glucoregulation during and after exercise kaitlin deason and confidential group members fcs 607
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Glucoregulation During and After Exercise
Kaitlin Deason and Confidential Group Members
FCS 607
Overview
•Normal glucose metabolism vs. endurance glucose metabolism
•Glucose needs for the endurance athlete•Review of current literature
Men Vs. Women and Glucoregulation High sugar food and endurance exercise Exercise vs. Calorie restriction &
Glucoregulation•Diabetes and Glucoregulation•Future Research
Why is Glucose Regulation Important?
•Glucose is essential fuel for the brain
•Prolonged hypoglycemia can lead to brain
death
•Major source of energy formation through
the TCA cycle and hexose-monophosphate
shunt
Regulation of Glucose1. Metabolic or allosteric• Phosphorylation of glucose
Glucose uptake by GLUT 2 • Cori Cycle
2. Hormonal• Insulin• Glucagon• Epinepherine• Growth Hormone• And more….
Fig. 15.7 The Cori Cycle.
Boyer, R. (2002). Concepts in biochemistry. Toronto, Canada: John Wiley and Sons, Inc.
Hormone Regulation of Glucose
Boyer, R. (2002). Concepts in biochemistry. Toronto, Canada: John Wiley and Sons, Inc.
Table 20.2 Biochemical actions of major hormones
http://www.scienceinschool.org/repository/images/diabetes_glucose_large.jpg
Glucose and Exercise•Carbohydrates, specifically glucose, are the
primary fuel during exercise above 65% VO2max
•Energy during exercise is largely dependent on glycogen stores ▫Remember: muscle glycogen is largest store of
glycogen in the body followed by liver glycogen▫Liver: 75-100g of glycogen can deplete in 18-
24 hrs▫Muscles: 300-400g of glycogen
•Also relies on blood glucose▫~25g of glucose
Fuel for Different Types of Exercise
Boyer, R. (2002). Concepts in biochemistry. Toronto, Canada: John Wiley and Sons, Inc.
Table 20.4 Biochemical characteristics of sprinting and endurance running
Carbohydrate Recommendations for Endurance Athletes•Daily recommended intake:
7-10 g CHO/kg Ultraendurance athletes may need more
than 11g/kg•Recommended intake prior to exercise:
3 hours prior: 3 g/kg 2 hours prior: 2 g/kg 1 hour prior: 1 g/kg
•Recommended intake during exercise: 30-60 g per hour of exercise
•Recommended intake post exercise: 1.5 g/kg immediately following exercise
(within 30 minutes) plus another 1.5 g/kg 2 hours later
Utilization of Glucose During Exercise•At rest:
Glucose primarily used for brain and CNS >20% of glucose is being used by the
muscles Glycogen stores are full
•During endurance exercise: Muscle glucose uptake increases. Initially- Liver produces glucose from
glycogen (glycogenolysis) As exercise continues- Glycogen stores
decrease and more glucose is produced from gluconeogenesis
Glycogen Repletion Following Exercise•Used to restore blood glucose levels back
to normal range•Glucose consumed immediately following
exercise promotes muscle uptake of glucose to replete glycogen stores (glycogenesis).
•More effective immediately following exercise because:1. Blood flow to muscles is increased2. The muscle cells are more sensitive to
effects of insulin which promotes glycogen storage
3. Muscle cells more likely to uptake glucose
http://www.elmhurst.edu/~chm/vchembook/604glycogenesis.html
Hypoglycemia vs. Hyperglycemia
Hypoglycemia Hyperglycemia
• Low glucose in the blood• Lower than 70 mg/dL• Causes:
▫ Too much circulating insulin▫ Lack of food▫ Missed meals or snacks▫ Increased exercise or
strenuous activity▫ Alcohol intake without food
• Symptoms:▫ Intense Hunger▫ Sweating▫ Trembling▫ Weakness
• Excessive glucose in the blood
• Higher than 180 mg/dL• Causes:
▫ Too little insulin production
▫ Insulin resistance▫ Increased food intake
• Symptoms:▫ Polyuria▫ Polydipsia▫ Weight loss▫ Fatigue▫ Electrolyte disturbances
Men vs. Women:Previous Regulatory Studies Found:
Men Women
• Lipolysis
• Free fatty acid (FFA) mobilization
• Lipid oxidation
Glucoregulation is More Precise in Women Than in Men During Postexercise Recovery
• Objective: Determine the rates of glucose
appearance (Ra), disappearance (Rd), and metabolic
clearance (MCR) before, during, and after
isoenergetic moderate and hard-intensity exercise.
• Design: 10 men and 8 women
▫ Received continuous infusion of glucose tracer to measure
glucose kinetics.
▫ Studied under 3 different conditions with diet unchanged
between trials
Henderson, Fattor, Horning, Faghihnia, Johson, et. al, 2008.
