Fundamentals of Nutrition

Session 2

Instructor: Andrea Bartels B.A. CNP, NNCP, RNT

SESSION #2

� Objectives:

� To gain an understanding of the digestive and elimination processes of the body

� To define metabolism, the role of calories and enzymes

� To gain an understanding of the role carbohydrates � To gain an understanding of the role carbohydrates have in the diet and the relationship of quality,

insufficiency and excess to state of health.

DIGESTION AND ELIMINATION

FOOD FOR THOUGHT:QUOTES WORTH ‘DIGESTING’

� “The first step to good nutrition is to know the origin, processing, and contents of anything we take into our bodies.” – Elson M. Haas, M.D.

� “Merely eating the right foods does not necessarily ensure adequate nutrition. Once the food is in the digestive tract, it adequate nutrition. Once the food is in the digestive tract, it may or may not be absorbed. A vast number of factors are involved in the digestion and absorption of food: for example, how it is chewed, the secretion of enzymes and the condition of the lining of the digestive tract which the nutrients must cross. Even absorption from the intestines is not the final step since the nutrients, if they are to be used properly, must reach the cells where they are needed.” – Rudolph Ballentine, M.D.

THE HUMAN DIGESTIVE SYSTEM

� The human digestive system is a complex series of organs that processes food.

Functions:

� Digestion – reduction of foods into their simplest componentscomponents

� Absorption – uptake of nutrients from the digestive tract into the body

� Elimination – disposal of wastes (i.e. substances that cannot be digested are now toxins, with the exception of fibre)

THE PROCESS OF DIGESTION

A LOOK INSIDE…HOW ALL THE ORGANS COMMUNICATE

� Your senses: sight, smell, taste and sound:• trigger salivation

• Flavours that trigger the digestive process: salty, bitter, sweet, sour, pungent* and astringent*.

� Your mouth� Your mouth• Teeth grind the food into smaller bits (CHEWING)

• Salivary amylase (in saliva) begins to break down carbohydrates only.

• Fact: saliva secretion is approximately 1 liter per day.

• A bolus (from Latin bolus, ball) is a mass of food that has been chewed and swallowed.

THE STOMACH - DIGESTIONYour stomach:

� The stomach is a large, sack-like organ that churns the smaller bits of food and bathes it in a very strong acid (gastric acid a.k.a. hydrochloric acid), pH of 1-3.• Amylase becomes inactivated here as it requires an alkaline

environment.

� Fact: Most bacteria are destroyed by hydrochloric acid.

� Food that is partly digested and mixed with stomach acids is called � Food that is partly digested and mixed with stomach acids is called chyme.

� HCl, pepsin and rennin are involved in digestion of proteins.

� HCl triggers pepsin to breakdown proteins � split chains.

� Fact: Mucous protects the stomach wall from being digested!

THE SMALL INTESTINE -

ABSORPTION

� After being in the stomach, food enters the duodenum (first part of the small intestine). It then enters the jejunum and then the ileum (final part of the small intestine).

� In the small intestine, bile (produced in the liver and � In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food.

� Bile, pancreatic amylase, chymotrypsin, trypsin, and lipase breakdown fats, proteins and carbohydrates into their smallest components, ready for absorption.

� Fatty acids (fats), amino acids (proteins) and monosaccharides (carbohydrates) are absorbed.

THE LARGE INTESTINE:

ELIMINATION

� Next, food passes into the large intestine. In the large intestine, some of the water and electrolytes (for ex. sodium) are removed from the chyme.

� Many microbes/bacteria (such as Lactobacillus Acidophilus & Bifidus) in the large intestine help in the digestion process.

� Many microbes/bacteria (such as Lactobacillus Acidophilus & Bifidus) in the large intestine help in the digestion process.

� The first part of the large intestine is called the cecum (the appendix is connected to the cecum). Food then travels upward in the ascending colon, travels across the abdomen in the transverse colon, goes back down the other side of the body in the descending colon, and then through the sigmoid colon.

� All the ‘leftovers’ are sent here, and stool is made (stool: bile, cholesterol, bacteria, dead cells, fiber and water.)

