Carnitine: money is wasted
Fat burning and "magic" carnitine
Ruslana Radchuk, ABC magazine
Among those who hope for a miracle pill in pursuit of a beautiful figure, L-carnitine is one of the most popular dietary supplements. The domestic dietary supplement market is flooded with carnitine, which is offered as an effective fat burner, as well as as an "energy supplement" for bodybuilding and aerobics classes. On many sites, you can even find a description of the mechanism of action, recommendations on dosage and intake regimens, and, of course, a lot of enthusiastic consumer reviews.
But what do scientists say about the effectiveness of carnitine? In order not to be misled, you will have to plunge a little into the biochemistry of your own body. At the same time, we will find out how fat is burned and what it depends on.
Anabolism – catabolismA living cell constantly balances between polar processes – oxidation and reduction, accumulation and decay, life and death... Metabolism and energy in the body and in each of its cells – metabolism – represents two multidirectional processes: catabolism (decomposition of complex organic compounds to simpler ones with the release of energy) and anabolism (synthesis of proteins, fats, carbohydrates, nucleic acids and other complex biomolecules currently needed due to the energy and simple molecules obtained on the counterflow of metabolism).
Among other things, sensitive molecular sensors are involved in maintaining homeostasis (constancy of the internal environment of the body), which effectively detect deviation in one direction or another and "switch" systems to synthesis or combustion. One of such effective sensors in living organisms are special enzymes-kinases, which remain unchanged under evolutionary pressure in yeast, plants, and animals. In animals, they are called AMPK (AMP-activated protein kinase). They capture the energy status of the cell and, when the "cellular fuel" – ATP – disintegrates and the concentration of adenosine monophosphate – AMP increases, they are activated, directly or indirectly starting the machinery of the whole organism to supply fuel to the cell and at the same time turning off the energy–intensive processes of fat storage. The synthesis of enzymes necessary for fat burning and proteins serving the energy production process is enhanced, transport systems that supply fuel to the energy stations of the mitochondrial cell are activated…
Now we have come close to what is the fuel for the body that gives us energy.
First of all, it is glucose, which, provided sufficient oxygen is supplied, decomposes to pyruvate (pyruvic acid), or (with anaerobic, oxygen–free glycolysis) - to lactic acid. In both cases, the energy obtained is enough to attach two phosphoric acid residues to two AMP molecules and again obtain two energy molecules of adenosine triphosphate.
During physical activity, glucose dissolved in the blood is first "burned". The signal about the lack of fuel enters the brain, which in response sends the body a command to start consuming glycogen stored in the liver – "animal starch". But for a long time these 100-120 grams of "light" carbohydrates will not be enough: with high energy costs, more serious sources are needed.
The inviolable fuel reserve for ATP production is lipids deposited in adipose tissue. We will focus on them in more detail, because it is their burning that carnitine contributes to – according to its sellers and manufacturers.
Lipids are deposited in the form of fats – triacylglycerols, which, under the action of an activated lipase enzyme, are split into one molecule of glycerol and three molecules of fatty acids. This is called fat mobilization. In addition, lipase is activated by some other hormones, such as adrenaline and glucagon. Fat breakdown products enter the bloodstream. Glycerol is retained in the liver and, when the need for high energy consumption ceases, and the blood glucose level returns to normal, it is used together with sugars to restore glycogen reserves. And fatty acid molecules are delivered to muscle cells, where they are just needed.
By themselves, fatty acids are chemically inert, and in order for them to enter into subsequent chemical transformations, they need to be activated. With the help of the enzyme thiokinase, the so-called coenzyme A binds to the fatty acid molecule and an energy-intensive acyl-CoA compound is formed, which is able to penetrate the cell membrane, but cannot overcome the double lipid membrane of the mitochondria. Here a tricky transport mechanism comes into play. There are special gates on the mitochondrial membrane – protein globules floating in the lipid bilayer, on which the "conductor" sits – the same carnitine. He temporarily attaches himself to atzil in place of KoA and climbs through the gate with him. Inside the mitochondria there is a KoA, to which the first gives this acyl, and he returns outside. The whole bulky structure is called a "carnitine shuttle". Having made its way into the mitochondria, acyl-CoA enters a complex beta-oxidation cycle, which leads to the synthesis of acetyl-CoA molecules, which are already fuel for the citrate cycle. The citrate cycle, also known as the Krebs cycle, or the cycle of cellular respiration, is a furnace where raw materials (acetyl–CoA and / or pyruvate) enter and in the process of dozens of successive reactions, each of which is provided by a separate enzyme, decomposes to water, carbon dioxide and energy–intensive molecules.