Rate of Glucose Appearance (Ra)
Glucose Ra significantly decreased in both sexes in trial C (65% VO ₂ peak)
Rate of Glucose Disappearance (Rd)
Glucose Rd significantly decreased in both sexes in trial C (65% VO ₂ peak)
Rate of Metabolic Clearance (MCR)
Glucose MCR significantly decreased in both sexes in trial C (65% VO ₂ peak)
SummaryMen (n= 10) Women (n= 8)
Time and Trial Ra Rd MCR Ra Rd MCR
Pre-exercise, pooled
3.1 +/- 0.2 3.1 +/- 0.2 3.6 +/- 0.2 3.6 +/- 0.3 3.6 +/- 0.3 4.0 +/- 0.3
Exercise
45% 6.4 +/- 0.4 6.5 +/- 0.4 8.7 +/- 0.6 5.4 +/- 0.4 5.3 +/- 0.4 6.7 +/- 0.7
65% 9.0 +/- 0.6 9.2 +/- 0.6 12.7 +/1.0 8.6 +/- 1.0 8.5 +/- 0.9 11.1+/-1.4
Recovery
Control 2.4 +/- 0.1 2.4 +/- 0.1 2.8 +/- 0.1 2.4 +/- 0.1 2.4 +/- 0.1 2.9+/- 0.1
45% 2.8+/- 0.1 2.7 +/- 0.2 3.5 +/- 0.2 2.4 +/- 0.1 2.4 +/- 0.1 3.0 +/- 0.2
65% 3.1 +/- 0.2 3.1 +/- 0.2 3.8 +/- 0.2 2.6 +/- 0.2 2.7 +/- 0.2 3.3 +/- 0.2
Men vs. Women Conclusion
•Women have a greater capacity for lipid
oxidation which correlates to the lower
glucose Ra, Rd, MCR
•Women are able to regain control over
glycemic levels and glucose flux more
rapidly in recovery than men
Glucoregulation, Exercise and Endothelial Cells?
• Regular physical activity is linked to a decreased risk
of cardiovascular disease.
• Part of the benefit may be due to exercise induced
improvements in endothelial function.
• After meal (postprandial) glycemia is reduced by
exercise that was performed hours to days earlier
• It inconceivable that acute endurance exercise
minimizes the postprandial impairment in endothelial
function.
Endothelial Function After High-Sugar Food Ingestion Improves with Endurance Exercise Performed on the Previous Day
Objective Design
• Determine whether endurance exercise performed 17 hours before a high-sugar food ingestion attenuates postprandial impairment in endothelial function.
• 13 men and women (48 +/- 17 years) were studied on two occasions:▫ 48 hours after a 60 minute
endurance exercise (control)
▫ 17 hours after a 60 minute endurance exercise
• Brachial artery flow mediated dilation (FMD) was used to assess endothelial function before and after the ingestion of a candy bar (Snickers) and soft drink (Sprite).Weiss, Arif, Villareal, Marzetti, & Holloszy, 2008
Summary
Glucose (a) and
insulin (b) response
to a candy bar and
soft drink 17 hours
(exercise) and 48
hours (control) after
endurance exercise
Summary
Time dependent changes
in the diameter (a) and
endothelial function (b)
of the brachial artery in
response to ingestion of
candy bar and soft drink
17 hours (exercise) and
48 hours (control) after
endurance exercise.
Summary
Endothelial function improved after a high-
sugar food ingestion by a single bout of
exercise performed 17 hours before
testing.
This improvement is correlated to the
glucoregulation induced by exercise
Conclusion
“Acute endurance exercise
enhances glucoregulation
and reduces postprandial
glycemia.”
The study supports this
hypothesis because:
“exercise induced
improvement in
postprandial endothelial
function was accompanied
by significant reductions
in plasma glucose and
insulin concentrations.”
Improvements in Glucose Tolerance and Insulin Action Induced by Increasing Energy Expenditure or Decreasing Energy Intake
• Objective: To determine that improvements in
glucoregulation and insulin action are directly
attributed to weight loss through exercise-induce
energy expenditure, compared to weight loss
through calorie restriction.
• Participants: Sedentary men and women, ages
50-60 y.o., with a BMI of 23.5-29.9 (considered
overweight, not obese)
Study Design• 1 year• Exercise energy expenditure – n = 18
▫Increase energy expenditure by 16% first 3 months and 20% for the following 9 months
• Calorie restriction – n = 18▫Decrease calorie intake by 16% during first 3
months and 20% remaining 9 months• Healthy lifestyle – n = 10 (control group)
▫Did not receive instructions to change diet or exercise behaviors. If requested, could have dietary counseling and were offered yoga classes
Testing
• Oral-Glucose-Tolerance Test & Fast Blood
Collection
▫ Two-hour, 75 g, OGTT
▫ Performed at baseline and at end of intervention
• Body weight and composition
• Energy Intake
• Aerobic capacity
• Physical activity levels
Results
•Both groups – Exercise expenditure
• and calorie restriction – resulted in
•significant improvements in glucose
tolerance & insulin action
•Surprisingly, there was no difference
between groups as what was originally
hypothesized
Results - Explained
• There was a decrease in body fat – more specifically,
abdominal fat, which is a main factor in insulin improvements.
Not significantly different between the two groups.
• Different mechanisms for insulin improvements in both groups.
• Calorie restriction-specific skeletal muscle adaptation has been
shown to augment insulin-stimulated glucose transport in a
different manner than exercise training-specific mechanism.
