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Effects and mechanism of L-Carnitine on weight loss
Xiaotian Liu1
1Department of Food Science and Engineering, College of Biological Science and
Technology, Beijing Forestry University, Beijing, China
Liuxt02@bjfu.edu.cn
Abstract. L-Carnitine, as an essential coenzyme in fat metabolism, can promote the metabolism
of human fat, accelerate the burning of fat, and may achieve the desired fat burning slimming
effect; This papers studies the effect of L-carnitine on weight loss and the possible side effects
it may bring to the human body, explains the weight loss principle and metabolic pathway of L-
carnitine from the molecular level, and discusses the relationship between exercise and L-
carnitine in combination with metabolism, give the author recommendations for using L-
Carnitine. A brief explanation of the current state of development of L-carnitine diet pills
(supplements) in the field of health was described. Combined with the comparison and summary
of existing databases, it is concluded that L-carnitine alone is not an ideal choice, and L-carnitine
alone is used without exercise: For people with normal weight, L-carnitine has no effect on
weight loss. Obviously, only overweight, and obese people, taking L-carnitine combined with a
lot of training have obvious weight loss effect.
Keywords: L-carnitine, Lose weight, supplements.
1. Introduction
Overweight and obesity are one of the world's leading health factors, while they also play an important
role in the progression of several noncommunicable diseases, including cardiovascular disease, diabetes,
and cancer [1, 2]. According to a World Health Organization report, more than 2 billion adults aged 18
and over are overweight. In fact, obesity rates continue to increase globally, and obesity rates tend to be
higher in high-income countries.
With the improvement of living standards, the continuous development of the health industry,
people's requirements for the body are getting higher and higher, following fat loss training, healthy diet,
drugs and surgery, a variety of anti-obesity drinks, diet pills and supplements are also widely mentioned;
L-carnitine is one of the much-hyped diet pills, and manufacturers advertise its powerful weight loss
benefits, inducing some people who do not have a deep understanding of their situation to eat it by
mistake: they claim that it can lose weight, but still does not have a clear effectiveness to prove that.
This article wants to let the public understand the actual role of L-carnitine and choose their own "health
path" reasonably.
This article will summarize the relationship between L-carnitine and exercise, the mechanism of L-
carnitine's ability to lose weight, the effect on the liver, and the impact on human indicators in obese
people. And whether it is suitable for obese people to lose weight and the side effects to them and give
advice on whether L-carnitine should be used.
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DOI: 10.54254/2753-8818/4/20220523
© 2023 The Authors. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0
(https://creativecommons.org/licenses/by/4.0/).
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2. Metabolic mechanism of L-carnitine
2.1. The Role and Synthesis Mechanism of L-Carnitine
The most important role of L-carnitine is to act as a carrier for transporting fatty acyl-CoA to the
mitochondrial matrix on the inner membrane of mitochondria, allowing β-oxidation of fatty acids to
provide energy for the body (Figure 1). Lactic acid is the end product of the body’s anaerobic glycolysis
and is an important cause of body fatigue. L-carnitine can reduce the concentration of lactic acid
produced by anaerobic exercise, relieve the accumulation of lactic acid, and avoid muscle fatigue. L-
carnitine controls the value of free Co-A/Acetyl-CoA within a certain range, this ratio will inhibit the
activity of pyruvate dehydrogenase and affect energy metabolism, expel acyl groups, and avoid acyl
metabolism poisoning in the body [3]. Carnitine can promote the excretion of shore by reacting with
ammonia in urine and prevent the accumulation of ammonia. L-carnitine is also an antioxidant that
captures free radicals by preventing the formation of iron chelates. When the primary antioxidant
defense barrier cannot completely remove free radicals, L-carnitine participates in the repair process,
which is beneficial to repair the (cell) membrane in time. L-carnitine also has a certain effect on the
absorption of fat-soluble vitamins, calcium and phosphorus. Adding L-carnitine to peritoneal dialysis
fluid can improve a series of symptoms caused by carnitine deficiency in uremia patients on the one
hand and improve the long-term high glucose effect of peritoneal dialysis fluid on the inhibition of
peritoneal skin cell proliferation and reduce high glucose levels. Induces apoptosis of peritoneal
mesothelial cells.
In body, the main physiological function of L-Carnitine is to act as a carrier of fatty acid transport,
in the form of acetyl L-Carnitine, the medium and long chain fatty acids are transferred from the
extramembrane membrane of the cellular mitochondria to the membrane, so that it oxidizes in the
mitochondrial matrix to produce energy and improves the body's tolerance.
