FOOD SUPPLEMENTS FOR WEIGHT LOSS
Overweight and obesity cause more deaths worldwide than underweight. The overweight and obesity states are more likely to develop hypertension, type 2 diabetes, arthritis, sleep apnea, dyslipidemia, cardiovascular diseases, various types of cancer, and premature death. Therefore, the importance of prevention and treatment of obesity is widely acknowledged .
There are various stated mechanisms of action in currently available dietary supplements, including improved carbohydrate metabolism, increased lipolysis or energy expenditure, and reduced appetite. As a result, more high-quality evidence is needed, however many of the investigated products seem to be effective, although of little clinical relevance when taken alone. In order to determine synergistic or additive activities in the absence of major adverse events, combinations aiming to target more than one mechanism of action should be adequately examined both from an efficacy and safety standpoint .
1. Reduced Nutrients Absorption as Purported Mechanisms of Action
Orlistat, a commercially available obesity medicine, works by inhibiting fat absorption in the intestine. Many food supplements exert their beneficial action through the same pathway, by delaying or limiting the absorption of lipids or carbohydrates. Notably, most of these compounds also recognize other mechanisms of action possibly contributing to their beneficial effect on metabolism, such as gastric emptying delay influencing appetite .
1.1 Green Tea
Green tea is an unfermented, popular beverage made from the leaves of the plant Camellia sinensis, historically used for medicinal purposes and, in recent decades, studied for its potentially beneficial health effects. Catechins, such as epigallocatechin-3-gallate (EGCG), and caffeine, the predominant component of tea, have been confirmed to possess a broad range of biological activities, including weight loss, improvement of the metabolic syndrome, prevention of cardiovascular diseases and cancer, and protection against neurodegeneration. Furthermore, green tea has been shown to be safe, with little side effects or adverse events .
One of the most effective ways tea can help people lose weight is by suppressing enzymes like pancreatic lipase, amylase, and glucosidase in the gastrointestinal tract. By inhibiting these enzymes, tea polyphenols lower the rate of absorption of fats and sugars, thus reducing caloric intake in the body and decreasing weight-gain .
The composition of gut microbiota is highly correlated with obesity and related diseases such as Type 2 Diabetes, as intestinal bacteria have been shown to affect fat storage, blood glucose balance, and appetite hormones. Green tea has two mechanisms for influencing the gut microbiome. The presence of undigested carbohydrates in the GI tract increases when amylase and glucosidase are inhibited, causing the microbiota to produce short-chain fatty acids, which have recently been discovered to be capable of activating AMP-activated protein kinase (AMPK) and inducing weight loss by down- and up-regulation lipogenesis and lipolysis, respectively. Moreover, most tea polyphenols (>90%) will pass through the small intestine unabsorbed due to their low bioavailability, eventually coming into direct contact with the gut microbes. These are capable of breaking them down into smaller and more bioavailable phenolic components, and in turn are modulated in terms of bacterial composition. Although no direct evidence is available to date attributing green tea induced weight loss to gut microbiota modulation, it is reasonable to assume that this might be one of the possible underlying mechanisms .
Green tea extract enriched beverages, differing by catechin and caffeine content and serving frequency, were compared for their effects on body weight and body composition in moderately overweight subjects for 90 days without any calorie restriction. The daily consumption of a green tea extract drink containing 886 mg catechins and 198 mg caffeine/day resulted in the greatest percent decrease in intraabdominal and total fat mass as well as total body mass, attended by a slight decline in lean body mass. Similarly, daily consumption of a beverage containing 625 mg catechins and 39 mg caffeine/day for 12 weeks resulted in greater total weight loss and fat mass loss in the abdominal area compared to placebo. Fat mass loss 86% of overall weight reduction, whereas lean body mass loss 14% .
1.2 White kidney bean
White kidney beans, commonly known as common beans, are a species of Phaseolus vulgaris L. that originated in South American countries such as Mexico and Argentina . White Kidney Bean is abundant in proteins (22-27% of seed weight) and carbohydrates (39-47% of seed weight), with a high content of bioactive compounds, such as peptides, among which are the α-amylase inhibitor named phaseolin, polyphenols, oligosaccharides, and lectins. Notably, the significant amount of lectins also raised some concerns, as these peptides may also act as toxins and allergens in addition to their anti-cancer and anti-obesity activities. Several reports are available regarding clinical adverse effects after ingestion of white kidney beans .
The Phaseolus vulgaris extracts (PVE) is rich in phaseolin, classical α‐amylase inhibitors (α‐AI), and known as “starch blocker.” In humans, the α‐AI is a natural bioactive component that belongs to the glycoside hydrolase class and antiamylase activity. The α‐AI interferes with the breakdown of complex carbohydrate leading to a reduced digestibility or prolonged digestion. Therefore, energy derived from the carbohydrate and the rate of body absorption of the energy in form of glucose are reduced. α‐AI can lower body weight, blood sugar, and blood lipids by inhibiting saliva and pancreatic amylase activity in the gastrointestinal tract, delaying or preventing the hydrolysis and digestion of the major carbohydrates in diet, and reducing the decomposition and absorption of starch sugars in foods .
