Obesity is a global epidemic, increasing the risk of various diseases, including type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). Modest weight loss can significantly reduce disease risk for overweight or obese individuals. However, successful weight management, encompassing both weight loss and preventing weight regain, is a complex challenge. Traditional weight management programs centered on calorie restriction and increased physical activity often fall short of achieving significant and sustained weight loss on their own. Many consumers turn to dietary supplements, especially those with thermogenic, lipotropic, or satiety properties, to support their diet and lifestyle efforts. This review examines the safety and efficacy of several commonly used ingredients in weight management supplements.
Understanding Weight Management Supplements
Dietary supplements are defined by the FDA as products taken orally containing dietary ingredients intended to supplement the diet, but not to treat, diagnose, mitigate, prevent, or cure diseases. They may include structure and/or function claims with a disclaimer that these claims have not been evaluated by the FDA. Manufacturers must have evidence to support these claims and adhere to Good Manufacturing Practices. They are also required to report serious adverse events and notify the FDA before marketing a new dietary ingredient (NDI).
Given the high interest in weight management strategies and recent safety concerns, this review identifies six commonly used components representing a broad range within the category. The review summarizes the safety evidence for each ingredient, along with the status of clinical evidence regarding weight management and relevant clinical health benefits.
The highest quality evidence is considered, focusing on reports from authoritative sources and published systematic reviews and meta-analyses. Randomized clinical trials are the preferred evidence for establishing cause-and-effect relationships. Assessments consider the relevance of the science to key questions, generally following the population, intervention, comparator, and outcome (PICO) approach.
Key Ingredients in Weight Management Supplements
This review focuses on several common ingredients found in weight management supplements, including caffeine, green tea extract (GTE), green coffee bean extract (GCBE), choline, glucomannan, and capsaicinoids and capsinoids.
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Caffeine
Caffeine (1,3,7-trimethylxanthine) is a widely consumed dietary substance known for its central nervous system stimulant properties. It is believed to increase thermogenesis and fat oxidation. Caffeine is commonly consumed through beverages like coffee, tea, and cola. The FDA generally recognizes caffeine as safe (GRAS) for use in cola-type beverages. As a supplement, caffeine sources include guarana, kola nut, yerba maté, and other herbs.
A search of the Mintel GNPD found 579 caffeine-containing supplements with weight management claims, with 164 listing the caffeine content. 93% of these recommended intake levels of ≤400 mg/day, while the remaining 7% recommended 400 to 420 mg caffeine/day.
Safety of Caffeine
Federal agencies and scientific organizations have extensively researched caffeine safety. Health Canada concluded in 2003 that an intake of ≤400 mg caffeine/day was not associated with adverse effects in healthy adults. They also deemed consumption of ≤300 mg/day safe for pregnant or lactating women and those planning pregnancy, and 2.5 mg/kg/day safe for children. Similarly, EFSA indicated that ≤400 mg caffeine/day poses no safety concerns for non-pregnant adults, establishing a limit of 200 mg/day for pregnant women. An updated systematic review in 2017 also found that ≤400 mg/day in healthy adults is not associated with adverse cardiovascular, behavioral, reproductive, developmental, acute, or bone effects. The DGA 2020-2025 addressed caffeine intake, noting that the FDA has identified ≤400 mg/day as an amount not generally associated with dangerous, negative effects.
Most weight management supplements provide caffeine within the recommended amount of ≤400 mg caffeine/day when used according to the manufacturer’s instructions. However, concerns exist regarding higher intake levels. Acute intake of caffeine >500 mg/day may lead to headache, jitteriness, agitation, anxiety, dizziness, and tinnitus. The FDA notes that caffeine metabolism slows after consumption of >500 mg, with adverse effects like tachycardia, ventricular arrhythmia, and seizures at consumptions >1200 mg. Responses vary based on individual sensitivity, co-morbidities, and concomitant medications or supplements.
Fatality due to caffeine poisoning is rare, with reviews concluding a potential for death following acute exposures of ~10 g of caffeine for adults and adolescents. The FDA has moved to restrict the sale of highly concentrated powdered and liquid caffeine due to the potential for delivering higher amounts.
