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BIO 1102 Lec. 9: Chapter 14 -- Nutrition and Digestion

Nutrition

Many of us grew up with this food pyramid

In 2005, the US Department of Agriculture created a new pyramid, which they called “My Pyramid”

However, it was difficult to understand and apply

• Now we have “My Plate” – http://www.choosemyplate.gov/

• Visually simpler and easy to apply – What do you find helpful about this diagram? How could it be

improved?

• What is a serving?

– “Portion” sizes have been increasing in recent years (“Super Size” fries and drinks, for example)

• Especially for not-so-good-for-you foods

– A recommended serving size of meat, bread, pasta, or dairy is quite a bit smaller than the typical American portion

– On the other hand, a serving of fruits or vegetables is probably smaller than you think…

– Vegetables

• 1 cup leafy greens

• ½ cup other vegetables, raw or cooked

– Fruits

• 1 medium apple, banana, or orange

• ½ cup chopped fruit

• ¾ cup fruit juice

– Breads, Rice, Pasta

• 1 slice bread

• 1 oz cereal

• ½ cup cooked cereal, rice, or pasta

– Dairy:

• 1 cup milk or yogurt, or 2 oz cheese

– Meat:

• 2-3 oz cooked lean meat, poultry, or fish

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Protein – Protein RDA is calculated as your body weight X 0.4g/lb (so

a 120lb woman would need 120X0.4= 48g protein per day) • A 3 oz serving of meat/fish/poultry contains about 21-24g protein

– Protein sources for vegetarians? • 1 cup cooked quinoa contains 8g protein – and it’s

“complete” protein • 1 cup cooked soybeans contains 29g protein (also complete

protein) • 1 cup of cooked beans contains 12-14g protein • 1 oz nuts/seeds (like peanuts, almonds, or sunflower seeds)

contains 9g protein • 2 Tbsp peanut butter contains 7g protein • 1 large egg contains 6g protein • 3 oz tofu contains 6g protein

• Most Americans eat – Too many “unhealthy” breads and cereals (white

bread, refined grains, white pastas) • Healthy alternatives are whole-grain products

– Too much red meat and dairy products (cheeses) • Lean meats include fish and poultry, but protein can

also be obtained from beans, legumes, quinoa, and other vegetable sources

– Too many “bad” fats (saturated fats and trans fats) and sweets • “good” fats include olive and canola oils

– Not enough fruits and vegetables • On average, only 3 servings of fruits & veggies

• Should be eating at least 5 servings

• The human body needs a variety of MACRONUTRIENTS and MICRONUTRIENTS

• Macronutrients are required in greater quantities than micronutrients

• 4 Macronutrients: – Water

– Carbohydrates

– Lipids

– Proteins

• Water – Critical to many chemical reactions in the body

– Makes up ~60% of body weight

– The average person requires ~2 liters of water a day • Some can be obtained from food, most from drinking

fluids – 8 glasses of fluids a day is typically recommended

• Amount required varies with environmental and metabolic activities

• Activity increases water loss and metabolism

• Fever also increases water loss (physiological basis of “drink lots of fluids…” when sick)

– Drinking too little water can lead to dehydration

• Mild dehydration can make you tired

• Other symptoms: thirst, dry mouth, headache, dizziness, and muscle weakness

• Kidney stones can develop (deposits of calcium and other materials; damage kidneys and cause pain)

• Carbohydrates

– An important source of energy

– Includes sugars and starches

– Recall “Cellular Respiration”… glucose is broken down to obtain energy in the form of ATP’s to do cellular work

– Bread, rice, pasta, and many vegetables such as corn and potatoes are high in starch

• Starch is broken down into glucose

• Glucose enters blood and circulates through body, providing energy

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– Excess glucose stored as glycogen in liver and muscles • Used in-between meals and during exercise

– Cellulose is a carbohydrate that is water-insoluble and humans cannot digest it • Important, nonetheless, in aiding movement of feces

through intestines

• Sources: whole wheat, corn, oat bran, flaxseed, peels and skins of most fruits and vegetables

– Water-soluble fiber, found in fruits and vegetables, also important in diet • Lowers blood cholesterol

• Sources: chia seeds, beans, oat bran

• Also, most fruits and vegetables

• While we’re talking carbohydrates…

• Refined flour versus whole grains

– Refined, white flour is made by removing the bran (husk) from the wheat grain; vitamins and fiber lost

– Recent study: people who ate mostly refined flour (i.e. white bread) had a waistline on average 1/5 inch larger than those who ate a diet high in whole grains

• Even though the whole grain diets were higher in carbohydrates overall

• Why? Refined grains are more rapidly metabolized by the body and turn into fat more quickly

