Efficacy of Fat-Loss Supplements: What Does the Science Say?

教育 2024-10-12 14:45 江苏

The prevalence of obesity and overweight has increased globally, contributing to a surge in the demand for fat-loss supplements. While many people use these supplements to accelerate weight loss and fat reduction, their effectiveness and safety remain subjects of debate.

Fat-loss supplements are designed to promote weight loss by enhancing fat metabolism, suppressing appetite, or blocking fat absorption. Fat-loss supplements can be classified into several categories based on their active ingredients and mechanisms of action. These include thermogenics, fat blockers, appetite suppressants, and carbohydrate blockers. Each of these classes operates differently in the body.

Thermogenic Supplements

Thermogenics are fat-loss supplements that aim to increase energy expenditure by raising body temperature, thereby stimulating fat oxidation. Common ingredients in thermogenics include caffeine, green tea extract, and capsaicin. Research suggests that these substances enhance metabolic rate and promote lipolysis, which can lead to increased fat loss over time.

Caffeine: Known for its stimulant properties, caffeine increases energy expenditure and enhances fat oxidation during exercise. It stimulates the central nervous system, leading to the release of catecholamines such as norepinephrine, which help break down fat stores.
Green Tea Extract (EGCG): The catechins in green tea, particularly epigallocatechin gallate (EGCG), have been shown to promote fat oxidation and increase thermogenesis.
Capsaicin: Found in chili peppers, capsaicin can boost metabolism and promote fat burning by activating thermogenesis.

Fat Blockers

Fat blockers work by inhibiting the absorption of dietary fat in the gastrointestinal tract. These supplements usually contain substances like orlistat, which blocks the enzyme lipase responsible for breaking down fat in the digestive system. By preventing fat from being absorbed, the body excretes it through feces, thereby reducing calorie intake.

Orlistat: An FDA-approved weight-loss medication, orlistat inhibits the activity of pancreatic and gastric lipases, reducing fat absorption by approximately 30%. Clinical trials have shown its effectiveness in promoting weight loss, but it can lead to gastrointestinal side effects such as steatorrhea (fatty stools).

Appetite Suppressants

Appetite suppressants work by reducing hunger and increasing satiety, making it easier for individuals to consume fewer calories. These supplements often contain fiber, protein, or substances that affect the central nervous system, such as 5-HTP or glucomannan.

Glucomannan: A water-soluble fiber derived from the root of the konjac plant, glucomannan expands in the stomach, promoting feelings of fullness and reducing food intake. Studies suggest that it can help with weight loss when combined with a calorie-restricted diet.
5-HTP (5-Hydroxytryptophan): A precursor to serotonin, 5-HTP can reduce appetite by influencing the release of serotonin in the brain, which regulates mood and hunger.

Carbohydrate Blockers

Carbohydrate blockers, also known as starch blockers, inhibit enzymes that digest carbohydrates, such as alpha-amylase. This prevents the breakdown of carbohydrates into simple sugars, reducing their absorption and preventing blood sugar spikes.

White Kidney Bean Extract: This extract inhibits alpha-amylase, an enzyme responsible for breaking down starch into glucose. By blocking this process, it reduces the number of calories absorbed from carbohydrates and may aid in fat loss.

While fat-loss supplements are widely marketed for their purported benefits, scientific evidence supporting their efficacy varies. Several randomized controlled trials (RCTs) have evaluated the impact of thermogenic, fat-blocking, and appetite-suppressing supplements on weight loss and fat reduction.

Caffeine and Weight Loss

Caffeine is one of the most widely studied substances in relation to fat loss and weight loss, primarily due to its thermogenic and fat oxidation properties. Research suggests that caffeine increases metabolic rate and enhances lipolysis, the breakdown of fat. It does so by stimulating the central nervous system, which leads to the release of catecholamines like norepinephrine that promote the release of fatty acids from fat tissue. Caffeine also increases energy expenditure, particularly during exercise, further enhancing fat oxidation.

A meta-analysis of 13 studies confirmed that caffeine can lead to modest reductions in body weight, BMI, and body fat percentage, particularly when combined with physical activity. However, the degree of weight loss varies depending on the dosage, individual tolerance, and lifestyle factors.

