Weight Loss Supplements
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- GUAR GUM
- GREEN TEA
- CHROMIUM (CHROMIUM PICOLINATE)
- GARCINIA CAMBOGIA (HYDROXYCITRIC ACID)
- GREEN COFFEE EXTRACT
- RASPBERRY KETONE
- CONJUGATED LINOLEIC ACID
- CITRUS AURANTIUM (BITTER ORANGE)
- POLYGLYCOPLEX (PGX)
- IRVINGIA GABONENSIS (AFRICAN MANGO)
WHAT ARE THEY?
Weight loss supplements are, as their name suggests, dietary supplements that are promoted for body weight reduction. A wide variety of such products exist, ranging from vitamins and minerals to herbs/plant extracts, dietary fibres, and other compounds . They may be sold as isolated ingredients or as mixtures of multiple supplements. Such products are often marketed with claims of “clinically proven” effects and are commonly advertised on television and health-related talk shows . Manufacturers and promoters of weight loss supplements may describe their products using terms such as:
- “Metabolism boosting”
- “Melting” or “flushing fat”
- “Miracle” weight loss
- “Natural” weight loss
- “Magic bullet” or “scientific breakthrough” for obesity/weight loss
- Other hyperbole
Different weight loss supplements are claimed to work via a variety of mechanisms, including appetite suppression (i.e. making a person less hungry), “fat-burning” processes (i.e. increasing the body’s use of its accumulated fat), increasing the body’s overall energy use (i.e. “increasing metabolism”), and blocking fat/sugar absorption into the body . For the majority of supplements, these proposed mechanisms are based on theoretical ideas, test-tube studies, or animal experiments, and have not been reliably demonstrated in humans [1, 3].
Clinically Relevant/Meaningful Weight Loss
An important concept in obesity research (and all other areas of clinical research) is the notion of a “clinically relevant” or “clinically meaningful” effect. When a given drug or medical intervention (e.g. a proposed weight loss supplement) is tested for clinical effectiveness (i.e. does it work or not?), researchers aim to determine whether or not the drug/intervention in question has a “significantly different” effect from a control/placebo intervention (i.e. a “fake” or “sugar” pill). To determine if an effect is “significantly different” from a placebo, researchers use statistical calculations. If these calculations suggest that the effect is indeed different from a placebo, it is said to be a “statistically significant difference”. However, this conclusion does not necessarily mean that the effect is clinically relevant or meaningful. This is because “statistical significance” does not actually mean anything about the size of the effect.
For example, imagine two hypothetical drugs for weight loss: Drug “A” and Drug “B”. Drug A was found to promote a “statistically significant” weight loss of 0.5 lbs, while Drug B was found to promote a “statistically significant” weight loss of 25 lbs. Based on the researchers’ mathematical analyses, both drugs produced “statistically significant” effects – but Drug A was clearly much less effective than Drug B (0.5 lbs vs 25 lbs weight loss). That is, the size of Drug A’s effect was smaller. In fact, the effect of Drug A was so small that patients using it would probably not even notice the 0.5 lbs reduction in body weight and would likely not experience any health benefits from it. Therefore, while the effect of Drug A was statistically significant, it was not clinically meaningful or helpful for patients. In other words, Drug A is probably not effective for weight loss.
According to current clinical guidelines from the American Heart Association and The Obesity Society, a “clinically meaningful” reduction in body weight should be defined as a greater than 5% reduction in body weight (although a reduction of at least 3% might produce minimal benefits) . This means that, for a 150 lbs person, a reduction of 4.5-7.5 lbs would be considered “clinically meaningful”.
DO THEY WORK?
Generally speaking, no. There is little to no reliable evidence to support the use of dietary supplements for promoting meaningful weight loss.
WHAT'S THE EVIDENCE?