• Determined that calorie-restriction and exercise training are
additive effects
Conclusion
•While exercise and calorie restriction are
effective methods in reducing the incidence
of T2DM, more research must be done on
the independent effects of both methods.
•Both can greatly improve glucose tolerance
and insulin action in non-obese, healthy,
middle aged men and women.
Diabetes Management/Prevention & Exercise•Exercise is one of the most important
factors in managing and/or preventing diabetes
•Benefits – ▫Reduced cardiovascular risk factors▫Maintain healthy weight▫Reduce body fat▫Enhance wellness
Type I Diabetes
•Exercise should be carefully integrated into diabetes management plan, as this type of diabetes lacks the metabolic adjustments needed to maintain fuel homeostasis during exercise.
•Must be able to maintain optimal blood glucose levels during exercise
•Insulin adjustments & carbohydrate supplements can be used to maintain optimal blood glucose levels
Direct Effects of Exercise on Blood Glucose Levels in T1DM•Level of training and fitness•Intensity & duration of exercise•Time & type of exercise•Metabolic control•Nutrition status•Glycogen stores•Circulating insulin levels
Endurance Athletes & T1DM
•Use carbohydrate supplements (sport drinks, diluted juices, sport bars, sport jelly beans) conservatively
•Refrain from taking extra insulin when CHO is consumed during exercise for the purpose of maintaining proper blood glucose levels
•Extra CHO may be needed post-exercise due to increased insulin sensitivity and glycogen synthesis
Physiological Benefits of Exercise for Type II Diabetes•Increases peripheral insulin sensitivity•Reduction of insulin requirements•Decreased plasma insulin levels•Improves glucose tolerance•Help improve glycemic control in T2DM•Normalize glucose homeostasis in pre-
diabetics•Lower blood pressure•Increased lipid profile
Exercise Training-Induced Improvements in Insulin Action•Single bout of exercise increases skeletal
muscle glucose uptake through a separate insulin-dependent mechanism that is completely different than the typical insulin signaling defects in diabetics
•Found that this “sensitive insulin” effect is short lived and disappears within about 48 hours
•Conversely, repeated physical exercise results in an increase in skeletal muscle insulin action in insulin-resistance and obese individuals
Why the difference?
•This has been found to occur due to the increased expression and/or key signaling activity of proteins associated with muscle glucose uptake and metabolism in skeletal muscle (AMP-activated protein kinase (AMPK) & protein kinase B substrate – AS160)
•Lipid oxidation has been found to be another mechanism which increases and improves insulin sensitivity (weight loss)
Pre/During/Post-Exercise Nutrition Suggestions• Pre-Exercise – 30 min (must be easily digested and
absorbed to provide immediate energy)▫ Small piece of fruit▫ Gatorade▫ 100% fruit juice▫ ½ Sports bar
• During Exercise▫ Sport Jelly Beans▫ Sports drink▫ Gu▫ Sports bar▫ Fruit
• Post-Exercise (must be within 30-45 min of finishing exercise)▫ Chocolate Milk▫ Piece of fruit with cottage cheese▫ ½ Turkey Sandwich on Whole Wheat bread▫ Graham crackers with peanut butter▫ Fruit smoothie with low-fat yogurt
Future Research• More research needs to be done on precise
methods for glucoregulation during and post-exercise in diabetics – signaling proteins and the physiological/biological mechanisms behind skeletal muscle glucose uptake?
• More research on GLUT4? GLUT4 is the insulin-regulated glucose transporter for adipose and muscle tissue.
• Improve insulin resistance before the onset of T2DM?
• Research varies on pre/during/post-workout nutrition and how much is appropriate for the specific exercise
References• Boyer, R. (2002). Concepts in biochemistry. Toronto,
Canada: John Wiley and Sons, Inc.
• Dunford, M. (Ed.). (2006). Sports nutrition: A practice manual for professionals. Chicago, Illinois: American DieteticAssociation.
• Hawley, J.A., and Lessard, S.J. (2008). Exercise training-induced improvements in insulin action. Acta Physiologica, 192(1) 127-135.
• Henderson, G., Fattor, J., Horning, M., Faghihnia, N.,Johnson, M. , et al. (2008).Glucoregulation is more precise in women than in men during postexercise recovery. American Journal of Clinical Nutrition, 87 (6), 1686-1694.
References• Mahan, K.L. & Escott-Stump, S. (2008). Krause’s Food &
Nutrition Therapy. St. Louis, MI: Saunders Elsevier.
• Weiss, E., Arif, H., Villareal, D., Marzetti, E., & Holloszy, J. (2008). Endothelial function after high sugar-food ingestion improves with endurance exercise performed on the previous day. American Journal of Clinical Nutrition, 88(1), 51-57.
• Weiss, E., Racette, S., Villareal, D., Fontana, L., Steger-May, K., Schechtman, K., Klein,S., Holloszy, J. (2006). Improvements in glucose tolerance and insulin action induced by increasing energy expenditure or decreasing energy intake: a randomized controlled trial. American Journal of Clinical Nutrition, 84, 1033-42.