β-Glucans are natural bioactive fibers or polysaccharides composed of D-glucose monomers, linked by 1,3, 1,4, or 1,6 β-glycosidic bonds. They can be taken orally as a food supplement or as part of a daily diet and are found naturally in the cell walls of bacteria, fungus, algae, and higher crops such as cereals. The study of the effects on health of β-glucans is complicated by the variability of their biological activities which depend on the source, the extraction and purification methods .
Antitumor, antimutagenic, immune-modulating, anti-osteoporotic, and antioxidant effects of β-glucans have been identified in several pre-clinical and clinical trials. Furthermore, they attracted the attention of nutritionists due to their beneficial effects on glucose and lipid metabolism. When glucans are included in a meal, the rate of carbohydrate and lipid absorption slows, leading to a reduction in plasma glucose and lipids. Alongside the well-established anti-diabetic and lipid-lowering properties, preclinical studies suggest that glucans may have anti-obesity effects through stimulating the gut-hypothalamic (Peptide YY- Neuropetide Y) axis, therefore increasing satiety in diet-induced obese mice. A dose-dependent increase in peptide YY levels has also been demonstrated in overweight adults following oat β-Glucans ingestion, suggesting that glucans may exert anorexigenic effects in humans as well. At the moment, there are no clinical trials that have evaluated the effect of β-glucans on weight loss other than one placebo controlled study in which overweight women followed a low-calorie diet plus β-glucans supplementation showing a similar decrease in body mass .
While there is promising evidence supporting the use of β-glucans 5–9 g/day as an anti-diabetic and lipid-lowering dietary supplement, data investigating their effects on body weight are lacking and uncertain, therefore no recommendations can be made regarding their use as weight loss supplements .
Psyllium is a water-soluble fiber derived from the husks of seeds from Plantago ovata, an officinal plant native to western and southern Asia. Soluble fiber can dissolve in water and form a viscous gel, which may decrease appetite by occupying the stomach and it may interfere with the absorption of carbohydrates, lipids and bile acids. Some evidence suggests that psyllium may be capable of lowering serum lipids, delaying gastric emptying, improving glycemic control, and promoting satiety. However, little is known relative to the role of psyllium in aiding body weight loss [2, 6].
The effectiveness of psyllium in inducing weight loss has been studied in the literature, with findings indicating that its consumption may have some beneficial effects in reducing body fat, particularly in long-term clinical studies with a duration between 6 and 12 months, when it was combined with a dietary program and lifestyle modifications .
Overall, the quality of evidence in literature evaluating the effects of psyllium consumption on weight loss is low and limited by the great heterogeneity between different studies in terms of duration, design, type of intervention, and dose utilized. Therefore, the use of psyllium supplementation for inducing weight loss cannot be recommended at the moment .
Ginseng refers to different varieties of a short, slow-growing plant with fleshy roots belonging to the Araliaceae family. The two main types of ginseng are Panax ginseng (Asian ginseng), also known as Korean Ginseng and Panax quinquefolius (American ginseng). Asian ginseng can be red or white depending on the drying method of the root. Different ginseng extracts are being studied for the treatment of several medical conditions, including body weight management .
Ginseng is supposed to contribute to weight loss through its elevated content of saponins which can delay the intestinal absorption of dietary fat by inhibiting pancreatic lipase activity .
Although P. ginseng has been shown to exert anti-obesity effects in several animal studies, there have been relatively few studies investigating its effects in humans. And in conclusion, the clinical relevance of ginseng as a weight loss aid remains uncertain, as the evidence quality supporting its use is low and the dose range very high (100 mg – 18 g/day). More research is needed to compare the effects of the two main types of Panax ginseng is also necessary .
2. Improved Fat Metabolism as Purported Mechanisms of Action
The World Health Organization defines obesity as a condition of fat excess rather than a simple increase in BMI. It should go without explanation that no weight loss intervention is clinically relevant if it does not coincide with a reduction in body fat. Supplements claiming to “burn” fat are widely used, although only a few of them have been shown in preclinical studies to effectively and safely improve fat metabolism. Even fewer have demonstrated efficacy in human studies. Herein, we provide detail on those supplements supported by the most clinical evidence .
2.1 Garcinia Cambogia
The fruit Garcinia cambogia (GC) is endemic to Southeast Asia. The rind is used as a food preservative, flavoring agent, or food bulking agent, as well as a traditional cure for constipation, edema, and a variety of other common ailments . Although many compounds have been extracted from GC fruit, hydroxycitric acid (HCA) is considered the active ingredient for the anti-obesity properties that this dietary supplement has shown .
