Vitamin A

Today's lesson is the eye saving Vitamin A! Vitamin A has many important roles besides the well known vision function. So, let's get started!

Vitamin A is fat-soluble, which means it needs fat to be absorbed by the body. Insufficient fat intake can lead to a secondary Vitamin A deficiency. Fat soluble vitamins are stored in the body for longer periods of time than water soluble vitamins.

Vitamin A, aka the retinoids, consist of 3 preformed compounds: retinol (an alcohol), retinal (an aldehyde), and retinoic acid (an acid). These active forms of Vitamin A can only be found in animal products (liver, fat of eggs and milk).

The liver plays a major role in the transport and storage of Vitamin A. Liver disease can cause secondary Vitamin A deficiencies. Fun fact: 50-80% of the Vitamin A in your body is stored in your liver!

Carotenoids, found in dark green leafy, yellow-orange vegetables (carrots, sweet potatoes, kale, spinach), can yield retinoids when metabolized in the body. Fun fact: the deeper the color of the vegetable, the higher the levels of carotenoids. The amount of Vitamin A available from dietary carotenoids depends on how well they are absorbed and converted to retinol in the body. Beta carotene, a subgroup of the carotenoids, is well known for its antioxidant capacities.

Vitamin A plays essential roles in vision, cell differentiation, recognition, and growth, bone development, immune functions, and reproduction.  Retinal is a structural component of visual pigments of the rod and cone cells of the retina. Retinoic acid acts as a hormone to affect gene expression.

Vitamin A deficiencies can be very serious. The most significant cause of blindness is due to Vitamin A deficiency.
-->Xerophthalmia: clinical eye disease consisting of atrophy of the periocular glands
-->Nyctalopia: night blindness, failure of retina to regenerate rhodopsin, cannot adjust from bright light to darkness
-->Spontaneous abortions
-->Impaired spermatogenesis
-->Phrynoderma: blockage of hair follicles with plugs of keratin, which causes "toad skin" (rough, scaly, dry skin).

RDA for Vitamin A
-adult females: 700ug
-adult males: 900ug

Toxicity of Vitamin A occurs when persistent large doses (more than 100 times the required amounts) are consumed. Toxicity can eventually lead to liver disease. The most common side effect of excessive carotene intake is hypercarotenodermia, which causes an orange tint to the skin. This is reversible by decreasing carotenoid intake.

UL for Vitamin A
-adult females: 3000mg
-adult males: 3000mg

Impact of Carbohydrates on Metabolism

Last post we talked about the basics of carbohydrates.  Now, let's delve into how carbohydrates impact your metabolism!

Through the activity of enzymes (amylase, brush border, digestive), dietary carbohydrates are digested into glucose, fructose, and galactose. Digestion is altered by factors such as: the availability of starch to enzyme action, presence of fat, which slows stomach emptying, non-absorbable oligosaccharides, and fibers. A diet rich in fruits and vegetables will slow the pace of glucose absorption in the body.

Glycemic Index
The glycemic index ranks carbohydrates based on their ability to raise blood glucose levels. The glycemic index uses of a scale of 0-100. Higher values are given to foods that cause the most rapid rise in blood glucose (Pure glucose = GI of 100). The glycemic index has been an important factor for diabetics that are trying to control their blood sugar spikes.

Glycemic Load
The glycemic load takes the glycemic index further by factoring in the type and amount of carbohydrate consumed. (Grapefruit: GL of 3, Potato Chips: GL of 30).

Regulation of Blood Lipids
A high carb diet leads to hypertriglyceridemia (high blood triglycerides). According to the NIH, "As compared with starches, sugars (particularly sucrose and fructose) tend to increase serum triacylglycerol concentrations by approximately 60%). Two hours after consuming a meal, blood glucose levels begin to drop. The body secretes counter-regulatory hormones that release free fatty acids from fat cells. The fatty acids are packaged into VLDLs and serum triglyceride levels are increased. On the other hand, a high fat diet does not translate directly into blood lipid changes.  The body regulates macronutrient levels to provide adequate supplies of fuel to body tissues.

Fiber and Blood Lipids
Fiber is an important factor in weight loss and blood cholesterol control. Fiber prevents fat and cholesterol absorption by binding bile acids of fats and lipids and excreting them.

Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004. 

www.healthbasic.org

Types of Carbohydrates

Today's lesson features carbohydrates!

Monosaccharides
-The sweet taste of edible sugars (fructose and sucrose) was an evolutionary advantage because sweetness guided humans to select plants with the highest energy value.
-Reducing Sugars: hydroxyl group can reduce (donate hydrogen); examples are glucose and galactose
-Glucose, Galactose, Fructose

Glucose
-Most widely distributed sugar in nature
-Glucose + Fructose = Sucrose (make up a large content of fruits and vegetables)
-Also referred to as "blood sugar"

Fructose
-Other names: levulose, fruit sugar
-The sweetest
-Fruits are generally 1-7% fructose
-Vegetables have 3% fructose
-Honey is 40% fructose
-As fruit ripens, enzymes cleave sucrose into glucose and fructose resulting in a sweeter taste.

