Energy From Food And Macronutrients Flashcards
Coenzymes
Organic molecules that function as enzyme helpers. Include vitamins.
Cofactors
Organic or inorganic substances that facilitate enzyme action. Vitamins are organic, minerals are inorganic
Breaking down glucose for energy
Glucose broken down through glycolysis to 2 pyruvate (3 carbon molecule)
Pyruvate converted to lactic acid anaerobically (without oxygen)- lactate formed when hydrogen added to pyruvate. Liver cells recycle muscle lactic acid through Cori cycle.
Acetyl coA aerobically (with oxygen). Acetyl coA synthesises days when the body has enough ATP, generates ATP when the cell is low in energy
Breaking down glycerol and fatty acids for energy
Glycerol and pyruvate are both three carbon molecules so easy to break down.
Fatty acids to Acetyl coA reactions are called fatty acid oxidation
Fatty acids cannot be used to synthesise glucose. Glucose must be available to provide energy to the red blood cells, brain and nervous system.
Breaking down amino acids for energy
AA to glucose (gluconeogenesis)- most AAs are a fairly good source of glucose when carbohydrate is not available (glucogenic AAs)
Amino acids to Acetyl coA after deamination (ketogenesis)-
Some AAs will not give rise to glucose at all instead produce ketone bodies (ketogenic AAs), results in keto acid and ammonia.
Ammonia is converted to urea- a much less toxic compound in the liver. Urea is excreted through the kidneys to rid the body of unused nitrogen. Transanimation is the transfer of the amino acid group from an amino acid to a keto acid. Low rate of ATP Production.
Breaking down nutrients for energy
Glucose and fatty acids are primarily used for energy, amino acids to a lesser extent.
Glucose is made from all carbs, most amino acids, and the glycerol portion of fat.
All energy yielding nutrients consumed in excess can contribute to fat storage.
The TCA cycle produced NADH and FADH2 which feed into the electron transport chain to produce ATP.
The etc- consumes oxygen, produces CO2 and water, produced energy as ATP.
Energy in energy yielding nutrients
Carbs- 17kJ/g
Protein- 17kJ/g
Fat - 37kJ/g
Alcohol- 29kJ/g (not a nutrient)
Energy balance
Overeating- storage of fat.
Storage of fat can be from all energy yielding nutrients, but most effective in excess fat.
Fasting- glucose is needed for the brain, protein can meet glucose needs. The shift to ketosis- ketones are produced when glucose is not available. Ketosis supports a suppression of the appetite. Slowing of the metabolism occurs.
Symptoms of starvation
Muscle wasting
Decreased heart rate, respiratory rate, metabolic rate and body temp.
Impaired vision
Organ failure
Decreased immunity
Depression, anxiety and food related dreams
Energy in: the kJ’s food provides
Bomb calorimeter- instrument measures the best energy released when foods are burned.
Direct calorimetry- measures heat energy released.
Indirect calorimetry- measures amount of
Oxygen consumed and CO2 expelled.
Physiological fuel value is the difference between the number of kJs measured with
calorimetry and the number of kJs that the human body derives from a food
Energy Out: The kJ the body expends
Energy expenditure includes basal metabolic activities, physical activity, thermic effect of food and adaptive thermogenesis.
These energy requirements differ from person to person and are affected by age, gender weight and height.
