Introduction
Dietary supplements for weight loss have gained immense popularity over the past several decades, with millions of people turning to these products in hopes of shedding excess weight. The prevalence of obesity and overweight has reached epidemic proportions globally, with over 1.9 billion adults classified as overweight or obese (World Health Organization, 2021). In the United States alone, more than two-thirds of adults are considered overweight or obese (Hales et al., 2020). This alarming trend has fueled the demand for weight loss solutions, including dietary supplements.
Despite their widespread use, the safety and effectiveness of dietary supplements for weight loss remain controversial. Many products make bold claims about their ability to promote rapid weight loss with minimal effort, but the scientific evidence supporting these claims is often limited or inconsistent. Additionally, some supplements have been linked to serious adverse effects, raising concerns about their safety (Dwyer et al., 2018). Given the popularity of these products and the potential risks associated with their use, it is crucial to critically evaluate the available evidence on the safety and effectiveness of dietary supplements for weight loss.
This article aims to provide a comprehensive overview of the current state of research on dietary supplements for weight loss. We will examine the most common ingredients found in these products, including caffeine, green tea extract, green coffee bean extract, glucomannan, and capsaicinoids/capsinoids. The article will discuss the proposed mechanisms of action, the available evidence on their effectiveness for weight loss and metabolic health, and the potential side effects and safety concerns associated with their use. By synthesising the findings from randomised controlled trials, systematic reviews, and meta-analyses, this article seeks to provide an evidence-based perspective on the role of dietary supplements in weight management.
Common Ingredients in Weight Loss Supplements
Caffeine
Caffeine is a central nervous system stimulant commonly found in weight loss supplements. Its primary mechanism of action is to increase metabolism and fat oxidation, potentially leading to enhanced weight loss (Tabrizi et al., 2019). A meta-analysis by Tabrizi et al. (2019) found that caffeine intake significantly reduced body weight, BMI, and body fat compared to placebo. The study also noted that the optimal dose for weight loss appears to be 400-500 mg per day, which is roughly equivalent to 4-5 cups of coffee.
However, it is essential to consider the safety aspects of caffeine consumption. While moderate intake of caffeine (up to 400 mg per day) is generally considered safe for most adults, higher doses may lead to adverse effects such as insomnia, anxiety, digestive issues, and increased heart rate (Wikoff et al., 2017). Pregnant women, adolescents, and individuals with certain medical conditions should limit their caffeine intake. It is crucial to monitor the total caffeine intake from all sources, including supplements, to avoid exceeding the recommended limits.
Green Tea Extract (GTE)
Green tea extract, derived from the leaves of Camellia sinensis, is another popular ingredient in weight loss supplements. The active compounds in GTE are catechins, particularly epigallocatechin gallate (EGCG), which have been shown to increase energy expenditure and fat oxidation (Jurgens et al., 2012). A Cochrane systematic review by Jurgens et al. (2012) concluded that green tea preparations containing catechins and caffeine led to a small but statistically significant reduction in body weight and maintenance of weight loss.
The exact mechanisms behind the weight loss effects of GTE are not fully understood but may involve the inhibition of lipogenesis, increased thermogenesis, and the modulation of appetite-regulating hormones (Jurgens et al., 2012). The optimal dose of EGCG for weight loss is considered to be around 400-500 mg per day, which is equivalent to about 4-5 cups of green tea (Hu et al., 2018).
Regarding safety, GTE is generally well-tolerated when consumed in moderate amounts. However, high doses of EGCG (above 800 mg per day) have been associated with liver toxicity in rare cases (Hu et al., 2018). People with pre-existing liver conditions or those taking medications metabolized by the liver should exercise caution when consuming GTE supplements.
Green Coffee Bean Extract (GCBE)
Green coffee bean extract, derived from unroasted coffee beans, has gained popularity as a weight loss supplement. The primary active compound in GCBE is chlorogenic acid, which is thought to reduce carbohydrate absorption and increase fat metabolism (Onakpoya et al., 2011). A meta-analysis by Onakpoya et al. (2011) found that GCBE supplementation led to a modest reduction in body weight compared to placebo, with an average weight loss of 2.47 kg.
However, the quality of the studies included in the meta-analysis was poor, with small sample sizes and short durations. More recent, well-designed trials have yielded mixed results, with some showing no significant effect of GCBE on weight loss (Roshan et al., 2018). The optimal dose of chlorogenic acid for weight loss is not well-established, but most studies have used doses ranging from 180-400 mg per day.
