit to glycogen storage

• once maximized, the excess glucose is converted to fatty acids via lipogenesis

Glucose Homeostasis

What are the steps for insulin?

1. BG increases after meal

   1. CHO content → monosaccharides → portal vein to the liver

2. Pancreas (specifically beta cells) produce insulin → enters the blood stream

3. At the cell level: insulin promotes transport across cell membranes

   1. common target tissues: liver, skeletal muscle (also: fat, brain cells, all cells)

   2. majority through insulin mediated glucose transporter: GLUT4 (# of transporters increase)

4. Insulin stimulates glucose storage

Glucose Homeostasis

Do all cells have insulin receptors?

Yes

Glucose Homeostasis

What are the steps for glucagon?

1. When BG is low, glucagon is a hormone that prompts the liver to increase circulation of glucose

2. Glucagon is produced by pancreatic alpha cells

3. Liver is the source of stored glycogen, and the breakdown of glycogen into glucose is glycogenolysis

4. Release of newly mobilized glucose from glycogen stores into circulation

5. Glucagon stimulates formation of glucose from other substrates, such as glucogenic amino acids, via gluconeogenesis

Glucose as Energy

What provides fuel between meals?

• stored glucose

Glucose as Energy

What happens if you don’t eat for multiple hours?

• breakdown of liver glycogen to make glucose via glycogenolysis

• glycogen stores in the liver can be depleted and replenished

Glucose as Energy

What happens to extra glucose if the glycogen stores are replenished?

• converted to triglycerides and stored as fat via lipogenesis

Glucose as Energy

What happens when glycogen stores are depleted but there is still a demand for glucose? Where does this usually occur?

• mobilize other substrates from stored fat and/or amino acids via gluconeogenesis

  • this primarily occurs in the liver

Intake Recommendations: Carbohydrate DRIs

What is the RDA for carbohydrate? Are they the same across ages, and what are the requirements based on?

• RDA for carbohydrate: 130g per day

  • same across ages

  • minimum recommended amount to fuel cells

  • based on glucose requirements for the brain

Intake Recommendations: Carbohydrate DRIs

What is the AMDR for carbs? Are they the same for children and adults?

• 45 - 65% of daily kcals

  • same for children and adults

Food Sources of Carbohydrates

What is the current debate about 130g/day?

• debate about whether the recommended amount of 130g/day is really necessary because

  • there are other mechanisms, such as breaking down glycogen to glucose, or using other materials such as amino acids to form glucose

• people think the foods provide more energy than nutrients needed

Food Sources of Carbohydrates

What are good sources and moderate sources of carbs?

• good sources

  • grains, fruits, starchy veg

• moderate sources

  • plant-based protein

  • dairy such as legumes

  • some non-starchy vegs such as carrots

Types of Fiber

What are the classifications of fiber?

• insoluble fiber

  • does not dissolve in water

  • cellulose

  • increase bulk and weight of the formation of stool

  • stimulates peristalsis → speeds up transit time

  • helps reduce constipation

• soluble fiber

  • dissolves in water

  • pectin

  • fermentable by GI flora

  • viscous: forms gel that slows gastric emptying

  • reduces blood cholesterol

Types of Fiber

What does insoluble mean for our poops?

• contribute to frequent and comfortable bowel movements

Types of Fiber

Why is adequate fiber necessary?

• If food is traveling too slow through the large intestine, it will continue to reabsorb water, which makes the stool formation very hard

• this leads to an uncomfortable stool formation/passage

• adequate fiber thus helps increase transit speed

Whole Grains and Refined Fiber

What are abundant in complex carbohydrates?

• starch and fiber

Whole Grains and Refined Fiber

What are the 3 component parts of a grain?

• bran

• germ

• endosperm

Whole Grains and Refined Fiber

What is the bran? What is this the source of?

• hard, outer husk/shell

• the big source of fiber because it is the non-digestable material

Whole Grains and Refined Fiber

What is the germ? What does it also contribute?

• kind of like the egg yolk of an egg

• contributes a bit of dietary fats

Whole Grains and Refined Fiber

What is the endosperm?

