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The SI unit of energy is the Joule. 1 Joule is a small amount of energy, and in nutrition and physiology it is usual to work in kJ (1,000 Joules) or MJ (1,000,000 Joules)
Many people prefer to use the calorie. 1 calorie is the amount of heat required to raise the temperature of 1 g of water through 1 degree C, from 14.5C to 15.5C. Again in nutrition and physiology it is usual to work in kcal (1,000 cal); this is sometimes shown as Cal with a capital C, to differentiate it from a single calorie with a lower case c.
The basal metabolic rate is the energy cost of maintaining metabolic homeostasis, nerve and muscle tone and circulation and breathing.
It is the energy expenditure measured when completely at rest, but awake, at a comfortable temperature (i.e. under conditions of thermal neutrality, so that the subject is not expending energy to keep warm or cool down), and several hours after the last meal, so that the subject is not expending energy on processing the products of digestion to synthesise body reserves of fat and glycogen.
The importance of being awake is that some people show an increase in metabolic activity when they are asleep, as a result of partial uncoupling of electron transport from ATP synthesis - this is a mechanism for regulating body weight as food intake varies. Other people show a fall in metabolic activity when they are asleep; such people are metabolically efficient, but are more likely to gain weight as a result of increased food intake.
Basal
metabolic rate depends on metabolically active lean body tissue; mainly muscle,
but all tissues make a contribution - although it is largely inert reserves
of triacylglycerol, adipose tissue also makes a contribution to metabolic rate.
Body weight is therefore an important factor in determining BMR, but gender
and age are also important.
Women have a higher proportion of body weight as fat than do men. This means that a woman has a lower BMR than a man of the same body weight.
With increasing age, even if body weight does not change, lean muscle tissue is gradually replaced by fat, so that the proportion of fat in the body increases with age. This means that an older person has a lower BMR than a younger person of the same age.
It is not always possible to determine BMR under strictly controlled conditions. When the conditions are not completely controlled, the resultant measurement of energy expenditure is called the resting metabolic rate; for practical purposes, resting metabolic rate can be considered to be approximately equivalent to basal metabolic rate.
PAR is the energy cost of an activity, expressed as a multiple of BMR. Values range from only just > 1.0 for very gentle activities up to 8 x BMR or even higher for very intense activity.
PAR
1.0 – 1.4
lying, standing or sitting at rest, e.g. watching TV, reading, writing, eating,
playing cards
PAR
1.5 – 1.8
sitting: sewing, knitting, playing piano, driving, standing: preparing vegetables,
washing dishes, ironing, office and lab work
PAR
1.9 – 2.4
standing: mixed household chores, cooking, playing snooker or bowls
PAR
2.5 – 3.3
standing: dressing, undressing, showering, vacuum cleaning, walking: 4 –
6 km /h, playing cricket,
occupational: tailoring, shoemaking, electrical and machine tool, industry,
painting and decorating
PAR
3.4 – 4.4
standing: mopping floors, gardening, cleaning windows, walking: 4 – 6
km /h, playing golf,
occupational: motor vehicle repairs, carpentry and joinery,
chemical industry, bricklaying
PAR
4.5 – 5.9
standing: polishing furniture, chopping wood, heavy gardening, walking: 6 -
7 km /h,
exercise: dancing, moderate swimming, gentle cycling
occupational: labouring, hoeing, road construction, digging
and shovelling, felling trees
PAR
6.0 – 7.9
walking: uphill with load or cross-country, climbing stairs,
exercise: jogging, cycling, skiing, tennis, football
Some-one's overall physical activity level is calculated by summing the various activities during the day, multiplied by the time spent in each activity as a proportion of the day. Again it is expressed as a multiple of BMR. The UK Department of Health classification of occupational work during the typical 8 hours working day (excluding leisure activities) are as follows:
Light
work: PAR = 1.7
professional, clerical and technical workers, administrative and managerial
staff, sales representatives, housewives
Moderate
work: PAR = 2.2 (women) – 2.7 (men)
sales staff, domestic service, students, transport workers, joiners, roofing
workers
Moderately
heavy work – PAR 2.3 (women) – 3.0 (men)
machine operators, labourers, agricultural workers, bricklaying, masonry
Heavy
work: PAR = 2.8 (women) – 3.8 (men)
labourers, agricultural workers, bricklaying, masonry, where there is little
or no mechanisation
These figures exclude leisure activities; a desirable physical activity level for cardiovascular and general health is 1.7 x BMR, a figure that is achieved in UK by only some 22% of men and 13% of women. The average PAL in UK is 1.4 x BMR.
In the simulation program you will complete an activity diary for your subject, which will permit you to determine PAL and total energy requirement.
The increase in metabolic activity after a meal, as a result of the energy cost of digestion and absorption, and, more importantly, the energy cost of synthesising reserves of glycogen, triacylglycerol and protein. It may be as much as 10 - 15% of the energy yield of the meal.
The total expenditure of energy (and hence the total energy requirement to maintain body weight) in kJ or kcal, calculated from BMR x PAL + an estimate of DIT.