GCBE appears to be safe and well-tolerated in healthy individuals at the doses typically used in supplements. However, as with any supplement, it is essential to consult with a healthcare professional before starting use, especially for those with pre-existing medical conditions or taking medications.
Glucomannan
Glucomannan is a soluble dietary fiber derived from the root of the konjac plant (Amorphophallus konjac). It is often included in weight loss supplements due to its ability to promote satiety and reduce calorie intake (Zalewski et al., 2015). When consumed, glucomannan absorbs water and forms a viscous gel in the stomach, which delays gastric emptying and increases feelings of fullness.
A systematic review and meta-analysis by Onakpoya et al. (2014) found that glucomannan supplementation led to a small but statistically significant reduction in body weight compared to placebo, with an average weight loss of 0.79 kg over 4-8 weeks. The study also noted improvements in total cholesterol, LDL cholesterol, and triglyceride levels, suggesting potential benefits for metabolic health.
The optimal dose of glucomannan for weight loss appears to be around 3 grams per day, taken in divided doses before meals (Onakpoya et al., 2014). It is essential to consume glucomannan with sufficient water to prevent digestive issues such as bloating, flatulence, and abdominal discomfort. In rare cases, glucomannan has been associated with esophageal obstruction when taken without adequate fluid intake (Vanderbeek et al., 2007).
Capsaicinoids and Capsinoids
Capsaicinoids and capsinoids are compounds found in chili peppers and sweet peppers, respectively. They have been investigated for their potential weight loss effects due to their ability to increase energy expenditure and fat oxidation (Whiting et al., 2014). Capsaicinoids, particularly capsaicin, are responsible for the pungent sensation associated with chili peppers, while capsinoids are non-pungent analogs.
A meta-analysis by Whiting et al. (2014) found that capsaicinoid and capsinoid supplementation led to a small but statistically significant increase in energy expenditure (50 kcal per day) and fat oxidation (6 g per day) compared to placebo. However, the effects on body weight were not significant, possibly due to the short duration of the studies (2-12 weeks) and the small sample sizes.
The optimal dose of capsaicinoids for weight loss is not well-established, but most studies have used doses ranging from 2-10 mg per day (Whiting et al., 2014). Capsaicinoids are generally well-tolerated, but some individuals may experience gastrointestinal discomfort, such as burning sensations in the mouth and stomach, at higher doses.
Safety and Side Effects of Weight Loss Supplements
While dietary supplements for weight loss are often marketed as safe and natural alternatives to prescription medications, it is essential to consider the potential risks and side effects associated with their use. The safety of weight loss supplements has been a topic of concern, with some products linked to serious adverse events and even death (Dwyer et al., 2018).
The most common side effects reported with weight loss supplements are mild gastrointestinal symptoms, such as nausea, diarrhea, constipation, and abdominal discomfort (Dwyer et al., 2018). These side effects are often related to the high doses of stimulants (e.g., caffeine) or fiber (e.g., glucomannan) found in some products. In most cases, these symptoms are transient and resolve with continued use or dose adjustment.
However, more serious adverse events have been reported with certain ingredients. For example, high doses of green tea extract have been linked to liver toxicity in rare cases, particularly in individuals with pre-existing liver conditions (Hu et al., 2018). Synephrine, a compound found in bitter orange (Citrus aurantium), has been associated with cardiovascular events such as hypertension, myocardial infarction, and stroke when used in combination with caffeine (Stohs et al., 2012).
The long-term safety of many weight loss supplements has not been established, as most studies are short-term (less than 12 weeks) and have small sample sizes (Dwyer et al., 2018). There is a need for more rigorous, long-term safety data to fully understand the potential risks associated with prolonged use of these products.
Another concern is the potential for interactions between weight loss supplements and medications. Many supplements contain ingredients that can alter the metabolism or effectiveness of certain drugs, leading to adverse effects or treatment failure (Asher et al., 2017). For example, green tea extract may interact with beta-blockers, antidepressants, and blood thinners, while glucomannan may reduce the absorption of oral medications when taken simultaneously (Asher et al., 2017).
To minimize the risk of adverse effects and interactions, it is crucial for individuals to consult with a healthcare professional before starting any weight loss supplement, especially if they have pre-existing medical conditions or are taking medications. It is also essential to follow the recommended dosage instructions and not exceed the suggested intake levels.
Effectiveness of Weight Loss Supplements
Despite the popularity of dietary supplements for weight loss, the evidence supporting their effectiveness is often limited and inconsistent. Many studies have methodological limitations, such as small sample sizes, short durations, and lack of long-term follow-up, making it difficult to draw firm conclusions about the efficacy of these products (Dwyer et al., 2018).