• Lipids – Fats, Oils and Steroids such as Cholesterol

– Function as energy stores, or structural components of cells, or hormones

– Triglycerides – one of the most common • Animal fats and vegetable oils

• Store 2X the energy of glucose

– Stored in fat cells (and circulate in blood)

– Triglycerides from animal fats contain saturated fatty acids • Contributes to atherosclerosis (build up of cholesterol

on artery walls, restricting blood flow and leading to heart attacks and strokes)

– Heart Disease is the most common cause of death in United States (>610,000 deaths annually, according to the CDC in 2017)

– Risks of atherosclerosis can be reduced by: • Cutting back on red

meat and animal fats

• Cooking with vegetable oils

• Low-fat dairy products

– Saturated fats are linear molecules and take on a solid form at room temperature

• No double bonds; molecule is “saturated” with hydrogens

• Sources: animal fats

• Examples: butter; fat in steak or bacon

• Increase the liver’s production of cholesterol

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– Unsaturated fats are liquid at room temperature • Example: oils from vegetables and nuts

(such as olive oil and canola oil)

• Polyunsaturated fats reduce risks for cardiovascular disease – Contain more than one double bond

– Omega-3 fatty acids are polyunsaturated; sources include fatty fish (e.g. salmon), walnuts, ground flax seeds or flax seed oil, chia seeds, and eggs from free-range chickens

– May help increase good cholesterol (HDL) and reduce triglyceride levels

• Avacados contain monounsaturated fats, which are also healthy; can help reduce cholesterol levels

– “Good” and “Bad” Cholesterol

– LDL Cholesterol: Low Density Lipoprotein

• Bad because it can build up in walls of arteries that feed the brain and heart (i.e. contributes to atherosclerosis)

– HDL Cholesterol: High Density Lipoprotein

• Good because high levels seem to protect against heart attack

• May carry LDL cholesterol away from arteries, to the liver, where it removed from blood circulation

– Steroids are also lipids • Sex hormones (testosterone and estrogen) are steroids

• Cholesterol is a steroid – Necessary component of cell membranes

– Cholesterol-lowering drugs (statins, such as Lipitor and Zocor) • Lower LDL cholesterol only

• Statins inhibit action of the enzyme that controls cholesterol production in the body, and by increasing removal of cholesterol by the liver

• Also cause a slight increase in the good cholesterol (HDL)

• Some side-effects possible: reduction in an important antioxidant (CoQ10); might lead to muscle wasting in some people, and even heart failure

• Amino Acids and Proteins – Recall that Proteins are composed of chains of

amino acids, and that there are 20 different amino acids

– Humans can make some of these (~12) amino acids; the rest must be obtained from food • These are the “essential amino acids”

• Deficiencies can cause health problems

• Dairy products, meat, poultry, fish, and soy contain all essential amino acids

– When we eat protein (plant or animal), our bodies break it down into amino acids

– These amino acids can then be used to build new proteins in our bodies

• Overnutrition

– In the U.S., 70.7% of adults are overweight (2013-2014 CDC data)

– 37.9% obese (2013-2014 CDC data)

– Rate has increased significantly in last 30 years, including among young people

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– What causes us to overeat?

– Hormone Leptin is involved: it is generated by fat cells, and sent to the brain (hypothalamus); more fat cells = more leptin = more messages to the brain that you are “full” and should burn energy

– When we try to diet, there is a drop in fat cells, thus a drop in leptin, which leads the hypothalamus to signal you are hungry; also leads to conservation of energy by muscles

• Even if you exercise, you burn less energy

– Leptin drops within 24 hours of a drop in food consumption

– Leptin likely evolved in a context where food wasn’t plentiful

– Its action helps prevent starvation

– Leptin isn’t the only factor; there may be a dozen or more genes that interact to determine a person’s likelihood of obesity

Micronutrients

– Vitamins – organic compounds found in small quantities in our food

• Recycled in our bodies

– Too little, or too much, of a particular vitamin can cause health problems

– Water-soluble vitamins: vitamin C and eight forms of vitamin B

• Water-soluble vitamins are not stored in body (more difficult to get “too much,” but still possible)

– Fat-soluble vitamins: A, D, E, and K

• Stored in fat reserves in body

– Minerals: inorganic compounds obtained from food

• Examples: calcium, iron, sodium, and potassium

• Vitamin C – Most mammals can synthesize their own, but we have

lost the ability to do so – Important for manufacture of connective tissues, and

so plays important role in healing wounds; needed in formation of collagen in blood vessel walls to keep them flexible

