About Weight-Loss Supplements
What do you think of the hundreds of weight loss supplements
out there on the shelves today? Are they worth the money? Will
they actually help you lose weight? How do you know which ones
are going to work for you? Is there any proof that these products
work?
Criteria adapted from a recent review can be used to develop
clinical recommendations for each supplement. If there is strong
evidence for a product's quality, safety, and efficacy, it may
be reasonable to recommend that product and closely monitor the
patient. No supplements discussed in this review meet these criteria,
however. In contrast, it would be appropriate to discourage use
of products when there is strong evidence for lack of quality,
safety, or efficacy. For example, use of products that contain
ephedra should be actively discouraged because of serious safety
concerns. Chitosan appears to be ineffective for weight loss and
should also be discouraged. The use of guar gum for weight loss
should be discouraged because of its lack of efficacy.
For products that do not fall into the categories to recommend
or to discourage use because of insufficient or contradictory
evidence, physicians should caution their patients about the risks
and benefits of using the product given the uncertainty in safety,
efficacy, and/or quality control. Chromium, CLA, ginseng, glucomannan,
green tea, HCA, l-carnitine, psyllium, pyruvate, and St. John's
wort fall into this category. If a patient chooses to use one
of these supplements, the physician should monitor the patient
closely for adverse effects as well as benefit
Supplements Purported to Increase Energy Expenditure
Ephedra alkaloids and caffeine compounds
Ephedra sinica (or Ma huang in Chinese) is a shrub native to
China and Mongolia that contains sympathomimetic compounds referred
to as ephedra alkaloids. Bitter orange and country mallow contain
related chemicals. Ephedra alkaloids commonly are combined with
caffeine or botanical sources of caffeine (e.g., guarana, yerba
maté) for weight loss. A recent meta-analysis of RCTs showed
a weight loss of 0.9 kg (2 lb) more per month for ephedra-containing
supplements compared with placebo. However, no long-term data
(i.e., greater than six months) on efficacy were available.
Using adverse event data from 50 trials of ephedra, a 2.2- to
3.6-fold increase in the odds of psychiatric, autonomic, cardiovascular,
and gastrointestinal symptoms was estimated.8 Another review9
of adverse events possibly associated with ephedra use included
87 reports to the FDA MedWatch program between June 1997 and March
1999. These reports included episodes of hypertension, arrhythmias,
myocardial infarction, stroke, and seizures. Ten events led to
death and 13 yielded permanent disability. Of these 23 reports,
nine occurred at recommended dosages of ephedra in persons without
significant preexisting cardiovascular risk factors.
Ephedra products comprised only 0.8 percent of all dietary supplement
sales in 2001, yet they were responsible for 64 percent of all
herb-related adverse events reported to U.S. Poison Control Centers
during the same year. Although ephedra-caffeine combinations may
be effective for modest weight loss, safety issues motivated the
FDA to ban their sale in April 2004.
Supplements Purported to Modulate Carbohydrate Metabolism
Chromium and ginseng
Chromium deficiency is associated with hyperglycemia, hyperinsulinemia,
hypertriglyceridemia, and low levels of high-density lipoprotein
cholesterol. Chromium is thought to play a role in carbohydrate
and lipid metabolism, potentially influencing weight and body
composition. However, data on healthy persons without diabetes
do not support this theory, and data on patients with diabetes
are inconclusive.
Most weight-loss supplements use chromium picolinate in daily
dosages of 200 to 400 mcg. The results of three RCTs that studied
the role of chromium in obesity did not show any differences in
weight loss between the treatment and placebo groups. However,
drawing conclusions from these studies is difficult because of
their small size (n = 15 to 36). Although short-term trials using
chromium picolinate did not report significant adverse effects,
there are theoretical concerns that this form of chromium could
generate free-radical damage. Rhabdomyolysis and renal failure,
possibly related to ingestion of more than 1,000 mcg daily of
chromium picolinate, have been reported. Because of the lack of
large, well-designed studies, the efficacy of chromium for weight
loss and its long-term safety profile remain uncertain.
Although preliminary data suggest that ginseng (Panax ginseng)
may improve glucose tolerance, no RCTs in humans have shown greater
weight loss with ginseng compared with placebo.
Supplements Purported to Increase Satiety
Glucomannan, psyllium, and guar gum
Numerous weight-loss products contain sources of soluble fiber,
which theoretically could absorb water within the gut, causing
increased satiety and lower caloric intake. Fiber also may improve
control of diabetes and hyperlipidemia, two common comorbidities
in patients with obesity. Examples include guar gum (derived from
the Indian cluster bean, Cyamopsis tetragonolobus), glucomannan
(Amorphophallus konjac), and psyllium (derived from the seed husk
of Plantago psyllium).