How to reach the target cells of the muscle is the most complex problem now. There has been
speculation that long-term use of L-Carnitine will increase the amount of L-Carnitine reserves in muscle
cells to a certain extent, but there is no definitive evidence to prove this. The absorption rate of carnitine
from food in the human body is about 63% to 75%, while the absorption rate of L-carnitine from dietary
supplements is only 14% to 20% [3]. Most of the L-carnitine in food is catalyzed by the intestinal
mucosal acylcarnitine to be absorbed by the intestinal mucosa, and the rest is used or degraded by
microorganisms in the intestine.
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Figure 1. Endogenous L-carnitine synthesis pathway [3].
2.2. Effects of L-Carnitine on Metabolism
Lipid metabolism: Abnormal lipid metabolism can cause problems with obesity, and obesity can cause
more diseases to be induced or worsened. Exercise combined with L-Carnitine supplementation
promotes metabolism, improves physical condition, and reduces body fat percentage. The most
important function of L-Carnitine is to perform β-oxidation in the mitochondria, promote the positive
progression of the tricarboxylic acid cycle (TCA) and produce adenosine triphosphate (ATP) (Figure 2).
Amino acid metabolism: within the body, L-Carnitine is synthesized from raw materials such as
methionine and valine, so it regulates by negative feedback; In addition, as a carrier, some metabolites
containing branched-chain acyl groups (usually valine, leucine and isoleucine) of the mass transport, so
that can accelerate the synthesis of these amino acids to achieve the purpose of accelerating metabolism.
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Figure 2. The simple principle of action of L-Carnitine involved in intramuscular fat burning.
3. Relationship between L-Carnitine and Exercise
3.1. Effect of Exercise on L-Carnitine Level
At present, the relatively agreed view is that the exercise process does not have much effect on the total
content of carnitine in the plasma, the free L-carnitine content decreases, but the acylcarnitine (AC)
content increases, and there is no obvious gap about the total carnitine content in the body between
normal people in a quiet state and well-trained athletes. Xiequn Li et al. observed that the concentration
of total plasma carnitine content before and after athlete training did not change, and L-carnitine is an
essential cofactor of fatty acid metabolism, which can be used as a carrier to transport long-chain fatty
acids from outside the mitochondrial membrane to the mitochondrial membrane for β-oxidation in the
form of acylcarnitine so the content of acylcarnitine increases accordingly [4]. There is currently no
conclusive as to what exactly caused this phenomenon. Exercise can affect the metabolism of L-carnitine,
if it is a long-term heavy load of exercise, it can increase the discharge of carnitine in the urine.
Exogenous supplementation with L-Carnitine can improve the body's ability to use fat to provide energy
and prolong the tolerance time of exercise. After exercise, the concentration of L-carnitine in human
muscle tissue decreases, so appropriate supplementation of L-carnitine is beneficial to improve
explosiveness and enhance tolerance [5].
3.2. Effect of L-Carnitine on Athletic Ability
A certain amount of L-carnitine intake before exercise can significantly increase the maximum oxygen
consumption in adults [6]. Because long-term adherence to aerobic exercise can improve the function
of the respiratory and circulatory systems and enhance the maximum oxygen uptake and utilization of
each cell, aerobic exercise combined with supplementation of L-carnitine supplements to promote the
body's maximum oxygen uptake may accelerate the role of aerobic exercise, so that significantly
increase the oxygen uptake. Experiments by Giamberardino et al. confirmed that L-carnitine can
accelerate fatty acid transport rate and increase fatty acid oxidation, thereby significantly reducing body
weight [7]. There is currently no unanimous conclusion on the effects of aerobic exercise
supplementation with L-Carnitine. However, most opinions agree that supplementing with a certain
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amount of L-carnitine has a certain effect on improving aerobic exercise [8]. In addition, during extreme
exercise and ultra-extreme exercise, when muscles begin to use the energy obtained under anaerobic
conditions to produce lactic acid, L-carnitine can improve the body's anaerobic capacity by removing
too much lactic acid.
4. Effect of L-Carnitine on weight loss
The underlying mechanism of how L-Carnitine improves obesity is shown in Figure 3. In principle, L-
carnitine is a substance that does promote fatty acid oxidation, but at the same time we must not forget
that we can synthesize this substance ourselves. According to Nasir Talenezhad research, through meta-
analysis and inputting relevant keywords, and incorporating systematic evaluation criteria,
comprehensive evaluation of weight, body mass index (BMI), waist circumference (WC), body fat
percent (BFP) and body fat mass (BFM) with their standard deviations (SDs) and other body indicators,
including Asia, Europe, America and other places. Its results, presented in studies with no conflict of
interest or unrelated industry funding, were able to demonstrate that the use of L-carnitine-related weight
loss products can influence body weight, BFM and BMI [9]. L-carnitine significantly led to weight loss
(1.21kg). But it worth noting that based on the analysis showing that obese and overweight adults were
more likely to lose weight and BMI in this study, L-carnitine use in normal-weight people is not very
ideal [10].