ACCESSORY ORGANS:

PANCREAS, GALLBLADDER AND LIVER

� Pancreas: Makes digestive enzymes and bicarbonate, secreting them in the right amounts into the small intestine.intestine.

� Gallbladder: Holds the bile made by the liver and used to emulsify consumed fats.

� Liver: Makes the bile stored by the gallbladder.

REVIEW:

THE HUMAN DIGESTIVE SYSTEM

MACRONUTRIENTS

= Nutrients needed in large quantities, i.e. grams/day.

� Provide the majority of energy to an organism.

� Three types: Carbohydrates, Proteins and Fats.

� Macronutrients are metabolized with the help of � Macronutrients are metabolized with the help of enzymes to form building blocks and energy sources.

ENERGY

� Calorie - a unit of measurement for energy. It is

defined as:

• The amount of energy available from a particular food or

drink.

• The energy potential of a food/drink.• The energy potential of a food/drink.

� To retrieve the energy from macronutrients they

must be metabolized.

METABOLISM

= The modification of chemical compounds (nutrients,

foodstuffs) into energy or calories, with the help of

enzymes

� Recall: building (anabolism), cleansing (catabolism)

and maintenance as metabolic processesand maintenance as metabolic processes

ENZYMES

=specialized protein molecules that start or speed up

a specific chemical reaction.

� Clue: each has an “ase” ending

� Necessary for digestion and many other chemical

reactions in the body.reactions in the body.

Examples:

� Digestive enzymes: protease, lipase, amylase

� Immune enzymes: superoxide dismutase (SOD),

glutathione peroxidase

CARBOHYDRATES

WHAT MAKES CARBOHYDRATES

UNIQUE?

� Consist of only 3 elements: carbon, hydrogen and oxygen (CHO).

� Relatively quick to digest, providing quick fuel for internal organs, nervous system and muscles.

� A storable fuel, (glycogen) in the liver and muscles.A storable fuel, (glycogen) in the liver and muscles.

� Preferred fuel source by the brain and muscles

� Exception: Fiber consists of indigestible carbohydrate. Instead, it adds bulk to stool, aids bowel movement/elimination.

CARBOHYDRATES

� There are 3 types of carbohydrates:

1) Sugars:

• Simple carbohydrates:

• Monosaccharide

• Disaccharides• Disaccharides

2) Starches:

• Complex carbohydrates:

• Polysaccharides

3) Fiber

SUGARS

� Simple sugars are:• Monosaccharide• Disaccharides� Require little to no digestion

� Complex carbohydrates are:• PolysaccharidesPolysaccharides� Require more complex digestion

� Oligosaccharides:• Special carbohydrates� Cannot be completely digested• They feed our necessary bacteria/flora – probiotic

medium (enhance the growth of good/”friendly” flora); • example: fructo-oligosaccharides (FOS) found in onions,

garlic, asparagus, human milk

SUGARS - SIMPLE CARBOHYDRATES

� Monosaccharide

� Mono = one; one sugar –basic unit

� Absorbed directly into the bloodstream, no enzymes required.

� There are 3 kinds of

1. Glucose• Accessible sugar in the body.• Examples: some fruit, grapes

2. Fructose• Example: fruits and honey

3. Galactose• Example: product of lactose � There are 3 kinds of

monosaccharide: glucose, fructose and galactose.� Ex. : fruit, honey and milk.

• Example: product of lactose digestion (milk)

DISACCHARIDES

= Two monosaccharidesjoined together

� Require enzymes for digestion

1. Lactose• milk sugar of animal origin

• consists of glucose + galactose

• Requires lactase; common deficiency

2. Sucrose2. Sucrose• Cane sugar, maple syrup,

sugar beets, pineapple

• glucose + fructose

• Requires sucrase

3. Maltose• Cereal grain, malt sugar

• glucose + glucose

• Requires maltase

SIMPLE SUGARS: PROS AND CONS

� Advantage:

• virtually instant energy

-requires little to no

digestion.

� Disadvantages (with overuse):

• Degenerative diseases - tooth

decay, obesity, diabetes (Type II).

• Stresses pancreas (insulin).digestion.

-rapid absorption into

bloodstream

• Stresses pancreas (insulin).

