今天去药店买药，看见药店正在非常给力地宣传一个产品左旋肉碱L-CARNITINE,居然还叫嚣：“不信上百度搜去啊”。明知没有什么有效的减肥药品，但处于好奇，还是Google一些学术论文。其中注意到了这篇在99年发表的《The effectiveness of popular, non-prescription weight loss supplements 》：https://www.mja.com.au/public/issues/171_11_061299/egger/egger.html
文章中提到的无任何减肥效果的药物除了左旋肉碱之外，还有Brindleberry (Garcinia cambogia/indica)，Capsaicin，Caffeine/Guarana，Chitosan，Chromium picolinate，Fucus vesiculosus，Ginkgo biloba，Pectin，Grapeseed extract，Lecithin，Horse chestnut (escin),Sweet clover/soy beans (isoflavones), St John's wort, milk thistle, inositol, collagen hydrolysate, citrin K, glycerine, aminogen, pyruvate, various amino acids, potassium sorbate, sodium benzoate and demineralised water
附:《The effectiveness of popular, non-prescription weight loss supplements》全文
The effectiveness of popular, non-prescription weight loss supplements
Garry Egger, David Cameron-Smith and Rosemary Stanton
MJA 1999; 171: 604-608
Objectives: To review the evidence for the effectiveness of popular, non-prescription weight loss supplements.
Data sources: A detailed literature search including all relevant medical and supplementary medicine databases and evidence submitted from manufacturers.
Data synthesis: The theoretical basis and rationale for the use of each substance is considered along with available research in the published literature on effectiveness and potential risks. We classified the level of evidence represented by the main research studies on each substance.
Conclusions: There is no good evidence for any weight loss benefits from most of the substances reviewed here. There is some support for mild effects of capsaicin, caffeine and fibre, but only in whole foods. In some cases (eg, chitosan), there is a plausible theoretical basis for the product, but no supporting proof of effect in humans in the absence of a calorie-controlled diet. Possible synergistic effects of different ingredients cannot be dismissed, but cannot be assessed from current data. There is an absence of good quality research on many substances, which means that advertising claims may be misleading.
Obesity is increasing in Australia, as it is worldwide.1 Over 63% of Australian men and 47% of women are now overweight or obese.2 Lifestyle change is generally regarded as a prerequisite for successful long-term weight loss. However, this takes time and is often difficult to achieve in an "obesogenic" environment.3 As a consequence, there is a big demand for weight loss medications. The lack of effective prescribed medications and the fact that there is no formal approval or clinical testing required for non-prescribed products has increased the opportunities for these products in the marketplace. This article reviews the evidence for the effectiveness of the most popular ingredients included in these products.
We surveyed weight loss products available in the marketplace to create a list of non-prescription weight loss treatments and their most popular ingredients. We then conducted detailed searches through PubMed, Medline, Medscape, Reuter's Health Service, and the Dietary Supplements database of the US National Institutes of Health. Search terms used were weight loss, obesity, drugs, medicines, medication, supplements, herbal supplements, and treatments. We also sent letters to all Australian manufacturers or distributors of products on our list, asking for supportive evidence of effectiveness (only one response was received).
Published evidence from peer-reviewed journals was considered primary, although the theoretical basis of claims from promoters and non-peer-reviewed publications was also evaluated. We used a structured format to review each substance, rating levels of evidence according to National Health and Medical Research Council guidelines (see Box).4 Evidence below level IV was discounted. Secondary sources of evidence and animal studies are excluded, but are available in a wider review that is available from the authors.
All weight loss is considered to be mediated through changes to energy intake and/or energy expenditure, and substances claiming effects without mediation through either or both of these mechanisms have been discounted.
Source: Rind of an exotic citrus fruit (Malabar tamarind). Active ingredient is hydroxycitric acid.
Products: "Slim Life", "Brindleslim", "Medislim", "Beer Belly Busters".
Proposed action: Reduces lipogenesis de novo; reduces appetite through glucostatic mechanisms.
