By Richard B. Kreider, PhD, FACSM, FISSN
It seems you can’t open a magazine, turn on the television, or listen to the radio without hearing an advertisement about a fat-loss supplement. While it used to be easy to dismiss these types of advertisements as gimmicks, the truth is that we have come a long way in understanding that certain nutrients can affect fat metabolism, fat digestion, appetite and/or weight. Research has shown that some of these supplements can play an important role in helping people lose and/or maintain weight after fat loss. These supplements generally fall within one of five categories: meal replacements, thermogenics, fat metabolizers, fat blockers and appetite suppressants.1
So which are worth your hard-earned money? Read on.
Most of the products in this category represent low-fat/high-protein food alternatives.3 They typically consist of pre-packaged food bars, meal-replacement powders (MRP) or ready-to-drink (RTD) supplements. They are designed to serve as a lower calorie meal replacement or a low-fat snack to help people follow a diet.
Research has generally shown that if you replace a meal with a MRP or RTD, you typically lose weight by reducing total caloric intake. For example, Cheskin and co-workers4 reported that a diet using portion-controlled meal replacements yielded significantly greater initial weight loss and less weight regain after one-year follow-up than a standard self-selected food-based diet in patients with type 2 diabetes. The composition of the meal replacement may also influence results. For example, Treyzon and associates5 evaluated the effects of ingesting a high-protein (2.2 grams of protein per kg of lean mass) or high-carbohydrate (1.1 grams of protein per kg of lean mass) isocaloric meal replacement for 12 weeks on weight loss in 100 obese men and women.
Subjects ingesting the high-protein meal replacement lost significantly more fat mass (-3.6 lbs) than those consuming the high-carbohydrate meal replacement (-01.4 lbs). The type of meal replacement may also influence appetite. Thicker liquid meal replacement drinks suppress appetite to a greater degree than less dense drinks.6 In addition, meal replacement bars have been reported to be more satisfying in terms of reducing hunger than liquid meal replacements.6 These findings and others suggest that if you want to lose weight, meal-replacement bars and drinks certainly can help!
Thermogenics are supplements designed to increase resting energy expenditure and promote weight loss. For many years, most thermogenic supplements contained the “ECA” stack of ephedra alkaloids (e.g., ma huang, 1R,2S Nor-ephedrine HCl, Sida cordifolia), caffeine (e.g., guarana, bissy nut, kola) and aspirin/salicin (e.g., willow bark extract). Although a significant amount of research showed efficacy and safety of use of these supplements in healthy populations to promote weight loss,7,8 the Food and Drug Administration (FDA) banned the sale of dietary supplements containing ephedra alkaloids, citing safety concerns. Since then, most thermogenic supplements contain a combination of green tea extract, guarana (naturally-occurring caffeine), synephrine (e.g., Citrus aurantium, bitter orange), willow bark (a naturally occurring form of aspirin), capsicum (chili pepper), etc.10,11
A number of studies have found that ingestion of these types of supplements can increase energy expenditure.11-14 For example, Taylor and colleagues12 reported that ingestion of a coffee-containing green tea with extra caffeine increased resting energy expenditure (REE) by 14 percent, compared to a slight decrease in the coffee-only group. Rudelle and workers14 reported that ingestion of three 250ml servings of a beverage containing green tea, caffeine and calcium for three days, significantly increased 24-hour energy expenditure. In another study, Boschmann, et al.13 reported that ingestion of 300mg/day of green tea for two days significantly increased fat oxidation compared to controls. In another study, Auvichayapat and associates16 investigated the effects of supplementing the diet with green tea in obese individuals administered a diet. Participants who ingested green tea during the diet lost significantly more weight (5.9 to 11.2 pounds) and had a higher REE than subjects dieting while taking a placebo.
