To burn fat for energy the body first degrades triglycerides to free fatty acids

Carnitine in the form of L-carnitine tartrate is a biochemical that is synthesised in the liver and kidneys from the amino acids lysine and methionine. Although it is made out of amino acids carnitine does not get incorporated into protein. Instead it has an essential function in the cell’s lipid metabolism. It is necessary for the transport of fatty acids across the mitochondrial membranes into the mitochondria where the fatty acids can be burned for energy in a process known as beta-oxidation. Without sufficient amounts of carnitine the body is unable to burn fat and has to use other sources of energy such as protein. An optimum level of carnitine is necessary for a high lean muscle to fat body ratio.

To burn fat for energy the body first degrades triglycerides to free fatty acids. The free fatty acids must then enter into the mitochondria to undergo beta-oxidation. However, fatty acids with chains longer than ten carbons cannot just diffuse across the mitochondrial membranes. Carnitine acts as a shuttle binding to fatty acyl-CoA esters to form acylcarnitine, which is transported across the membrane. The compound is then broken up by an enzyme located on the inner mitochondrial membrane, releasing carnitine which crosses to the outside of the mitochondrion, ready to take the next fatty acid across the membrane. Without this shuttle fatty acids cannot enter the mitochondrion, and can’t be metabolised.

Although carnitine can be synthesised by the body, and is therefore not considered a strictly essential nutrient, there is a lot of evidence that shows that consuming it in the diet is necessary for optimal levels. A study published in the in the Journal of Physiology in 2011 demonstrated that carnitine is elevated by 21% in the muscle of subjects taking a carnitine tartrate supplement for six months compared to subjects taking a placebo. The higher carnitine levels resulted in sparing of glycogen during low intensity exercise, showing that muscle cells were utilising fatty acids as fuel to a greater extent. Carnitine can therefore increase the amount of fat burned during exercise, an important factor for people trying to lower their body fat ratio.

Not only that, but the study also found that people who took carnitine had lower levels of lactate in their muscle after high intensity exercise. Lactate is the result of anaerobic respiration, when muscle cells are not producing sufficient energy through oxidation of carbohydrates or fats. The lactate buildup is responsible for muscle soreness after exercise and limits the amount of contraction muscles are able to do. A lower lactate level results in improved performance during workout and faster recovery afterwards.

In fact studies suggest that carnitine has ergogenic actions, improving performance in a work trial. This can be explained through its dual action on muscle metabolism during exercise. On the one hand it spares glycogen, by stimulating fat oxidation. On the other hand it decreases the amount of lactate produced, and lactate accumulation is one of the factors that limits how much a muscle can contract. One interesting fact that emerges from the studies with carnitine is that effects are only seen after prolonged use, of approximately six months.

However, another study revealed that carnitine can significantly improve recovery after exercise after only three weeks of taking the supplement. In the study volunteers taking L-carnitine tartrate, or a placebo, performed sets of squat repetitions. After the exercise the extent of damage to their muscle was assessed using MRI, and the levels of different hormones in their blood was measured. The researchers found that taking the L-carnitine tartrate supplement resulted in less damage to muscles than a placebo, and that levels of IGFBP-3 (insulin-like growth factor binding protein-3) levels were elevated. IGFBP-3 enhances the action of insulin-like growth factor, an anabolic protein secreted when the levels of growth hormone are high. Although the researchers did not find a difference in the levels of other hormones they studied, they hypothesised that, since carnitine reduces the damage to muscle, there would be more cells with intact receptors, in the group that took the supplement. More undamaged cells with hormone receptors could mean that the muscles react more strongly to the hormones, even if the hormone levels are not altered.

Carnitine was also observed to have a very beneficial effect on blood triglyceride and low-density lipoprotein levels. Presumably the optimal fatty acid metabolism that can happen when carnitine levels are elevated improve the blood lipid profile. High levels of triglycerides and LDL-cholesterol are associated with several diseases, including type II diabetes and heart disease. Carnitine is also thought to protect against type II diabetes by conserving muscle glycogen, which stabilised blood sugar levels.

Carnitine tartrate supplements were also shown to have an interesting effect on testosterone signalling. Whereas many of the supplements taken to increase muscle gain, such as BCAA amino acids or nucleotides, affect hormone levels by stimulating secretion of anabolic hormones such as testosterone, carnitine appears to increase the level of androgen receptors in cells. Testosterone achieves its anabolic effects, including increased protein synthesis and improved muscle gain by binding tot he androgen receptor and activating it. More androgen receptors make cells more sensitive to testosterone, in effect multiplying its effect. This makes carnitine a particular good supplement to take in combination with amino acids and biochemical that increase the levels of testosterone, since they will work synergistically to create an anabolic state.

Carnitine L-tartrate’s main function is to act as a shuttle transporting fatty acids across mitochondrial membranes for oxidation. Clinical studies show that taking a carnitine supplement does increase its level within cells, and does result in burning more fat. This obviously makes it easier to improve the lean muscle to fat body ratio. The change in muscle metabolism also has benefits during and after exercise. By burning more fatty acids the cells spare glycogen and appear to accumulate less lactate from anaerobic respiration. This results in less muscle damage, less exercise-induced soreness, so there is better performance during, and better recovery after the workout. Carnitine also appears to increase the amount of androgen receptors in muscle cells, making them more responsive to testosterone. Finally carnitine is a powerful antioxidant and helps protect the body from oxidative stress.

Further Reading:

L-carnitine tartrate boosts fat metabolism and improves exercise performance:

L-carnitine tartrate decreases exercise-induced muscle damage and improves recovery: