7- Chapter Energy Balance and Obesity Ecological Perspective Thrifty metabolism o A genetically determined, energy efficient metabolism, requiring few calories for daily activities. o Retain more of their body weight o In modern environment with a large surplus of calories, a thrifty metabolism contributes to the development of obesity Overview of Macronutrient Metabolism Anabolism o Body processes that create more complex chemical compounds for energy storage or for the synthesis of tissue o Body building itself (seen in infants, pregnancy, weight gain, muscle building) o Glycogen synthesis is an anabolic process Make glycogen from glucose or amino acids, but never from fat o Protein synthesis Make protein from dietary amino acids o Triglyceride synthesis Any macronutrient eaten in excess of energy needs will be converted to triglyceride and stored in adipose tissue o Insulin directs anabolism Causes glucose and fat to move into cells from the bloodstream, where they are stored or used Catabolism o Body processes that break down complex chemical compounds for energy release or for tissue breakdown o Body breaking itself down (exercise, fasting, physiological stress, when the body needs energy) o Adenosine triphosphate (ATP) is high energy chemical compound used in the body to transfer energy from nutrients to various life processes Carries energy from food to cell Powers our movement o Epinephrine, norepinephrine, and glucagon direct catabolism o We can produce ATP in a variety of ways From blood sugar, muscle glycogen, body fat sores, or breakdown of muscle protein o Anaerobic metabolism Used for high intensity exercise, energy is produced without oxygen Glucose is converted to lactic acid to produce ATP Fat can never be used as fuel anaerobically o Aerobic metabolism
Used in lower intensities Oxygen is used for energy production Body can use carbohydrates, fatty acids and amino acids as fuel Fate of a Bowl of Oatmeal o If you went on a long bike trip and then didn't eat that much, when you do eat your oatmeal in the morning, the starch goes partly into replenishing muscle glycogen o If you hadn't been active yesterday and burned off your glycogen, it would go into body fat instead o Protein in the oatmeal and milk is incorporated into muscle growth stimulated by yesterday's exercise o Without exercise, much of this would have been converted to fat and stored in adipose as well. All anabolic processes o Without having rebuilt glycogen stores, you would have to rely on fat for energy, which means you won't be able to run as fast or burn as many calories o Fat only supports lower intensity exercise
Energy Conservation of Energy o Energy can neither be created or destroyed o Goes from nuclear energyheat and lightchemical energyto mechanical energy and heatenergy of motion (kinetic energy)heat o All our energy comes from chemical energy stored in food, which comes from photosynthesis, and ultimately from the sun Efficiency of Conversion o Not all first form energy becomes second form o Some energy is always lost as a third form That's why you become hot as you run Energy Balance o Reflects the net flow of energy into and out of the body o We take in energy only in the form of chemical energy stored in macronutrients We can tell if we're gaining or losing energy by whether we are gaining or losing weight o In energy balance, neither gaining or losing weight (energy) o Energy intake=energy expenditure Energy Expenditure (3 ways) o Basal Metabolism Involuntary activities Heartbeat, respiration and basic biochemical reactions Basal Metabolic Rate (BMR) Rate of expenditure under these conditions Occur in lean tissue
Food restriction and chronic dieting lowers BMR o Aging, meal skipping, female gender, sleeping Building lean tissue and eating regular meals increase BMR o Caffeine, stress, exposure to cold temperatures Resting Energy Expenditure (REE) Rate of your day's total expenditure by these activities Makes up about 2/3 of total energy expenditure in a person o Physical Activity Energy expenditure through voluntary physical effort The heavier you are, the more calories it will cost you (burn more calories as a fatter person because you have more excess) o Thermic Effect of Food Energy expended in digesting, absorbing, transporting, storing, metabolizing, handling food Amounts to about 10% of ingested calories Estimating Energy Expended in Activity o Activity Factors Energy consumed in general activity is expressed as a percentage of REE and is used a multiplier of REE o Expenditure by Activity and Body Weight Estimate total expenditure by looking at expenditure hour-by-hour More precise than using activity factors Thermic Effect of Food o REE + physical activity. Take 10% of this total to get TEF Total Energy Expenditure o Sum of REE, physical activity and TEF
Obesity Disease Consequences of Obesity o Heart disease o Type II diabetes o Hypertension o Cancer o Stroke o Arthritis Defining Obesity o Compare height and weight o Height-weight tables Describe normal or typical weights o Body Mass Index A height-weight relationship used to assess obesity. Equal to weight in kilograms over height in meters squared (weight (kg)/ height squared (m)) BMI of greater than 25 is overweight, and more than 27 is obese