A systematic review by Onakpoya et al. (2011) evaluated the evidence for various weight loss supplements, including green tea extract, conjugated linoleic acid (CLA), and chromium. The authors found that while some supplements led to statistically significant weight loss compared to placebo, the magnitude of the effect was small (less than 2 kg) and of questionable clinical relevance. The review also noted the poor quality of many studies and the need for more rigorous, long-term trials.
Similarly, a meta-analysis by Jurgens et al. (2012) examined the effectiveness of green tea preparations for weight loss and weight maintenance. While the analysis found a small but statistically significant reduction in body weight and BMI compared to placebo, the authors cautioned that the clinical significance of the effect was modest and that the quality of the evidence was low.
One of the challenges in evaluating the effectiveness of weight loss supplements is the heterogeneity of the products and study designs. Supplements often contain multiple ingredients with varying doses, making it difficult to attribute effects to specific components (Dwyer et al., 2018). Additionally, the baseline characteristics of study participants, such as age, sex, BMI, and comorbidities, can influence the response to supplementation.
Another issue is the potential for publication bias, where studies with positive results are more likely to be published than those with negative or null findings (Onakpoya et al., 2011). This bias can lead to an overestimation of the effectiveness of weight loss supplements in the published literature.
It is also important to consider the role of industry funding in the research on weight loss supplements. Many studies are sponsored by supplement manufacturers, which may introduce bias in the design, conduct, and reporting of the trials (Dwyer et al., 2018). Independent, third-party research is needed to provide unbiased assessments of the effectiveness of these products.
Overall, while some dietary supplements may lead to modest weight loss in the short term, the long-term effectiveness and sustainability of these effects remain uncertain. The evidence suggests that supplements should not be relied upon as a sole strategy for weight management and that lifestyle modifications, such as a balanced diet and regular physical activity, are essential for achieving and maintaining a healthy weight (Dwyer et al., 2018).
Metabolic Health Effects of Weight Loss Supplements
In addition to their potential effects on body weight, some dietary supplements have been investigated for their impact on metabolic health markers, such as blood glucose, lipid profiles, and blood pressure. Improving these markers can have important implications for reducing the risk of chronic diseases, such as type 2 diabetes and cardiovascular disease (Golzarand et al., 2018).
Green tea extract has been one of the most studied supplements in this regard. A meta-analysis by Zheng et al. (2013) found that green tea consumption significantly reduced fasting blood glucose and hemoglobin A1c levels in individuals with and without diabetes. The analysis also noted improvements in total cholesterol, LDL cholesterol, and blood pressure, suggesting potential benefits for cardiovascular health.
Similarly, a systematic review by Onakpoya et al. (2014) examined the effects of glucomannan supplementation on metabolic health markers. The review found significant reductions in fasting blood glucose, total cholesterol, LDL cholesterol, and triglycerides compared to placebo, although the effects on blood pressure were not significant.
Chromium, a mineral often included in weight loss supplements, has been studied for its potential effects on glucose metabolism and insulin sensitivity (Hua et al., 2012). A meta-analysis by Hua et al. (2012) found that chromium supplementation significantly improved glycemic control in individuals with diabetes, as evidenced by reductions in fasting blood glucose and hemoglobin A1c levels. However, the effects on lipid profiles and blood pressure were not significant.
While these findings suggest potential metabolic health benefits of certain weight loss supplements, it is important to interpret the results with caution. Many of the studies have limitations, such as small sample sizes, short durations, and lack of long-term follow-up (Golzarand et al., 2018). Additionally, the optimal doses and formulations of these supplements for metabolic health effects have not been established.
More research is needed to fully understand the long-term impact of weight loss supplements on metabolic health markers and disease risk. It is also important to consider the potential interactions between supplements and medications used to manage metabolic conditions, such as insulin and oral hypoglycemic agents (Asher et al., 2017).
As with weight loss, lifestyle modifications, such as a healthy diet and regular physical activity, remain the cornerstone of metabolic health management (Golzarand et al., 2018). Dietary supplements should be used judiciously and under the guidance of a healthcare professional, as part of a comprehensive approach to optimizing metabolic health.
Conclusion
The popularity of dietary supplements for weight loss has soared in recent decades, driven by the increasing prevalence of obesity and the desire for quick, easy solutions. However, the evidence supporting the safety and effectiveness of these products is often limited and inconsistent. While some supplements, such as green tea extract, glucomannan, and caffeine, have shown modest benefits for weight loss and metabolic health in short-term studies, the long-term sustainability and clinical relevance of these effects remain uncertain.
