THE BLOG
06/17/2014 05:16 pm ET Updated Aug 17, 2014

Science or Science Fiction? Evaluating 4 Popular Fat Loss Supplements

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Burn fat fast. Crank up your metabolism. Get a beach body by summer.

You've read the hyperbolic promises fat loss supplements often make, accompanied by before-and-after pictures of a former overweight person who used that product and now looks absolutely fabulous.

Then you read the fine print. Maybe that "miracle supplement" isn't such a miracle after all...

Rather than rely on hype or savvy marketing, I looked at the science behind four popular fat loss supplements. Will they increase your metabolism or otherwise help you lose fat fast? An emphatic maybe is my short answer. Read on.

Green coffee bean

What is it?

An extract found in raw coffee. The polyphenol antioxidant chlorogenic acid (CGA), also found in some fruits and vegetables, seems to provide most of green coffee extract's (GCE) benefits. Extracted GCE becomes frequently marketed as a weight loss supplement. Among its purported benefits include reduced gut glucose absorption and decreased glucose accumulation after meals.

What do the studies say?

Studies have been fairly favorable about supplementing with green coffee extract (GCE).

One mice study found GCE possibly effective against weight gain and fat accumulation. Another mice study showed decaffeinated green coffee improves diet-induced insulin resistance and brain energy metabolism.

Fewer human studies about GCE exist. One 22-week randomized, double-blind, placebo-controlled, linear dose, crossover study using GCA (a brand of GCE) found GCE can help reduce "weight in preobese adults, and may be an inexpensive means of preventing obesity in overweight adults."

And a meta-analysis that reviewed three eligible clinical human trials found "a significant difference in body weight in GCE compared with placebo." However, researchers found every study they reviewed "associated with a high risk of bias" with poor methodological quality.

Studies show humans absorb and metabolize chlorogenic acid and other nutrients in GCE very well.

My thoughts

Studies appear promising about green coffee extract (GCE). I wouldn't expect any miracles on its own, but combined with an intelligent eating plan that addresses food intolerances, GCE might become that needle mover to overcome plateaus and nudge you towards fat loss.

Conjugated linoleic acid (CLA)

What is it?

A naturally-occurring fatty acid found in many dairy products and meat. Among CLA's purported benefits as a dietary supplement include improving fat loss.

What do the studies say?

Most have been positive. Some show CLA can help decrease body fat mass and increase body lean mass as well as reduce fat accumulation.

CLA seems to target abdominal (belly) fat -- the type of stubborn, won't-vacate fat we all want to get rid of.

Several longer-term studies confirm those benefits. A one-year double-blind, placebo-controlled study found long-term CLA supplementation helps reduce body fat mass (BFM) in healthy overweight adults, while another study found CLA could prevent holiday weight gain and "significantly reduced body fat over six months."

Getting the right amount of CLA becomes crucial here. One meta-analysis found supplementing with 3.2 grams of CLA daily creates modest fat loss in humans.

Some researchers express concern about potential adverse effects using CLA, including lipid profile, glucose metabolism, and insulin sensitivity. Yet for most people, CLA seems safe at the recommended dose.

My thoughts

Patience and taking the right amount become crucial with CLA supplementation. Don't expect dramatic overnight changes, but combined with a smart diet and exercise, supplementing with CLA might provide a favorable nudge on the scales. To get the 3.2 grams the above study recommended, you'll need to take four or five soft gels daily.

Garcinia Cambogia

What is it?

Perhaps the most-hyped supplement currently on the market, mostly due to Dr. Mehmet Oz calling Garcinia cambogia "an exciting breakthrough in natural weight loss."

The Garcinia cambogia plant's skin contains hydroxycitric acid (HCA), which seems to provide most of the supplement's benefits.

While marketed as a fat-loss supplement, researchers aren't entirely clear how HCA works. Some speculate it increases fat breakdown, others that it down-regulates obesity genes; still others believe HCA can increase your feel-good neurotransmitter serotonin to suppress appetite.

What do the studies say?

Almost all involve animals. One using high-dose Garcinia cambogia found it suppressed fat accumulation in obese rats but also created toxicity in the testis. Later reviews found design flaws in this study and argued the HCA used may have been contaminated.

Regardless, human studies haven't been as promising. Researchers in one review found little evidence to support using Garcinia cambogia. Another randomized control trial with 135 people concluded, "Garcinia cambogia failed to produce significant weight loss and fat mass loss beyond that observed with placebo."

A meta-analysis using nine studies found small but statistically significant difference in weight loss in the HCA group. Researchers concluded Garcinia extracts and HCA can benefit short-term weight loss, although one study noted gastrointestinal side effects occurred twice as often in the HCA group.

Garcinia cambogia seems to work best combined with other nutrients. One very recent study that combined Garcinia cambogia with Ascophyllum nodosum extract and l-carnitine concluded these nutrients as a team could suppress appetite.

My thoughts

Combined with other nutrients as a synergistic fat loss formula, Garcinia cambogia might become beneficial, though studies don't support those benefits using it alone.

Raspberry Ketones

What is it?

Rheosmin or raspberry ketone resembles capsaicin and synephrine, two compounds that favorably alter fat metabolism. Reported benefits as a supplement include fat loss and improved lean body mass.

What do the studies say?

Almost all raspberry ketone studies involve animals. One involving mice found raspberry ketones prevented fat accumulation and increased fat breakdown in fat cells. Another rodent study showed raspberry ketones help break down fat.

In both studies, researchers fed these rodents massive amounts of raspberry ketones -- potentially impractical or unsafe to replicate on humans -- to get those effects, and no human studies using raspberry ketones alone exist.

One human study did use a branded product that combined raspberry ketones with other weight loss aids like caffeine and ginger.

Researchers found beneficial body-fat changes in the overweight men and women who used this product compared with the placebo, though we're not sure whether raspberry ketones or another component provided those benefits.

My thoughts

As a supplement, raspberry ketones seem to have the most effect when combined with other nutrients to create a synergistic fat loss supplement. Even then, I would hardly consider it the "miracle supplement," as some folks describe raspberry ketones.