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Energy expenditure is the heat released and mechanical work completed by the body which is essential to maintain life and lifestyle. It can be measured with the use of a calorimetry, direct or indirect. With the use of the direct calorimetry, researchers can measure the rate of heat emitted from the body to the calorimeter (Levine, 2005). However using the indirect calorimetry researchers can measure oxygen (O2) consumption and carbon dioxide (CO2) production. In that case researchers convert O2 consumed and CO2 produced by the body to energy expenditure, with the use of a formula (Levine, 2005). Douglas Bag is an example of an indirect calorimetry and it used to complete the experiment. In the Douglas bag the subject's air is collected and it is available for laboratory analysis and volume measurement (Garry and Douglas, 1956).
There are three factors which contribute to the total energy expenditure measurement, the resting energy expenditure which counts approximately 60% of total energy expenditure, the thermic effect of feeding which is approximately 10% and nonresting energy expenditure which is approximately 30% (Leibel et.al., 1995). Firstly, resting energy is the energy expended when the subject is at rest (in neutral temperature environment and when subject is in a post stage of absorption). This energy is usually referred as basal metabolic rate (BMR) or resting metabolic rate (RMR). A further component that contributes in energy expenditure is the thermic effect of feeding. According to Reed and Hill, (1996), the thermic effect of food, described as the increase in metabolic rate after food consumption. Fundamentally is the essential energy for digestion, absorption and removal of ingested nutrients (Crovetti et al., 1998). The remaining percentage of energy is commonly found in the type of physical activity and it is referred as non-resting energy expenditure (Leibel et al., 1995).
Metabolic rate is general, influenced by genetics, gender, age and weight. However, different meals can have different effects on BMR. For example, according to Swaminathan (1985) study, a high protein meal tends to increase metabolic rate more than a high CHO or high fat meal. However a high CHO meal tends to increase metabolic rate more than a high fat meal (Swaminathan, 1985). Numerous studies have shown that protein is more satiating than either carbohydrate or fat (Latner and Schwartz,1999) (Poppitt et.al., 1998). Thus, may empower weight loss over the longer period (Luscombe et.al., 2002).
There are several factors which must be considered when calculate the thermic effect of food (TEF). TEF influenced by bodyweight, growth rate, fast duration, meal size (Luketich et.al., 1989). Therefore, anthropometric measurements have to be taken in order to have more accurate results such as height, weight, mid-upper arm perimeter, and skin folds (Piers et.al., 1992). Furthermore the thermic effect of a treatment meal depends on its energy concentration and nutrient composition (Piers et al., 1992). Finally, sex influences the EE and according to Luscombe et al. (2002), TEF tends to be higher for men in comparison with women
The aim of this experiment was to investigate whether food and different macronutrients composition increase the metabolic rate differently.
From the available literature it was hypothesised that the high protein meal is expected to increase metabolic rate more than either high carbohydrate or high fat meal (Swaminathan, 1985). Accordingly, the order of macronutrients depending to their thermogenesis is: protein, carbohydrate and then fat.
In order to carry out this study a list of objectives was cited and referred to what is needed to achieve the aim of the experiment:
Recruit 4 healthy non-smoking adults for overnight fasting.
Define their characteristics through anthropometric measurements.
Recruit subjects consume four experimental treatments with the same calorie content (500kcal) but different macronutrient composition.
Measure the energy expenditure after the meal consumption using indirect calorimetry (Douglas Bag).
Perform a series of measurements to investigate and calculate the thermic effect of food and the RQ.
Firstly a recruiting process was conducted. Four subjects aged 19-22 were used to investigate the thermic effect of food. At the day of the experiment, the subjects came to the laboratory early in the morning at 9 o' clock after an overnight fast. After 5 minutes of relaxation, anthropometric measurements have been taken (Table 1) in order to define their characteristics. The anthropometric measurements which took place was the measurement of weight and height. Afterwards, each subject had to consume a meal with the same calorie content (500kcal) but different macronutrient composition. Subjects 1, 2 and 3 consumed a high CHO, protein and fat meal respectively, whereas subject 4 remained fasted during the experiment time.