Quick Definition: "Systematic Review"
A systematic review (and/or “meta-analysis”) is a scientific study that examines the agreement between many clinical trials. Instead of looking at a single study, systematic reviews attempt to analyse the totality of evidence related to a topic. By doing so, the true answer to a given question can be more accurately estimated. For example, a single study might indicate that a particular treatment is effective, leading readers to believe that this treatment works. However, what if three other studies conclude that the same treatment does not work? A systematic review might analyse the data from all four of these trials and conclude (correctly) that the totality of the evidence indicates that the treatment does not work (3 say no, only 1 says yes). The relative importance of each study is determined by things like study size (number of participants – more is better), chance for bias, consistency of measurements, and many others.
Because of their strength, systematic reviews are generally considered one of the highest standards of evidence. However, they are also not perfect, and are subject to the quality of the contributing clinical studies. Hence, if only low-quality studies are used, low-quality results will emerge (a.k.a. “garbage in, garbage out”).
Many systematic reviews of the clinical evidence for weight loss supplements have assessed the overall effectiveness of the most common and best-studied products. The vast majority of these studies reach the same, or similar, conclusion: there is little to no reliable evidence to support the use of natural supplements/diet pills to promote meaningful weight loss [5-9]. For example, a 2013 systematic review compiled the results of 14 clinical trials that assessed the effectiveness of multiple plant-based supplements promoted for weight loss as “appetite suppressors” . After considering the data from all 14 trials, the authors concluded that “the evidence is not convincing in demonstrating that plant extracts used as appetite suppressants for weight loss in the treatment of obesity are effective and safe” . A 2011 systematic review came to similar conclusions . This study aimed to compile the results of 9 other systematic reviews (a “systematic review of systematic reviews”), each of which assessed numerous clinical trials of various weight loss supplements. In total, over 130 clinical trials were accounted for. These contributed to the conclusion that “the existing systematic reviews of clinical trials testing the efficacy of food supplements in reducing body weight fail to provide good evidence that any of these preparations generate clinically relevant weight loss without undue risks” . In other words, those supplements that produced the most promising results were either outweighed by potentially harmful side effects, or generated such small improvements in weight loss that they were unlikely to be actually helpful for patients and consumers. Other systematic reviews have arrived at similar or worse (i.e. no effect from supplements) conclusions [6, 8-9].
Reflective of this overall lack of evidence to support weight loss supplements, several medical bodies have warned clinicians and patients about the use of such products. The journals of both the American Academy of Family Physicians and The College of Family Physicians of Canada (CFPC) have published recommendations related to the use of weight loss supplements, emphasizing the lack of evidence that exists to support their effectiveness [10-11]. Similarly, a position statement published by The Obesity Society warns healthcare professionals that the marketing claims of most diet supplements are not supported by reliable scientific evidence . The Canadian Pediatric Society and CFPC also discourage the use of diet supplements for weight loss in children and adolescents [11, 13].
The specific evidence (or lack thereof) behind some of the most popular and common weight loss supplements is outlined below.
Chitosan is a carbohydrate that is closely related to and derived from chitin, the polymer found in the exoskeletons of insects and crustaceans. Chitosan is believed to bind to fat molecules in the gastrointestinal tract, thereby blocking their absorption into the gut. For this reason, it has been proposed as a weight loss aid by preventing the uptake of food-energy into the body. While this appears to be true in animal models [14-15], the evidence is not as flattering in humans.
A Cochrane systematic review of 14 clinical trials concluded that chitosan appears to promote weight loss in humans, but the effect is so small that it is unlikely to be of any significance for consumers . Compared to a placebo (a “fake” diet pill), the use of chitosan was associated with a 1.7 kg (3.7 lbs) reduction in body weight . However, the review also found that when only high-quality trials (i.e. more participants, longer duration, more rigorous methodology) were analysed, the apparent effect of chitosan on weight loss was even smaller (0.6 kg or 1.3 lbs). This highlights the fact that lower-quality, and potentially flawed, trials had a noticeable impact on the final estimate of chitosan’s effectiveness, thus further calling into question its true value as a weight loss aid. However, even if the questionable accuracy of some of the included trials was not a factor, both estimates (1.7 kg and 0.6 kg) fall below the recommended cut-off for clinically meaningful weight loss .
