What Are Green Coffee Beans?
According to the National Coffee Association, coffee belongs to a genus of plants called Coffea, with over 500 genera and 6000 species if tropical trees and shrubs. There are an estimated 25-100 species of coffee plants. The genus was first described in the 18th century by the Swedish botanist, Carolus Linneaus, who also described Coffea Arabica in his Species Plantarum in 1753.
The most commonly used varieties of coffee used by the commercial coffee industry are Coffea Arabica and Coffea Robusta.
Coffee plants are now cultivated in over 70 countries, primarily in the equatorial regions of the Americas, Southeast Asia, Indian subcontinent, and Africa.
The beans you brew in your coffee maker are the processed and roasted seeds from a fruit, which is called a coffee cherry. The coffee cherry's outer skin is called the exocarp. A thin layer of pulp, called the mesocarp lays underneath, followed by a slimy layer called the parenchyma.
A paper-like envelope called the endocarp or parchment surrounds two green beans, lying side-by side. It is these beans that are ultimately processed by removing them from the cherry and roasting then into the beans ground into your morning brew.
Green coffee beans are, therefore, the unroasted coffee beans. They are not typically put into a drinkable form but are crushed and put into pill form and referred to as green coffee extract (GCE). The two main chemical components of coffee beans to which health benefits have been attributed are (1) caffeine and (2) polyphenols.
Polyphenols are plant metabolites involved in the defense against ultraviolet light and pathogens. In recent years, there has been renewed interest in the potential health benefits of dietary polyphenols as antioxidants. The main classes include phenolic acids, flavonoids, stilbenes and lignans. 
Coffee contains many polyphenols, especially chlorogenic acids (CGA) with purported antioxidant properties. However, roasting coffee beans at a high temperature (475ºF) changes its chemical composition and eliminates much of its CGA in content.
Despite this, coffee beans are still considered to be a main source of CGA in the human diet, with caffeoylquinic acids (CQA) the major form. A cup of coffee contains anywhere from 70-350 mg of CGA, depending on the variety and brewing method. The same amount of green coffee beans contain much, much more of CGA, 5000-12,000 mg.
From now on in this review, we will be talking about green coffee extract (GCE) unless otherwise stated.
The major CGAs in green coffee are caffeoylquinic acids (CQA), dicaffeoylquinic acids (diCQA), feruloylquinic acids (FQA), and p-coumaroylqunic acids (p-CoQA).
There are a limited number of studies on the bioavailability and metabolism of CGA from GCE. LeFay et al  found that CGA is absorbed in its intact form in the stomach of rats, while Konishi and Kobayashi  found that CGA is broken down to caffeic and quinic acids by an esterase before being absorbed in the large and small intestine.
Two human studies, produced by the labs of Farah and Monteiro, found that CGAs from GCE are highly bioavailable (using 10 healthy adults) from 0.5 to 8 hours after ingestion of CGE  , but that there was a large difference in absorption and metabolism of CGAs between individuals .
The content of CGA and caffeine can vary widely in different brands of CGE. Caffeine contained in popular OTC GCE brands vary from 20-50 mg/capsule .
However, the daily dose of GCE might require multiple capsules per day depending on the CGA content of the supplement (often reported as a 10-50% content). That could lead to a pretty high dose of caffeine and may not be advisable for all people.
Studies using GCE tend to be dosed based on their CGA content, which in isolation are taken in the 120-300mg range. Based on this, recommended intakes of GCE would be approximately:
- 1,200-3,000mg for a 10% chlorogenic acid supplement
- 600-1,500mg for a 20% chlorogenic acid supplement
- 240-600mg for a 50% chlorogenic acid supplement 
It should be noted that the optimal dosage of either GCE or CGA is unknown at the present time.
There are several sources of chlorogenic acid. Although the quantity of CGA in most plants is miniscule, a few types of plants accumulate chlorogenic acid, especially in the skin, in quantities sufficient to have a physiological effect on individuals who consume them. These foods include:
- sunflower seeds
Lower content, but still higher than most other foods
- Chinese parsley
Is There Any Research?
