What Is Metabolism? Catabolism –Reactions that break down compounds into small units

What Is Metabolism? Anabolism –Reactions that build complex molecules from smaller ones

What Is Metabolism? ATP is the body’s energy currency –ATP = adenosine triphosphate

Breakdown and Release of Energy –Anaerobic Partial breakdown glucose Do not req oxygen Lactic acid is main end-product little ATP –Aerobic Complete breakdown glucose, fat, and protein Occurs in mitochondria Releases most energy CO 2, H 2 O, ATP and heat Req oxygen

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Breakdown and Release of Energy Extracting energy from carbs –Glycolysis Splits glucose into two pyruvates Produces some ATP –Pyruvate to acetyl CoA Releases CO 2 Enters TCA cycle if O 2 is present

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Breakdown and Release of Energy Lipolysis –Triglycerides broken down into fatty acids and glycerol Extracting energy from fat –Promoted by glucagon, growth hormone, epinephrine –Takes place in mitochondria –Beta-oxidation Breaks fatty acids into acetyl CoA –Fat burns in a flame of carbohydrate Ketogenesis –Ketone bodies formed by incomplete fatty acid oxidation

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Breakdown and Release of Energy Extracting energy from protein –Split protein into amino acids –Split off amino group Converted to urea for excretion –Carbon skeleton enters breakdown pathways –End products ATP, H 2 O, CO 2, urea

16 Protein Metabolism Gluconeogenesis –Forming glucose from glucogenic amino acids and other compounds –Typical fatty acids cannot be converted to glucose, although glycerol can Disposal of Excess Amino Groups –Converted to ammonia; then urea cycle –Urea excreted in the urine

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Breakdown and Release of Energy

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Biosynthesis and Storage Making carbs –Gluconeogenesis Uses pyruvate, lactate, glycerol, certain AA Storing carbohydrate (glucose  glycogen) –Liver and muscle make glycogen from glucose Making fat (fatty acids) –Lipogenesis Uses acetyl CoA from fat, amino acids, and glucose Storing fat (triglyceride) –Stored in adipose tissue

Biosynthesis and Storage Making ketone bodies (ketogenesis) –From acetyl CoA When inadequate glucose in cells Making protein (amino acids) –Amino acid pool supplied from Diet, protein breakdown, and cell synthesis –Biosynthesis Different pathways used to build amino acids from carbon skeletons

22 Fasting and Feasting Fasting encourages: –Glycogen breakdown –Body fat and protein breakdown –Gluconeogenesis –Ketogenesis –Urea synthesis Feasting encourages: –Glycogen synthesis –Body fat synthesis (lipogenesis) –Protein synthesis

Special States Feasting –Excess energy intake from carbs, fat, protein Promotes storage –Fat  adipose –AA  protein synthesis –Carbohydrate  adipose

Special States Fasting –Inadequate energy intake Promotes breakdown –Prolonged fasting Protects body protein as long as possible

Special States Fasting –Survival priorities and potential energy sources Preserve glucose-dependent tissue –RBC, brain cells, central nervous system Maintain muscle mass –The prolonged fast: In the beginning Blood glucose drops, liver breaks down glycogen to glucose Gluconeogenesis Fat and protein are primary fuel

Special States Fasting –The early weeks Several energy-conservation strategies –Several weeks of fasting Rely on stored body fat –The end is near Muscle atrophy and emaciation Sacrificed muscle tissue in attempt to preserve brain tissue

Box 1: DSM IV-TR Criteria for Anorexia Nervosa Criteria Refusal to maintain body wt at or above a min wt for age/ height: Body weight less than 85% of that expected. Intense fear of wt gain or becoming fat, even though under wt. Disturbance in the way one's body shape are experienced, Denial of the seriousness of the current low body weight. Amenorrhea (at least three consecutive cycles) in postmenarchal girls and women. Amenorrhea is defined as periods occurring only following hormone (e.g., estrogen) administration. Type Restricting type: During current episode the person has not regularly engaged in binge-eating or purging behavior (self- induced vomiting or misuse of laxatives, diuretics, or enemas). Binge-eating–purging type: During the current episode the person has regularly engaged in binge-eating or purging behavior (self-induced vomiting or the misuse of laxatives, diuretics, or enemas).

Box 2: DSM IV-TR Criteria for Bulimia Nervosa Criteria Recurrent episodes of binge eating characterized by both: Eating, in a discrete period of time (within a 2-hr period), an amount of food definitely larger than most people would eat during a similar period of time under similar circumstances A sense of lack of control over eating during the episode Recurrent inappropriate compensatory behavior to prevent wt gain Self-induced vomiting Misuse of laxatives, diuretics, enemas, or other medications Fasting Excessive exercise The inappropriate behavior at least twice a week for 3 months. Self evaluation is unduly influenced by body shape and weight. Type Purging type: Regularly engaged in self-induced vomiting or the misuse of laxatives, diuretics, or enemas. Nonpurging type: Used inappropriate behavior but not engaged in self-induced vomiting,misused laxatives, diuretics, or enemas.

Weight Management Adopting a healthy weight- management lifestyle Diet and eating habits –Total calories –Crash diets don’t work –Balancing energy sources: fat, carbohydrate, and protein –Eating habits –Physical activity

Thrifty Gene and weight loss What happens to metabolism when calorie intake is severely restricted? WHY?

In general, when non-athletes loss wt: - loss 50 % adipose & 50% lean tissue - wt gain 75% adipose & 25% lean tissue One definition of yo-yo dieting: restricted eating –loss 10 lbs or so, plateau (doesn’t seem to loss any more wt), gets frustrated – go off “diet” and regain the weight.

Scenario: 1. Steve weights 200 lbs and wants to loss wt.. Over the course of 6 months, he goes on 3 yo-yo diets. At the end of the 6 months he still weights 200 lbs – did anything change? Explain what happened to his body composition over the 6 months.

2. From the previous scenario, how could the amount of muscle mass lost be altered?

This time Steve decides to exercise & restrict calories. Over the course of a month, Steve losses 10 lbs. but then plateaus out. What might be happening?