Metabolic Fuels & Other Dietery Componenets Flashcards
Metabolic
Refers to the sum of the chemical reactions that take place within each cell of a living organism.
There is a sequence of chemical reactions: a particular molecule is converted into some other molecule or molecules in a defined fashion.
Dietary components are metabolised in cells through 4 main pathways:
Biosynthetic- anabolic
Fuel storage- anabolic
Oxidative processes- catabolic
Waste disposal- either catabolic or anabolic
Anabolic
synthesise larger molecules from smaller components
Anabolic pathways require energy which essentially comes from catabolic pathways in the form of ATP
This process produces ADP and Pi
Actions of insulin are anabolic
Catabolic
break down larger into smaller
This process releases energy in the form of ATP and CO2 and heat
This process requires oxygen
Xenobiotics
Compounds considered foreign to the body- not required as have nutritional value
Biosynthetic pathways
Forms body components such as proteins
Fuel storage pathways
Energy storing products
Fuel oxidative pathways
Energy rich molecules are broken down with the release of energy
Macronutrients
Enzymes require these to function
Cofactors are macronutrients
Cofactors include thymine (TPP)
Thymine is required to allow acetyl coA to enter the Krebs cycle and in the conversion of 5C to 4C
High carbohydrate requirement of the body means high requirement of TPP
Adipose tissue
85% fat, storage of energy-rich molecules
Insulin increases the uptake of glucose by the adipose tissue to then store it as storage compounds such as triglycerides
Slide 20
Liver
metabolically active (e.g. Gluconeogenesis, removal of toxins)
Metabolism of xenobiotics to get them into a state for the removal of these foreign compounds out of the body
The liver also takes up lactate and converts it to pyruvate
Insulin promotes the synthesis of fatty acids in the liver which then move into adipose tissue for storage
Muscle
Activity-uses fuel to provide kinetic energy
3 main deuterium energy sources
● Carbohydrates
● Lipids
● Proteins
Energy currency of the cell is
ATP
Proteins
● Amino acids in chains
● Carbon
● Oxygen
● Hydrogen
● Nitrogen (16% by weight)
Lipids
● Triacylglycerols
(triglycerides)
● 3 fatty acids esterified to one glycerol moeity
● More reduced than other energy sources
● “saturated” with hydrogen
Storage of Dietary Fuels
● Fat - Adipose tissue (only 15% water)
● Carbohydrate – as glycogen in liver and muscles
● Protein - Muscle (80% water)
What happens to excess energy intake?
Store as triglycerides in adipose (approx 15kg),
Store as glycogen (up to 200g in liver & 150g in muscle), 80g in the liver after overnight fast,
Store as protein in muscle (approx 6kg).
The oxidative system
The oxidative system (aerobic) is the primary source of ATP supplied to the body at rest and during low intensity activities and uses primarily carbohydrates and fats as substrates.
Basal Metabolic Rate (BMR)
Energy needed to stay alive at rest
A measure of the energy required to maintain non-exercise bodily functions such as;
● respiration,
● contraction of the heart muscle,
● biosynthetic processes,
● repairing & regenerating tissues,
● ion gradients across cell membranes
BMR = 1kcal/kg body mass/hr (24kcal/kg/day), an adult requires approximately 0.8g/kg ideal body weight protein per day
Conditions essential for measuring BMR
• Post-absorptive (12 hour fast)
• Lying still at physical and mental rest
• Thermo-neutral environment (27 – 29oC)
• No tea/coffee/nicotine/alcohol in previous 12 hours
• No heavy physical activity previous day
• Establish steady-state (~ 30 minutes)
If these conditions are not met, referred to as REE
Factors decreasing BMR
● Age (as you get older, BMR decreases)
● Gender (female have lower BMR since they have less metabolically active tissues)
● Dieting/Starvation
● Hypothyroidism (less thyroid hormone = lower BMR)
● Decreased muscle mass
How do thyroid hormones affect BMR
Thyroid hormones regulate metabolic rate, core body temperature, appetite, sympathetic activity and more
How do muscle cells affect BMR?
Muscle cells require more energy to maintain than fat cells, so people with a higher muscle to fat ratio tend to have a higher BMR.
As we get older, we tend to gain fat and lose muscle. This explains why the BMR tends to decrease with age.
