Download MBBS The Feed Fast Cycle Lecture PPT

THE FEED-FAST CYCLE
OVERVIEW OF THE ABSORPTIVE PHASE
The absorptive (well-fed) state is 2-4 hrs period after

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ingestion of a normal meal

During this interval, transient increases in plasma glucose,

amino acids and TAG is seen

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Islet tissue of pancreas responds to elevated level of

glucose with increased secretion of insulin and decreased

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secretion of glucagon

The elevated insulin/glucagon ratio and the ready

availability of circulating substrates make the absorptive

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state an anabolic period characterized by increase

synthesis of TAG and glycogen as well as increased

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synthesis of protein
During this absorptive period, virtually all tissues use

glucose as a fuel, and metabolic response of the body

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is dominated by alterations in the metabolism of liver,

adipose tissue, skeletal muscle and brain
LIVER:NUTRITION DISTRIBUTION

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CENTER

The liver is uniquely situated to process and distribute

dietary nutrients because the venous drainage of the

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gut and pancreas passes through the hepatic portal

vein before entry in to general circulation

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Thus, after a meal, the liver is bathed in blood

containing absorbed nutrients and elevated levels of

insulin secreted by pancreas

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During the absorptive phase, the liver takes up

carbohydrates, lipids and most amino acids

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ADIPOSE TISSUE: ENERGY STORAGE

DEPOT

Adipose is second only to liver in its ability to

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distribute fuel molecule

In a 70 kg man, white adipose tissue weighs around 14

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kg or about half as much as total muscle mass

Nearly the entire volume of each adipocyte in WAT

can be occupied by anhydrous,calorically dense TAG

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SKELETAL MUSCLE

Skeletal muscle accounts for nearly 40% of the body

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mass in individuals of healthy weight and it can use

glucose, amino acids, and ketone bodies as fuel.

Skeletal muscle is unique in being able to respond to

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substantial changes in the demand for ATP that

accompanies muscle contraction

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At rest, muscle accounts for 25% of oxygen

consumption of the body ,whereas during vigorous

exercise ,it is responsible for up to 90% of total

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oxygen consumed
BRAIN

Although contributing only 2% of adult

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weight, brain accounts for a consistent 20%

of basal oxygen consumption of the body

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at rest

In the fed state, brain exclusively uses

glucose as a fuel ,completely oxidising

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140g/day to carbon dioxide and water


OVERVIEW OF FASTING STAGE

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Fasting begins if no food is ingested after the absorptive

period

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It may result from inability to obtain food, the desire to

lose weight or clinical situation in which an individual can

not eat

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In the absence of food, plasma level of glucose falls,

triggering a decline in insulin secretion and increase in

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glucagon, epinephrine and cortisol secretion

Decrease insulin/glucagon ratio and decreased availability

of circulating substrates make the postabsorptive period a

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catabolic period characterized by degradation of glycogen,

TAG and protein
Starve cycle is divided in two four stages:

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Early fasting (4-16 hrs after food)

Prolonged Fasting (16-48 hrs after food)

Starvation (2-3 days without food)

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Prolonged starvation (>5 days without food)

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