It is crucial for consumers to approach weight loss supplements with caution and realistic expectations. These products are not a magic bullet for obesity and should not be relied upon as the sole strategy for weight management. The most effective approach to achieving and maintaining a healthy weight is through a combination of a balanced diet, regular physical activity, and other lifestyle modifications. Dietary supplements, if used, should be considered as an adjunct to these foundational strategies, rather than a replacement.
When considering the use of weight loss supplements, it is essential to prioritise safety and consult with a healthcare professional. Some supplements have been associated with adverse effects, particularly when taken in high doses or combined with other substances. Interactions with medications and pre-existing health conditions are also a concern. By working closely with a qualified healthcare provider, individuals can make informed decisions about the potential risks and benefits of specific supplements in the context of their unique health status and goals.
Ultimately, more research is needed to fully understand the long-term safety and effectiveness of dietary supplements for weight loss. Well-designed, independently-funded clinical trials with larger sample sizes and longer durations are essential to provide definitive answers. In the meantime, prioritising evidence-based lifestyle habits and seeking guidance from healthcare professionals remain the most prudent approaches to managing weight and optimising overall health.
Key Highlights
- Caffeine, green tea extract (GTE), green coffee bean extract (GCBE), choline, glucomannan, and capsaicinoids/capsinoids are generally safe when taken as directed and may provide some metabolic health benefits for overweight and obese people.
- Caffeine, GTE (specifically EGCG), and choline have recommended intake limits that are typically not exceeded when products are used according to manufacturers’ instructions. Serious adverse events are rare.
- GTE has the most consistent clinical evidence for modest weight management benefits. The other ingredients reviewed show mixed results for weight loss but may improve some markers of metabolic health.
Actionable Tips
- Follow the manufacturers’ recommended dosage instructions for weight management supplements. Do not exceed recommended intake limits for caffeine (400 mg/day for adults), EGCG from GTE (300-338 mg/day), or choline (3500 mg/day for adults).
- Be aware of potential gastrointestinal side effects and possible interactions with medications or other supplements. Consider your overall health status before taking these ingredients.
- Incorporate proven lifestyle changes like a balanced diet and regular physical activity for the most effective approach to weight management. Supplements should not be relied upon as a sole strategy for weight loss.
What are the most common side effects of the weight management ingredients reviewed?
The most commonly reported side effects of caffeine, green tea extract, green coffee bean extract, choline, glucomannan, and capsaicinoids/capsinoids are gastrointestinal symptoms like abdominal discomfort, diarrhea, constipation, and nausea. These effects are usually mild, transient, and related to individual tolerance. Rarely, green tea extract has been linked to liver injury when taken in high doses.
Can these ingredients be taken safely long-term for weight management?
There is limited research on the long-term safety and efficacy of these ingredients for weight loss. Most clinical studies have only tested supplementation for 12 weeks or less. While serious adverse events appear uncommon, it’s best to use supplements for a limited time under medical supervision as part of a comprehensive weight management plan.
Do these supplements interact with any medications?
Yes, some of these ingredients may interact with certain medications. For example, caffeine can interfere with some antibiotics, antidepressants, and blood thinners. Green tea extract may interact with chemotherapy drugs and blood thinners. Choline should be used cautiously by people taking anticholinergic medications. Always check with your doctor before combining supplements with prescribed medicines.
Are these ingredients safe and effective for children and adolescents?
Most of the safety and efficacy research on these ingredients for weight management has been conducted in adults. There is very little data available on their use in children and adolescents. Given the lack of evidence and the potential for adverse effects, these supplements are not recommended for pediatric weight loss. Children and teens should focus on adopting healthy eating and activity habits for weight management.
How do these supplements compare to prescription weight loss medications?
Prescription weight loss drugs like phentermine, orlistat, and liraglutide undergo extensive clinical testing and are approved by regulatory agencies for safety and efficacy. They tend to produce more clinically significant weight loss results (5-10% of body weight on average) compared to over-the-counter supplements. However, these medications also carry more potential side effects and are only indicated for certain patients. The ingredients reviewed here may lead to modest weight loss and metabolic improvements but should not be considered a replacement for medication when prescribed.