– Also an important antioxidant, slowing the aging process and preventing cancer

– Vitamin C content of food declines when exposed to air, light, and heat

– Good sources: red bell peppers, kale, broccoli, brussels sprouts, citrus fruit, and strawberries

• B-vitamins – 8 individual vitamins (B1, B2, B3, B5, B6, B7,

B9 and B12)

– B-complex vitamins play important role in converting glucose into ATP energy

– Also necessary for normal function of nervous system

– Also important for health of skin, hair, eyes, mouth, and liver

– B12 is necessary for production of red blood cells

– B12 is a product of bacteria; some animals can absorb sufficient B12 from bacteria in their digestive tracts; that is not reliable for humans, however

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– Only reliable source is animal products (eggs, dairy, fish, poultry, red meat, especially organ meats like liver)

– Therefore, strict vegetarians should take a B-complex vitamin supplement

– But, our bodies do store B12 (unlike the other water soluble B vitamins); it is stored in liver, kidneys, and other places; a deficiency would take years to show up because we store extra B12

• Vitamin A – A family of nutrients that includes

• Retinol (important for vision)

• Retinal (important for vision)

• Retinoic acid (important for growth and differentiation)

• Carotenoids (which can be converted to vitamin A)

– Beta-carotene is the carotenoid with greatest vitamin A activity, and also acts as an antioxidant

– Rich sources of pre-formed vitamin A include fish liver oil, milk, cheese, butter, eggs, and all meats

– Carotenes are found in plants; best sources include dark leafy greens (spinach, kale, beet greens, etc.) and orange vegetables/fruits (carrots, cantaloupe, sweet potatoes, butternut squash, etc.)

• Vitamin D

– A group of related, fat-soluble vitamins

– Often, vitamin D2 is added to foods as a supplement (such as in orange juice or milk)

– Vitamin D3 is naturally found in cold-water fish, egg yolks, and butter

– Vitamin D is produced by our skin when exposed to sunlight (aka the “Sunshine Vitamin”)

– Many cells throughout body have receptors for Vitamin D, so it acts almost like a hormone

– Important for immune function, and for bone health (helps body absorb calcium and phosphorus)

– Vitamin D may also help prevent cancer:

– http://www.youtube.com/watch?v=MOUiIvp2j18

– But don’t take high doses of supplements, as too much can be harmful:

– http://www.youtube.com/watch?v=tjRfxvsFrMI

• Vitamin E

– Includes eight related compounds

– Primary role is as an antioxidant

• Oxidants react with other molecules and can alter cellular structure

• Oxidation can contribute to cancer when the oxidant damages DNA

• Oxidation can lead to blood clot formation, too

• Antioxidants like Vitamin E react with the oxidants, instead of the body’s cells and molecules, taking the damage on themselves and preventing cellular damage

– Sources of Vitamin E include vegetable oils, raw seeds and nuts, and soybeans; some Vitamin E also found in leafy green vegetables and grains such as brown rice

• Vitamin K – Consists of three forms

• K1 – found in food

• K2 – produced in intestinal tract by bacteria

• K3 – synthetic form

– Vitamin K is sometimes called the “bandaid vitamin” because it plays important role in blood clotting • Necessary for formation of 4 of the 13 clotting factors

– Also plays role in bone formation (study: women with low vitamin K had more hip fractures)

– Sources: dark leafy greens, cabbage, broccoli, green tea, peas, asparagus, whole wheat, and oats

– About half of our daily need is produced by our bodies, but we must consume the other half

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• Calcium

– Most abundant mineral in body

– Important for bones and teeth (98% of calcium in our bodies is located here)

– Also necessary for release of neurotransmitters, muscle stimulation, and regulation of heartbeat

– Dairy products contain significant amounts

– Canned sardines and salmon (containing the softened bones) also a good source

– Best vegetable sources: tofu (varies – check label) and leafy green vegetables

• Iron

– Necessary for blood’s ability to transport oxygen

• Makes up central core of hemoglobin molecule

– Also necessary for formation of myoglobin, found in muscle cells; helps muscles gain access to oxygen

– Also necessary for collagen production, and for neurotransmitter synthesis

– 2 forms of iron: heme and non-heme

• Heme iron: found in meats (23% bioavailable) – Clams, liver, oysters, beef, egg yolks

• Non-heme iron: found in plants (3-8% bioavailable; but with vitamin C, increases 200-300%) – Richest sources: kelp, beans, lentils, peas, pumpkin seeds,

almonds, Brazil nuts, raisins, spinach (?), and kale

– Vitamin C increases absorption of iron

• Antioxidants

– A group of helpful chemicals found in many fruits and vegetables, as well as tea, soy products, wine, and dark chocolate