Galactose
-Produced from lactose (milk sugar) by hydrolysis in the digestive process.

Disaccharides
-Monosaccharide units joined by glycosidic linkages.
-Sucrose= fructose + glucose
-Maltose = glucose + glucose
-Lactose = glucose + galactose

Sucrose
-When used in preparation of acidic foods it becomes inverted and sweeter

Honey
-More calorie dense because monosaccharides are packed more closely together than disaccharides
-1 tbsp honey = 64 kcal
-1 tbsp sugar = 46 kcal

HFCS
-Manufactured by changing glucose in cornstarch to fructose
-Added to canned/frozen fruits to preserve

Oligosaccharides
-Polymers containing 2-20 sugar molecules.
-Water soluble and often sweet
-Nondigestible oligosaccharides: resistant to stomach acid and action of amylase, enter intestine intact
-Raffinose: in sugar beets (galactose + glucose + fructose)
-Stachyose: in legumes and squash (2 galactose + glucose + fructose)

Polysaccharides
-Plants store carbohydrates as starch granules in plastids within cellulose walls
-Edible plants make 2 types of starch (amylose, amylopectin)
-In whole foods, starch is poorly digested. Moist cooking will improve digestibility.
-Carbohydrates that cannot be digested are classified as dietary fiber.

Resistant Starch
-Remains intact throughout cooking
-Limited glucose is produced for absorption

Waxy Starch
-Obtained from corn and rice strains bred to increase amylopectin
-When dissolved in water, forms a smooth paste
-Used as a thickener for frozen pies and sauces

Modified Food Starch
-Used for instant puddings, salad dressings, and baby food
-Adds viscosity and gel-like properties

Cellulose
-A nondigestible carbohydrate found in celery, broccoli, carrots, and many other vegetables
-Falls in the category of insoluble fiber

Pectins/Gums
-Contains sugars and sugar alcohols that make them water soluble
-Pectin is found in apples, citrus, strawberries, jams, and jellies
-Gums are galactose units combined with other sugars found in oats, legumes, and barley

Fructooligosaccharides
-Poorly digested in the upper GI tract
-Provide 1kcal/g, half as sweet as sucrose
-Used as a sugar replacement
-Naturally found in onions, garlic, bananas
-Increase colonic bacteria growth and have been added to yogurts marketed as a prebiotic

Lignin
-Woody insoluble fiber found in stems and seeds of fruits and vegetables and flaxseed
-Also found in the bran layer of grains

Carrageenan
-Extracted from macroalgae or seaweed.
-Used to stabilize food mixtures in pudding and infant formula
-Some studies have shown at high doses to increase cancer risk
http://www.webmd.com/vitamins-supplements/ingredientmono-710-carrageenan.aspx?activeIngredientId=710&activeIngredientName=carrageenan

Chitosan
-Sugar extracted from the shells of crabs, lobsters, and shrimp
-Hypocholesterolemic effect
-Positive charge on chitosan binds negatively charged lipids and blocks their absorption
http://www.webmd.com/vitamins-supplements/ingredientmono-625-chitosan.aspx?activeIngredientId=625&activeIngredientName=chitosan

See the next post on how carbohydrates impact health!

Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004. 

Energy: Expenditure and Requirements

Energy in, energy out. Calories in, calories out. Let's break down the science aspect to see how energy and calories fit into your daily life.

Components of Energy Expenditure
Energy is expended by the human body in the form of resting energy expenditure (60-75%), the thermic effect of food (10%), and energy expended in physical activity (the most variable).

Resting and Basal Energy Expenditure
-REE: the energy expended in the activities necessary to sustain normal body functions and homeostasis. Activities include respiration, circulation, maintenance of body temperature, and synthesis of organic compounds.
-Basal Energy Expenditure: reflects the amount of energy used over 24 hours while physically and mentally resting. One way to think about the BEE is the energy used if you were laying on a bed for 24 hours without moving.
-Basal Metabolic Rate: energy needed to sustain metabolic activities of cells, tissues, and various processes.

Factors Affecting Resting Energy Expenditure
-Body Size: larger people have higher metabolic rates than smaller people. Tall, thin people have higher metabolic rates than short, wide people.
-Body Composition: Athletes with greater muscle have 5% higher basal metabolism than non-athletes.
-Sex: women have 5-10% lower metabolic rates than men.
-Other: fevers increase metabolic rate by about 7% for each degree increase in body temperature.

Hormones and Energy Expenditure
Women, did you ever wonder why you get more or less hungry during your menstrual cycle? This happens because the metabolic rate of women fluctuates. About 1 week before ovulation, there is an average of 400 kcal/day difference in BMR. During the second half of the menstrual cycle, there is an increase in energy expenditure. The increase in energy expenditure leads to the increase in hunger.

