2. Specific Dynamic Action(SDA) of food
• Definition:The phenomenon of the extra heat production by the body
over and above the calculated Caloric value, when a given food which
is metabolised by the body is known as specific dynamic
action(SDA). or
SDA is increased metabolic rate following the intake of food .
• SDA = Calorigenic action = thermic(effect)action /thermogenic
action of food = diet induced thermogenesis
• Part of this due to the expenditure of energy for digestion,
absorption and active transport of products of digestion of food
responsible for regulatory thermogenesis.
3. Specific Dynamic Action(SDA) of food
Intake of Nutrient
(25g)
Calorie value
(kcal)
Heat liberation in human body
(kcal)
SDA(%)
Carbohydrate 100(=25X4) 105 5
Protein 100(=25X4) 130 30
Lipid 100 115 15
Mixed diet
( regularly consumed)
10
Increased/ extra heat output after taking food is known as SDA. It is due
to the activity of tissues mobilising these foodstuffs.
Proteins have the highest SDA and carbohydrates have the lowest SDA.
The energy is trapped from previously available energy, so that the actual
energy from the food is lesser than that of calculated of SDA.
4. Thermogenic effect of food
• Heat production (thermogenic effect of food)
e.g. intake of carbohydrate :250 g
• energy should produce = 250x 4 (kcal/g)=1000 kcal
• energy trapped ( =10%) =100 kcal
• Net energy generated =1000-100 = 900 kcal
• If need is 1000 kcal then intake of food worth of 1100 kcal.
5. Specific Dynamic Action for proteins
Highest SDA for proteins(30%) i.e. for 100 g of dietary proteins consumed , the energy
available for doing useful work is 30% less than calculated value. Therefore it is not
good source of energy. Diet very rich in protein unfavourable to heavy muscular activity.
Expected heat generation on intake of 25 g of protein after overnight = 100 kcal(25 g x4)
Actually heat output =130 kcal( rise of 30%)
The presence of fats and carbohydrates reduces the SDA of proteins.
SDA for proteins: to meet energy need / requirements for deamination , synthesis of urea
, biosynthesis of proteins, biosynthesis of Triacylglycerol (from carbon skeletons of
amino acids) , no absorption of proteins as such . Phenylalanine , Glycine and Alanine
are fed increase SDA.
Intravenous administration of amino acids or oral administration of proteins gives the
same SDA. This indicates SDA of proteins ,is not due to their digestion and absorption.
Benefits of SDA of protein : Consumption of protein rich diet makes us feel warm and
comfortable in cold weather.This is due to the high SDA which help in maintenance of
body temperature particularly in cold climate.
6. Specific dynamic action of lipids
• SDA of lipid/fat =15%
Heat output after ingestion of 11g of fat =113 kcal (11x9.1+13)
not 100 kcal
SDA for lipids : may be due to mobilisation ,storage and more
rapid oxidation of fat.
Fats is the best source of energy due to its lowering effect on
SDA. However ,excessive utilisation of lipids leads to ketosis.
7. Specific dynamic action of carbohydrates
• SDA of carbohydrates = 5%
Heat output after ingestion of 25g carbohydrate
=105 kcal (25x4)not 100 kcal.
• SDA for carbohydrates : is attributed to the energy
expenditure for conversion of Glucose to Glycogen.
8. Specific Dynamic action of a mixed diet
SDA for mixed diet =10%(an extra energy/ calories should be
provided in diet to account for loss of energy as SDA.
e.g.calorie requirement to maintain basal metabolic needs:
1700 kcal/day
Heat output after eating food = 1700+170 kcal(excess calorie
derived from his own tissue)
Energy requirement to maintain his weight =1900
kcal(1700+170)
If persisted intaking 1700 kcal ,it would result in loss of the
body weight .
9. Mechanism of Specific Dynamic Action
• Excess energy (SDA) is required for digestion,absorption ,transport,
metabolism and storage of foods in the human body.
• SDA for carbohydrates(5%): is attributed to the energy expenditure for
conversion of Glucose to Glycogen.
• Higher SDA of proteins (30%) is due to meet extra energy requirement for
energy utilisation for deamination , synthesis of urea , biosynthesis of
proteins, biosynthesis of Triacylglycerol (from carbon skeletons of amino
acids) , no absorption of proteins as such . Therefore ,it is not good
source of energy. Phenylalanine , Glycine and Alanine decrease SDA.
Intravenous administration of amino acids or oral administration of
proteins gives the same SDA. This indicates SDA of proteins ,is not due
to their digestion and absorption.
• SDA for lipids(15%) : may be due to mobilisation ,storage and oxidation
of fat.
10. Significance of specific Dynamic action:1
• Additional 10% calories should be added to the total energy needs of
the body towards SDA for:
1. the extra heat liberated over and above the calorie value. It may be due
to a specific stimulating effect of food on metabolism.
2. digestion,absorption ,transport, metabolism of foods in the human
body.
3. consumption of certain amount of energy for utilisation of nutrients
from the body stores(e.g. glycogen, triacyl glycerol, protein) by the
human body.
4. synthesis of reserve materials such as glycogen , triacylglycerol ,
protein etc. from small molecules available after digestion in the
human body .
5. the activation energy needed for a chemical reaction and this
activation energy to be supplied initially. It is closely connected with
the metabolic functions of liver.
11. Significance of specific Dynamic action:2
6. Higher SDA of proteins (30%) is due to extra energy utilisation for
deamination , synthesis of urea , biosynthesis of proteins, biosynthesis
of Triacylglycerol (from carbon skeletons of amino acids) , no absorption
of proteins as such . Therefore ,it is not good source of energy.
7. for conversion of Glucose to Glycogen and fatty acids to
Triacylglycerol for storage of energy.
8. Fats is the best source of energy due to its lowering effect on
SDA. However ,excessive utilisation of lipids leads to ketosis.