– Help eliminate “oxidants” in blood

• contribute to build up of cholesterol in artery walls

• May also contribute to cancer

• Example: antioxidant EGCG in green tea – http://www.youtube.com/watch?v=H-7rfIWgO5E

• For Good Health: – More fruits and vegetables

• “Eat food, not too much, mostly plants” – Michael Pollan

• Variety

• “Slow food” instead of “fast food”

– More exercise

– Stress management

– Plenty of water

– Fewer saturated and trans-fats

– Fewer sweets

• Michael Pollan seems to promote a “flexitarian diet”

– Not as rigid as vegetarian diets

• Vegetarians do not eat meat, but may eat dairy products and/or eggs

• Vegans eat no meat, no dairy, and no eggs

– But promotes eating less meat

• Example: “Meatless Monday” movement (http://www.meatlessmonday.com/)

• A different take on diet and health: the vegan diet

– The China Study by Dr. T. Colin Campbell

– Research has found link between animal protein and risk for cancer and heart disease

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Digestion The Digestive System

• Mouth – Physical break down of food (teeth and jaws)

– Chemical break down • Saliva – released by salivary glands in mouth

• Release triggered by smell, feel, taste or thought of food

• Functions: – Liquefies food

– Dissolves food particles for tasting

– Begins chemical break-down (amylase enzyme)

– Cleans teeth

– Tongue

• Aids in swallowing, as well as speech

• Also contains taste buds – Sensors that detect 5 basic flavors: sweet, sour,

salty, bitter, and umami

• Esophagus

– Food is pushed into the esophagus with the help of the tongue during swallowing

– Is prevented from entering trachea (“windpipe”) by the epiglottis

• Closes over trachea during swallowing

• After swallowing, movement of food through digestive system is involuntary

• Stomach – Muscles at the attachment site of esophagus to

stomach regulate movement of food into stomach, and prevent stomach acid from entering esophagus (gastroesophageal sphincter) • Failure results in irritation of esophagus, called

heartburn

– Gastric pits lining the stomach lead to gastric glands

– Some gastric glands secrete hydrochloric acid (HCl) • HCl helps break kill most bacteria

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– Acidic secretions yield a pH of about 2, which could damage stomach; how protected?

• Gastric glands also secrete basic mucus

• “Tight junctions” among cells in stomach lining; makes it “leak-proof”

• Ulcers may occur as a result of excessive stomach acid production or, more often, a bacterial infection

• Heliocobacter pylori causes ~70% of ulcers

– Many cells lining the stomach secrete pepsinogen • Pepsinogen is a precursor molecule that becomes a

protein-digesting enzyme called pepsin once it is exposed to HCl

– The combination of the HCl, pepsinogen, and fluid secreted into the lumens of the gastric glands is called gastric juice

– Some mucosal cells lining stomach also produce intrinsic factor, a protein that binds to vitamin B12 and enables it to be absorbed in the small intestines

– The mixture of partially digested food and gastric juice is called chyme

• Small Intestine – Food exits stomach through another ring of

muscles, controlling its entry into the small intestine (pyloric sphincter) • Usually occurs 2-6 hours after a meal

• When stomach empties, churning of muscles is felt as “hunger pangs”

– Small intestine is where most absorption of nutrients takes place • Long coiled tube over 10 feet long

• First region = duodenum (carries out digestion)

• Second region = jejunum (carries out absorption)

• Third region = ileum (carries out absorption)

– Mucosa of small intestines conains large folds covered in villi, which are in turn covered with microvilli

– Within each villus are capillaries and a small lymphatic vessel called a lacteal • Lacteals help transport

especially large nutrient molecules into the lymph, and then into the blood stream

– Enzymes break food down into particles small enough to be absorbed across the lining into the bloodstream

– Enzymes used in the intestine are produced in two locations • Lining of the small intestine

itself

• Pancreas

– Located below stomach

– Also releases sodium bicarbonate (neutralizes acids)

– Once broken down, small food particles can be absorbed across lining of intestine via diffusion

• Liver – Located in right side of abdomen, above stomach

and beneath the ribs

– Large organ; performs ~500 functions • Stores glucose and fat, and releases them as needed

• Synthesizes some proteins

• Removes harmful chemicals from body

– Regarding digestion… • Liver produces bile

– Bile salts (steroids) help break down fats

• Bile is stored in gallbladder – Releases bile into the small intestine

– Gallstones – blockages in gallbladder and ducts

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• Large Intestine – Leads from small intestine to anus; about 5 feet

long

– Most nutrients have been absorbed already in small intestines

– Water, sodium, and potassium is absorbed; what remains is feces

– Feces propelled by smooth muscle contractions

– Rectum is the end of the large intestine; waste expelled

Activity #9

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