L-Carnitine produces about 0.02 g per 24 hours, which in general can easily meet the daily needs of
a normal person. To date, subjects in scientific studies have said that the dose of L-carnitine ingested
ranges from 2g-6g, and it varies from 1 month to 6 months continuously. However, each intake of 1 to
2 g is meaningless to the human body, the maximum intake of about 18% of the total amount of L-
carnitine can eventually reach the blood, considering the entire metabolic process, 1g of L-Carnitine can
only use 0.08g.
Figure 3. L-Carnitine improves the underlying mechanism of obesity [3].
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5. Effects of L-Carnitine diet pills (supplements)
5.1. Effect of L-Carnitine on Human Indicators in Overweight People
If the addition of L-Carnitine is really as effective as advertised, then it should be easy to find in
experiments, because after a certain cycle of ingestion of L-Carnitine, the body fat rate should have a
significant decrease. However, according to the results of the study, the reduction of body fat after
ingestion of L-Carnitine is not so effective in practical applications [11]. Based on it again, the results
of the experiment showed that among 36 women with an average age of 27 years, they were asked to
take a placebo twice a day (2 g each time) or L-carnitine twice a day for two months and were allowed
to exercise 4 times a week for 30 minutes each time and did not prescribe a diet. In this way, a lot of
uncertainty can be circumvented and only two variables - training and L-carnitine supplementation can
be retained [12]. Except for the subjects who withdrew from the experiment due to dizziness and
diarrhea, the rest completed the experiment as required. But by the time the experiment was completed,
no one's body composition ratio changed significantly. The subjects in this experiment should be the age
of greatest interest in weight loss and fitness, that is, most of them should be potential targets of this
product, and they themselves are willing to use L-carnitine to help them work out. But as the results of
the experiment were, two hours of exercise per week combined with L-Carnitine did not improve their
figure in a few months without changing their diet. That is, they need to exercise more to possibly
achieve their goals. In addition, the basal metabolic rate (BRM) of the subjects was observed to be
increased from the experimental data, which proved that the subjects were performing exercise plans,
but at the time of the experiment, they were not required to change their eating habits or necessarily eat
according to a certain pattern. That said, they may eat more. If they increase the amount of training again,
as a countervailing to the further increase in their food intake, and at this time reach an energy balance,
and eventually do not use much fat, so that the body fat rate does not change much.
5.2. Side Effects of L-Carnitine Supplements
As a weight loss pill, it should be used by consumers for a long time to achieve weight loss goals.
However, long-term use of L-carnitine will lead to decreased spleen and stomach function, resulting in
constipation or diarrhea, so it is not recommended to use it. The harm of L-carnitine is mainly reflected
in the digestive tract and the heart. Rapid, palpitation, shortness of breath and other symptoms can easily
induce arrhythmia. In weak patients, cardiac function is affected. Large doses of L-carnitine can cause
diarrhea in patients, and such as dizziness, mental health, and decreased concentration. Causes diarrhea,
dizziness, and nausea (in the report on the effects of L-carnitine on overweight women, 4 of 36 dropped
out of the experiment due to diarrhea) [13]. These side effects are not fatal or life-threatening, but they
can make people uncomfortable.
6. application of L-carnitine to diet pills
In general, L-Carnitine slimming products are usually divided into beverages and tablets. In the.
advertisement. of L-Carnitine slimming products promoted by manufacturers, the ability to quickly
consume fat, promote metabolism and decompose fat and convert them into energy is the most
mentioned point, or it promotes the conversion of fat into energy. At present, the emerging products are
functional drinks, and the taste of the drink is used as another selling point to attract consumers. Another
noteworthy point is that in their publicity, a large number of manufacturers will say that L-carnitine and
sports will be better combined, which is a very interesting thing, never manufacturers are willing to
promote the effect of using L-carnitine alone.
7. Conclusion
The use of L-carnitine supplements to achieve weight loss is not suitable for everyone, because it has
proved to be of little use. Because L-carnitine alone is of no use, in obese people, a small amount of L-
carnitine combined with exercise may help speed up the weight loss process, but this still needs to be
proven. If you must consume L-carnitine, the daily intake should not exceed 5g, and take it about 30
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minutes before exercise. Bodybuilders shouldn’t have high hopes for L-carnitine’s efficacy, its only
confirmed function should be as a placebo. According to the current 30 years of research, there is no
very accurate conclusion about some of the effects of L-carnitine, but L-carnitine is still hyped by
merchants and manufacturers as a weight loss drug or fat reduction supplement. So far, more research
reports that have not been funded by relevant companies have not provided clear evidence of weight
loss.
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