A search of PubMed using the term “green coffee extract” yielded 148 articles of which 26 were clinical trials and one was a review. Using the term “green coffee beans” I found 192 articles with 8 reviews and 3 clinical trials. I also searched for the term “chlorogenic acid” and found 128 articles, include one review and 62 clinical trials.
I then went to ClinicalTrials.gov where there were 5 trials on “green coffee extract.” Of these 5, two were completed, and one was withdrawn. There were 15 studies on chlorogenic acid, of which one was terminated.
In comparison, using the broader category of “coffee” on PubMed, I found 14,093 articles, 1171 reviews, and 726 clinical trials. There were 74 studies at ClinicalTrials.gov
Does Green Coffee Bean Help Weight Loss?
Let’s get back to the Dr. Oz controversy. As you may imagine, after Oz’s show, green coffee extract became one of the internet’s most searched terms, and bottles of extract went flying off store shelves. Dr. Oz apparently based most of his enthusiasm about GCE on a study by Vinson et al .
The study claimed that a brand of GCE called GCA® led to significant weight loss- over 8 kg (17 lbs) on average. The study included only 16 subjects and all subjects received either high GCA, low GCA or placebo on a rotation schedule.
All subjects lost about the same amount of weight, although the authors claimed that subjects lost more weight during the periods when they were on CGA. The main problem with this study (if you don’t count the unusual study design) was that it was later retracted from publication by the paper’s authors! The scientists wrote:
“The sponsors of the study [Applied Food Science- makers of GCA®] cannot assure the validity of the data so we, Joe Vinson and Bryan Burnham, are retracting the paper.”
Applied Food Science later settled with the Federal Trade Commission for $3.5 million on charges that it used a bogus study to support its weight loss claims. Dr. Oz was later brought before a Senate panel on health and science to testify on the danger of OTC diet pills and other products.
According to the Washington Post, Oz “spent an uncomfortable, sometimes tension-filled morning getting berated by U.S. senators for the things he says and the products he exuberantly promotes on his shows.”
So, are there any peer-reviewed scientific papers that support the idea that GCE can help weight loss? A few. A prospective study by Lopez-Garcia et al  of caffeine intake in 18,417 men and 39740 women from 1986-1998 found an inverse relationship between coffee consumption and weight gain.
Another prospective study by Greenberg et al  found that both caffeinated and decaffeinated coffee were associated with weight loss, suggesting that caffeine is not the only component of coffee with an effect on weight loss.
A 2016 comprehensive review of the scientific literature concerning the effect of CGA on health by Tajik et al  found 11 studies that examined the association of CGA ingestion and obesity- 6 in animals and 5 in humans (one of which was the retracted Vinson article above).
A study in rats by Tanaka et al  found that rats fed CBE had a significant decrease in body weight and adipose tissue compared to those without CBE in their diet. Measuring fatty acid synthesizing and oxidation enzymes, their results suggested that these effects are caused “at least in part by the suppression of lipogenesis [fat building] and the acceleration of lipolysis [fat breakdown].”
Studies in high-fat diet induced obese rats and mice by Song  and Cho  found decreased fat accumulation in rats/mice given decaffeinated GCE or CGA. Song suggests the result are due to decreased activity of genes responsible for fat formation and decreases in inflammation in adipose tissue.
Cho, on the other hand, suggests that CGA modifies obesity-related hormones and upregulating fatty acid breakdown in the liver and decreasing fatty acid and cholesterol synthesis.
Other animal studies [14-16] have not shown any significant effect of GCE or CGA on body weight.
Human studies have also produced mixed results. Bakruradze et al  enrolled 33 healthy volunteers who consumed 750 ml/day of a high-antioxidant coffee enriched with both green or roast bean constituents (CGA- 580mg/l). Although the study lasted 12 weeks, the first and last 4-week periods were considered “wash-out phases” when no coffee was given.