According to a paper published in JISSN, There are a multitude of confounding variables vis a vis the effects of caffeine on weight loss. One issue is the lack of consistency in dietary intake standardization. Another variable to consider is whether the participants were caffeine-naïve before the study. Additionally, the dose of caffeine used and whether participants were overweight or not can be contributing factors. Therefore, the current body of evidence does not support the use of caffeine as a fat loss aid.

Green Tea Extract and Weight Loss

Scientific research on green tea extract, particularly its key component epigallocatechin gallate (EGCG), has shown promising effects on fat loss and weight loss. Green tea extract is rich in catechins, which have been found to increase thermogenesis and fat oxidation, both of which contribute to weight reduction.

Several studies suggest that green tea extract can enhance fat metabolism during exercise and even at rest. For instance, a meta-analysis concluded that green tea catechins combined with caffeine led to significant reductions in body weight, body mass index (BMI), and waist circumference compared to placebo groups. Another randomized controlled trial showed that daily supplementation with green tea extract helped individuals reduce visceral fat and overall body fat.

However, while the effects are statistically significant, the magnitude of fat loss is often modest, suggesting that green tea extract is more effective as part of a broader weight management strategy, including diet and exercise, rather than a standalone solution.

Capsaicin and Weight Loss

Scientific research suggests that capsaicin can promote fat loss through several mechanisms, including increasing energy expenditure, enhancing fat oxidation, and reducing appetite. Capsaicin induces thermogenesis by activating the transient receptor potential vanilloid subtype 1 (TRPV1) channels, which leads to increased heat production and calorie burning. Additionally, studies have shown that capsaicin consumption can reduce calorie intake by increasing satiety. A meta-analysis by Whiting et al. (2012) demonstrated that capsaicin supplementation modestly reduced body fat and body weight in humans. Furthermore, the compound has been found to enhance fat oxidation during exercise, further supporting its role in weight management.

The NIH published a fact sheet (see the sheet screenshot below white kidney beans) on weight loss supplements for health professionals, it said capsaicin may reduce energy intake, but it has no effect on weight.

Orlistat and Weight Loss

Orlistat, a lipase inhibitor, has been extensively studied for its effects on fat and weight loss. Scientific research shows that orlistat reduces fat absorption by approximately 30%, leading to significant weight loss when combined with a calorie-restricted diet. A meta-analysis of clinical trials found that individuals taking orlistat typically experience a weight loss of 5-10% of their body weight over six months to one year. The XENDOS study, a large, four-year clinical trial, demonstrated that orlistat not only promoted weight loss but also reduced the risk of developing type 2 diabetes in obese individuals.

However, orlistat’s effectiveness is coupled with side effects like gastrointestinal discomfort, oily stools, and flatulence due to undigested fats. Despite these side effects, orlistat remains one of the few FDA-approved over-the-counter weight loss medications, with evidence supporting its efficacy in reducing body fat and aiding long-term weight management.

White Kidney Bean Extract and Weight Loss

Research has shown that white kidney bean extract inhibits the enzyme alpha-amylase, which is crucial for digesting carbohydrates. By blocking this enzyme, the extract reduces the breakdown of dietary starches into simple sugars, leading to fewer calories absorbed from carbohydrates. Clinical studies have demonstrated that supplementation with white kidney bean extract can result in modest weight loss and improved body composition. For instance, a study by Zhi et al. (2009) found that participants taking white kidney bean extract lost significantly more weight compared to those receiving a placebo, attributing this effect to reduced carbohydrate absorption and enhanced fat loss.

However, white kidney bean extract does not prevent the absorption of simple sugars (sucrose, juice, etc.) and oils that do not require alpha-amylase digestion. At present, studies in humans have produced some effects in the short to medium term (28 to 84 days), but the long-term efficacy of white kidney bean extract has not been studied. Also, The NIH said white kidney bean extract may have moderate effects on body weight and body fat.

Glucomannan and Weight Loss

Research on glucomannan’s role in weight loss has yielded mixed results. Some studies suggest that glucomannan can lead to modest weight loss of 1-2 kg over 8-12 weeks, particularly when combined with a low-calorie diet. However, other studies have found no significant difference in weight loss between glucomannan and placebo groups.