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Caffeine and Weight Management
Caffeine stimulates noradrenaline and dopamine secretions, potentially decreasing body weight (BW) and body fat (BF), and increasing thermogenesis in brown adipose tissue. A meta-analysis showed that caffeine intake led to a reduction in BW, BF, and body mass index (BMI) in a dose-dependent manner. However, most studies included caffeine with other substances with potential weight loss properties, indicating that more clinical evidence with caffeine alone is needed for confirmation.
Caffeine and Metabolic Health
Observational evidence suggests caffeine may be protective against T2DM. However, clinical studies have shown mixed results. Some trials found significantly decreased insulin sensitivity indexes, suggesting caffeine might possess a hyperglycemic activity by acutely impairing insulin action in adipose and muscle tissue.
Conclusion on Caffeine
Extensive research indicates that caffeine consumption of ≤400 mg/day is safe for adults with minimal risk of adverse events. Most supplements fall within this recommended amount. Current evidence supports caffeine's beneficial effects on cognition, particularly attention, and exercise performance. The evidence on weight management is mixed, with some data suggesting benefits in supporting healthy blood glucose levels.
Green Tea Extract (GTE)
Green tea contains phytochemicals known as antioxidants. Some studies suggest that green tea extracts could increase calorie burning, even at rest, and may offer protection against heart disease and cancer. However, experts warn that large doses could cause liver damage, indicated by symptoms like yellowing of the skin or eyes, nausea, and stomach pain.
Green Coffee Bean Extract (GCBE)
Green coffee bean extract is a newer ingredient gaining popularity for weight management support.
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Choline
Choline is a supplement with expected lipotropic effects.
Glucomannan
Glucomannan is a supplement known for its satiety effects.
Capsaicinoids and Capsinoids
Capsaicinoids and capsinoids are becoming popular for weight management support.
Probiotics
Probiotics are beneficial bacteria that reside in the gut, aiding in the breakdown and digestion of food. A 2018 review indicated that probiotics, whether in foods or supplements, helped overweight and obese individuals reduce body weight and body fat. Some manufacturers combine probiotics with prebiotics, a fiber type that feeds gut bacteria. Probiotics have a long history of safety, particularly in healthy individuals, according to the NIH. However, rare side effects may occur in individuals with weakened immune systems.
Berberine
Early research suggests that berberine could aid in weight loss. However, it may cause gastrointestinal symptoms such as nausea, diarrhea, bloating, and constipation, and may interact with prescription medications.
Other Weight Loss Aids
Prescription Anti-Obesity Medications (AOMs)
The pharmacological treatment of obesity is rapidly evolving, with new medications emerging frequently. Determining candidacy for weight loss medications begins with assessing BMI, and the doctor and patient should discuss current health issues, other medications, and family medical history.
The average weight loss with AOMs varies from 5% to 21%, and most people regain weight if AOMs are discontinued. While some medications are FDA-approved only for adults, others, like semaglutide and liraglutide, are approved for children 12 and older with a BMI >/= 95th percentile.
Commonly Used Medications:
- Semaglutide (Wegovy, Ozempic): A GLP-1 receptor agonist, Wegovy is administered as an injection and approved for use in adults and children aged 12 years or more with obesity or some adults with excess weight who also have weight-related medical problems. The dose is gradually increased to 2.4 mg to alleviate side effects like gastrointestinal symptoms, headache, dizziness, and fatigue.
- Tirzepatide (Zepbound, Mounjaro): A dual GIP and GLP-1 receptor agonist approved to treat obesity in adults with a BMI of 30 or greater. It reduces appetite and is meant to be used with diet and exercise.
- Liraglutide (Saxenda, Victoza): A daily injectable medication that acts on hormones to increase feelings of fullness and decrease hunger signals. Doses range from 0.6 mg to 3 mg a day. Side effects include nausea, diarrhea, constipation, vomiting, headache, decreased appetite, dyspepsia, fatigue, dizziness, abdominal pain, increased lipase, and renal insufficiency.
- Phentermine: The oldest and most widely used weight loss medication, now added to long-term therapy in newer medical guidelines. Side effects include headache, overstimulation, high blood pressure, insomnia, rapid or irregular heart rate, and tremor.