The intensity and duration of physical activity also make a difference o
kJ out- BMR
2/3 or energy expenditure
Supports the basic process of life
Resting metabolic rate RMR is a measure of energy slightly higher than BMR/bee
Factors affecting BMR
Fasting starvation slows BMR Malnutrition slows BMR Hormones- thyroid can increase or decrease BMR, premenstrual hormones can increase BMR Smoking increases BMR Caffeine increases BMR Sleep slows BMR Ageing slows Height- taller you are greater BMR Growth increases BMR Lean body mass increases BMR Fever increases Stress increases Both hot and cold temp raise BMR
kJ out- thermic effect of food
10% of total energy expenditure and involves digestion and absorption Carbs- 5-10% Fat- 0-5% Protein- 20-30% Alcohol- 15-20%
Adaptive thermogenesis (AT)- the adjustment in energy expenditure related to environmental changes
kJ out- physical activity
Most variable amount
Voluntary
Can be significant in weight loss and weight gain
Duration, frequency and intensity influence energy expenditure
Measuring energy expenditure - indirect calorimetry
measures rate of oxygen consumption (L/ minute) and carbon dioxide production (L/ minute). At rest or during exercise, the ratio between volume of CO2 produced and volume of oxygen consumed can be calculated (VCO2/VO2). This ratio is the respiratory exchange ratio and is inappropriate for habitual estimates of total daily expenditure.
Measuring energy
Expenditure - direct calorimetry
Involves continuous measurement of gaseous exchange in subjects confined in metabolic chambers, measures the amount of heat released
Characteristics:
Suitable for long term studies
Accurate
Impractical for estimates of energy cost in free- living subjects, especially athletes with busy training schedule
The metabolic chamber is an open circuit respiration chamber used to measure energy expenditure and substrate oxidation over 24 hours
Measuring energy expenditure- non- colorimetric methods
Factorial method:
Estimated energy requirements (EER)(kJ/d) = BMR X activity factor (PAL)
PAL= physical activity level- expressed as a ratio of total energy expenditure to BMR. Record of total time (min/d) spent in each of the various daily activities.
Individual activities have an estimated energy (metabolic) cost. METs are available for different activities.
Measuring energy expenditure- doubly labeled water (DLW) technique
Gold standard for measuring free living EE
- based on differential elimination of deuterium and oxygen from body water, following a dose of water labeled with these two stable isotopes.
Deuterium eliminated as water while oxygen
Eliminated as water and CO2
Difference between the two rates is a measure of CO2 production
Measure (accurately) TEE over period of time (7-14 days)
Aus reference standards for energy
No RDIs for energy
NRVs have a new standard:
- EER estimated energy requirements
Values are available for age, sex, pregnancy and lactation and are based on standard reference weight. Different PAL levels
Limitations
TEF, AT, spontaneous activity, genetics, ethnicity, environment, individual adaptation are not accounted for
Most common equations for calculating:
- Schofield
- Harris- Benedict
Enable you to calculate BMR and then multiply by an activity/ stress factor
Mechanisms for regulating energy balance
Energy balance is dynamic
Positive during meals, negative during intervals
Balances out over time, except during intentional growth
Regulation achieved by hypothalamus
- receives neural and endocrine signals from body
- integrates these through complex network of neural pathways
- follows by sending efferent neural signals to regulate appetite and energy expenditure
Signals indication energy efficiency
Short term
- blood glucose, amino acid, fatty acid levels
- stomach and gut derived hormones
- Vagal signals from liver
Long term
- hormones secreted by adipose tissue- to fat stored there- leptin
- leptin- directly proportional to fat stores, the body’s fuel gauge
During weight loss/ starvation body’s BMR can drop by ~20%
Defining healthy body weight
BMI measures relative weight for height. Underweight is a BMI below 18.5 - health risks - cannot handle medical stress - menstrual irregularities and infertility - pregnancy problems - osteoporosis and bone fractures Overweight is a over 25. Obese is above 30.
Physique/ body composition assessment (anthropometry)
Identifying physique characteristics - somatotyping Growth (height) - poor instrument calibration Weight - diurnal variation BMI mid arm muscle circumference - measure of malnutrition Girths - waist/ hip ratio Frame size
Chemical reactions in the body
Photosynthesis to produce carbohydrates which are consumed by humans.
Energy yielding nutrients broken down into composite parts.
Anabolism-building up of body compounds
Catabolism- breakdown of body compounds and releases energy
Take place inside of cells- especially the liver
