The mechanism(s) of the significant effects of GCA on weight loss, BMI, percent body fat, and heart rate are unknown. There have been some recent articles indicating that chlorogenic acid and its metabolite, caffeic acid, inhibit amylase at mM concentrations in vitro which, if it occurred in the gastrointestinal tract in vivo, would inhibit sugar absorption from starch consumption and thus decrease caloric input.12
That chlorogenic acid has a significant influence on glucose metabolism was well demonstrated by Rodrigues de Sotillo et al when they were able to demonstrate a significant improvement in glucose tolerance in Zucker rats.13
This relative deprivation of glucose could possibly explain the reduction in BMI as well as fat content seen in their other rat study14
and in our human study. Another group has clearly demonstrated that chlorogenic acid may in fact have an antagonistic effect on human glucose transport.15
Based on the dietary data in our study, the product was not an appetite suppressant. Extracts of green coffee beans inhibited pancreatic lipase in vitro with a 50% inhibitory concentration of 43 μM polyphenols.16
In support of this result, caffeinated but not decaffeinated coffee supplementation in humans produced a decrease in lipoprotein lipase.17
Animal experiments have additionally demonstrated the effect of green coffee extract on fat metabolism, with chlorogenic acid alone having a moderate effect.18
They were able to obtain significant data suggesting that chlorogenic acid not only retards the absorption of fats from the intestine but also activates fat metabolism in the liver. This was demonstrated by significantly lower levels of liver triglycerides after chlorogenic acid ingestion. A recent study in Japan found that coffee polyphenols enhance energy metabolism and reduce lipogenesis by downregulating sterol regulatory element-binding protein and similar molecules, which leads to the suppression of body fat accumulation.19
Recently, intraperitoneal injection of chlorogenic acid to hamsters fed a high-fat diet caused an improvement in lipid profile, reduction in hepatic lipase, reduction in glucose and insulin and increased expression of peroxisome proliferator- activated receptor. This is one of the key regulators of lipids and glucose.20
There have been a few human studies with green coffee extract. Thom investigated the efficacy and tolerability of a green coffee extract (Svetol®
) added to instant coffee and compared within a randomized, placebo-controlled, double-blind study.21
The product reduces the absorption of different types of sugar from the gastrointestinal tract. Forty obese volunteers were included in the 12-week study. Body weight, body composition, and blood pressure were recorded at baseline and every month during the study. The results show a significant difference in weight reduction in favor of the active group (5.4 kg versus 1.7 kg, a 4% decrease versus the placebo). BMI decreased 2.9% or 10%. There was a significant inhibitory effect of the product compared to glucose, and instant coffee, on glucose absorption in a glucose tolerance test. This same commercial product was investigated by another group.22
The weight loss after 12 weeks was almost 5 kg in the treated groups and 2.5 kg in the placebo. A roasted and blended Arabica coffee rich in both green and roast bean constituents was tested in humans.23
The coffee product caused a significant weight loss averaging 0.7 kg and a significant 5% loss of body fat along with a significant decrease in lymphocyte DNA damage. A meta-analysis of the three published and unpublished studies on these products concluded that the average weight loss of 2.5 kg was moderate and the results were promising.26
The results of our study are much more dramatic for weight loss and BMI than previous green coffee extract investigations. The subjects averaged slightly over an 8 kg weight loss which was more than 10% of the body weight. For our study 10 of 16 subjects showed at least a 10% weight loss; five of the remaining six showed at least 5% weight loss; and the last individual showed a 4% weight loss. The most remarkable result was the fact that all 16 of the subjects were classified as overweight at the beginning of the study and at the end six of the subjects were now in the normal BMI category, ie, a normal weight for their height. It must be said that the daily dose of GCA in this study ranged from 700 to 1050 mg and previous studies ranged from 180 to 200 mg/day.24
There were no adverse effects in our study with the higher doses nor in the previous human studies according to the authors of the meta-analysis paper. It should not be overlooked that there was a slight (4.88 ± 11.24 mmHg) though nonsignificant increase in systolic blood pressure over the course of the study, which appears to be isolated to the placebo arm (see ).
Other limitations were the small sample size of the study and the short washout periods between arms. Also, taking GCA three times per day in the high-dose arm and twice per day in the low-dose arm may have alerted subjects to dosage amount, at least in the low-dose arm. We do not believe sample size to have been a problem, given the linear crossover design of the study. This eliminates any possibility of the results reflecting a difference between groups, instead of between dosages. Also, all variables were objective measures, and follow-up showed that a majority of subjects (14 of 16) were able to maintain their lowered weight after the completion of the study.
Five drugs had been approved by the Food and Drug Administration, all of which exhibit weight loss. There are two currently approved for weight loss with sibutramine having been withdrawn from approval in 2011 due to tachycardia. 25
A recent review performed a meta-analysis of 30 trials of weight loss drugs of 1–4 years’ duration, ie, 16 orlistat (n = 10,631 participants), 10 sibutramine (n = 2623), and four rimonabant (n = 6365). Attrition rates averaged 30%–40%. Compared with placebo, orlistat reduced weight by 2.9 kg (2.9%) sibutramine by 4.2 kg (4.3%), and rimonabant by 4.7 kg (4.1%). BMI reductions were 1.0 with orlistat and 1.5 with sibutramine. Lack of adherence to treatment seems to be a major factor limiting the efficacy and effectiveness of antiobesity drugs.26
Thus the GCA with a weight loss of 8 kg (10.5%) and a BMI reduction of almost 3 makes the product superior to the prescription drugs. Weight loss of 5%–10% of initial body weight reduces cardiovascular and metabolic health risks associated with obesity.27
In a recent Israeli postmarketing study of over one million individuals, fewer than 2% completed 12 months of weight loss medication.28
Those who continued for at least 4 months experienced a decrease in BMI of only 1 with a cost of $50–100 per month. GCA should provide an all natural, lower cost source as an effective therapy for overweight individuals. The efficacy for type 2 diabetics who have more coronary heart disease risk remains to be investigated.