Metabolism of Weight Loss & Adaptations Flashcards
Which organs contribute the most to REE?
Liver (21%)
Brain (20%)
In 100 g of glycogen tissue how many grams of readily-available energy (glucose)?
20g
80 kcal
In 100 g of protein tissue, how many grams of energy (protien)?
20 g
80 kcal
To obtain 90 kcal from adipose tissue (fat), how much does the tissue weight?
10 g
Which tissues are GLUT4 dependant?
Heart, Muscle, Adipose
Which tissues are insulin independent?
Liver, CNS, RBC
On the blood glucose curve, what does the uptake slope depict (within 1 hour of ingesting a meal)?
- Increased GI glucose absorption and insulin release
- Decreased glycogenolysis, gluconeogeneisis
- Increased glycolysis
On the blood glucose curve, what does the decay slope depict (1.5-3 hours after ingesting a meal)?
- High insulin and high tissue uptake
- Increase glycogenesis
- Later, glucagon will increased
On the blood glucose curve, what does the steady phase depict (within 3-4 hours after ingesting a meal)?
- Decrease I:G
- Increased glycogenolysis
- Increase gluconeogenesis
When will secretion of glucagon accur?
Approx 2.5 hours after meal
What causes most changes in substrate utilization and circulation?
Ratio of insulin to glucagon
An initial increase in I:G causes an increase in:
A) Triglycerides, Pyruvate, Alanine, Total Amino Acids
B) Lactate, Free Fatty Acids, Glycerol
C) Free Fatty Acids, Triglycerides, Insulin:Glucagon Ration
A)
An initial decrease in I:G causes an increase in:
A) Triglycerides, Pyruvate, Alanine, Total Amino Acids
B) Lactate, Free Fatty Acids, Glycerol
C) Free Fatty Acids, Triglycerides, Insulin:Glucagon Ration
B)
An initial increase in insulin causes an increase in:
A) Urea Nitrogen, Pyruvate, Alanine,
B) Lactate, Free Fatty Acids, Glycerol, BCAA
C) Free Fatty Acids, Glucagon, Urea Nitrogen Keto acid
C)
Free fatty acids originate from ?
LIPOLYSIS of adipose tissue in the FASTED state (decreased I:G ration)
Triglycerides in circulation originate from?
The meal during the FED state (from circulating VLDL, originating from fat or carbs) increased I:G ratio
Why does lactate increase during fed state?
Glucose available for RBCs to undergo anaerobic glycolysis
Why does pyruvate increase in the fed state?
I:G increases glycolysis
Why do TGs increase in circulation in the later, fed state?
After fat from diet or conversion from carbs is packed into VLDL, TGs will be given off into bloodstream and tissues
Why do FFAs decrease in the early fed sate?
Insulin inhibits lipolysis
Why do ketone bodies decrease after fed? Increase later?
Oxidation of glucose now sufficient to replenish TCA cycle, then, lower amounts of OAA inhibits anaplerosis of TCA cycle which drives ketone body synthesis.
Why does glycerol decrease in early fed state?
Insulin inhibits lipolysis
Why does alanine increase during fed state? Why does it decrease?
Flux of AA in diet. after feeding, alanine may be used for gluconeogenesis in the liver.
Why do BCAA increase during fed state and increase later in circulation?
Influx from diet, then increase later in circulation due to minor endogenous protein breakdown to maintain blood glucose homeostasis.
Why do total amino acids drastically increase after fed state?
Influx from diet PLUS insulin promote the active transport of amino acids into muscles and other tissues that must travel through bloodstream to support adequate protein synthesis.
Why does urea nitrogen decrease with an increase in total amino acids during fed state?
Amino acids are being used for protein synthesis and NOT endogenous protein breakdown, therefore urea production decreases.
What are the claims surrounding insulin in fad dieting?
- Insulin is required to take up glucose into energy storage
- The release of insulin is the “fed signal”
- Carbohydrates have the most profound effect on insulin release, and are the most likely macronutrient to favour energy storage and weight gain
Why are carbohydrates often the target macronutrient in fat diets?
Since the have the most profound effect on insulin release, and are the most likely to favour energy storage and weight gain …
What would you counter with if someone claims that carbohydrates are the ultimate macronutrient that favours weight gain?
