INGRID ADAMS, PHD, RD, LD MATTHEW SAULNIER,RD,LD DIGESTION: WHAT HAPPENS TO THE FOOD WE EAT

INGR ID ADAMS, PHD, RD , LDMAT THEW SAULNIER ,RD ,LD

DIGESTION: WHAT HAPPENS TO THE FOOD

WE EAT

HOW DO YOU MAKE FOOD DECISIONS?

• What did you eat yesterday?• Why?• What will you eat for the rest of your life?• How will you decide?• Is it important to make wise food decisions?

Why or why not?• What role do you have to play in this

situation?

The Digestive Organs

DIGESTION: THE ENZYMES

• Digestive enzymes are produced in the salivary glands, mouth, stomach, small intestine, and pancreas.

• The pancreas produces digestive enzymes and secretes them into the duodenum via the pancreatic duct.

• Most digestive enzymes are inactive until they are secreted into the GI tract – protects our cells from self-digestion.

DIGESTION

•Digestion occurs along the gatrointestinal (GI) tract.

•Digestion requires enzymes and other chemical and physical factors.

MOUTH

Carbs Fats ProteinFood is chewedSalivary glands:

AmylaseLipase

CARBOHYDRATE DIGESTION

• Mouth• Starch digestion begins in the mouth. Salivary glands

secrete salivary amylase.• Salivary amylase is an enzyme that breaks down starch

into smaller polysaccharides and disaccharides.

CARBOHYDRATES – WHAT IS DIGESTED?

• Starch is the most common carbohydrate in the American diet. It is a large molecule composed of linked glucose units.• Digestion breaks starch down into single glucose

molecules.

STOMACH

HClPepsinLipase

CARBOHYDRATE DIGESTION

• Stomach• Starch digestion stops in the stomach where it is to acidic for salivary

amylase to work.

• Small Intestine• The majority of carbohydrate digestion occurs in the small intestine.

• The pancreas produces pancreatic amylase, which is secreted into the small intestine once food enters from the stomach and breaks down food into very small chains of glucose

• The cells that line the small intestine break down carbohydrates into simple sugars, which are absorbed directly into the blood stream.

SMALL INTESTINE

DuodenumLiver – produce bile which is stored in the gall bladderPancreas

AmylaseLipaseTrypsinChymotrypsin

Dietary fibers, other large molecules (undigested proteins, triglycerides, starches, etc…)

LARGE INTESTINE

CARBOHYDRATE DIGESTION

• Absorption• Glucose units are absorbed into the intestinal wall and

pass into the bloodstream. • Dietary fibers: NOT DIGESTED OR ABSORBED in the small

intestine

PROTEIN DIGESTION

• Mouth• No digestion of protein occurs here.

• Stomach• Stomach acid, hydrochloric acid, beings to break down

protein molecules.• Hydrochloric acid activates an enzyme called pepsin,

which breaks down protein into small polypeptides.

PROTEIN DIGESTION

• Small Intestine• Once these polypeptides enter the small intestine,

enzymes form the pancreas and intestine break down these chains into amino acids.

• Intestinal cells absorbed amino acids just like carbohydrates.

• Absorption• Amino acids enter the intestinal cells and pass into the

bloodstream.

FAT DIGESTION

• Digestion of fat is slightly different from carbohydrates and protein.• Mouth• Lingual lipase mixes with food. Lingual lipase plays a

more prominent role in children.

• Stomach • Lingual lipase acts in the stomach where it prefers a

more acidic environment.

FAT DIGESTION

• Small Intestine• Triglycerides mix with the bile from the gallbladder and

form micelles. The water soluble lipases from the pancreas and intestine act on the triglycerides in the suspended micelles.

• The main products of triglyceride digestion are fatty acids and monoglycerides.

• Absorption• Fatty acids, glycerol, and monoglycerides pass into the

intestinal cells and are reassembled into triglycerides. They are then packaged into chylomicrons and enter the lacteals of the lymphatic system.

WHAT IS NOT ABSORBED IN THE SMALL INTESTINE?

• Dietary fibers, other large molecules (undigested proteins, triglycerides, starches, etc…)

• Many food additives are digested to be unobservable, for safety and to reduce caloric content of the diet.

AFTER ABSORPTION, THEN WHAT?

• Fats, cholesterol, and fat soluble vitamins are repackaged in the intestinal cell, sent through the lacteal (lymphatic system), enter the general circulation through the thoracic duct.• Most other nutrients are sent through capillaries

from the small intestine to the portal vein and go directly to the liver.• Liver processes sugars to glucose; amino acids to

whatever amino acids are needed.

