Energy Balance & Metabolism. By the end of this unit you should be able to:- Define energy balance Describe regulation of food intake Identify metabolic rate and factors affecting it Describe thermoregulation. List disorders of body temperature List disorders of energy balance.
By the end of this unit you should be able to:-
Define energy balance
Describe regulation of food intake
Identify metabolic rate and factors affecting it
List disorders of body temperature
List disorders of energy balance
The tem metabolism means change. It refers to all chemical and energy transformations that occur in the body. Energy intake and output are balanced under steady state conditions.
Under normal conditions 75-80% 0f the chemical energy released from food oxidation appears as heat
It is the balance between energy input (.i.e. intake) and energy output (.i.e. expenditure).
.e.g. During child growth , Overweight & obesity
.e.g. inanition , anorexia & cachexia
Energy intake = The ingested amount of CHO, fat and protein in gm x its physiological heat value.
calorie; is the unit used to express energy amount. It is the amount of heat required to raise the temperature of one gm of water from 15 -16 °C
Calorie or Kilocalorie =1000 calorie
It is the ratio of CO₂ production to O ₂ utilization in the same time. (RQ=Volume of CO₂ produced/ Volume of O ₂ consumed) .
RQ between 0.7- 1 represent the approximate ratio of CHO to fat metabolism.
Stability of total body mass and composition requires that energy intake match energy expenditure.
The hypothalamus contains:-
The hypothalamic nuclei also influence the secretion of several hormones that are important in regulation of energy balance and control like thyroid hormone & glucocorticoid.
Fine tuning of energy
input &output is the
function of hypothalamus
Oral factors as chewing, salivation, swallowing and tasting meter the food as it passes through the mouth and after a certain amount of food has passed , it inhibit the feeding center. The inhibition caused by this metering system is short( 20- 40 min)
Long term regulation of food intake (maintain constant nutrient stores):-
leptin hormone is released from adipose tissue & act on leptin receptors in the hypothalamus to induce:-
In a healthy adult person energy intake is equal to energy output ( expenditure).
It determines the total quantity of heat liberated from the body in a large specially constructed calorimeter (respiration calorimeter) in a given time.
Direct calorimetry is expensive and difficult to perform and is used for research purpose.Measurement of metabolic rate of the body
In this method , heat liberated by the subject is calculated by:-
Energy equivalent of O₂is the amount of heat liberated by consumption of 1 L O₂ .
Metabolic rate (Kcal /unit time)= O₂ consumption L/unit time x 4.82 Kcal
Muscular exercise ( Maximal labor increase metabolic rate 3.5 times that of inactivity).
It is the obligatory increase in energy output during assimilation of food(Digestion , absorption & processing of food), thus reducing the amount of calories obtained from food. It equals 30% for protein, 6 % for CHO & 4% for fat and 10% for mixed diet.Factors affecting metabolic rate
It start 1 h after eating, reach a peak after 4-5 h &last for 12 h after eating . Its cause is uncertain but could be due to:-
Environmental temperature ( high or low environmental temperature increase metabolic rate).
Large animals have higher metabolic rate than small animals but when calculated /Kg or m² surface area, small animals have higher MR
↑body temperature 1°C→↑ metabolic rate 10-14%
Energy output can be partitioned into separate measurable components which include:-
The minimum amount of energy required to exist . It accounts for 50-70% of daily energy expenditure in most sedentary individuals.
BMR is expressed in terms of calories/ h
In a 70 Kg man , it is estimated to be 65-70C/h
Skeletal muscles even under basal conditions account for 20-30 % of BMR. This explains ↓ BMR in:-
BMR investigates the metabolic rate in absence of the major factors affecting it, so it is valuable in:-
BMR is expressed as % ↑ or↓ from expected normal value.
prolonged ingestion of protein increase BMR about 10% more than BMR with mixed diet.
Disorders of thyroid gland (Hypothyr-oidism →↓BMR, hyperthyroidism →↑BMR).
Determine the individual´s energy output and supply him with an equal amount of calories:-
Muscle contraction requires much energy, the production of which needs sufficient O₂ supply & nutrients.
ADP →AMP+ energy
Most of the energy required for resynthesis of ATP & Creatine pohospahate is derived from glucose or glycogen.
During muscular exercise , the body tries to supply sufficient O₂ to the exercising muscles.
O₂ debt occurs during exercise and is paid during recovery. i.e. during recovery , O₂ consumption by the muscle remains increased until O₂ debt is paid back.