That possessing an energy balance within the excess of our needs ultimately determines if we will gain weight or not and does NOT depend on what kind of macronutrients that we are consuming
Why do diabetics experience reactive hypoglycemia? (brief period of hypoglycemia after fed state)
Their excessive secretion of insulin promotes a smaller secretion of glucagon.
What does reactive hypoglycemia cause?
Decrease in glycogenolysis and glucneogeneisis, less glucose available to estabish blood glucose homeostasis
What ratio dictates energy storage?
Insulin:Glucagon
Fed signal causes change in several _____ over a 4-hour period
blood parameters
Changes in ____ (2) are the basis for several fad diets?
I:G GI index (glucsoe cures)
What are the goals when adapting to fasting?
- Meet energy needs
- Meet glucose requirements
- Spare protein (lean mass)
Describe the energy paradox
Our brain needs 500 kcal of soluble fuels per day (usually glucose) but almost all energy is stored as FA and not glycogen. Fatty acids cannot be converted to glucose.
Describe the fuel flux in early fasting (24 hours)
- Insulin decrease and accelerates lipolysis
- FFA fuel the heart
- Blood glucose homeostasis supported by remaining glycogen, glycerol and gluconeogenic amino acids
- Muscles participate in Cori/Cahill cycle
What inhibits the suppression of lipolysis and proteolysis ?
Low insulin
In prolonged fasting, we have established a __
decrease energy expenditure (1500 kcal)
Describe the fuel flux is prolonged fasting
- Glycogen stores exerted& less participation in gluconeogenesis by muscle inhibits anaplerosis of TCA cycle
- Acetyl-Coa bulid-up and production of ketone bodies
- Cori/Cahill cycles continue, but less contribution to glucose
What are the main fuels in prolonged fasting?
Glucose (gluconeogenesis) and ketone bodies
What are the main fuels in initial fasting?
Glycogen, free-fatty acids, gluconeogenesis
What proportionally decreases as length of fasting increases?
proteolysis (inhibited by low I:G ration)
What is used within the first hour of fasting?
Exogenous glucose
After a 12 hour fast, what are the main fuels?
50/50 mix of glucose from glycogen and gluconeogenesis
What increases linearly as fasting increases?
Ketogenesis
What is the origin of blood glucose between 1-4 hours? What tissues use glucose?Main fuel for brain?
Exogenous
All
Glucose
What is the origin of blood glucose between 4-16 hours? What tissues use glucose? Main fuel for brain?
Liver glycogen, gluconeogenesis
All except liver (Muscle and AT decrease)
Glucose
What is the origin of blood glucose between 16-28 hours? What tissues use glucose? Main fuel for brain?
Liver gluconeogenesis, glycogen
All except liver (Muscle and AT decrease)
Glucose
What is the origin of blood glucose between 2 and 24 days of fasting? What tissues use glucose? Main fuel for brain?
- Gluconeogenesis from hepatic and renal
- Brain, RBCs, renal medulla (small amount in muscle)
- Glucose, ketone bodies
What is the origin of blood glucose after 24 days of fasting? What tissues use glucose? Main fuel for brain?
- Gluconeogenesis from hepatic and renal,
- Brain decreased rate, RBCs, renal medulla
- Ketone bodies, glucose
Why does the brain use glucose at a decrease after 24 days of fasting vs RBCs and renal medulla?
RBCs and renal medulla absolutely dependant on glucose (derived from gluconeogenesis) whereas the brain can utilize ketone bodies for fuel
Why is thee a high amount of NH4+ in urine after fasting?
As ketone body production exceeds renal capacities, will be spilled into urine where it must be buffered with NH4+, increasing urinary ammonia
Endogenous protein breakdown occurs during fasting, how come this is not reflected by an increase in urea nitrogen AND ammonia?
If there is a high enough amount of ketone bodies being produced, this means that insulin is low we enough to suppress proteolysis, thus decreasing endogenous protein breakdown and consequently urea nitrogen.
It is ideal that ketone bodies are buffered in the kidney with ammonia, but what tends to happen?