Although guar gum is relatively safe, a meta-analysis of 11 RCTs
of guar gum versus placebo for weight loss showed no benefit.
Three RCTs suggest that glucomannan in dosages of 3 to 4 g per
day may be well tolerated and yield modest weight loss. However,
these trials were small (n = 20 to 50) and had methodologic limitations.
Although psyllium improved glucose and lipid parameters significantly
more than placebo in 125 overweight patients with type 2 diabetes,
there were no differences in weight loss.
Supplements Purported to Increase Fat Oxidation or Reduce Fat
Synthesis
Hydroxycitric acid
Hydroxycitric acid (HCA) is derived from the Malabar tamarind
tropical fruit (Garcinia cambogia) native to India. HCA has been
found to inhibit mitochondrial citrate lyase, leading to decreased
acetyl coenzyme A production and decreased fatty acid synthesis.
A 12-week RCT of mildly overweight women (n = 89; mean BMI of
28.6 kg per m2) reported a 1.3 kg (2 lb, 14 oz) greater weight
loss in women who received 750 mg of HCA per day versus placebo.
In contrast, an RCT comparing a different formulation of HCA at
1,500 mg per day and placebo in 135 men and women with a higher
average BMI (31.2 kg per m2) showed no differences in BMI or adverse
events. Although HCA appears to be well tolerated, the evidence
for efficacy currently is contradictory.
Conjugated linoleic acid
Conjugated linoleic acid (CLA) refers to a family of trans-fatty
acids that have been found to reduce fat deposition in obese mice,
possibly through increased fat oxidation and decreased triglyceride
uptake in adipose tissue. A 12-week RCT31 of 60 patients using
3.4 to 6.8 g per day of CLA reported no change in BMI. Persons
taking CLA reported mild to moderate gastrointestinal symptoms.
Currently, no human data support the efficacy of CLA in weight-loss
products.
Green tea, licorice, pyruvate, vitamin b5, and l-carnitine
In one study, green tea increased fat oxidation and thermogenesis
in 10 patients, but the study was not designed to assess weight
loss. Licorice reduced body fat mass without changing BMI in 15
persons of normal weight. However, licorice has been reported
to cause pseudoaldosteronism, hypertension, and hypokalemia. Six
weeks of pyruvate, in a dosage of 6 g per day, was associated
with a weight loss of 1.2 kg (2 lb, 10 oz), compared with placebo.
Although vitamin B5 has been postulated to cause weight loss,
no human trials support this. Similarly, no trials demonstrate
that l-carnitine is effective for weight loss.
Supplements Purported to Block Dietary Fat Absorption
Chitosan
Chitosan, derived from chitin found in crustacean shells, is
a positively charged polymer thought to prevent fat absorption
by binding negatively charged fat molecules within the intestinal
lumen. A meta-analysis of five RCTs that evaluated chitosan and
placebo for weight loss showed a greater mean weight reduction
for chitosan (3.3 kg [7 lb, 4 oz]) over placebo. All of the studies
were conducted by the same team of investigators and several methodologic
concerns were noted.
Subsequently, three other researchers reported well-designed
RCTs that failed to show any differences in weight loss. Furthermore,
healthy persons taking chitosan have not shown clinically significant
increases in fecal fat excretion. Given the totality of the evidence,
chitosan appears to be safe in short-term studies, but is likely
ineffective for weight loss.
Supplements Purported to Increase Water Elimination
Dandelion (Taraxacum officinale) appears to have diuretic activity
and cascara (Rhamnus purshiana) acts as a laxative. Neither of
these herbs has been studied specifically for weight loss in humans.
Regarding safety, long-term use of these supplements theoretically
could cause adverse effects similar to those of conventional diuretics
and laxatives (e.g., dehydration, electrolyte abnormalities).
Other Common Supplements Used for Weight Loss
Although botanical remedies for depression such as St. John's
wort (Hypericum perforatum) often are found in weight-loss products,
no data support their role in weight loss. Laminaria (kelp) has
not been studied for weight loss. Spirulina (also known as blue-green
algae) contains phenylalanine, which is purported to inhibit appetite.
In 1981, the FDA declared spirulina ineffective for weight loss,
and no subsequent studies to the contrary have been published.
Guggul (derived from the myrrh tree, Commiphora mukul) and apple
cider vinegar, which contains various vitamins and minerals, have
not been studied for weight loss.