PROBLEMS WITH DIGESTION

HIATAL HERNIA• Portion of stomach

pressed into chest cavity through esophageal hiatus (passageway for esophagus) of diaphragm• Symptoms: GERD,

dysphagia (swallowing difficulty), heartburn, and epigastric pain. • Rx: weight control

and methods used to control GERD

DISEASES OF THE STOMACH AND SMALL INTESTINE—PEPTIC ULCER DISEASE (PUD)

PUD: Ulceration of the gastric or duodenal mucosa penetrating the submucosa with potential for perforation

Antrum

Duodenum

LACTOSE INTOLERANCE• Insufficient lactase production in brush border• Poor digestion of lactose

PRIMARY LACTASE NON-PERSISTENCE PREVALENCE IN US

Northern European American 5%Mexican American 62%African American 80%Asian American 90%Native American 95%Vietnamese American 100%

LACTOSE INTOLERANCE—SYMPTOMS

• Symptoms usually begin 30min to 2hrs after consuming lactose• Crampy pain• Bloating, flatulence• Fermentation of lactose by colonic bacteria (CO2, H2, methane)

• diarrhea• Lactose draws water into gut by osmosis peristalsis fluid,

electrolyte, nutrient losses

• Nausea

LACTOSE INTOLERANCE—SYMPTOMS

• Severity of symptoms depend on• Degree of lactase insufficiency• Lactose load 

• Many lactase insufficient individuals can tolerate some lactose• Some enzyme activity often present to varying

degrees• Fermentation of undigested lactose by colonic

microorganisms  • Up to 1 cup of milk (12g of lactose) WITH MEAL can be well tolerated without significant symptoms by those who are lactose maldigesters

SOURCES OF LACTOSE• Lactose naturally present only in milk and

products made from milk• 7% human milk• 5% cows milk• 4.5 % goat milk

• Usually less lactose in milk products than in milk• Yogurts—less lactose than milk; may contain active

bacterial cultures capable of metabolizing lactose • Ice cream—fair amount compared with milk• Cottage cheese—contains little lactose; can usually

be eaten with no adverse effects • Hard cheeses—contain less than cottage cheese

LACTOSE INTOLERANCE • Remove lactose to the level of tolerance• Consume lactose containing foods with meals• dilutes lactose and slows its movement

• Elimination of lactose worsens tolerance less favorable mix of colonic microflora• Fermented milk products (yogurt with active

cultures) • Non-fermented milk products (acidophilus milk

or yogurt milk) may or may not be tolerated• Chocolate and whole milk better tolerated

than skim• Aged cheese well tolerated• Cottage cheese and ice cream—lower lactose

content than milk

LACTOSE INTOLERANCE—MNT

• Lactose free milk• Enzyme replacement—lactase tablets • Dairyease®, Lac-Dos®, Lactaid®, Lactrase®,

RiteAid® Dairy Relief™, Surelac®, Walgreens® Dairy Digestive™

• Check medication labels• powder filler used in medication may contain

lactose • Teach patients to read foods labels for

hidden sources• Ca, vitamin D, vitamin B12, and riboflavin

supplementation depending on milk intake

CELIAC DISEASE

• Also known as:• Gluten sensitive enteropathy• Celiac sprue• Nontropical sprue• Prevalence: 1 in 133• Higher prevalence in females• Underdiagnosed—symptoms resemble those of

other diseases• Caused by an allergic reaction to protamine in

certain grains

CELIAC DISEASE (CD)

Also known as: Gluten sensitive enteropathy Celiac sprue Nontropical sprue

Prevalence: 1 in 133 Higher prevalence in females Underdiagnosed—symptoms resemble those of other

diseases Caused by an allergic reaction to protamine in

certain grains

OFFENDING GRAINSGrain Prolamin

Wheat gliadin

Rye secalin

Barley hordein

Oats? avenin

Certain peptides from these proteins induce the celiac response in sensitive individuals.

OFFENDING GRAINS

• Triticale – hybrid of rye and wheat• Spelt – wheat • Kamut – wheat • Einkorn – wheat • Emmer – wheat

• Wheat (bulgur, wheat bran or germ, wheat germ oil, wheat starch or food starch, couscous, pastas made from wheat, matza, seitan, semolina)

• Barley (malt)

“GLUTEN”

• Protein found only in wheat• The main protein in wheat• Composed of glutenin and gliadin

• The term “gluten” has come to mean any cereal peptides inducing a celiac response• What is the celiac response?• Both cellular and humoral• Lymphocyte infiltration of the intestinal epithelium• Flattening of the villi

VILLUS ATROPHY

The Internet Pathology Laboratory, University of Utah

CLASSIC SYMPTOMS• Weight loss, wasting• Weakness, malaise• Failure to thrive (FTF), short stature• Dental enamel defects• Iron deficiency anemia (Fe malabsorption;

occult blood loss)• Steatorrhea • Diarrhea due to malabsorption• Constipation in some cases• Irritability in children• Abdominal discomfort, bloating, flatus,

belching, GERD• Physical signs of nutrient deficiency

More on symptoms

• Many celiacs do not exhibit the classic symptoms

• Some have no clinical GI symptoms• Because of many and varied symptoms:

– Average time to diagnosis CD: 11 years!

Dermatitis herpetiformis (DH)

medline plus

Graphics: Microsoft Online, USDA Food and Nutrition Services

Ingrid Adams, Ph.D., R.D. L.D. Associate Professor , Nutrition and Food Science, University of KentuckyExtension Specialist for Physical Activity and Weight Management

Date: February 27, 2015

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