What is L-Carnitine?
L-Carnitine is an amino acid derivative formed within the body from the essential amino acids L-lysine and L-methionine. It plays a critical role in energy metabolism and is an integral part of the system that provides the human body with usable energy. L-Carnitine is found naturally in many foods, with red animal foods (such as beef and lamb) being the best sources. Other good sources include fish, poultry, and milk [1].
What Does L-Carnitine Do?
This nutrient plays several roles in the body. Still, one of its most important is transporting long-chain fatty acids into the mitochondria, the energy-producing factories of our cells, where they are burned for fuel [1, 2]. Muscle metabolism relies on this process, and physical exercise depletes the body’s stores of L-Carnitine [3].
In addition to its role in energy production, L-Carnitine shunts off excess acetyl-CoA from the mitochondria, helping the liver function and metabolise lipids [2]. It has been proposed that direct administration of L-Carnitine supplements helps burn liver fat and steady insulin levels, perhaps preventing Non-Alcoholic Fatty Liver Disease (NAFLD) from progressing to its fullest extent [2].
Furthermore, it has been proposed as a treatment for cardiac or heart failure and angina (chest pain) and weight loss through its antioxidant properties that directly lower oxidative stress [1]. It has been suggested that carnitine supplementation enhances exercise recovery by increasing blood flow to muscle tissues, relieving muscle soreness (for instance, after performing the biological maximus muscle-building routine) and limiting any hypoxic stress-induced tissue damage [4].
What is L-Glutamine?
L-Glutamine is classified as ‘semi-essential’ as the body produces it in itself and, therefore, can be obtained through food. It is the most abundant free amino acid in the bloodstream and skeletal muscle and holds significant importance in multiple biochemical processes [5, 6, 7].
L-Glutamine is an amino acid – one of a group of 20 essential and nonessential amino acids from which proteins are composed. Essential amino acids must be obtained through food, whereas nonessential amino acids, such as L-Glutamine, are produced naturally by the body in sufficient quantities when circumstances are expected [7].
What Does L-Glutamine Do?
L-Glutamine is a nitrogen shuttle, sequestering too much ammonia and combining it to form urea. It also helps to make other amino acids, glucose, nucleotides, protein, and glutathione, a potent antioxidant [5].
L-Glutamine is a critical intermediate in the reciprocal relationship between carbohydrates and proteins. It contributes to fibroblast, lymphocyte, and enterocyte growth, improves nitrogen balance, and helps maintain glutamine levels in skeletal muscle [8].
L-Glutamine is a precursor in protein production and is critical for cell growth, lipid metabolism, insulin secretion and other nutritional functions in cellular homeostasis [6].
Moreover, L-Glutamine has proved therapeutic in its own right. It can be shown to improve intestinal villous height, induce gut mucosal cellular proliferation and maintain mucosal integrity. It is effective at decreasing the incidence of infection in trauma and surgical patients. It may offer significant benefits in the condition where muscle glutamine is most depleted – in cancer patients [5].
L-Glutamine plays a modulatory role by protecting the brain against ischaemic injury via its ability to up-regulate the stress protein (heat shock protein-70), reduce oxidative stress and neuronal apoptosis, and increase the production of superoxide dismutase, glutathione, and brain-derived neurotrophic factor [9].
L-Carnitine vs L-Glutamine: Differences and Similarities
L-Carnitine and L-Glutamine are critical compounds in the body, playing crucial roles in various metabolic processes. However, they have distinct functions and are involved in different pathways.
L-Carnitine is used to metabolise fatty acids and transport the acyl groups into the mitochondrion, where the fatty acids' beta-oxidation occurs. This amino acid is synthesized in the liver, kidney, and brain from lysine and methionine [10]. It also regulates the level of acyl-CoA and CoA in mitochondria. The cytosol provides acetyl moieties for acetylcholine synthesis and participates in the catabolism of L-Glutamine, increasing the formation of glucose and urea from L-Glutamine [11, 10].
On the other hand, the most abundant amino acid in the human body, L-Glutamine, is essential in numerous metabolic pathways [12]—it’s the principal fuel of glutaminolysis, a central metabolic pathway of many aggressive cancers [12]. It’s a major gluconeogenic precursor and a shuttle for interorgan carbon transport [13]. It’s a precursor to the biosynthesis of proteins. It also contributes to nutrition-related metabolic processes, including cell growth, lipid metabolism, and insulin secretion [6].
In terms of similarities, both L-Carnitine and L-Glutamine are involved in metabolic processes and contribute to energy production in the body. They are both synthesized in the body and can be obtained from dietary sources.
However, they’re known as (and act as) different compounds in the body, providing energy through different metabolic pathways. So, L-Carnitine is involved in fatty acid metabolism, compared with L-Glutamine, and is a significant player in protein synthesis, gluconeogenesis, and other roles. L-Carnitine has been seen to promote weight loss [10], whereas L-Glutamine is used in medicine to help patients with impaired intestinal health [6].
Is L-Carnitine or L-Glutamine Better For Weight Loss?
Both L-Carnitine and L-Glutamine have shown potential benefits for weight loss. However, the effects can vary depending on individual factors such as body composition and lifestyle.
L-Glutamine supplementation promotes weight loss in obese and overweight female patients. The body weight and waist circumference significantly decreased after glutamine supplementation in a pilot RCT (body weight from 85.0±10.4 Kg to 82.2±10.1 Kg; waist circumference from 102.7±2.0 cm to 98.9±2.9 cm) [14].
Conversely, taking L-Carnitine pills, on the other hand, was reported to be a positive factor in weight reduction. It was indicated by a meta-analysis that L-Carnitine supplementation decreased the level of weight by -1.129 kg, body mass index (BMI) by -0.359 kg/m², and fat mass by -1.158 kg. [15] In another study investigating the potential of L-Carnitine in weight reduction revealed that L-Carnitine supplementation didn’t appear to promote weight loss among moderately obese women [16].
In conclusion, both L-Glutamine and L-Carnitine have therapeutic implications for weight loss. Still, individual variation in response to its supplementation can be used post-workout in a balanced, healthy diet and exercise routine. It is also essential to consult with a healthcare professional before starting any new supplement regime.