References
Buchman, A. L., Ament, M. E., Sohel, M., Dubin, M., Jenden, D. J., Roch, M., Pownall, H., Farley, W., Awal, M., & Ahn, C. (2001). Choline deficiency causes reversible hepatic abnormalities in patients receiving parenteral nutrition: Proof of a human choline requirement: A placebo-controlled trial. JPEN Journal of Parenteral and Enteral Nutrition, 25(5), 260-268. https://doi.org/10.1177/0148607101025005260
Dekant, W., Fujii, K., Shibata, E., Morita, O., & Shimotoyodome, A. (2017). Safety assessment of green tea based beverages and dried green tea extracts as nutritional supplements. Toxicology Letters, 277, 104-108. https://doi.org/10.1016/j.toxlet.2017.06.008
Fulgoni, V. L., Keast, D. R., & Lieberman, H. R. (2015). Trends in intake and sources of caffeine in the diets of US adults: 2001–2010. The American Journal of Clinical Nutrition, 101(5), 1081-1087. https://doi.org/10.3945/ajcn.113.080077
Gao, X., Wang, Y., Randell, E., Pedram, P., Yi, Y., Gulliver, W., & Sun, G. (2016). Higher dietary choline and betaine intakes are associated with better body composition in the adult population of Newfoundland, Canada. PLoS ONE, 11(5), e0155403. https://doi.org/10.1371/journal.pone.0155403
Hu, J., Webster, D., Cao, J., & Shao, A. (2018). The safety of green tea and green tea extract consumption in adults—Results of a systematic review. Regulatory Toxicology and Pharmacology, 95, 412-433. https://doi.org/10.1016/j.yrtph.2018.03.019
Lejeune, M. P., Kovacs, E. M., & Westerterp-Plantenga, M. S. (2003). Effect of capsaicin on substrate oxidation and weight maintenance after modest body-weight loss in human subjects. British Journal of Nutrition, 90(3), 651-659. https://doi.org/10.1079/BJN2003938
Ludy, M. J., Moore, G. E., & Mattes, R. D. (2012). The effects of capsaicin and capsiate on energy balance: Critical review and meta-analyses of studies in humans. Chemical Senses, 37(2), 103-121. https://doi.org/10.1093/chemse/bjr100
Nawrot, P., Jordan, S., Eastwood, J., Rotstein, J., Hugenholtz, A., & Feeley, M. (2003). Effects of caffeine on human health. Food Additives & Contaminants, 20(1), 1-30. https://doi.org/10.1080/0265203021000007840
Oketch-Rabah, H. A., Roe, A. L., Rider, C. V., Bonkovsky, H. L., Giancaspro, G. I., Navarro, V., Paine, M. F., Betz, J. M., Marles, R. J., Casper, S., Gurley, B., Jordan, S. A., He, K., Kapoor, M. P., Rao, T. P., Sherker, A. H., Fontana, R. J., Rossi, S., Vuppalanchi, R., Seeff, L., & Stolz, A. (2020). United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. Toxicology Reports, 7, 386-402. https://doi.org/10.1016/j.toxrep.2020.02.008
Onakpoya, I., Posadzki, P., & Ernst, E. (2014). The efficacy of glucomannan supplementation in overweight and obesity: A systematic review and meta-analysis of randomized clinical trials. Journal of the American College of Nutrition, 33(1), 70-78. https://doi.org/10.1080/07315724.2014.870013
Shin, K. O., & Moritani, T. (2007). Alterations of autonomic nervous activity and energy metabolism by capsaicin ingestion during aerobic exercise in healthy men. Journal of Nutritional Science and Vitaminology, 53(2), 124-132. https://doi.org/10.3177/jnsv.53.124
Tabrizi, R., Saneei, P., Lankarani, K. B., Akbari, M., Kolahdooz, F., Esmaillzadeh, A., Nadi-Ravandi, S., Mazoochi, M., & Asemi, Z. (2019). The effects of caffeine intake on weight loss: A systematic review and dos-response meta-analysis of randomized controlled trials. Critical Reviews in Food Science and Nutrition, 59(16), 2688-2696. https://doi.org/10.1080/10408398.2018.1507996
Wikoff, D., Welsh, B. T., Henderson, R., Brorby, G. P., Britt, J., Myers, E., Goldberger, J., Lieberman, H. R., O’Brien, C., Peck, J., Tenenbein, M., Weaver, C., Harvey, S., Urban, J., & Doepker, C. (2017). Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food and Chemical Toxicology, 109(Pt 1), 585-648. https://doi.org/10.1016/j.fct.2017.04.002
Yates, A. A., Erdman, J. W., Shao, A., Dolan, L. C., & Griffiths, J. C. (2017). Bioactive nutrients—Time for tolerable upper intake levels to address safety. Regulatory Toxicology and Pharmacology, 84, 94-101. https://doi.org/10.1016/j.yrtph.2017.01.002