Table 1: Physical characteristics of the subjects
Meal Calorie-Macronutrient Concentration
High Carbohydrate Meal
115g cornflakes and 150ml of semi-skimmed milk
High Protein Meal
315g of grilled skinless chicken and 60g of tomato and basil
High Fat Meal
Lindt dark chocolate96g
Procedures-Design of the study
Indirect Calorimetry (Douglas Bag)
An indirect calorimetry used in order to conduct the experiment. The indirect calorimetry used was the Douglas Bag which consists of a leak-proof material bag of approximately 100-150 litre capacity (Levine, 2005). After the consumption of the treatment, subjects sat for a five minutes to get costume to breathing without collecting their expired air into the Douglas bag. Subjects were sat and relaxed in a thermoneutral environment of 18°C. At the time which subjects became familiar with the environment and were completely relaxed, they had to breath normally in the Douglas Bag for 5 minutes (-length of air collection time). That was the baseline reading. This process repeated after 30 and 60 minutes and gas analyser and gas meter were used to analyse the air content of the Douglas bag.
After the collection time a small sample of expired air was taken to be analysed using the gas analyser (Hitech Instruments Ltd, model: GIR250) and the Douglas bag closed using the sampling tube in order to avoid any expired air of leaking out. The gas analysed tube was connected with the sampling tube and the gas was analysed. At the same time, stopwatch started to count the air collection time (approximately 2 minutes). When the indication of oxygen and carbon dioxide percentage values were stabled, the quoted value was recorded.
Dry Gas Meter
The dry gas meter (Harvard), was connected with a tube to the large valve of the Douglas bag. The gas meter reseat to zero. At the same time the air form Douglas Bag was released and a vacuum pump pulled the air content out. The value of the volume of air was recorded.
Data Record and Calculations
The received data and the calculations of the results were conducted using Microsoft Office Excel (see Appendix 1). With the use of the indirect calorimetry; the respiratory gas exchange, oxygen consumption and carbon dioxide production was measured and used to calculate the EE (Seale, 1995). EE and RQ were calculated using McArdle, Katch and Katch (1996). A sample of the calculations is available at the end of this report (see Appendix 2).
RQ=Volume of CO2/ Volume of O2
Energy Expenditure=Volume of O2 x Caloric Valve
The results were analysed using formulas in Microsoft Excel and the most important information were selected and presented in the following table and figures.
As shown in Table 2, subject 2 who consumed a high protein meal had the highest decrease of energy expenditure followed by subject 4 who did not consume any treatment and subject 1 who consumed a high carbohydrate meal. However, subject 3 who consumed the high fat meal had the highest increase of the energy expenditure. In addition subject 4 had the highest increase of RQ followed by subjects 2 and 3 respectively. Nevertheless subject 1 who consumed the high CHO meal had the lowest increase, in comparison with the other 3 subjects. Thus, in general the experimental data which collected and analysed, did not much with the available hypothesis.
Table 2: Results and mean of difference from baseline
Mean values compare to Baseline (0min)
Results- Subject 1 (High CHO meal)
Respiratory Quotient (RQ)
Energy Expenditure (kcal/min)
Results- Subject 2 (High Protein meal)
Respiratory Quotient (RQ)
Energy Expenditure (kcal/min)
Results- Subject 3 (High Fat meal)
Respiratory Quotient (RQ)
Energy Expenditure (kcal/min)
Results- Subject 4 (No meal)
Respiratory Quotient (RQ)
Energy Expenditure (kcal/min)
*For the subject 2, 90 minutes has been used rather than 60, which have been discarded, in order to calculate the mean RQ and energy expenditure. The results of 60 minutes have been discarded due to the error of measurement.
Subject 1 had the highest RQ alteration in throughout the experiment period. Figure 1 clearly shows that subject 1 started with an increased rate from 0-30 minutes and then during 30-60 minutes the RQ rapidly fell. However, subject 4 had the lowest RQ change throughout the experiment as expected because subject 4 stayed fasted. Subjects 2 and 3 had parallel alteration with subject 2 having the highest RQ at the end of the experiment. Figure 2 illustrates the thermic effect of feeding depending on time. Subject 3 had almost no alteration during the 60 minutes period instead of subject 4 who had a continually decrease of energy expenditure. However, subjects 1 and 2 had almost the same alteration, with subject 2 started with the highest level of energy expenditure whereas at the end of the experiment had almost the same value with subject 1.
Figure 1: The alteration of RQ depending on the time. (* Error made â€‹â€‹when using the Douglas bag at 60 minutes (for subject 2), the measuring process was repeated in 90 minutes and 90 minutes values used instead of 60 minutes).
Figure 2: Thermic effect of food in one hour period.(* Error made â€‹â€‹when using the Douglas bag at 60 minutes (for subject 2), the measuring process was repeated in 90 minutes and 90 minutes values used instead of 60 minutes).
This study describes the post-prandial effect of food consumption on energy expenditure. With the use of the Douglas Bag, a number of data received and analysed. According to the available literature and the cited hypothesis it was expected to see energy expenditure rise in a higher level for the subject who consumed a high protein meal (Crovetti et. al, 1998). Then in a lower level for the subject who consumed a high CHO and finally for subject who consumed a high fat meal (if subject who remained fasted excluded) (Swaminathan, 1985).