HCA is an organic acid which has been proved to be a potent competitive inhibitor of adenosine triphosphate-citrate lyase, therefore reducing the availability of acetyl-coenzyme A for fatty acids and cholesterol synthesis .
In vivo studies confirmed the role of GC/HCA in stimulating fat oxidation, increasing serotonin release in the brain cortex and normalizing lipid profiles in humans. Clinical studies in obese subjects indicate that it may help with weight loss via raising serotonin levels. When used alone, the extract is safe; however, in efficacy studies, it is often combined with other components in weight loss formulas. In a clinical research with 92 overweight subjects following a moderate calorie-restricted diet for 12 weeks, a supplement containing standardized extracts of Garcinia cambogia, Camellia sinensis, unroasted Coffea arabica (green coffee fruit), and Lagerstroemia speciosa (banaba leaf) was given. Although the supplemented group had a significantly greater reduction in total body fat, approximately half of the weight lost was comprised of LBM .
Grapefruit is a citrus fruit, known for its bitter taste. It is rich in water, vitamins, minerals, and polyphenols, such as phenolic acids, flavonoids, lignans and stilbenes. Naringin and hesperidin, two of its polyphenols, have shown antioxidant, lipid-lowering, and antihypertensive activities in animal models and human clinical trials. Naringin and hesperidin are also able to improve glycemic control, enhancing insulin secretion and inhibiting gluconeogenesis. Naringin, like many other polyphenols, has been shown to stimulate the AMPK pathway, which increases fatty acid oxidation and inhibiting lipogenesis. Grapefruit extract and polyphenols inhibited cAMP-phosphodiesterase and activated hepatic peroxisome proliferator-activated receptor γ and α in cell and animal studies, resulting in lipolytic actions .
A 2014 review and meta-analysis, taking into account RCTs that analyzed the effect of grapefruit on weight and body composition in humans, showed no benefit regarding weight loss, but a positive effect on waist circumference and body fat percentage reduction. Of these, only one study found that eating half a grapefruit before meals three times a day for 12 weeks resulted in a significant weight loss in 24 obese subjects, while the group given grapefruit juice and grapefruit capsules did not lose weight. Interestingly, none of the studies included in this literature reported a significant reduction in daily caloric intake when subjects following ad libitum diets or hypocaloric diets received grapefruit or grapefruit juice, compared to placebo. These results may indicate that grapefruit effect on adiposity is independent of caloric intake and may be a consequence of the whole fruit consumption. However, the small number of trials included in the revision and their short duration may limit the results. It’s also worth noting that different results may be noticed if grapefruit is consumed in different quantities and modalities, taking into account that the included studies only investigated grapefruit or grapefruit juice as a preload before meals. Overall, low-quality evidence supports grapefruit or grapefruit juice as a weight loss agent. Moreover, grapefruit may alter the metabolism of several drugs through cytochrome P450 interactions. This should be kept in mind in people receiving daily pharmaceutical treatment, and grapefruit eating in large quantities should be avoided in these individuals. Altogether, its use cannot be recommended at this time .
Single-nutrient strategies may not be as effective as dietary strategies that include multiple potentially beneficial pathways. Furthermore, some strategies may work better in some individuals than others, depending on preference, which may be important for adherence, as well as individual susceptibility to weight regain and the underlying mechanism, which varies from person to person .
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- Watanabe M, Risi R, Masi D, Caputi A, Balena A, Rossini G, et al. Current Evidence to Propose Different Food Supplements for Weight Loss: A Comprehensive Review. Nutrients. [Internet]. 2020 [cited 2022 May 12]; 12: 1-43. Available form: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7551574/
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- Han Li-Kun, Zheng Yi-Nan, Yoshikawa M, Okuda H, Kimura Y. Anti-obesity effects of chikusetsusaponins isolated from Panax japonicus rhizomes. BMC Complementary Medicine and Therapies [Internet]. 2005 [cited 2022 May 13]; 5: 1-10. Available form: https://bmccomplementmedtherapies.biomedcentral.com/articles/10.1186/1472-6882-5-9#Sec13
- Fassina P, Scherer Adami F, Terezinha Zani V, Kasper Machado I, Garavaglia J, Quevedo Grave M, et al. The effect of Garcinia Cambogia as coadjuvant in the weight loss process. Nutrition Hospital. [Internet]. 2015 [cited 2022 May 13]; 32: 2400-8. Available form: https://pubmed.ncbi.nlm.nih.gov/26667686/
- Van Baak M, Mariman E. Dietary Strategies for Weight Loss Maintenance. Nutrients. [Internet]. 2019 [cited 2022 May 13]; 11: 1-12. Available form: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6722715/