L-carnitine has risen in popularly with active supplement use cases for: weight loss, brain function, exercise performance, circulation, and recovery.Considered inexpensive and generally safe, there really isn’t any reason for supplement formulators not to weigh the inclusion of this ingredient (1).Though, the actual results produced by l-carnitine may be rather lackluster for its most popular application: weight loss (2)(3).Unless you are utilizing it correctly, of course? That’s the question that we plan to answer.What is l-carnitine?L-carnitine is a natural compound made in the body and also obtained in the diet by eating meat.While sites like WebMD call l-carnitine an amino acid, this isn’t actually true.L-carnitine is made from the amino acids l-lysine and l-methionine, but it is itself considered to be a quaternary ammonium compound (4)(5).We wouldn’t consider it an amino acid by function either. Instead we look upon l-carnitine as a metabolic co-factor similar to CoQ10 and/or malic acid which participate in cellular metabolism.What exactly does l-carnitine do?As we alluded to above, l-carnitine participates in cellular metabolism by facilitating the transportation of fatty acids within every cell’s mitochondria. That means l-carnitine is needed to effectively metabolize calories.Digging deeper, l-carnitine is also necessary for the maintenance of co-enzyme A (an energy source used during exercise). That means l-carnitine is necessary to exercise your hardest, and thus burn more calories.As you would expect, a body depleted of l-carnitine isn’t going to function that well.What do the 5 different types of l-carnitine do?There is more than just one type of supplemental l-carnitine, and they all have different use cases. Here is a review of each l-carnitine type.1. L-carnitine tartrateL-carnitine tartrate is the most common form of supplemental l-carnitine. It absorbs easily, saturates muscle tissue, and is cost effective. Athletes can benefit the most from this form, as prolonged exercise can result in carnitine stores depleting.The results from l-carnitine supplementation in athletes include reduced markers of muscle damage and improved recovery (8). However, in advanced level athletes who eat properly, l-carnitine has a less pronounced effect as their bodies are already self-optimized for l-carnitine production (9).2. Acetyl-l-carnitine (ALCAR)Acetyl-l-carnitine is the second most common form of supplemental l-carnitine. What makes acetyl-l-carnitine different form l-carnitine tartrate, is that the acetyl version is significantly more usable by the brain (10).Due to this, you will find that acetyl-l-carnitine in many memory and focus supplements (11) and is extremely popular in supplements that cater to age-related cognitive decline(12).Though, weight loss supplements will also sometimes choose ALCAR for its ‘premium’ grade. This may or may not improve weight loss above standard l-carnitine tartrate.3. Propionyl-l-carnitinePropionyl-l-carnitine is a more specialized form of l-carnitine, and we believe its use-case should be more specialized as well.Compared to l-carnitine tartrate and acetyl-l-carnitine, the propionyl version has a significant blood thinning effect not linked to nitric oxide (13). This makes propionyl-l-carnitine attractive in treatment for individuals with heart disease, blood pressure abnormalities, and circulation problems (14). Though, risks being a complication for dieters.In athletes, propionyl-l-carnitine may improve performance, but it is extremely dose dependent (15). Too little and nothing will happen, too much and effects can be negative.4. Pure l-carnitineMany brands advertise using ‘pure l-carnitine’. We have found that there really isn’t a free-form of l-carnitine available. Rather, these pure l-carnitine supplements are simply l-carnitine tartrate.5. D-carnitineD-carnitine is the ineffective d-isomer of carnitine (16). L-carnitine on the other hand is the effective isomer. You really don’t need to worry about this, as no proper supplement brand is out there trying to sell d-carnitine.However, if you were to notice it in the ingredients section, you should avoid it. Not only does d-carnitine lack the benefits of l-carnitine, but it also blocks natural l-carnitine from being utilized (17).Which type of L-carnitine is best for weight loss?Despite l-carnitine’s widespread use, there really isn’t a lot of clinical research studying the weight loss effects of this ingredient (in humans). From what we have found, l-carnitine tartrate is the preferred pick for both weight loss and exercise performance improvements.For weight loss, l-carnitine was found effective in a meta-analysis of 9 studies. The overall conclusion was that l-carnitine supplementation enhanced fat metabolism however over time its effects dwindled (18).This is likely due to the body adjusting itself over time to meet its own l-carnitine needs realizing that the diet isn’t going anywhere.For athletes (and dieters going to the gym), l-carnitine supplementation increases muscular l-carnitine concentrations which positively reduces the perception of effort (19). That means, your workout will feel easier.Something else we liked in the same study, was a comparison of acetyl-l-carnitine levels between groups receiving l-carnitine tartrate and not. They found that both l-carnitine and acetyl-l-carnitine was increased by supplementing with standard and pure l-carnitine tartrate.How can l-carnitine be used for weight loss?All of the positive studies that we have cited above all shared a similar dosing protocol.That is: take about 2 grams of l-carnitine tartrate per day, every day.The result?You should burn more calories as well as perform and recover better with exercise. Interestingly, this effect will be most predominant in the beginning, as over time your body will adjust to exercise and increase its own natural stores of l-carnitine.Who should take l-carnitine?Vegans in particular are low in l-carnitine due to a meat-free diet (20). If you are new to exercising, your body likely isn’t storing enough l-carnitine to adequately fuel your workouts. For both of these situations, l-carnitine supplementation can be an aid.Digging deeper, if your liver or kidneys aren’t the healthiest or are under stress; then l-carnitine may help. The majority of body-made l-carnitine is produced in the liver and kidneys.Overall, alongside a progressive diet and exercise program l-carnitine can be a notable weight loss aid. However, if you remain in a state of caloric surplus and do not exercise – then you are unlikely to experience any benefit at all.Are there any risks with l-carnitine supplements?The only risk that we found regarding l-carnitine supplementation has to do with increasing TMAO production in some individuals with specific gut flora (21). Basically, heavy meat eater that don’t eat enough vegetables have floras that seek to metabolize l-carnitine into TMAO. Though, with proper diet, the bacteria are happily occupied with healthy fibers. This is particularly a problem for anyone with atherosclerosis or hardening of the arteries.Final ConclusionAs you can see, l-carnitine has its pros and cons for weight loss. On one side, it isn’t going to do all the work for you. But on the other side, it can enhance the efforts you’re already making.So to answer our original question: if you’re dieting and exercising, then daily l-carnitine supplementation of about 2 grams should have an effect. This will be more pronounced based on the more exercise you perform, or if your diet generally lacks meat.What l-carnitine supplement should you take? While ‘fancy versions like QuadraLean do exist, we prefer to opt for any reputable brand providing pure l-carnitine tartrate capsules. From there, aim for 2,000 mg’s of l-carnitine per day, every day. The information on BWSB has not been evaluated by the Food & Drug Administration or any other medical body. We do not attempt to diagnose, treat, cure or prevent any illness or disease. This content is shared for educational purposes only. You must consult your doctor before acting on any presented information contained in this website, especially if you are pregnant, nursing, taking medication, or have a medical condition.Was this article helpful?