A more recent update of the above systematic review came to similar conclusions: “There is some evidence that chitosan is more effective than placebo in the short-term treatment of overweight and obesity. However, many trials to date have been of poor quality and results have been variable. Results obtained from high quality trials indicate that the effect of chitosan on body weight is minimal and unlikely to be of clinical significance” .
Thus, there is little evidence to support the use of chitosan as a weight loss aid.
Guar gum is a type of dietary fibre obtained from guar beans that is used as a thickening agent in food applications. Because of its fluid-thickening properties, it has been proposed as an appetite suppressant by giving users an increased sense of “fullness” (satiety). By suppressing appetite, it is suggested that guar gum can help consumers lose weight .
A systematic review analysing 11 clinical trials of guar gum for weight loss concluded that the overall evidence suggests that guar gum is not effective for this purpose . When compared to a placebo, guar gum was no more effective at promoting weight loss. A more recent clinical trial also suggested that guar gum ingestion has no significant impact on appetite reduction . Thus, the use of guar gum as a weight loss supplement is not supported by reliable evidence.
Green tea, either as a beverage or concentrated extract, is commonly promoted as a weight loss aid. It contains caffeine and compounds known as catechins, both of which are believed to “increase metabolism” and promote energy expenditure in humans . Unfortunately, the best available evidence does not support this belief.
A 2012 Cochrane systematic review analyzed 15 clinical trials of green tea for weight loss and 3 trials of green tea for weight maintenance . The study found that green tea does not promote significant reductions in body weight and does not contribute to weight maintenance . Similarly, a more recent systematic review found that green tea does not contribute to weight loss, but it does decrease body fat percentage, the percentage of body mass that is fat . Unfortunately, the authors point out that this apparent effect on body fat percentage was so small that it was not clinically important . Even two of the most positive (and older) systematic reviews of green tea for weight loss have demonstrated that any influence green tea may have on weight reduction is not clinically relevant for consumers [4, 22-23].
Therefore, overall, there is no reliable evidence to justify the use of green tea as a weight loss supplement.
Chromium (Chromium Picolinate)
Chromium is a metal that is required in the body in small quantities for normal metabolism. It has been proposed that chromium can also aid weight loss by promoting fat-burning metabolic processes and appetite suppression . However, the evidence to support this proposal is weak.
A 2013 Cochrane systematic review compiled the results of 9 clinical trials assessing the effectiveness of chromium supplementation as a weight loss aid . Overall, chromium was found to be associated with approximately 1 kg (2.2 lbs) of weight loss “of debatable relevance” when compared to control groups (placebo). However, the authors emphasized that the quality of the analysed studies was low, such that their results were considered highly questionable. The authors therefore concluded: “We found no current, reliable evidence to inform firm decisions about the efficacy and safety of [chromium] supplements in overweight or obese adults” . In other words, there was no reliable evidence to support the use of chromium for weight loss.
Another 2013 systematic review came to similar conclusions . This study, which combined the data of 11 clinical trials, found that chromium use was associated with a 0.5 kg (1.1 lbs) reduction in body weight – equivalent to only a 0.06% weight loss on average . Thus, as noted by the authors, the clinical relevance of chromium’s apparent weight-reducing effects is debatable . Additionally, the authors warned that their results should be interpreted with caution, given that the results of the included clinical trials were highly variable (high “heterogeneity”). Therefore, the true (and already low) value of chromium as a weight loss aid might be overstated.
Overall, there is little reliable evidence to support the use of chromium as a weight loss supplement.
Glucomannan is a dietary plant fibre that is used as a food additive for thickening. Like guar gum (above), it is thought to promote weight loss by increasing feelings of “fullness” (satiety) after eating. At least two systematic reviews have assessed the effectiveness of glucomannan as a weight loss aid, and both call into question its usefulness.