Evidence: Conversion of carbohydrate into fat (lipogenesis de novo) is not the basis of most fat storage in humans.5 Similarly, the "glucostatic" model of appetite is now regarded as an oversimplification of the appetite process.6
Six peer-reviewed studies have examined hydroxycitric acid and weight loss in humans. Of these, five reported some positive results7-12 (E31-E4), but all had experimental inadequacies (for a more detailed review see reference 12). Two were reported as abstracts only.9,10 A recent randomised controlled study (E2) found no differences in weight loss between a group of obese individuals given 1500 mg of hydroxycitric acid daily and another group given placebo over a 12-week period.12
Conclusions: There is no strong support for the use of brindleberry in weight loss. The theoretical basis of claims made is also questionable.
Source: Major pungent ingredient of hot chillies and peppers.
Products: "Optislim 2000". Also found in spicy foods.
Proposed action: Increases metabolism; decreases appetite.
Evidence: Capsaicin activates neurons and neuropeptides thought to suppress appetite.13 It may also increase secretion of epinephrine, which stimulates gluconeogenesis and lipolysis.14 One recent study (E31) has shown that a spicy food entree containing capsaicin may reduce food intake by about 200 kcals.15 Two studies (E32) have not shown any changes in oxygen consumption, fat utilisation or body temperature.16-17 However, different concentrations of capsaicin in various types of foods may affect research outcomes.18 There is no evidence that capsaicin exerts a thermogenic effect as a supplement.
Risks: Very spicy food can cause short-term pain.19
Conclusions: Capsaicin in low-fat, spicy foods may add variety to a low energy diet, with some possible benefits on energy balance. There is no support for taking the substance as a supplement.
Source: Caffeine is found in coffee, tea, cocoa and cola drinks and guarana, which is extracted from the leaf of a South American vine (Paullinia cupana).
Products: "Slim Life", "Beer Belly Busters", "Body Lean".
Proposed action: Increases alertness and decreases fatigue; may increase availability of free fatty acids for oxidation.
Evidence: The role of caffeine in increasing free fatty acids into the circulation and sparing glycogen in endurance events is well accepted.20 Some studies (E31) have shown that the lipolytic effect of caffeine may be less in the elderly21 and in individuals needing to lose excess body fat.22 Caffeine has been shown in at least four studies (E2-E4) to stimulate the metabolic rate for up to 24 hours after ingestion.22-25 It has also been shown (E31) to decrease the perception of work effort.26
Several good quality studies27-33 (E2-E32) have examined the effects of caffeine on weight loss in humans, but usually in combination with other substances. Only one has examined caffeine alone (200 mg daily) added to an energy-restricted diet in a placebo-controlled, double-blind trial.27 In that study caffeine was no more effective than placebo in promoting weight loss. The remaining studies examined the effectiveness of caffeine in combination with ephedrine,28-31 fibre or chromium.32 Caffeine-chromium-dietary fibre combinations have not been found to cause greater weight loss (E2).32 A caffeine-ephedrine combination has, but results in adverse side effects (tolerance and addiction).33 Hence, there is a theoretical basis for caffeine in weight control, and good evidence for its lipolytic effect. However, controlled studies have not shown fat loss in overweight individuals using caffeine without an energy-restricted diet. No studies have reported on the effects of guarana on weight loss.
Risks: Large doses of caffeine can cause nervousness, anxiety, gastrointestinal discomfort, insomnia, heart arrhythmias and mild hallucinations, and may lead to dependence.34
Conclusions: Caffeine, as part of a normal diet, may, at best, have some minor effects on energy balance. However, this has not been proven by research on caffeine alone. No studies are reported of the effects of guarana on weight loss.
Source: An amino acid found in meat and dairy products or made in the liver and kidney from the amino acids lysine and methionine.
Products: "Fat Metaboliser", "Pro-sport L-Carnitine" and "ProteCol".
Proposed action: Increases fat metabolism.
Evidence: Two studies (E31 and E32) have shown no changes in the rate of fat oxidation following L-carnitine supplementation.35,36 Supplements can increase plasma carnitine concentrations, but have no effect on muscle carnitine levels.35 The uptake of carnitine by muscle is a controlled process, with the concentration inside the cell 50-100 times greater than that circulating in the plasma, suggesting the involvement of a controlled, active transport mechanism and biological compensation.37 No controlled studies examining the effects of L-carnitine on weight loss have been published.
Risks: Oral supplementation may cause diarrhoea, but no other major adverse effects have been noted.
Conclusions: There is no evidence that L-carnitine assists weight loss.
Source: Chitosan is an amino polysaccharide derived from the powdered shells of marine crustaceans such as prawns and crabs.