Please note: carnitine does not mobilize fats in adipose tissue, but works in muscles, where fatty acids arrived after mobilization.
Acetyl-CoA is formed not only from fats, but also from the aforementioned pyruvate. In addition, if there is a great need, even more valuable fuel can go into the furnace – proteins that break down into amino acids, which will also be obtained (decomposition of proteins for energy needs is already an extreme measure that the body is forced to go to, for example, prolonged starvation). But the final raw material for the furnace, which is obtained from proteins, fats, and carbohydrates, is acetyl-CoA.
CarnitineNow that we already know how this whole energy machinery works, we can focus our attention on carnitine.
It is obvious that when the body receives enough nutrients and does not waste them on physical exercises, all metabolic processes are set up to store fats in adipose tissue. Carnitine is idling in the muscle cell membrane. And eat it as much as you want, it will not lead to fat burning. In order for carnitine to work, it is necessary at least to give the body a signal that would switch the processes in adipose tissue from the lipid storage mode to the burning mode, which would lead to the mobilization of fats and their supply to muscle cells. Perhaps it will be more useful if we take carnitine during exercise?
It turned out that here, too, not everything is simple. Carnitine has been isolated for a long time, the mechanism of its action has been studied in detail, but the regulation of its synthesis and excretion from the body has long remained a white spot. This has led to speculative theories that carnitine, presumably, may be a limiting factor in the success of beta-oxidation of fatty acids. Pharmaceutical companies, without hesitation, splashed carnitine on the market as an absolutely undoubted stimulant of catabolism and a dietary supplement for athletes. And only by about 2000, a critical mass of studies had accumulated that refuted the limiting role of carnitine in metabolic processes. The AMRK fuel sensor subtly "feels" the energy deficit and turns on the catabolism system, and it also sensitively takes care of a sufficient number of all components for these processes. On the one hand, we consume enough carnitine with meat products, and as soon as a deficiency occurs, carnitine is synthesized in the kidneys and liver from the amino acids lysine and methionine.
The level of carnitine in various tissues of the body is a constant value, when there is a shortage of it, it is actively transported to the right organs, and the excess is immediately excreted by the kidneys. For example, in blood plasma its concentration is 60 micromol / liter, in the liver – 900 micromol / kg, in muscles – 40,000 micromol/ kg. During one hour of light physical exertion, neither the carnitine content nor the acyl-carnitine balance in the muscles changes at all. Only during heavy physical exertion with a lack of oxygen, an increase in the level of acyl carnitine in the muscles is observed, which may be a consequence of the accumulation of lactic acid caused by this temporary violation of metabolic equilibrium. And how did the level of carnitine in the blood plasma, which should have supplied carnitine to the muscles, change? Clinical studies show that there is no way!
Thus, the assumption that carnitine may be a factor limiting the intensity of beta-oxidation of fatty acids has not been confirmed. There is one animal study that shows the theoretical possibility of carnitine's action to accelerate oxidation – but not fatty acids, but glucose, and only in heart muscle cells, but no one has yet found even such an effect in a healthy person.
Multiple clinical studies of the relationship between the consumption of different doses of carnitine and exercise in untrained and trained people have NOT confirmed its effects on metabolism.
What happens to carnitine when it gets into the body in the form of an expensive pill?The bioavailability of carnitine when ingested is 5-15%, no more.
If at the time of using carnitine the body does not have a need for it, then after swimming for some time in the blood plasma, it is completely excreted in the urine. Some nutritionists maliciously call the use of carnitine the production of expensive urine.
A completely useless product?Of course not.
A number of diseases have been described that are associated with disorders of carnitine synthesis, its transport, metabolism and maintenance of homeostasis. These can be hereditary diseases, and the consequence of violations of one of the many sites of this coordinated mechanism of regulation acquired as a result of various diseases. These are cancer, diabetes, Alzheimer's disease, kidney disease, and a number of other diseases that have been successfully treated with carnitine drugs for a long time.
The use of carnitine by vegans may be justified, since they do not eat meat – the main source of carnitine. But, as studies show, for a healthy person, even one who puts his body in order with physical exercises, additional carnitine is an extra waste of money.
Related links:
Eric P Brass, Supplemental carnitine and exercise – American Journal of Clinical Nutrition, Vol. 72, No. 2, 618S-623s, August 2000
Carnitine: The Science Behind a Conditionally Essential Nutrient
Carnitin im Sport: Die Wahrheit
Portal "Eternal youth" http://vechnayamolodost.ru30.08.2011