Garcinia cambogia is an exotic fruit whose dried rind contains high concentrations of hydroxycitric acid (HCA) at levels ranging from 10% to 30%. This fruit acid is closely related to citric acid, which is a key component of the metabolic pathway (the citric acid cycle) through which cells derive energy from carbohydrate and protein. Garcinia cambogia is mainly marketed for weight loss and appetite suppression.
How does Garcinia cambogia work?
The hydroxycitric acid present in Garcinia cambogia extract blocks a metabolic enzyme (adenosine triphosphatase citrate-lyase) which is needed to convert citric acid to substances (oxaloacetate and acetyl coenzyme A) involved in fatty acid synthesis.
By competitively blocking the citric acid cycle, hydroxycitric acid supplements work by reducing the conversion of excess dietary carbohydrate into fat. Instead, hydroxycitric acid causes excess carbohydrate to be stored as starchy glycogen in muscle and liver cells.
These effects interfere with the main metabolic cycle involved in energy production in cells. In fact, the citric acid cycle is arguably the most important series of metabolic reactions that occurs in your body. Also known as Krebs cycle after the biochemist, Sir Hans Adolf Krebs who shared a Nobel Prize for its discovery, the citric acid cycle takes place within the mitochondria of all your cells, with the exception of mature red blood cells (which lack mitochondria).
While hydroxycitric acid may help to curb appetite and promote weight loss, it has the potential to cause serious side effects and its safety has been called into question. Given that it is such a popular supplement, you would expect it to be highly effective for weight loss, but does Garcinia cambogia work?
Garcinia cambogia and weight loss
Some early studies found that taking hydroxycitric acid supplements for four weeks produced weight losses of between 2.2kg and 5.5kg with no other changes in calorie intake or lifestyle.
However, other trials have not find any weight changes in people taking Garcinia cambogia extract for ten weeks, and a study published in the JAMA did not find any significant weight loss in men and women taking Garcinia cambogia (equivalent to 1500mg hydroxycitric acid per day) compared with placebo over 12 weeks.
A meta-analysis which combined the results of 9 clinical trials, involving data from 465 people, found a small but statistically significant difference in body weight (0.88 kg greater reduction) between those taking Garcinia extract or hydroxycitric acid compared with placebo, in trials lasting up to 12 weeks. This translates to about 1% in body weight loss more than with placebo, which is not that impressive for a three-month intervention.
Is Garcinia cambogia safe?
A safety assessment of Garcinia cambogia and hydroxycitric acid published in 2012 found there was little evidence to support their potential effectiveness and long-term benefits. Most studies involved low numbers of people and none lasted more than 12 weeks.
A follow-up safety assessment of hydroxycitric acid, published in 2017, again concluded that there is a lack of adequate safety data in humans – especially in relation to the male reproductive system; high doses in animals has been associated with testicular shrinking and lowered sperm counts.
As Garcinia cambogia supplements affect the citric acid cycle, which is key to cell energy metabolism, they may have serious side effects in people with pre-existing metabolic disorders, such as diabetes or polycystic ovary syndrome, or who are taking other medications – especially those that are metabolised by a liver enzyme called CYP2B6.
If you have diabetes, or are taking any prescribed drugs for any condition, avoid Garcinia cambogia supplements to prevent liver side effects. If you do choose to take them, avoid alcohol to help limit effects on the liver. Instead, seek weight loss advice from your doctor. You are likely to achieve better results from following a lower glycemic index diet or the Mediterranean-style DASH diet, for example, especially if you have high blood pressure.
Garcinia cambogia side effects
Non-serious side effects reported in clinical trials include headache, skin rash, the common cold, and gastrointestinal symptoms such as nausea or abdominal pain (which may relate to liver changes). In one study, these gastrointestinal side effects were twice as common in those taking Garcinia extracts compared with placebo.
In real life users, there have been a few case reports of serious side effects with Garcinia cambogia, ranging from liver, heart, kidney and testicular toxicity (with decreased sperm counts) to muscle pain.
Taking Garcinia cambogia has been found to raise levels of liver enzymes in some people within one week of starting to take it. In one case, Garcinia cambogia was associated with liver failure that required transplantation in a 34-year-old male who took two 80 mg capsules of a Garcinia cambogia 5:1 extract (equivalent to 400mg of standard preparation) three times daily before meals for five months.
One woman with type 2 diabetes took Garcinia cambogia extract for a month and lost around 40 pounds in weight, but was then admitted to intensive care with diabetic ketoacidosis and pancreatitis. As she was also taking nine prescribed medications, and had significantly cut back on food intake, it was unclear whether or not the Garcinia cambogia was the cause.
While these cases are unusual, and certainly more rare than those associated with many prescribed drugs, it is important to be cautious. If you decide to take Garcinia cambogia for weight loss, seek medical advice first.
If you have diabetes, or are taking any medications, it is best to avoid Garcinia cambogia as interactions are likely due to the way it affects cell metabolism. Garcinia extracts should never be taken during pregnancy or breast-feeding.