• what is leftover in the grain

• the starchy texture

Whole Grains and Refined Fiber

Why is whole grain intake recommended?

• reduced risk of chronic disease

• higher in fiber

Whole Grains and Refined Fiber

What are refined grains?

• after grains goes through processing, nutrients are added back to the refined flour

Whole Grains and Refined Fiber

What are refined grains added with?

• nutrients are added back to refined grains

• iron, folic acid, vitamins B1-B3

• prevention of Type II diabetes

Whole Grains and Refined Fiber

Why is folic acid added to refined grains?

• very important for early pregnancy because the neural tube during around week 4 is closed

• since a lot of people consume this product, adding folic acid can help decrease a birth defect

Good Sources of Fiber

What products contain and don’t contain fiber?

• most plant foods contain both soluble and insoluble fiber

• animal foods do not contain fiber

  • fish, meat, chicken, eggs, dairy

• functional fiber

  • manufactured by the food industry

  • included for health benefits

  • ex: psyllium in metamucil

Whole Grains and Refined Fiber

Is protein a good source of fiber?

• category of proteins is limited in terms of providing fiber

  • primarily from beans

Dietary Fiber Recommendations

What is the DRI of fiber?

• DRI is Adequate Intake (AI)

  • 14g of fiber per 1,000 kcal intake

Dietary Fiber Recommendations

As age increases to 50, what is the fiber need intake? Is this realistically met?

• fiber needs tend to dip lower after age 50, but because the average fiber intake is so low, fiber still needs to be incorporated

Health Applications & Diseases of Digestion

What causes lactose intolerance?

• absence of the lactase, a brush border enzyme, that digests the bond in lactose to galactose and glucose

Health Applications & Diseases of Digestion

Is lactose intolerance the same as milk protein allergy?

No, not the same

Health Applications & Diseases of Digestion

Follow lactose in the system for those with lactose intolerance

• lactose passes through the small intestine undigested

  • undigested lactose pulls water into the GI tract → diarrhea and gas

• lactose is digested by bacteria in the large intestine

  • fermentation of sugars lead to gas production

Prevalence of Lactose Maldigestion

Babies and lactase levels?

• babies have sufficient lactase to digest breastmilk and/or formula

• lactase production declines after infancy

Prevalence of Lactose Maldigestion

What is the general rule of thumb between fluid diary products and lactose levels?

• more fluid dairy products tend to be higher in lactose

  • cheese (hard cheese) < yogurt < milk

Dietary Fiber & Health

What is adequate fiber intake associated with?

• manages regular bowel movements through increased transit time

• increases satiety

  • because it takes longer to digest, people feel full for longer

• decreased risk of heart disease

• diabetes

• cancer

Dietary Fiber & Health

What is consumption of fiber absolutely necessary with?

• absolutely necessary to increase fluids, and may reduce absorption of some minerals

Fiber Prevents Constipation

Why is a slow transit time bad?

• longer duration in the colon = more H2O absorption = harder stool

Fiber Prevents Constipation

What does insoluble and soluble fiber do?

• insoluble fiber decreases transit time (speeds it up)

• soluble fiber retrains water

Fiber Prevents Constipation

What can chronic constipation lead to?

• diverticulosis

  • increases with age

  • increased pressure in the colon causes pouches (out pockets) to form along the wall called diverticula

• diverticulitis

  • infection of the diverticula leads to diverticulitis

What does soluble fiber reduce?

• soluble fiber reduces blood cholesterol levels

How does soluble fiber reduce blood cholesterol levels?

• bile acids contain cholesterol

• soluble fiber is a bile acid sequestrator

  • excreted in feces

• bile is reabsorbed in GI tract & recycled

  • soluble fiber interferes with reabsorption

  • “bound” cholesterol in bile excreted

How does fiber reduce the risk of diabetes?

• soluble fiber helps slow digestion and absorption of glucose

How does fiber reduce the risk of cancer?