Products: "Chitorich", "Exofat", "Fatsorb", "Fat Breaker" and a number of other products labelled "Chitosan".
Proposed action: Binds to dietary fat, preventing digestion and storage.
Evidence: Most studies have been in animals. Some studies in humans (E32-E4) have shown lipid-lowering38 as well as weight loss with chitosan,39-41 although none have been published in peer-reviewed journals and all were limited by methodological flaws, including small numbers, high drop-out rate and lack of adherence to a high-fat diet. Trials (E32 and higher) have shown a weight-loss effect when chitosan was given with a hypocaloric diet for up to 4 weeks,40,42-46 but a meta-analysis of these studies47 shows discrepancies in the data, suggesting that the studies are flawed. In a recent randomised controlled trial, no effect of chitosan was found without a reduction in food intake.48 However, this study involved only 17 people over one month. Malabsorption of fat in the digestive tract may theoretically affect energy uptake, but there is no long-term evidence showing the effectiveness of this strategy for weight loss with a substance such as chitosan.
Risks: Some malabsorption of essential nutrients is possible. If chitosan was effective, steatorrhoea could be a potential problem.
Conclusions: Malabsorption of fat in the digestive tract may have a limited effect on restricting energy uptake. However, in the absence of a low energy diet, the available evidence does not show that chitosan can assist in weight loss in humans.
Source: An organic derivative of chromium, an element required for normal carbohydrate and lipid metabolism.
Products: "Body Lean", "Chromaslim", "Medislim", "Beer Belly Busters" and "Protecol".
Proposed action: Increases satiety. Increases energy expenditure through thermogenesis.
Evidence: A number of double-blind, placebo-controlled studies (E2) have reported on the effects of chromium supplementation and exercise on body composition in non-obese individuals. Two showed a greater effect on fat loss with supplementation,49-50 but have been criticised on methodological grounds.51 The remaining five, reviewed by Anderson,52 showed no effect. Two further studies of obese individuals randomised to either diet or diet plus exercise programs (E2 and E31) failed to show greater weight or fat loss with chromium supplementation.32,53
Conclusions: There is no good-quality evidence to support any benefits of chromium picolinate in fat loss.
Source: Fucus vesiculosus is a seaweed.
Products: "Cellasene", "Medex", and "Bioslim" diet patches.
Proposed action: Iodine in Fucus vesiculosus increases thyroid response, leading to excess energy expenditure.
Evidence: There is only one, inconclusive published study (in French) on the effects of Fucus vesiculosis in obesity.56
Risks: Possible hyperthyroidism if taken in excess.
Conclusions: Obesity can result from hypothyroidism, but it is a rare cause. The human thyroid gland can tolerate wide fluctuations in iodine levels and there is no evidence that increasing iodine intake in non-thyroid-deficient individuals has any effect on weight loss.
Source: The leaves of the maidenhair tree (Ginkgo biloba).
Products: "Cellasene", "Cellusense" and related products.
Proposed action: Stress reduction, leading to reduced eating.
Evidence: Ginkgo has been associated with a reduction in adrenal peripheral benzodiazepine receptors57 and hence may reduce the corticosteroid response to stress. Some stress-related medications have neural-mediation effects similar to those of appetite-suppressant drugs,58 and in some cases there are indications of an effect on weight loss. However, their anxiolytic effects may be a contraindication in the treatment of people for whom stress reduction may actually increase eating.59 Some well-controlled trials support the use of ginkgo as a mild anxiolytic,60 but there are no studies showing it affects weight loss.
Risks: Possibility of "serotonin syndrome" if combined with antidepressant medications, or some non-prescription preparations.61
Conclusions: Gingko may have some effect on stress and therefore theoretically help in cases where obesity is due to stress-related overeating. However, there is no available evidence to support this, and gingko could be contraindicated in some cases.
Source: Soluble fibre extracted from fruit.
Products: "Zellulean", "Beer Belly Busters", "Exofat" and "Fatsorb".
Proposed action: Satiation and decreased energy density leading to decreased food intake.