These findings support contentions that ingestion of green tea and caffeine can increase resting energy expenditure. There is also some preliminary evidence that chronic intake of green tea and caffeine can promote weight loss and/or help maintain weight after weight loss. For example, Westerterp and colleagues15 reported that habitual caffeine consumers were able to maintain weight loss after dieting to a greater degree than low-caffeine consumers. Moreover, supplementation of a green tea/caffeine mixture helped maintain weight loss in the group of habitually low-caffeine consumers. Collectively, these findings suggest that ingesting green tea and caffeine can increase resting metabolism, leading to greater weight loss over time.
A number of nutrients have been purported to promote fat metabolism. The rationale is if you burn more fat as a fuel at rest and/or during exercise, you can manage body composition to a better degree. The following are some of the most common fat metabolizers found in dietary supplements.
Calcium pyruvate hit the weight-loss scene about 10 years ago. Initial studies reported that calcium pyruvate supplementation (16-25 grams/day with or without dihydroxyacetone phosphate [DHAP]) promoted fat loss in overweight subjects following a medically supervised weight-loss program.17-19 Although the mechanism for these findings was unclear, the researchers speculated that it might be related to appetite suppression and/or altered carbohydrate and fat metabolism. Since calcium pyruvate is fairly expensive, several studies attempted to replicate these findings with smaller doses (i.e., 6-10 g/d). Kalman and colleagues20 reported that calcium pyruvate supplementation (6 grams/day for six weeks) significantly decreased bodyweight (-2.6 pounds), body fat (-5.5 kg) and percentage of body fat (-2.7 percent). However, Stone and colleagues21 reported that pyruvate supplementation did not affect hydrostatically-determined body composition during five weeks of in-season college football training. In a study from my lab,22 we found that 30 days of calcium pyruvate supplementation (5 grams taken twice a day) in moderately overweight females participating in a supervised exercise program produced a modest, but significant change in body fat (-0.3 kg). Collectively, there is evidence that taking at least 6 grams/day of calcium pyruvate can promote fat loss. It is unclear whether taking lower doses has any influence on body composition.
Carnitine serves as an important transporter of fatty acids into the cell for metabolism. Theoretically, increasing availability of carnitine in the cell would enhance fat metabolism. For this reason, L-carnitine has been one of the most common nutrients found in various weight-loss supplements. Over the years, a number of studies have been conducted on the effects of L-carnitine supplementation on fat metabolism, exercise capacity and body composition. Although there is some data showing that L-carnitine supplementation may be beneficial for some patient populations, most well-controlled studies indicate that L-carnitine supplementation does not affect muscle carnitine content, fat metabolism, and/or weight loss in overweight or trained subjects.23-25 For example, Villani et al.25 reported that L-carnitine supplementation (2 grams/day for eight weeks) did not affect weight loss, body composition, or markers of fat metabolism in overweight women. Actually, there is more evidence that carnitine L-tartrate may help athletes tolerate training stress26-28 rather than serve as a weight-loss supplement.
Interest in chromium as a potential body composition modifier emanated from studies suggesting that chromium may enhance insulin sensitivity/glucose disposal in diabetics. An initial study reported that chromium supplementation during resistance training improved fat loss and gains in lean body mass as determined by skinfold measurement.29 However, recent studies using more accurate methods of assessing body composition have mostly reported no effects on body composition in healthy non-diabetic individuals. For example, Volpi and associates30 reported that supplementation of 400 micrograms/day of chromium picolinate for 12 weeks did not significantly affect body composition, REE, or insulin levels in 44 overweight but otherwise healthy women. Lukaski and colleagues31 reported that 200 micrograms of chromium picolinate supplementation for 12 weeks did not enhance weight loss or influence body composition in 83 women placed on a diet. These findings and others do not support contentions that chromium picolinate supplementation promotes fat loss. However, Martin and co-workers32 recently reported that three months of supplementation with 1,000 micrograms per day of chromium picolinate significantly improved insulin sensitivity and glucose control while attenuating weight gain and visceral fat accumulation in type 2 diabetics. Consequently, it appears that if you have diabetes, chromium picolinate may help manage weight.