The most recent systematic review (conducted in 2014) compiled the results of 8 clinical trials of glucomannan for body weight reduction . Overall, glucomannan did not have a statistically significant effect on weight loss . As a result, the authors concluded that “there is no good reason to recommend glucomannan for body weight reduction” . An earlier 2008 systematic review was slightly more positive, but with similar results. This study, compiling 9 clinical trials, determined that glucomannan can account for a small reduction in body weight of approximately 0.79 kg (1.7 lbs), or a 1% decrease in mass . Unfortunately, as previously discussed, a change in body weight this small is unlikely to be important for patients . Therefore, as suggested by the 2014 study, there is little to no reliable evidence to support the use of glucomannan as a weight loss supplement.
Garcinia cambogia (Hydroxycitric Acid)
Garcinia cambogia is a fruit-bearing plant native to South Asia. It contains a compound called hydroxycitric acid, which is believed to promote weight loss by numerous hypothetical mechanisms . While extracts of Garcinia fruit have been highly popularised as over-the-counter weight loss supplements by the media (and more specifically, by a notable TV-doctor with questionable credibility ), there is little to no reliable evidence to support its effectiveness.
A systematic review of clinical trials assessing Garcinia extract as a weight loss supplement compiled the results of 9 studies to determine its effectiveness . Overall, Garcinia was responsible for producing a 0.88 kg (1.9 lbs) reduction in body mass of “borderline statistical significance” (i.e. it was just barely statistically significant), which represented approximately a 1% decrease in weight . As noted previously, and as suggested by the authors, such a small reduction in weight is of questionable importance for patients . Importantly, however, when only the most rigorous (i.e. highest-quality) trials were re-analysed, the apparent weight-reducing effect of Garcinia was found to be insignificant . In other words, the best available clinical evidence suggests that Garcinia extract is not effective for weight loss.
Green Coffee Extract
Green Coffee Extract (GCE) is a plant extract derived from raw (“green” or “unroasted”) coffee beans. It has been widely popularized and promoted as a weight loss supplement in the media (and, again, by a specific TV-doctor ). While some preliminary evidence supports such claims, it is of low quality and questionable significance.
A 2011 systematic review of 3 clinical trials of GCE for weight loss found that the supplement promoted a 2.47 kg (5.4 lbs) reduction in body mass compared to placebo . However, the authors questioned the clinical relevance of this small effect and noted that the 3 included trials were of low quality (i.e. few participants, short duration, and other methodological flaws). Thus, the authors concluded: “The evidence from RCTs seems to indicate that the intake of GCE can promote weight loss. However, several caveats exist. The size of the effect is small, and the clinical relevance of this effect is uncertain. More rigorous trials with longer duration are needed to assess the efficacy and safety of GCE as a weight loss supplement” .
Of note, a more recent clinical trial of GCE as a weight loss supplement seemed to show highly positive results (weight loss of 8 kg/17.6 lbs) and was subsequently heavily promoted in the media . However, in 2014, the paper was retracted because “the sponsors of the study cannot assure the validity of the data” . In other words, the results of the paper (and the ensuing marketing campaigns) were likely invalid.
Overall, there is little evidence to support claims of effectiveness for GCE as a weight loss supplement.
Raspberry Ketone is the naturally-occurring compound that gives raspberries their distinctive smell. Test-tube studies have shown that raspberry ketone may increase fat-burning processes in fat cells , and animal studies suggest that high doses of raspberry ketone may prevent fat accumulation in the body . Because of these interesting results, raspberry ketone has been proposed as a weight loss supplement for humans (and, yet again, has been promoted by the same questionable TV-doctor ).
However, no clinical trials of raspberry ketone as a weight loss aid (or for any other purpose) have ever been performed in humans . Current marketing claims that promote raspberry ketone for weight loss are therefore not based on any clinical evidence whatsoever. In other words, there is currently no reason to believe that raspberry ketone is effective for weight loss in humans.