Nevertheless according to the received data and the analysed results all the subjects had a decrease of energy expenditure except from the subject who consumed the high fat meal. Moreover the RQ values increased during the period of measurements for all subjects except from the subject who consumed the high CHO meal which increased during the first 30 minutes and then it decreased during 60-90 minutes. However the final value of the RQ for all subjects was higher than the value of start point as expected because the time which every nutrient needs to be completely oxidised. The body has a limited ability to oxidize fat compared with the ability to oxidize carbohydrate and protein (Westerterp, 1993). The final values of RQ confirm the literature but evidently the results of EE did not much with the sited hypothesis and the available literature.
Firstly energy requirements within the calorimetry bag were considerably lower than those for free-living conditions (Seale,1995). Thus, the entire results of the experiment refer to experiment conditions. However in comparison with other studies which conducted under the similar conditions, the results of this study are undoubtedly different and this is possibly due to the weaknesses which the experiment was undertaken.
Subjects were not completely relaxed because there was not enough relaxation time and they were not completely comfortable the time of the measurements. According to several studies which exanimated the similar topic (Crovetti et. al, 1998; Reed and Hill, 1996) subjects had the time to relax for approximately 30-45 minutes in order to conclude in optimum results. However, the biggest error of the period of measurement was the error at 60 minutes for the subject who consumed the high protein milk. Specifically, the bag of subject 2 accidentally dropped down in 60 minutes and all the expired air lost. Consequently, the process was repeated in 90 minutes. This error may cause an alteration to the actual results because 30 minutes later (at 90 minutes time) the digestion process may influence the results. In addition, the experiment was done in 4 different individuals, thus the results maybe cannot be comparable because subjects had different anthropometric characteristics, age, sex and metabolism. Subsequently, the a better practice was to set the four different individuals to consume the same 3 treatments and each time the EE could be measured in order to conclude in more representative results. In addition, the meals provided were 500 Kcal which was a low calorie meal in comparison with Weststrate's study (1993), who sited that the thermic effect of feeding can be accurately assessed within 3 hours for meals providing 2508 kJ ( Ì´ 600 Kcal). Thus, the experiment could have a longer duration and higher calorie meal content in order to conclude in more accurate results. However, this process need time which was unavailable due to the strict duration of the experiment (3 hours). Furthermore, the RQ is precisely calculated by measuring the urinary nitrogen excretion but in this study it was impracticable, so a gross RQ calculated used in order to measure the RQ (Piers et al., 1992). This caused an error to the results. But there is no suggestion to improve this weakness due to the environment of the experiment and the lack of equipment (university practical).
However, except from the weaknesses, several strengths supported the experiment process. For example subjects came at laboratory early morning after overnight fasting as requested. Digestion and absorption process were completed so the stomach was empty. Therefore, treatment could have its effects and the expired air could be analysed and referred to that particular meal. Moreover the meals had equal calorie content for all the subjects (500Kcal), so straight comparisons could be made. The use of the indirect calorimetry (Douglas Bag) can be characterised of one of the best methods of analysing the energy expenditure. According to Levine (2005), the error of measurement of EE undertaken with the Douglas bags may be very small (3%) under the condition that the experiment was carried out in optimum conditions. Douglas Bag is easy to manage, readily flexible to a huge range of conditions and has the advantage of port- ability (Garry and Douglas, 1956). Moreover indirect calorimetry is participant friendly, thus subjects may feel more comfortable and relaxed in comparison with the direct calorimetry (Seale and Rumpler, 1997). Thus, more accurately measurements could be received because the expired air referred only to the particular meal consumption rather than stress or the feeling to discomfort. An additional strength of this study was that all the subjects were healthy and non-smokers thus results were unaffected by any illness or smoking.
In conclusion, this study has demonstrated that, almost all subjects had a decrease of energy expenditure during the period of measurement. The subject who consumed a high protein meal had the highest decrease of energy expenditure followed by subject who did not consume any treatment and subject who consumed a high carbohydrate meal. Nevertheless, the only increase of energy expenditure is shown on subject who consumed the high fat meal. However, the RQ for all subjects had an increase during the period of measurement as expected, due to the time which every nutrient needs to be completely oxidised. Subject who consumed the high protein meal had the highest value of RQ at the end of the experiment whereas the subject who did not consume any treatment had the lowest. The results of the previous similar research studies do not much with the results of this study. Moreover they do not much with the hypothesis which cited in the beginning of the report.