Prevalence Number of cases of a condition in a given population or the proportion of the population suffering from that condition Relative risk Increase in risk seen in a higher risk group over that seen in the lowest risk group Fails to discriminate between fat and lean tissue (would say footballs players are obese) o Body Composition Total body mass= sum of lean tissue mass and fat mass All problems of obesity stem from fat mass How much of our body weight is composed of fat (percentage) Generally see women with higher body fat than men Body fat increasing with age in adulthood Desirable for range men: 10-20% and women: 18-25% More could be considered obese Much harder to determine than height-weight and BMI even though more informative Underwater weighting Measures the density of the body by comparing dryland weight, underwater weight and the volume of water displaced by the body Victim is lowered into tank of water and after exhaling all air from the lings, kept there while being weight, then hauled out gasping and spluttering Fat floats and lean tissue sinks, density predicts fatness Skinfold calipers present an easy alternative Used to measure thickness of the fat layer under the skin in several locations Plug these values into an equation that yields percent body fat Most accurate for people with normal range of body fat o Less accurate for people who are extremely lean or obese Body Impedance Analysis (BIA) Small electrodes are attached to the hand and foot and a minute amount of electricity is passed through the body Body water, containing electrolytes, conducts electricity as well Adipose tissue, with little water, does not Can determine how much lean tissue, and by subtraction, how much fat, is in the body Works best on the people who need it the least (normal, average range)
o Body Fat Distribution Body has 3 fat depots Subcutaneous fat Right under the skin Gives skin its thickness when you find it. Skinfoldd calipers are measuring this Visceral or abdominal fat Under abdominal muscles inside the gut Intramuscular fat Interspersed with muscle fibers in the muscle Distribution is largely genetically determined Android obesity Most body fat is carried abdominally "Apple shape" More common in men Gynecoid "Pear shape" More fat is carried lower in the body o Hip-to-waste ration A measure used to define android obesity. A value of greater than 1.1:1 Prevalence and Distribution o Over 60% of U.S. adults are overweight Etiology o Obesity is the product of genetics and the environment o Twins are likely to be at similar body weight o 40% of obesity can be explained by genetics o More than 20 human genes have been linked to obesity Set Point Theory o Notion that one's body tends to gravitate to a particular weight, as if it were programed to be 160 pounds or whatever o Body resists changes in weight Changes in weight determines energy expenditure As body changes, so does energy expenditure o If you gain 20 pounds, your energy expenditure goes up (lose calories more quickly) o If you lose weight, energy expenditure decreases (harder to burn calories) o Hormone leptin Produced by adipose cells when they have reached a particular level of fat content Diminishes appetite and keeps cells from becoming fatter
When fat falls below a level, leptin production is decreased and appetite is restored. You eat more, and adipose cells acquire more fat Adipose Tissue o Where fat is stored o Essential for normal reproductive function in women o Amenorrhea When body fat drops too low, below about 15%, women get this Cessation of normal menstruation. Causes bone mineral loss leading to weakened bones o Female athlete triad The combination of low bone density, amenorrhea and eating disorder sometimes seen in female athletes with very little body fat o Shock Absorption Adipose tissue cushions internal organs and absorbs shock Fat pad is protection o Thermal Insulation Low body fat= cold High body fat= hot o Grows through hyperplasia (increase in cell number) and hypertrophy (increase in cell size) Plasia occurs more in growing children Harder to lose weight Part of the reason obese children become obese adults Trophic cells can more readily shrink o Body Weight Management Only way to burn fat is to burn it off 2700 kcals in a pound of body fat (and water associated) Muscle loss lowers metabolism If weight were to be regained, it'd come back as fat Fat replaces muscle Meal Skipping o 1. Slows metabolism- need fewer calories to maintain your weight, and it gets harder to lose weight o 2. Body responds with a binge when food becomes available o 3. You train yourself not to eat. Learn to ignore and suppress your appetite. o Tend to increase binging while lowering metabolism Low calorie diets o Very Low Calorie Diets (VLCD) o Less than 1200 kcals per day High protein diets o High protein, low carbs promote loss of water and lean tissue as well as fat o Lowers metabolism and reproduces rebound weight gain
o Tend to cause kidney stones Fad diets o Meal skipping, fasting, liquid diets, reliance on single food, eliminates whole food groups, no exercise involved, foods with magical properties (fat burners) Bariatric Surgery o Gastric bypass is stomach stapling o Reducing the size of the stomach- person eats less with little or no reservoir for food Drugs o 3 drugs for weight loss on the market o Sibutrimine, phentermine, and orlistat Fundamentals o Negative energy balance Reducing intake and increasing expenditure o Through exercise, physical and aerobic Raising heart rate and breathing o Increase energy expenditure= keep metabolism high Try eating every 3 hours or so but do not increase intake, just divide normal meals High complex carbohydrate, low fat snacks Popcorn, rice cakes Keep metabolism high by eating when you are hungry o Low energy density foods Lower energy density of your diet Fat has over twice the energy density of the other macronutrients (9 compared to 4) Eat less fat to lose weight Replace fat with complex carbohydrate Starch will meet energy needs and keep glycogen stores high Should be unrefined whole grains Keeping fiber intake high dilutes the calories present. Fiber requires more chewing, slows eating, eat less Limit alcohol and sweet drinks Vegetables are ideal weight loss food Eat way more for same amount of calories o Behavior change Be conscious of what you're eating in social situations Food can be a drug or reward