Today’s Dietitian
Vol. 16 No. 1 P. 58
Mounting scientific evidence continues to suggest that individuals can obtain several health benefits from drinking coffee in moderation. Studies indicate coffee consumption is inversely related to weight gain, may improve glycemic indicators that help prevent type 2 diabetes, and may even facilitate weight loss because of the thermogenic effects of caffeine and other pharmacologic elements found in coffee beans.1-3
With such promising results, it should come as no surprise that the multibillion dollar pharmaceutical and supplement industries aim to capitalize on coffee’s potential to improve health and well-being.
In 2014, the nutraceutical industry is projected to bring in more than $350 billion, in part because of the sale of products such as green coffee bean extract, a supplement heralded as a way to slim the waistline and maintain metabolic health with no changes to dietary behavior or physical activity level necessary.3
What Is It?
Commonly identified by the ingredient name Svetol or GCA (for green coffee antioxidant), green coffee bean extract is taken from coffee beans (the seed of the Coffea canephora plant) before roasting, which destroys some of its biologically active properties. What is thought to make green coffee bean extract a potential fat-burning powerhouse isn’t the caffeine but one of its other components: chlorogenic acid, a dietary phenol also found in some fruits and vegetables.1,2
Chlorogenic acids have been shown to exert powerful antioxidant effects in vitro, and evidence suggests that these compounds may beneficially alter serum lipid levels, postprandial glucose, and glucose tolerance and affect intestinal glucose uptake.2,4 However, what makes chlorogenic acid effective for weight loss and weight management remains unclear. The current hypothesis suggests that the alteration of intestinal glucose uptake (likely via the inhibition of hepatic glucose-6-phosphatase) affects glucose absorption and can decrease caloric input from carbohydrate consumption.2,5
TV Promotion
In May 2012, green coffee bean extract made its pop culture debut on The Dr. Oz Show, which features Mehmet Oz, MD. In September 2012, the extract was the focus of a segment where Oz positioned it as “one of the most important discoveries we’ve made” to help with weight loss.6
During this episode, Oz released the results of a study he and his medical team conducted using almost 100 volunteer fans of his show. Women between the ages of 35 and 49 who were overweight, defined as having a BMI between 25 and 45, and who didn’t have preexisting medical conditions such as diabetes or heart disease and who weren’t pregnant were eligible to participate in a two-week study during which they were randomly assigned to take green coffee bean extract or a placebo. The placebo group lost 41.5 lbs (approximately 1 lb each), even while instructed to alter nothing about their diet or exercise habits aside from keeping daily food logs. The experimental group, which took 400 mg of green coffee bean extract three times per day 30 minutes before eating, saw a total weight loss of 81.5 lbs (almost 2 lbs per person on average).
These results prompted Oz to conclude that taking green coffee bean extract, in the dosage and manner used for the study, could potentially produce double the weight loss of using food logs alone.
While this short, small, quasiexperimental trial appears promising, the results (including any statistical analysis) haven’t been made public or formally published beyond what was aired on the show, prompting many to question the study’s usefulness beyond its entertainment value. Oz tells his viewers that the study results are consistent with the existing research on green coffee bean extract, but what exactly does the research say?
The Evidence
To date, one meta-analysis looked at the effects of green coffee bean extract in human clinical trials to evaluate its effectiveness.1 Published in 2011, the study authors could identify only three studies eligible for their final analysis, which excluded studies that weren’t designed as randomized, double-blind, placebo-controlled clinical trials that reported BMI and/or body weight as an outcome when measuring the effectiveness of green coffee bean extract in overweight or obese individuals.
The meta-analysis of these three trials revealed a decrease of almost 5 lbs in body weight for individuals who received green coffee bean extract compared with placebo (a moderate effect). The study authors, however, remained cautious regarding the extract’s potential as a weight-loss supplement, noting major methodological limitations in the clinical trials done to date. These trials, they noted, were heterogeneous, consisted of very small sample sizes (the total number of participants was approximately 150 among the three studies), and short in duration, which makes drawing conclusions about the long-term efficacy of the extract imprudent.
The authors also raised concerns regarding green coffee bean extract safety and dosage, as little was reported regarding adverse side effects from taking the supplement, and noted that the type and amount of extract necessary to be effective remains unclear. Additionally, at least one of the clinical trials included for analysis was associated (at least loosely) with a pharmaceutical company that markets the extract as a weight-loss product.
Since the meta-analysis published in 2011, additional studies have reported success with green coffee bean extract as a weight-loss aid. The research receiving the most widespread attention was a crossover study published in 2012 that showed a significant weight loss of approximately 17 lbs—along with a corresponding decrease in body fat (4 percentage points)—in 16 overweight subjects taking the extract.3 Most interestingly, the observed weight loss and changes in body fat occurred only during phases of the study when participants were taking the extract and not during the placebo arm of the study.
Another study out of Korea found similar results in 23 overweight women, demonstrating a significant reduction in body weight and body fat percentage after eight weeks of green coffee bean extract use compared with a placebo group.7
Neither study reported widespread side effects associated with taking the extract, prompting one set of study authors to posit that it could be a natural, lower-cost, “superior alternative” to prescription weight loss aids such as orlistat—often associated with several adverse reactions—for comparable weight loss.3
More Research Needed
While these studies lend additional support to green coffee bean extract’s potential as a weight-loss aid, they don’t do much to address the major methodological concerns raised in the 2011 meta-analysis. Clinical studies continue to be tied to industry funding as well as include small sample sizes, short duration exposure, and varying types and dosages of the extract.
For now, and until more legitimate clinical research becomes available, dietitians should keep an eye out for clients using green coffee bean extract and spill the beans, cautioning them that the current evidence regarding its safety or efficacy isn’t strong enough to recommend its use as a weight-loss aid.
— Christin L. Seher, MS, RD, LD, is an instructor and nutrition consultant in northeast Ohio.
References
1. Onakpoya I, Terry R, Ernst E. The use of green coffee extract as a weight loss supplement: a systematic review and meta-analysis of randomized clinical trials. Gastroenterol Res Pract. 2011;2011:382852.
2. Thom E. The effect of chlorogenic acid enriched coffee on glucose absorption in healthy volunteers and its effect on body mass when used long-term in overweight and obese people. J Int Med Res. 2007;35(6):900-908.
3. Vinson JA, Burnham BR, Nagendran MV. Randomized, double-blind, placebo-controlled, linear dose, crossover study to evaluate the efficacy and safety of green coffee bean extract in overweight subjects. Diabetes Metab Syndr Obes. 2012;5:21-27.
4. Bonita JS, Mandarano M, Shuta D, Vinson J. Coffee and cardiovascular disease: In vitro, cellular, animal, and human studies. Pharmacol Res. 2007;55(3):187-198.
5. Narita Y, Inouye KJ. Kinetic analysis and mechanism on the inhibition of chlorogenic acid and its components against porcine pancreas alpha-amylase isozymes I and II. J Agric Food Chem. 2009;57(19):9218–9225.
6. Green coffee bean extract: the fat burner that works! The Dr. Oz Show website. http://www.doctoroz.com/episode/green-coffee-fat-burner-works. September 10, 2012.
7. Park JY, Kim JY, Lee SP, Lee JH. The effect of green coffee bean extract supplementation on body fat reduction in overweight/obese women. Kor J Nutr. 2010;43(4):374-381.