- Phentermine-Topiramate (Qsymia): Combines phentermine with topiramate to decrease appetite and cravings. Side effects include abnormal sensations, dizziness, altered taste, insomnia, constipation, and dry mouth.
- Naltrexone-Bupropion (Contrave): Combines an opioid receptor antagonist with an antidepressant to affect pleasure-reward areas of the brain, decreasing cravings and appetite. Common side effects include nausea, constipation, headache, vomiting, dizziness, insomnia, dry mouth, and diarrhea.
- Orlistat (Xenical, Alli): A lipase inhibitor that prevents the digestion of fat, which is then passed through the body. An over-the-counter formulation is available.
- Setmelanotide: A melanocortin-4 receptor agonist indicated for chronic weight management in patients six years and older with obesity due to certain rare genetic disorders.
- Plenity: A medical device consisting of a capsule that releases a biodegradable, super-absorbent hydrogel into the stomach, increasing satiety.
Future Medications:
Pharmaceutical platform Ozmosi predicts one to two GLP-1 launches annually starting in 2026, specifically for obesity. Lilly is developing orforglipron (an oral GLP-1 inhibitor) and retatrutide (targets GLP-1, GIP, and glucagon). Amgen is developing MariTide, a monoclonal antibody designed to increase GLP-1 receptor activity while reducing GIP receptor activity.
Important Considerations for AOMs
- AOMs are most effective when used as part of a comprehensive treatment plan including diet, exercise, and lifestyle changes.
- Insurance coverage varies and affects patient choices regarding weight loss medications.
- GLP-1s are not meant to be stopped and restarted at will, and dosing for some includes a long ramp-up period.
- The FDA warns against buying medications from any source other than a state-licensed pharmacy due to the risk of counterfeit medications.
- While no specific vitamin or supplement is considered a "treatment" for obesity, certain ones like calcium and vitamin D may support metabolic health.
Metabolic Research Center (MRC) Products
The Metabolic Research Center offers a variety of products to support weight loss efforts. These include protein bars, protein powders, and flavored drinks. Customer reviews highlight the taste and convenience of these products, with many users praising their effectiveness in curbing cravings and providing essential nutrients.
Examples of MRC Products and Customer Feedback:
- Raspberry and Chocolate Bars: Praised for satisfying cravings without the guilt.
- Unflavored Protein Powder: Versatile for adding to foods like cottage cheese without altering the taste. Provides protein with zero carbs and low calories.
- Diet Cappuccinos: Highly rated for taste, with users recommending specific mixing techniques for optimal enjoyment.
- MRC Nachos: Used as a flavorful addition to soups.
Customers consistently mention the friendly and supportive staff at MRC locations, particularly highlighting the encouragement and personalized guidance provided by coaches. Many reviewers express satisfaction with their weight loss progress and improved relationship with food.
Additional Strategies for Weight Management
The Importance of Lifestyle Changes
Fat burners are not miracle pills and won’t melt fat away on their own. A balanced diet and consistent exercise routine are essential for fat loss. Fat burners should be taken as a complementary supplement to aid your exercise regimen and healthy, whole foods diet.
Thermogenesis
Fat burners often contain ingredients that increase thermogenesis, the process of heat production in the body that helps raise metabolic rate and calorie expenditure. Ingredients like caffeine, capsaicin/cayenne pepper extract, and green tea extract are commonly included.
Lipolysis
Lipolysis is when your body breaks down stored fat into free fatty acids for energy.
Appetite Suppression
Natural appetite suppressants included in fat burning supplements are 5-HTP, green tea extract, and garcinia cambogia.
Other Considerations
- Dosage: Follow the instructions printed on the supplement container and do not exceed the recommended maximum dosage.
- Third-Party Testing: Choose supplements that have been tested by an independent third party to verify safety, purity, and nutrition label accuracy.
- Transparent Labeling: Opt for supplements with transparent labeling to avoid stimulants or check for possible interactions with existing medications.
- Customer Reviews: Consider supplements with customer reviews, ratings, or feedback.