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.