Usually buffered with K+, which could lea to hypokalemia
(T/F) Even with normal renal function, there are serious health risks associate with ketoacids
F
We should not advise the keto diet and should closely monitor patients at risk for starvation who have ____
decreased renal function, inability to salt out ketone bodies causing electrolyte an pH imbalance
What is the most prominent ketone body in the well fed state? After 5wks starvation?
Acetoacetate
B-hydroxybutarate
The key to energy deficit/decreased diets (weight-loss, starvation, surgery) is to increase _____ to establish ____ and prevent _____
protein
nitrogen balance
endogenous protein breakdown
What puts a higher requirement on our protein needs in absence of sufficient energy intake?
Higher rate of proteolysis
______, protein intakes should be higher to avoid endogenous protein breakdown
Dieting, weight loss, surgery, anorexia, starvation, low-carbohydrate diets
An energy intake as high of ___ should establish a zero nitrogen balance in energy deficient diets
1.5 g/kcal/day
What does the forbes equation describe?
Where the more body fat a person has, the less loss of lean body mass they will have during weight loss
High body fat, ___ lean body mass during weight loss
LESS
Low body fat, ___ lean body mass during weight loss
MORE
In the forbes prediction (1) _____ will lose less nitrogen than thin people
Obese individuals (more fat, less endogenous protein breakdown)
In the forbes prediction (2) the ____ the subject is, the less the contribution of LBM to total weight loss on energy restricted diets
fatter (more fat will contribute to weight loss, less LBM)
Describe cardiovascular changes to severe and rapid weight loss
- Decreased cardiac output, heart rate, BP and volume
- Tachardyia to compensate for decreased blood volume
Describe renal changes to severe and rapid weight loss
Stress on kidney due to acid/base balance, ketones
Describe immune function changes to severe and rapid weight loss
Impaired T-cell/lymphocyte function, less cytokines, overall smaller immune function
Describe GI changes to severe and rapid weight loss
- deceased lipid absorption (steatorrhea)
- decreases gastric, pancreatic and bile
What explains the GI changes to severe and rapid weight loss?
Atrophy of villous surface area, less absorption especially of lipids
Describe electrolyte changes to severe and rapid weight loss
- Potassium losses
- Hypokalemia
Could CNS be affected by severe and rapid weight gain?
Yes
What causes refeeding syndrome?
As we shift back from ketone bodies to glucose, there is a major influx of insulin and and huge uptake of glucose into the starved cells
During refeeding syndrome, what causes a lot of intracellular molecules to follow into the cell with glucose?
Recall Na+/Glucose pump, if lots of glucose in, lots of sodium out causing molecules to travel from hight to low into the cell
What is the HALLMARK of refeeding syndrome?
Movement of PHOSPHORUS into the intracellular space
What electrolyte imbalances are characteristic of refeeding syndrome?
Hypophosphatemia
Hypokalemia
Magnesium
What electrolyte imbalances are characteristic of refeeding syndrome?
Hypophosphatemia
Hypokalemia
Hypomagnesemia
What are the 6 main physiological changes during repletion (EGB-INS)
- ECF expansion
- Glycogen synthesis
- Increased BEE
- Increased insulin
- sodium retention
- Cell synthesis, growth and rehydration
Why should sodium and fluid intake be limited?
Introduction of CHO into diet after starvation (insulin) and inhibits renal excretion of sodium and water - may cause cardiac arrythmias
What are the steps in refeeding? (FMPS)
- Normalize fluid and electrolyte imbalances
- Provide mixed diet to JUST match energy expenditure
- Provide protein at 1,.5-2g/kg/day at CURRENT body weight
- Monitor serum electrolytes, weight, intake and output
What is indicative of refeeding syndrome?
Very rapid weight gain, which is likely water which means that fluid andelectrolyte imbalances are occuring
What is indicative of refeeding syndrome?
Very rapid weight gain, which is likely water which means that fluid and electrolyte imbalances are occurring
How much glucose should we give a patient at risk for refeeding syndrome?
100-150 g of glucose to stop LBM. Start with 25% of dose and increase gradually while monitoring electrolytes
In addition to K+, phosphate and Mg, what else may be supplemented and why?
Thiamine - needed in glucose metabolism
On first day of refeeding, what should protein intake be?
20g/day to allow for urea cycle enzymes to adapt