• Causes dramatic fluctuations in

blood sugar levels

(hypoglycemia).

STARCHES – COMPLEX

CARBOHYDRATES

= Polysaccharides

� Poly = many; several dozen to several thousand sugars

� glucose + glucose + glucose + glucose +…

� Whole foods, traditional diets (corn, maize, 100% wheat).

� Advantage:• Slower digestion and

absorption allow for more stable blood sugar levels.

� Disadvantage:Whole foods, traditional diets (corn, maize, 100% wheat).

� Examples: grains, beans, root vegetables

� Digestion: begins in mouth with amylase.

• More complicated break down requires good digestion (i.e. ample enzymes) for availability.

FIBER : NON-STARCHY POLYSACCHARIDES

� Indigestible polysaccharides; cannot be broken down by human enzymes or digestive juices.

� Little to no energy or caloric value.

� Soluble fiber• Dissolves in water to form a gel.

• Binds bile acids, holding fat and cholesterol and eliminates them.

• Pectin rich foods = apples, pears, mango, sweet potatoes, squash, avocado, legumes, barley, oats,…

Insoluble fiber� Hemicelluloses: pectins,

vegetable gums, glucans, mucilages (soluble).

� Cellulose: lignan (insoluble).

� Insoluble fiber• Does not dissolve in water

• Absorbs water.

• Roughage; chewy, woody.

• ‘the skeleton’ of the plant.

• Softens and expands stool volume.

• Celery, green leafy vegetables, whole grains; outer layer or plant.

FIBER: PROS AND CONS

� Advantages:

• Balances intestinal

functions = elimination

• Generally, will speed

transit time and add bulk

to stools.

� Disadvantage:

Too much :

• May promote gas,

distention of the belly

• May promote frequent

bowel movementsto stools.

• May protect against heart

disease by binding fats

and cholesterol (for ex.,

psyllium).

• Slows stomach emptying

and slows glucose entry

in the bloodstream.

bowel movements

DIGESTION AND METABOLISM

OF CARBOHYDRATES: A REVIEW

� Monosaccharides are directly absorbed into bloodstream through small intestine lining.

� Disaccharides are broken down into their monosaccharide components (fructose, galactose) by enzymes (sucrase, components (fructose, galactose) by enzymes (sucrase, lactase), then absorbed through the small intenstine.

� Polysaccharides: • Begin digestion in the mouth by salivary amylase.

• Amylase converts them into dextrin; a shorter-chain starch.

• Pancreatic enzymes released into the small intestine convert dextrin to maltose.

• Maltose converts to glucose with maltase in the small intestine.

CARBOHYDRATES:

DIGESTION AND METABOLISM

CONTINUED…

� Note: monosaccharides-- the basic units of all

carbs-- are the only absorbed forms of carbs-- are the only absorbed forms of

carbohydrates.

� Broken down in the mouth and small intestine,

carbohydrates are absorbed into the bloodstream

through the small intestine.

� Once in the blood, monosaccharide are directed

to the liver where fructose and galactose are

converted to glucose.

CARB EXCESS AND DEFICIENCY

� Extra carbohydrates (glucose) are stored in the liver and muscle as glycogen for times of need.

� Glycogen is a highly branched polysaccharide, which is stored in the liver and/or in the muscles.

� When carbohydrates are limited, i.e. no dietary carbohydrates available, the liver converts carbohydrates available, the liver converts glycogen back to glucose and returns it to the bloodstream, while muscles may use the glycogen directly.

� WARNING: excess carbohydrates consumed are converted into fatty acids and triglycerides that can be stored as body fat. Risks: weight gain, obesity, high LDL cholesterol and Type II Diabetes.

BLOOD SUGAR METABOLISM

� Maintenance of blood sugar levels when intake is

limited:

• Adrenaline (epinephrine) stimulates the liver to break

down glycogen (to glucose).

• Insulin stimulates uptake of circulating glucose.• Insulin stimulates uptake of circulating glucose.

REVIEW AND HOMEWORK

� Focus for next class:

Homework:

� Please review, and become familiar with Chapters

3 & 4 in Staying Healthy with Nutrition for next

class:class:

• Proteins

• Lipids: Fats and Oils