Thermic Effect of Food (TEF)
TEF is the increase in energy expenditure associated with the consumption of food. Components of the TEF includes energy required to digest, absorb, and metabolize nutrients.
-Fun Facts: Spicy foods enhance and prolong the effect of the TEF. When ingested every 2 hours for 12 hours, coffee increases the TEF by 8-11%.

Energy Expended in Physical Activity (EEPA)
This includes the energy expended in voluntary exercises (running and weight lifting) and involuntary exercises (shivering, fidgeting, and maintaining posture).
-Fun Facts: EEPA decreases with age due to a decrease in fat free mass and an increase in fat mass. Men generally have a higher EEPA than women.

What is a Calorie?
A calorie is the amount of heat energy required to raise the temperature of 1 ml of water 15 degrees Celsius by 1 degree.

Energy Expenditure Estimations
-The EER incorporates height, weight, age, gender, and level of physical activity (PA) to determine the amount of calories you need on a daily basis.
-PA has 4 categories: sedentary (use 1.0 for equation), low active (1.12), active (1.24), and very active (1.45).

                 For men:

EER= 662 - 9.53 × age (years) + PA × (15.91 x weight (kg) + 539.6 x height (meters)) 

                For women: 

                  EER= 354 - 6.91 × age (years) + PA × (9.36  x weight (kg) + 726 x height (meters))

                Example:

                  30 year old female, 150 lbs (68kg), low active (1.12 PA activity factor), 5'5'' (1.65m)

                  EER= 354 - 6.91 x 30 + 1.12 x (9.36 x 68 + 726 x 1.65)

                  EER= 2,201 calories

Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004. 
http://www.ncbi.nlm.nih.gov/pubmed/15534426
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1784117/

Nutrition Basics: Digestion

Today's topic is on the digestion, absorption, transport, and excretion of nutrients! I will incorporate both science, textbook-like information, and fun facts. For health professionals, this may serve as a brush-up on your past knowledge.

The GI Tract
The primary roles of GI tract are to: extract macronutrients from ingested food and drink, absorb micronutrients, and serve as a protective barrier to microorganisms and foreign material. Depending on the diet consumed, about 92-97% of food/drink is digested and absorbed. Since humans lack the enzymes to hydrolyze the chemical bonds of plant fibers, most of unabsorbed material is of plant origin.  The health of the body depends on the health and function of your GI tract. The GI tract is more susceptible to micronutrient deficiencies, drugs, and protein malnutrition. The nutrients passing through the lumen supply energy to both the small intestine and the colon. With a few days of starvation, the GI tract will begin to break down (decrease in absorption and function).

Digestion Overview
Mouth: limited starch and lipid digestion have taken place.
Stomach: protein digestion has just begun.
Small Intestine: macronutrients, vitamins, minerals, trace elements, and most water is absorbed. Most fat digestion takes place.
Colon/Rectum: remaining fluid and electrolytes are absorbed.
Enzymes: HCL, bile, sodium bicarbonate, lipases, etc.
Hormones: peptides, gastrin, secretin, CCK, GIP, GLP-1, GLP-2, motilin, somatostatin

Interesting Facts About Digestion
-Most of a liquid meal will empty the stomach in 1-2 hours.
-Most of a solid meal will empty the stomach in 2-3 hours.
-When eaten alone, carbohydrates leave the stomach the most rapidly, followed by protein, fat, and fibrous food.
-The small intestine is the primary site for digestion of food and nutrients.

Nutrient Absorption
-The small intestine is the primary organ of absorption.
-Fun fact: Each day, the small intestine absorbs 200-300g of monosaccharides, 60-100g of fatty acids, 60-120g amino acids and peptides!
-The large intestine absorbs the remaining of the water and salts.
-Transit time from your mouth to your anus can vary from 18-72 hours (fruits and vegetable rich diet decreases this time).

Fiber
-Valuable for maintaining healthy cells in the colon.
-Prevents excessive intracolonic pressure.
-Prevents constipation.

Carbohydrate Digestion/Absorption
-Glucose ("blood sugar") is transported from the liver to the tissues (some is stored in liver and muscles as glycogen).
-Consuming large amounts of lactose (milk sugar), fructose (fruit sugar), and sugar alcohols can result in them passing unabsorbed in the colon. This can lead to gas and diarrhea.
-Cellulose, pectin, gums, and other fiber forms cannot be digested by humans; thus, they are passed unchanged into the colon.

Just a final note about the processing of food:
-Cooking food at high temperatures for prolonged periods can destroy nutrients (ascorbic acid and folate), but in general, cooked food is more digestible than raw food.
-Cooking food helps to soften dietary fiber. This helps to make the nutrients attached to the fiber more available for digestion.
-During grain refinement for bread and cereal, nutrients, phytochemicals, and fiber are lost. The "enrichment" of the product will replace some nutrients but not the fiber or phytochemicals.





Mahan L, Escott-Stump, S. "Food, Nutrition, and Diet Therapy." Saunders. 2004.