Conjugated Linoleic Acid
Conjugated linoleic acid (CLA) is a type of fat molecule that is naturally found in animals. It is believed to have fat- and weight-reducing properties, possibly via the promotion of normal fat metabolism . As a result, it has been marketed as a weight loss supplement.
A 2012 systematic review compiled the results of 7 clinical trials of CLA for body weight and fat reduction . The study determined that CLA promoted a 0.7 kg (1.5 lbs) reduction in body weight (equivalent to a 0.91% decrease in mass) and a 1.33 kg (2.9 lbs) reduction in fat mass when compared to a placebo . Given the small size of these effects, the authors concluded that “the evidence from [randomized controlled trials] fails to convincingly demonstrate that CLA supplementation generates any clinically relevant effects on body composition on the long term” . The authors also noted that the results of their study agreed with previous systematic reviews of CLA for weight/fat loss [36-37]. A 2007 systematic review of clinical trials also found that CLA could reduce fat mass in humans – but the size of the effect was so small that it was unlikely to be useful . Likewise, a 2006 systematic review concluded that “there is not enough evidence to show that conjugated linoleic acid has an effect on weight and body composition in humans” . In other words, there is little reliable evidence to support the use of CLA as a weight loss or fat-reducing supplement.
Citrus aurantium (Bitter Orange)
Citrus aurantium (bitter orange) is a fruit-bearing citrus tree that is commonly grown for agricultural purposes. Compounds derived from the plant are used as additives in food and cosmetic products and are also employed for their medicinal properties in several pharmaceutical applications . Because of its known uses as a drug, including the ability to promote fat-burning processes, bitter orange has been proposed as a weight loss supplement .
A 2011 systematic review of 4 clinical trials of bitter orange as a weight loss aid found that the best available evidence was of low quality (i.e. unclear and poorly reported methods, questionable blinding of participants, too few participants, short duration) and inconsistent . Three trials showed a small effect (of questionable importance) of bitter orange on weight loss, ranging from 0.5 kg (1.1 lbs) to 1.67 kg (3.7 lbs) reduction in body weight. The fourth trial, however, suggested that bitter orange caused a 1.7% increase in body weight (i.e. weight gain instead of weight loss) . Furthermore, none of the included trials tested bitter orange alone (i.e. in isolation) – they each used a different combination of multiple herbs and compounds as one single “herbal weight loss supplement” that happened to contain bitter orange. This means that none of the trials could actually determine the true effectiveness of bitter orange as a weight loss aid, since any apparent effects could be due to the other herbs contained in the mixtures. Therefore, the authors concluded that “the evidence of efficacy for [bitter orange] and weight management is contradictory and methodologically weak. Until more rigorous [clinical trials] emerge, [bitter orange] cannot be recommended as a treatment for weight loss” . This conclusion was also in agreement with an earlier systematic review of bitter orange, which “found no evidence that the herb, [bitter orange], is effective for weight loss” .
Polyglycoplex (PGX) is a dietary fibre complex formed by the linking of three fibres: glucomannan (described above), alginate, and xanthan gum . PGX consumption is thought to increase satiety (“fullness”) after eating. It is therefore actively promoted as a weight loss supplement .
A 2015 systematic review compiled the results of 4 clinical trials of PGX for body weight reduction . None of the included trials found that PGX could promote weight loss. Therefore, the best available evidence suggests that there is no good reason to use PGX as a weight loss supplement.
Irvingia gabonensis (African Mango)
Irvingia gabonensis (African mango) is a fruit-bearing tree native to West Africa. The fruit is thought to promote weight loss and has thus been widely marketed as a weight loss aid .
A systematic review conducted in 2013 assessed the results of 3 clinical trials of African mango for body weight reduction . This study found that African mango appeared to promote a significant – and, most importantly, clinically relevant – decrease in body weight when compared to controls. Unfortunately, the quality of the evidence was quite low, with each trial having very small numbers of participants, short duration, and poor explanations of their methods. Thus, the authors warned that the results “should be interpreted with caution”. They concluded: “The results from available [clinical trials] suggest that [African mango] supplementation causes significant reductions in body weight and waist circumference. However, the reporting of the methodology of the [clinical trials] is poor and all the trials are of short duration. Until good quality trials demonstrating its efficacy are available, [African mango] cannot be recommended as a weight loss aid” .
