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Lipids, that are important for human organism, contain of triglycerides(neutral fat), phospholipids and steroids, including products of their metabolism.
By triglycerides hydrolysis glycerol and free fat acids are released(FFA), that are in mitochondrias subjected to β – oxidation process till the stadium of acetile rest, when decompositing is continued in Krebs cycle(lemon acid cycle).
Except of being important energy source, minimal lipid amount in organism is necessary to enable supplying with essential fat acids(linolein acid) and vitamins soluble in fats. Essential fat acids enter the composition of cell membrane, and influent its permeability, or moving various elements between cellular and intercellular space. Along with that, this fat acids are important for cholesterol metabolism, and also present hormone precursors for similar compounds – eicosanoids, that are important carriers of important functions in organism.
Small amount of triglyceride fraction is located in muscle cells. In one kilogram of muscle mass is located 5-15g of lipids, which represents 5% of total amount of lipids in adipose tissue.
Some amount of lipids that circulate in blood is connected to albumins.
At untrained people, fat reserves are 20-35% at females and 10-20% at males, and they are located mostly in subcutaneous adipose tissue. At athletes, adipose tissue is 5-15% at males and 10-25% at females, which is related to sports discipline as well. This amount of fat(around 7000kcal/kg) has huge influence and represents a great source at long physical activities, which have small intensity.
In soccer average athlete composition looks like this(for males): muscles 50-53%, fat 8-10%, bones 18-20%.
During chronic food apstinence, fat become dominant source for energy gaining. However, in this circumstances, some amount of carbohydrates is necessary for Krebs cycle. Then the process of gluconeogenesis is being activated, to secure the minimum amount of glucosis.
In order to come to increased lipids oxidation, it is necessary to be activated the whole series of chemical reactions, enzymes and hormones, so some time is needed to establish stabile condition(20 minutes). In the meantime, physical work is done by huge part on the account of carbohydrates. It is necessary first to activate stress hormones, like adrenaline, noradrenaline and ACTH, and decrease insuline activity during that. Flower of stress hormone increase the activity of enzyme lipase, and also the concentration of FFA, which originates from fat depoes.
Training features – intensity, lasting, carbohydrates availability, conditionate the degree of lipids utilization as an energy substrate. At high intensity physical work that is present in the most of sports disciplines, CHO availability is the factor that limits work. An amendment for this is the fact that this is oxygen energy equivalent, or energy amount that is gained from fat and carbohydrates by consumption of same oxygen amount, bigger than when an energy substrate are used carbohydrates.
In trainings for endurance increase, capacity of skeletal muscles to use lipids as an energy substrate is increasing, so carbohydrates are spared. Along with that training increases ability to release FFA quickly, or substrate availability is increased. It is also known that at “long-runners” fat resereves in fibers are increased, as a result of adaptation on intensive spending of this substrate.

Intake and lipids supplementation

In athletes’  nutrition carbohydrates intake should be 60-70%, and fat intake 20-30%. Reduction of fat intake can be done by non-fat meat intake, so as preparing the food with minimal use of fat. Plant oils should dominate in nutrition, and also saturated fat acids intake should be regulated(under 10%). Essenital fat acids, that have significant functions in organism, should be at least 1-7% in the nutrition.
During athletes nutrition planning, it is needed to regulate fat intake, increase carbohydrates intake, and keep energy balance along with that. For athletes that are related to long-term(ultra-endurance) activities(marathon, triathlon, mountain climbing…) small, often, easy digestible meals are an option, which contain prescribed relation CHO/proteins/fats.
Fat acids for which there is special interes in athletes nutrition are omega-3 fat acids and medium chain triglycerides(MCT). Omega-3 fat acids, just as others polyunsaturated fat acids, enter the composition of erythrocytes cell membrane; so it is thought that supplementation with this fat acid positively influences to oxygen take over in erythrocytes, and along with that on blood oxygenation, which is special for the ones that train on high altitudes. It is shown that MCT’s are rapidly absorbed in digestions, easy transported to mitochondrias(with the help of carnitine), where they become digested. Theoretically, it is thought that MCT’s are a good substrate, especially in long term sports activities. However, in researches is not shown that increased intake of these fat acids changed the expenditure degree of  CHO during exercising. However, in researches is not shown that increased intake of these fat acids changes the degree of CHO expenditure during training. Further researches are required.

"Athletes' nutrition", Marina Djordjevic Nikic

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