L7 energy metabolism

BD of nutrients for E, energy metabolism in diff states, metabolic states in health & diseases (low carb + diabetics having metabolic inflexibility)

(carbs) breakdown of glucose for nutrients

1. glycolysis where 1 glucose → 2 pyruvate

2. ideally, 2 pyruvate → 2 acetyl CoA

3. but if in need of energy, lactate is produced instead

   • lactate accumulates in the liver, converts to glucose when activity stops

why during high energy activity is lactate produced instead of acetyl CoA ?

during high energy activity, cells may lack mitochondria or sufficient O2

this process frees coenzymes for glycolysis to continue & produce more ATP

breakdown of triglycerides for energy

• glycerol backbone;

  • forms pyruvate or glucose

  • both becomes acetyl CoA

• FAs directly broken down into acetyl CoA

  • amount depends on length of FA chain

why is carbohydrates needs to fully oxidise FA for energy

• 1 molecule of triglyceride contains 1 glycerol + 3 FAs

• 1 glycerol forms 1 pyruvate while 1 FA forms 8 acetyl CoA, requiring 8 oxaloacetate to be fully oxidised for energy

having carbohydrates can provide enough pyruvate to fully oxidise FA for energy

how does oxaloacetate oxidise FA

oxaloacetate (4C) combines w acetyl CoA (2C) to form citric acid

fats provide the most __ per gram, due to the __

most energy

due to the many C-H bonds that produces more ATP & energy when oxidised

breakdown of proteins for energy

3 entry points of AAs in energy pathway

• converted to pyruvate (most common)

• converted to acetyl CoA

• or enter TCA cycle directly

during feasting, __ is used as the main E source. it is __ in __, any remaining will be __

glucose used as primary E source

stored in liver & muscle as glycogen

EXTRA → body fats

the rest, during feasting, FAs are __ while AAs are primarily __, any remaining are __

FAs → stored as body fats

AAs → mainly lost as urea in urine & used to synthesize body proteins ,, remaining → body fats

fasting period starts __ hrs after meals

2-3 hours

what happens during fasting

glycogen stores from liver & muscle + FAs stores from body fat are released

• glucose will be mainly used to provide E for the brain, nervous system & RBC

  • other cells also can

• FAs will be used as E for other cells

why brain & RBC only use glucose

brain hv blood brain barrier, large FAs X enter

RBCs lack mitochondria to utilize fats (FAs oxidation X occur)

what happens when glycogen stores are depleted

fats start to breakdown

AAs are also released from muscles

adaptations involving E conversions during fasting stage are __ and __

1. protein BD to release AAs for glucose

   • brain n RBCs need glucose

   • so proteins will be broken down instead to release AAs → yield pyruvate

   • ultimately, AAs will produce glucose & ketone that can be used by the picky ones + other cells

2. ketones are created as an alternative fuel by FAs

   • FAs from body fat stores are released

   • FAs can provide E for other cells, but most imptly → ketone bodies for picky 3

   • ultimately, slow down BD of body proteins

ketone bodies are formed through __, it yields __

condensation of 2 acetyl CoA

→ acetone

__ is an indicator that someone is on a keto diet (low carbs, high fats & proteins)

acetone levels (from breaths)

lvls of glucose and ketones during starvation

• glucose maintain at baseline levels

• ketones keep rising

an overarching adaptation by the body during fasting beyond glycogen stores is to __

conserve energy

• reduced energy output

• rate of metabolism is adjusted through hormones changes

energy conservation can __ but (downside)

can support weight loss

but includes the loss of fats & muscles

what happens during a LOW CARB diet

metabolism is similar to fasting (cus glucose supply is limited)

• glycogen stores will be used first

• when depleted (v fast) , switch to gluconeogenesis → use of body tissues / proteins (??) to provide glucose

some side effects of LOW CARB diet

nausea, fatigue, low bp, bad breath, elevated uric acid

usual metabolic flexibility

1. duirng eating, use glucose (glucose level & insulin lvls rose)

2. during fasting use lipids as energy

what happens during metabolic inflexibility

struggle to switch between the two E sources

• during fasting, instead of using fats, cont using glucose → glucose lvls cld fall below baseline → hunger

• during eating, failure to use glucose → insulin keeps producing → high insulin lvls

metabolic inflexibility is more often seen among __ & __

the diabetic and obese

• for diabetics ;

  • insulin resistance → glucose X efficiently utilised after eating → high glucose lvls remain

flexibility in metabolism is measured by __

RQ rati0 (respiratory quotient)

• looks at ratio of CO2 produced & O2 consumed during metabolism

• 1 glucose + 6 o2 → 6 co2

RQ = 1 → perfect flexibility , glucose is used accordingly

RQ ~ 0.7 → fatty acids are primarily used as energy (denominator is bigger bc more o2 is consumed for FAs oxidation)

RQ ratio may not be __ for healthy lean individual bc …

X exactly 1 bc the meal is usually a mixed meal, not just glucose

• but ultimately, there should be a significant increase in RQ ratio to show that more of glucose are utilised

a gradual increase / decrease in RQ ratio indicates __

fuel choice X change between fed-fast states