Therefore, overall, it appears that African mango might be useful as a weight loss supplement. Unfortunately, the best evidence supporting that conclusion is quite weak, so further trials are needed before consumers can be confident that related marketing claims are justified.
Many other supplements are promoted as weight loss aids. Perhaps unsurprisingly, most lack reliable evidence of effectiveness.
- Probiotics: A 2015 systematic review of clinical trials concluded that probiotics are not effective for promoting weight loss . Another systematic review found that probiotic use was associated with a 0.59 kg (1.3 lbs) reduction in body weight  – an effect too small to be considered clinically relevant.
- Phaseolus vulgaris (White Kidney Bean) Extract: A 2011 systematic review found that Phaseolus vulgaris extract consumption did not promote weight loss, but was associated with a small reduction in body fat . Unfortunately, the size of the reduction was not deemed clinically important. Additionally, the quality of the included trials was found to be low, further calling into question the true effectiveness of this supplement.
- L-Carnitine: A 2016 systematic review of clinical trials found a small effect (1.33 kg or 2.9 lbs) of L-carnitine consumption on weight loss . The clinical importance of this effect is questionable.
- Pyruvate: A 2014 systematic review of low-quality clinical trials determined that pyruvate consumption was associated with a small (0.72 kg or 1.6 lbs) reduction in body weight . Given the small size of the effect, and the poor quality of the data, the authors concluded that “the evidence from randomized clinical trials does not convincingly show that pyruvate is efficacious in reducing body weight” .
- Hoodia gordonii Extract: A single clinical trial of Hoodia gordonii for weight loss found that it was not effective .
- Grapefruit: A 2017 systematic review found that clinical trials do not support the use of grapefruit as a weight loss aid .
- Cactus Pear: A 2015 systematic review concluded that evidence from clinical trials does not support the use of cactus pear for weight loss .
SUMMARY OF COMMON WEIGHT LOSS SUPPLEMENTS
ARE THEY SAFE?
While some weight loss supplements are relatively harmless, others have been shown to be associated with notable adverse effects [8, 50]. An important example of the latter are supplements containing the herb “ephedra” (or the active ingredient: ephedrine alkaloids). Ephedra was a popular (and seemingly effective) weight loss aid before it was found to be associated with significant adverse effects, including heart attacks, psychiatric symptoms, and death [51-53]. Because of this, supplements containing ephedrine alkaloids have been banned in the United States [54-55].
Other popular weight loss supplements have also been associated with adverse effects. Examples include:
- Green tea and Garcinia cambogia products may be associated with liver damage [1, 56].
- Chitosan, Glucomannan, Guar Gum, and PGX have been associated with gastrointestinal symptoms such as diarrhea, constipation, bloating, and nausea [8, 26, 40].
- Citrus aurantium (Bitter Orange) has been associated with headache, anxiety, and elevated heart rate .
Given the apparent lack of clinical benefit from most weight loss aids, a systematic review of the adverse effects of weight loss supplements concluded that “…the reported risks are sufficient to shift the risk-benefit balance against the use of most of the reviewed herbal weight-loss supplements” . Similarly, another systematic review noted that given the lack of convincing evidence for most weight loss aids, “even minor adverse events shift the delicate risk-benefit balance against their use” . Thus, while most adverse effects may be mild, the absence of benefit for most weight loss supplements likely makes them not worth the risk.
For more information about the risks of herbal products (including weight loss supplements), please see: Herbalism
TOO LONG; DIDN'T READ!
There is little to no reliable evidence to support the use of most weight loss supplements. Those supplements that have been shown to promote weight loss usually produce effects that are so small that they are probably not relevant for consumers. In other words, the amount of weight lost would either not be noticeable or would not actually improve one’s health.
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