Evidence: High-fibre foods containing pectin (among other fibres) can help lower cholesterol levels and are also promoted for people with diabetes.62 One study (E4) claimed that as little as 5 g of pectin could delay gastric emptying and increase satiety,63 but the subjects were not overweight and no weight loss effect was shown. Another, uncontrolled study in Germany of eight overweight people over two weeks (E4) claimed success for a formula diet containing 3 g of apple pectin and 14.3 g of wheat bran.64 Longer-term studies show no effects on weight loss from fibre supplements.65
Risks: Low for most fibre, particularly soluble.
Conclusions: There is no long-term evidence of weight loss from fibre supplements. A diet high in fibre-rich foods, on the other hand, is known to be of benefit in weight loss.66
Source: Grape seeds.
Proposed action: Not specified.
Evidence: There is no rationale for weight loss presented in well-respected herbal texts and no published studies.
Risks: None known.
Conclusions: There is no evidence or rationale for grapeseed extract in weight loss.
Source: Phospholipid found in or soybeans, egg yolk and also made within the intestine.
Products: "ProteCol", "Cellasene", "Cellusense" and related products.
Proposed action: Prevents deposition of fat in fat cells.
Evidence: One two-year Swedish study (E31) looked at lecithin in protein powder with kelp and vitamin B6. There were negligible benefits for 24 women who started on this diet, although the authors note that compliance was poor.67
Risks: None known.
Conclusions: There is no support for the theory or practical use of lecithin in weight loss.
Source: Seed extract from horse chestnut.
Products: "Cellasene" and related products.
Proposed action: Aids circulation and prevents oedema.
Risks: None known.
Conclusions: Although reduced oedema may cause weight loss through loss of body fluid, this does not imply fat loss, so escin does not appear to be an effective treatment.
Source: Phytoestrogens from soybeans or sweet clover.
Products: "Cellasene" and related products.
Proposed action: Not specified.
Evidence: One study (E31) reported that women taking extra isoflavones had no change in body weight.68
Risks: None known for adults.
Conclusions: There is no evidence to support the use of isoflavones in weight loss.
Source: St John's wort is a herb.
Products: "Beer Belly Busters".
Proposed mechanisms: Not specified, but an antidepressant effect may reduce depression eating.
Evidence: Extracts of St John's wort are recognised as a mild antidepressant.69 However, there are no published studies showing any effects on weight loss.
Risks: Not known.
Conclusions: While St John's wort has been shown to have antidepressant effects, there is no evidence that it is effective in reducing weight.
Other substances in weight loss preparations include milk thistle, inositol, collagen hydrolysate, citrin K, glycerine, aminogen, pyruvate, various amino acids, potassium sorbate, sodium benzoate and demineralised water. There is no theoretical or practical rationale for the effectiveness of any of these substances in weight loss and no published data supporting their effectiveness, either singly or in combination.
There is little positive evidence that any of the ingredients reviewed here are effective in weight loss. For most, the data are equivocal or lacking in either quantity or quality. There is limited support for capsaicin, caffeine and fibre, but only when they are consumed in foods and, even so, the evidence is not strong. Only caffeine combined with ephedrine appears to be effective, but side effects limit the usefulness of this combination.
More detailed future research may show advantages for these and other non-prescribed substances. The possible benefits of synergistic effects between ingredients can not be ruled out and need further study. Average long-term weight losses, even with proven prescribed medications, are poor and only exist while a drug is being taken. If non-prescribed substances are to be successful, lifetime use may be needed, as in other chronic disorders.
Lifestyle changes should be considered the basis of any weight loss initiative, even though counselling about such changes takes time and is difficult to achieve in the modern "obesogenic" environment.
Consumer protection demands that weight loss claims should be based on evidence. Manufacturers of weight loss supplements should prove the effectiveness of their products through impartial, well-controlled trials. Lack of positive evidence, while not necessarily disqualifying sale of a particular product (provided safety issues are satisfied), should certainly disqualify the use of unverified claims relating to these products.
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(Received 1 Apr, accepted 23 Sep, 1999)
School of Health Sciences, Deakin University, Melbourne, VIC.
Garry Egger, MPH, PhD, Adjunct Professor of Health Sciences, and Director, Centre for Health Promotion and Research, Sydney.
David Cameron-Smith, BSc, PhD, Lecturer in Nutrition.
Moss Vale, NSW.
Rosemary Stanton, BSc, CNut/Diet, Consultant Nutritionist.
No reprints will be available from the authors.
Correspondence: Dr Garry Egger, PO Box 313, Balgowlah, NSW 2093.