5-HTP and Weight Loss

Limited research is available on 5-HTP for weight loss. Some small studies indicate that 5-HTP supplementation can reduce food intake and promote weight loss by increasing serotonin levels. However, more large-scale studies are needed to confirm its efficacy.

Although fat-loss supplements are widely available, many are not without risks. Potential side effects depend on the specific ingredients used, as well as the individual’s health status. The most common side effects include gastrointestinal discomfort, elevated heart rate, insomnia, and headaches.

Fat-loss supplements are regulated differently depending on the country. In the United States, the Food and Drug Administration (FDA) classifies dietary supplements as food, not drugs, which means they are not subject to the same rigorous testing as prescription medications. Manufacturers are responsible for ensuring the safety of their products, but the FDA can take action against unsafe supplements once they are on the market.

Fat-loss supplements are a popular option for individuals seeking to accelerate weight loss and reduce body fat. While some supplements, such as caffeine, green tea extract, and orlistat, have demonstrated modest efficacy in clinical trials, others offer limited or inconclusive evidence. Additionally, fat-loss supplements are not without risks, and their safety profiles should be carefully considered before use. Consumers are advised to approach fat-loss supplements with caution, particularly those with stimulant ingredients or unproven claims.

Ultimately, a balanced diet, regular exercise, and behavior modification remain the most effective strategies for achieving sustainable fat loss.

References

Dulloo, A. G., Duret, C., Rohrer, D., Girardier, L., Mensi, N., Fathi, M., & Chantre, P. (1999). Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. The American Journal of Clinical Nutrition, 70(6), 1040-1045.

Hursel, R., & Westerterp-Plantenga, M. S. (2010). Thermogenic ingredients and body weight regulation. International Journal of Obesity, 34(4), 659-669.

Onakpoya, I., Terry, R., & Ernst, E. (2011). The use of green tea extract as a weight loss aid: A systematic review and meta-analysis. International Journal of Obesity, 35(4), 456-465.

Acheson, K. J., Gremaud, G., Meirim, I., Montigon, F., Krebs, Y., Fay, L. B., & Tappy, L. (2004). Metabolic effects of caffeine in humans: lipid oxidation or futile cycling? The American Journal of Clinical Nutrition, 79(1), 40-46.

Antonio, J., Newmire, D. E., Stout, J. R., Antonio, B., Gibbons, M., Lowery, L. M., … Arent, S. M. (2024). Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 21(1).

Hursel, R., & Westerterp-Plantenga, M. S. (2010). Green tea catechin plus caffeine supplementation to a high-protein diet has no additional effect on body weight maintenance after weight loss. The American Journal of Clinical Nutrition, 91(3), 593-600.

Whiting, S., Derbyshire, E., & Tiwari, B. K. (2012). Capsaicinoids and capsiate for weight management: a systematic review and meta-analysis of randomised controlled trials. Appetite, 59(2), 341-348.

Ludy, M. J., & Mattes, R. D. (2011). The effects of hedonically acceptable red pepper doses on thermogenesis and appetite. Physiology & Behavior, 102(3-4), 251-258.

National Institutes of Health, Office of Dietary Supplements. Dietary supplements for weight loss, https://ods.od.nih.gov/factsheets/WeightLoss-HealthProfessional/

Torgerson, J. S., Hauptman, J., Boldrin, M. N., & Sjöström, L. (2004). Xenical in the prevention of diabetes in obese subjects (XENDOS) study: a randomized study of orlistat as an adjunct to lifestyle changes for the prevention of type 2 diabetes in obese patients. Diabetes Care, 27(1), 155-161.

Padwal, R., Li, S. K., & Lau, D. C. W. (2003). Long-term pharmacotherapy for overweight and obesity: a systematic review and meta-analysis of randomized controlled trials. International Journal of Obesity, 27(12), 1437-1446.

Zhi, M., Shikany, J. M., & Villareal, D. T. (2009). The effect of a white kidney bean extract supplement on weight loss and carbohydrate absorption in overweight individuals: A randomized, double-blind, placebo-controlled trial. Journal of Obesity, 2009, Article ID 279460.

Tio, S. S., & Nelson, P. D. (2014). Efficacy of white kidney bean extract in reducing body weight and body fat in overweight and obese individuals: A meta-analysis of randomized controlled trials. International Journal of Obesity, 38(4), 534-543.

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