Metabolism

Metabolism includes all physical and chemical processes that place into the organism, and it is contained of two opposite processes – catabolism and anabolism.

Processes of new enzymes, hormones and compounds synthetizing that enable growth and renewal of various tissues and organs, are called ANABOLISM. At physically high active people anabolism, among other things, secures muscular mass  and cell enzymes growth, that should enable better usage of nutrients and oxygen in energy production process.

CATABOLISM  or destructive metabolism means various compounds degradation on its integral parts.

Production and energy consumption in organism represent basic part of methabolic processes.

Organism needs are defined as the amount of energy required to keep energy balance of the person whose alimentation and body composition, so as the physical activity degree is in accordance with good health.

Organism daily energy needs are contained of following elements:

·         Basal metabolism energy(BM)

·         Energy needed for normal daily activities(RMR – resting metabolic rate)

·         Energy for physical activity, without RMR

·         Metabolic response to the food – specific dynamic food effect

The most important factors that effect daily energy needs are gender, ages, body mass and physical activity.

Basal metabolism(basal metabolic rate- BMR) means energy consumption that is needed for basic life functions(CNS, heart, lungs…) conducting in the period of rest – in postapsortive condition.

Factors that have the most significant influence on BMR value are: gender, growth and body mass.

Energy required for basal metabolism has the biggest value during the infant period, and it is decreased during childhood, adolescence and grown age, and the least values are in old age.

Average difference between genders is 10-15%, and it is conditioned by body composition differences. Bigger basal metabolism values at men are the result of bigger muscular representation according to body fat component. Also individual variations between people exist, and they can be up to 10%, even if two people have same weight, height, gender, physical activity level…

Resting metabolic rate(RMR) means basal metabolism along with additional energy consumption connected to food digestion, and activities like: standing, sitting, reading, and other sedentary activities.

Approximate equation for men basal metabolism is:

BM  = 1 kcal/kg/h(4,184 kJ/kg/h)

Approximate equation for women basal metabolism is:

BM  = 0,9 kcal/kg/h(4,184 kJ/kg/h)

Values could be 10% less or bigger, according to individual genetic variations.

It is thought that basal metabolism drops 2% with every decade of aging.

Significant changes in body composition, like fat decrease, and muscle component increase in body composition, can lead to BM increase; this change can also be the income of increased activity level, and also energy consumption due to muscular mass increase or relation body area/body mass.

Energy intake for physical activities is the component of total consumption on which it can be affected by chose of physical activity type and lasting. This component of daily energy consumption is used for professional activities, like in athletes – for training.

Specific dynamic food effect is oxygen increase, or basal metabolism increase after the food intake. It is thought that specific dynamic effect, or mentioned increase, is 30% for proteins, 6% for carbohydrates and 4% for fat. Since the food is usually mixture, normal effect is 5-10%.

Energy consumption conditioned by physical work(sport, recreation) can be increased 50 times related to dream condition. Basic factor that influents the metabolism degree is work intensity. Type of activity matters. Harder and longer training will lead to higher energy consumption.

Other factors are training degree, deviation from optimal body mass, too much fat in nutrition… Increased energy consumption that exists during physical exercising leads to(along with adequate nutrition) leads to body mass reduction(fat). In some researches it is said that RMR after training was elevated 7,5-28% above normal, which lasted 4-6 hours.

There are more various ways which can lead to energy prize consumption. This value can be expressed in multiple ways: kcal(kJ)/ kg TM, as oxygen intake in time unit and in METs that can represent RMR. Following approximations should be followed:

1 kcal = 4,18 kJ

1l O₂ = 5 kcal

1 MET = 3,5 mol O₂ /kg/min ( oxygen consumption during rest)

1g of carbohydrates = 4 kcal

1g of proteins = 4 kcal

1g of fats = 9 kcal

BMR estimation formulas

Several prediction equations exist. Historically most notable was Harris-Benedict equation, which was created in 1919.

The original equations from Harris and Benedict are:

                                   13.7516m        5.0033h       6.7550a                           kcal

- for men,  P=( --------------- + ------------- -  ------------ + 66.4730)     ------

                                    1kg                  1cm               1 year                          day

                                        9. 5634m         1.8496h           4.6756a                           kcal   

- for women,  P=(-------------- + ---------------- -  ----------- +  655.0955)    -------

                                           1kg                 1cm                1 year                             day

where P is total heat production at complete rest, m is the weight, h is the height, and a is the age, and with the difference in BMR for men and women being mainly due to differences in body weight. For example, a 55 year old woman weighing 130 lb (59 kg) and 5 feet 6 inches (168 cm) tall would have a BMR of 1272 kcal per day or 53 kcal/h (61.3 watts).

It was the best prediction equation until 1990, when Mifflin introduced the equation:

              10.0m            6.25h         5.0a                  kcal

P = ( ------------- + ------------ - ----------- + s)   --------

               1kg                 1cm          1year               day     , where s is +5 for males and −161 for females.

According to this formula, the woman in the example above has a BMR of 1204 kcal per day. During the last 100 years, lifestyles have changed and Frankenfield showed it to be about 5% more accurate.

These formulas are based on body weight, which does not take into account the difference in metabolic activity between lean body mass and body fat. Other formulas exist which take into account lean body mass, two of which are the Katch-McArdle formula, and Cunningham formula. It should be noted, however, that the Cunningham formula is used to predict RMR instead of BMR.

The Katch-McArdle Formula (BMR):

·         P=( 370+ 21,6x LBM) , where LBM is the lean body mass in kg.

According to this formula, if the woman in the example has a body fat percentage of 30%, her BMR would be 1263 kcal per day.

The Cunningham Formula (RMR):

·         P= 500+( 22xLBM), where LBM is the lean body mass in kg

Since lean body mass is metabolically active vs. fat cells which need very few calories to be sustained, these formula tend to be more accurate, especially with athletes who have above average lean mass and little body fat.
To calculate daily calorie needs, the BMR value is multiplied by a factor with a value between 1.2 and 1.9, depending on the person's activity level.

Energy consumption during physical training is bigger if bigger muscle groups are included in work, and if it is trained with high intensity, continuously, during longer period of time.

 http://en.wikipedia.org/wiki/Basal_metabolic_rate#BMR_estimation_formulas

“ Athlete nutrition”, Marina Djordjevic Nikic