Citrus Aurantium (Bitter Orange Extract)
Citrus aurantium is a naturally occurring plant extract that has been reported to promote fat metabolism and thereby potentially serve as a weight-loss supplement.33-35 Citrus aurantium contains amines that stimulate beta-3 cell receptors, which stimulates the breakdown of fat. In addition, Citrus aurantium has been reported to increase metabolic rate as well as suppress appetite. For this reason, Citrus aurantium or bitter orange extract is found in numerous weight-loss products, as it has become a common replacement for ephedra alkaloids. While more research is needed to examine the effects on weight loss, preliminary research is fairly positive.
Conjugated Linoleic Acids (CLA)
CLA has been marketed as a health and weight-loss supplement since the mid 1990s. Although research in animals is very promising, the effect of CLA supplementation on weight loss in humans is less clear. There is some data suggesting that CLA supplementation may modestly promote fat loss and/or increases in lean mass.36-40 However, other studies indicate that CLA supplementation has limited to no effects on body composition alterations in untrained or trained populations. Recent, longer-term CLA studies have shown more promising results. For example, Steck and co-workers44 reported that CLA supplementation (6.4 grams/day) for 12 weeks promoted a significant increase in lean body mass. Gaullier et al.45 reported that six months of CLA supplementation (3 x 4 grams/day) in healthy overweight and obese subjects significantly decreased fat mass in 118 subjects. In another study from this research group,46 the researchers found that CLA supplementation for 24 months decreased fat mass and was well-tolerated in a group. Consequently, in the long term, CLA supplementation may help manage body composition as well as support general health status.
Garcinia Cambogia (HCA)
HCA is a nutrient that has been theorized to increase fat oxidation by inhibiting the enzyme citrate lyase and fat synthesis. Theoretically, this may lead to greater fat burning and less fat accumulation over time. Initial studies did not seem to support the potential weight-loss effects of HCA. For example, Heymsfield and co-workers47 reported that HCA supplementation (1.5 grams/day for 12 weeks) while maintaining a low-fat/high-fiber diet did not promote greater weight or fat loss than subjects taking a placebo. In addition, Mattes and colleagues48 reported that HCA supplementation (2.4 g/d for 12 weeks) did not affect appetite, energy intake, or weight loss. More recent findings support the theoretical benefits of HCA as a weight-loss supplement. Pruess and colleagues49 reported that ingesting 2.8 grams/day of HCA for eight weeks during a walking program and controlled diet promoted a 5.2 percent decrease in bodyweight. Likewise, Roongpisuthipong and workers50 reported that HCA supplementation for eight weeks while dieting (1,000 kcals/day) promoted greater loss in fat mass than those receiving a placebo. While more research is needed, these findings suggest that HCA supplementation may help promote fat loss.
A number of weight-loss products are designed to fill you up before you eat, in order to reduce hunger (e.g., high-fiber meals and glucomannan) or interfere with fat digestion and absorption (e.g., chitosan). The theoretical rationale of these supplements is simple. If you feel full, you may eat less. In addition, if you block fat absorption, less fat (and calories) will be stored in the body. The following reviews some of the supplements in this category.
Chitosan inhibits fat absorption somewhat like the weight-loss drug orlistat. Theoretically, ingesting chitosan prior to a meal would block absorption of fat and reduce the caloric load of the meal.51 Several animal studies report decreased fat absorption, increased fecal fat content, and/or lowered cholesterol following chitosan feedings.52,53 The effects of chitosan ingestion on weight loss is less clear. In a paper that compiled results of 14 clinical trials, chitosan was found to promote a small but statistically significantly greater weight loss than subjects taking placebo.54 These findings support contentions that chitosan can help block fat, leading to weight loss. However, since people are often more prone to eat when they know they are taking a fat-blocking supplement, the value may be limited.