Factors affecting BMR/ REE
● Body weight (BMI)
● Hyperthyroidism
● Low ambient temp.
● Fever/infection/chronic disease
Equations for estimating BMR in health
• Harris Benedict Equations (1919)
• Schofield Equations (1985)
• Henry equations (2005)
Rough estimate: ~1kcal/kg body mass/hour
Example of Henry equation (Henry, 2005).
Equation for estimating basal metabolic rate from gender, age and weight; (formulae & examples are for interest);
Example: (70 kg X 16) + 545 = 1665 kcal/day (BMR)
Slide. 48
Henry equation (2005)- with or without height
in the clinical setting height can be difficult to obtain or include in calculations, & other variables may negate the advantage of including height
Adjust for metabolic stress
Adjust for activity and maybe diet-induced thermogenesis (DIT), for example in healthcare;
Starvation- overnight fast
● ↓insulin
● Glycogenolysis
The brain requires about 150 g of glucose a day.
After an overnight fast the liver only has about 80g glycogen
During a longer period of fasting/starvation, glucose must be formed from non-carbohydrate sources - gluconeogenesis
Starvation- 2-4 days
● ↓insulin
● ↑cortisol
(Lipolysis & proteolysis)
Gluconeogenesis uses
● Lactate
● Amino acids
● Muscle
● Intestine
● Skin
● Glycerol- ● Fat breakdown
Starvation- >4days
● Liver → ketones from fatty acids,
● Brain adapts to using ketones,
● ↓BMR = accommodation.
Define Malnutrition
A state of nutrition with a deficiency, excess or imbalance of energy, protein or other nutrients, causing measurable adverse effects
Adverse effects of malnutrition
Adverse effects are on tissue/body form (shape, size, composition), body function and clinical outcome.
Re-feeding syndrome:
● Re-distribution of phosphate, potassium, magnesium etc due to insulin
● Switch back to carbohydrates as the main fuel which requires phosphate and thiamine.
Micronutrients
-Trace elements and vitamins
● Co-factors in metabolism
● Gene expression
● Structural components
● Antioxidants
Essential vitamins
Vitamin c
Vitamin B12
Vitamin B1
Vitamin D
Vitamin C
● Ascorbic acid
● Fruit and vegetables
● Heat labile
● Collagen synthesis
● Improve iron absorption
● Antioxidant
Vitamin B12
● Protein synthesis
● DNA synthesis
● Regenerate folate
● (and therefore – cell division)
● Fatty acid synthesis
● Energy production
Vitamin B1
Helps with energy production in your body
Vitamin D
Increases the amount of calcium and phosphorus your body absorbs from foods.
Prudent diet
● 5+ servings fruit/veg
● Base your meals around starchy carbohydrate foods,
● no more than 5% of the energy we consume should come from free sugars
● 0.8g/kg/day protein
● The average man should have no more than 30g saturated fat a day, & women 20g.
● Adults should have no more than 2.4g of sodium per day, which is equal to 6g of salt.
● Men and women are advised not to regularly drink more than 14 units of alcohol a week (over >3 days).
● Avoid excess dietary supplementation
● Adequate Calcium
Dietary energy sources
Carbohydrates (4kcal/g),
Protein (4kcal/g),
Alcohol (7kcal/g)
Lipid (9kcal/g - gives the most energy per gram)
Alcohols
typically ethanol, highly energetic
Factors increasing BMR
high BMI
hyperthyroidism
low ambient temperature
fever/infection
pregnancy (due to increase in weight and thyroid hormone)
exercise
Daily energy expenditure (DEE)
Energy to support our BMR and our physical activity + energy required to process food we eat (diet induced thermogenesis)
Storage of excess energy
• Stored as triglycerides (excess lipid) (approx 15kg)
• Stored as glycogen (excess glucose) (approx 200g in liver & 150g in muscle)
• Stored as protein (approx 6kg)
• Carbohydrates account for 30% of ATP production at rest
• Lipids account for 70% of ATP production at rest
• Proteins are often used in longer periods of starvation
ATP
• ATP > Energy utilisation (biosynthesis or macromolecules, muscle contraction, active ion transport and thermogenesis)
ADP + Pi > Respiration (energy production from carbohydrate, lipid & protein, O2 IN and CO2 OUT > ATP