• decrease time cancer-promoting substances spend in contact with the GI tract

• encourages growth of colon-friendly bacteria and fermentation

How does fiber relate to energy balance?

• increases satiety

What are the cautions of eating fiber?

• must also increase fluid intake

• may reduce absorption of some minerals

Gut Microbiome

What is GI flora? Where are they mostly?

• bacteria exists throughout the GI tract

  • mostly in the colon

Gut Microbiome

How does the microbiome impact human health?

• GI functioning

• fermentation of undigested carbohydrates

• immune system

  • compete with pathogens

  • informs immune system response

• stress, behavior, mental health

Gut Microbiome

What is dysbiosis?

• imbalance of body’s microbial composition

  • can happen in the short-course due to antibiotics

Gut Microbiome

What is probiotics? And what are some sources of them?

• living organisms (bacteria) associated with health benefits

  • fermented diary

  • fermented vegetables

  • fermented soy

  • dietary supplements

Gut Microbiome

What is prebiotics? What are some sources of them?

• non-digestable resistant starches (fiber) that support growth and health of gut bacteria populations

  • banana, garlic, onions, asparagus, leeks, carrots, squash, sweet potatoes, whole grains

Gut Microbiome

How does the gut microbiota play a role in the host metabolism?

• reduced diversity associated with increase in metabolic disorders

  • changes in weight and changes in insulin resistance

What is an important byproduct of the gut bacteria? What is its key role?

• vitamin K

  • coagulation (blood clotting)

Added Sugar

What is the difference between natural and added sugars?

• sugar occurs naturally in some foods, such as fruits

• foods with naturally occurring sugars are often nutrient-dense

• added sugars introduced during food processing

  • most common added sugars: sucrose and fructose

What is the largest source of added sugar in U.S. diet?

• sugar-sweetened beverages

What is the research hypothesis regarding added sugar consumption?

• sugar in liquid form impacts hunger (doesn’t increase satiety), and leads to consuming more energy than the body might need

How does sugar cause tooth decay?

• it is a food source for bacteria in the mouth

• acid produced by the bacteria erodes the tooth enamel

What are sugar substitutes?

• polyols or sugar alcohols

• stevia

• aspartame

What are the benefit of using sugar substitutes instead of added sugar?

• able to use very small amounts to achieve the same level of sweetness than when using added sugar

What are the effects of polyols or sugar alcohols?

• fewer kcals than sucrose

• decreased impact on BG and risk for dental caries

• has a laxative effect

  • less absorption in our small intestine, and will change the osmotic composition in the large intestine by pulling water to experience diarrhea

What are the effects of stevia?

• does not provide any energy or calories

• does not raise BG

What are the effects of aspartame?

• made of amino acids

• does not provide much energy in terms of calories

• found in diet sodas

Who is aspartame not appropriate for?

• not appropriate for individuals with phenylketonuria (PKU)

What is phenylketonuria (PKU)? What is the treatment?

• a genetic disorder where there is an enzyme missing to convert the animo acids, and will lead to a buildup of phenylalanine

• the treatment is to avoid protein consumption to reduce the amount of byproducts

Digestion: Common Disorders

What is recommended for constipation?

• increase in fiber and water/fluid intake

Digestion: Common Disorders

What is diverticulosis → diverticulitis?

• the out pouches of the large intestine that gets infected

Digestion: Common Disorders

What causes diarrhea?

• too-fast transit time through the small/large intestine and loss of fluid

Digestion: Common Disorders

How can diarrhea be very dangerous for pediatric populations?

• dangerous area regarding hydration status

• more severe with pediatrics because they have smaller bodies, so they experience more severe effects

Digestion: Common Disorders

What is gastroesophageal reflux disease (GERD)?

• also known as heartburn

• inadequate/improper closing of the LES (between the esophagus and the stomach)

  • acidic juice from the stomach jumps to the esophagus, and comes in contact with epithelial cells to cause pain

Digestion: Common Disorders

What population is gastroesophageal reflux disease (GERD) common amongst?

• pregnancy because the diaphragm is displaced and organs are squished up