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• CO2 , H2O, 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 CO2• Enters TCA cycle ifO2 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, H2O, CO2, urea

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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

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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 aslong 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 NervosaCriteria•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 NervosaCriteria•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 lossWhat 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?