One of the oldest and most common methods of suppressing the appetite is to eat high-fiber foods prior to a meal or a high-fiber diet. Ingesting high-fiber foods (fruits, vegetables) or fiber supplements increases the feeling of fullness (satiety). They typically allow you to feel full while ingesting fewer calories. Theoretically, maintaining a high-fiber diet may serve to help decrease the amount of food you eat. In addition, high-fiber diets/supplements have also been purported to help lower cholesterol and blood pressure, as well as help diabetics manage glucose and insulin levels. Some of the research conducted on high-fiber diets indicates that they provide some benefit, particularly in diabetic populations. For example, Raben et al.55 reported that subjects maintaining a low-fat/high-fiber diet for 11 weeks lost 2.9 pounds of weight and 3.5 pounds of fat. Other studies report either no significant effects or modest amounts of fat loss. Collectively, these findings suggest that maintaining a high-fiber diet may have some health benefit, but do not appear to promote marked weight or fat loss.
A water-soluble, polysaccharide dietary fiber derived from konjac root (Amorphophallus konjac) that forms a gel in the stomach when consumed. Glucomannan is an attractive dietary fiber, because it can absorb up to 200 times its weight in water. Konjac is commonly used as a dietary fiber in cooking and can be found in a number of foods (e.g., konjac cakes, konjac noodles, konjac slices, konjac chips, konjac tofu, etc.), as well as in a number of weight-loss dietary supplements.56 Research has shown that ingestion of high-fiber foods and glucomannan serves to occupy space in the stomach, provide a feeling of fullness, and reduces food intake leading to weight loss.57-59 For example, Walsh and co-workers reported that glucomannan ingestion (1 gram with 8 ounces of water 30 minutes prior to meals) for eight weeks promoted a 5.5-pound loss in bodyweight. Kraemer and colleagues reported that adding glucomannan to a resistance and endurance exercise program significantly improved body composition changes during training. In addition, glucomannan has been reported to slow blood glucose release from a meal58 and lower cholesterol levels.53,57,60 These findings suggest that adding glucomannan to your diet can help promote weight loss and improve health status.
A relatively new supplement to appear on the weight-loss scene. It is purported to affect glucose and fat metabolism, as well as inhibit sweet cravings. In support of these contentions, some recent data have been published by Shigematsu and colleagues61,62 indicating that short- and long-term oral supplementation of Gymnema sylvestre in rats fed normal and high-fat diets may have some positive effects on fat metabolism, blood lipid levels and/or weight gain/fat deposition. Although these findings are interesting, I am aware of no published studies that have evaluated the effects of Gymnema sylvestre supplementation on lipid metabolism or body composition in humans. Consequently, more research is needed before conclusions can be drawn.
A plant from the Kalahari desert that is believed to have appetite-suppressing properties.63 It has received a significant amount of attention in the popular media as a potential weight-loss supplement. The basis for this attention appears to be reports from the Council for Scientific and Industrial Research in South Africa, which identified extracts from Hoodia piliferan and Hoodia gordonii as possessing appetite-suppressing effects.64 Current research is attempting to characterize and understand the potential appetite-suppressing effects of Hoodia. However, I’m not aware of any published study on the weight-loss effects of Hoodia to date. Nevertheless, this is certainly a nutrient worth keeping your eye on for future studies.
Numerous nutritional and herbal products are marketed to promote weight loss. The available research suggests that the most effective weight-loss supplements appear to be those that help individuals manage a low-calorie diet (e.g., diet foods, MRPs, RTDs) and thermogenic supplements containing green tea and caffeine. High-fiber diets and diets supplemented with glucomannan also appear to help manage weight. There is evidence that CLA and possibly HCA may offer some long-term benefits for weight loss. The potential value of the remaining supplements purported to promote weight loss are currently unclear. As more research is conducted, we will have a better understanding of whether these nutrients or others may serve as effective weight-loss supplements. In the meantime, remember that although some of these nutrients can help, the best way to increase fat metabolism and promote weight loss is through exercise and eating a well-balanced, but slightly hypocaloric diet. So keep pumping the iron, exercise aerobically, watch your diet and make wise decisions regarding whether to try some of these weight-loss nutrients/supplements.
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