They found a significant decrease in body weight (although the amount is not available in the abstract) as well as a significant decrease in “oxidative damage.”
On the other hand, Watanabe et al  and Kotycxka et al  did not find any significant decrease in BMI (body mass index) or body weight.
There are not enough large scale, double-blind, placebo-controlled studies in humans to confirm any effect of GCE on weight loss/obesity.
Does It Help Lower Blood Pressure?
Tajik’s review on CGA’s effect on health  found 10 studies looking at the effect of CGA on blood pressure. Two were in rats, and the remainder in humans (either healthy or mildly hypertensive).
The first paper was in 2002 by Suzuki et al . They compared the effect of GCE on systolic blood pressure (SBP) in hypertensive rats. They found a dose-dependent reduction in blood pressure after either a single ingestion or long-term ingestion (6 weeks) in the hypertensive rats, but not in a group of rats with normal blood pressure.
Two other studies by Suzuki [21, 22] found that although GCE decreased BP in hypertensive rats, roasted coffee with the same amount of CGA in it did not. They were able to determine that a chemical called hydroxyhydroquinone (HHQ), created during the roasting process, inhibited the BP-lowering effect of CGA.
Kozuma et al  did a randomized, double-blind, placebo-controlled, trial on 117 male volunteers with mild hypertension. The group was subdivided into four groups: placebo (control) or GCE at 46 mg, 93 mg or 185 mg/day.
After 28 days, all groups (including placebo) had a decrease in systolic BP, but only those in the 93 or 185 mg groups were significant compared to the control group. Similar results were found in the diastolic blood pressures.
Watababe , (who, above, found no effect on weight loss) did, however, find a significant decrease in BP in 28 patients with mild hypertension who consumed CGA (140 mg/day) from GCE (as compared to those who received a placebo).
Mubarak et al  recruited 23 healthy men and women to a randomized, double-blind, placebo-controlled, crossover trial using CGA (400mg , equivalent to 2 cups of coffee) daily for a week, with a 1 week washout period between testing dates. They also observed a modest but significant decrease in SBP (-1.53 mmHg) and DBP (-1.53 mmHg) with GCE compared to controls.
Revuelta-Iniesta and Al-Dujaili  studied 18 healthy volunteers who drank either roasted black coffee or green coffee for 2 weeks. Although the authors claim a significant difference in SBP with GCE compared to baseline, the difference is only 2.65 mmHg (± 1.37 mmHg)- again, modest change at most.
There was no significant difference between black and green coffee, and no significant change in diastolic BP.
Ochiai et al  studied 20 healthy males who ingested a test drink with 140mg/day GCE or a placebo drink for 4 months. They found no significant difference in systolic or diastolic blood pressure.
Although there is some evidence that GCE can have a lowering effect on blood pressure, the effect is modest and may be a little more significant in those with mild hypertension. In addition, the current studies are very small. Larger controlled, blinded studies are necessary to confirm these findings.
Does It Help Balance Blood Sugar Levels?
Diabetes mellitus is a metabolic disease of blood sugar and insulin. Population studies [27-29], looking at an association between coffee drinking and type 2 diabetes (T2DM) suggest that habitual coffee consumption is associated with a lower risk of T2DM.
The effect seems to be present in both caffeinated and decaffeinated coffee. Remember though- this kind of study only looks at an association between coffee and T2DM. It does not prove a causal relationship.
Is there scientific evidence specifically looking at green coffee extract and/or CGA and blood sugar and diabetes? Yes, there are some studies in animals and humans, but not many. Of the 17 studies examined by Tajik , 12 used animal models and 5 involved human subjects.
In rats, 3 papers by Karthikesan et al [30-32], examined the effect of CGA with and without tetrahydrocurcumin (THC- a metabolite of curcumin). Normal rats or rats made diabetic by giving streptozotocin-nicotinamide were given either CGA, THC, or a combination of THC/CGA for 45 days.
Rats who received CGA, THC, or THC/CGA had significantly lower glycosylated hemoglobin A1C (a measure of blood glucose over the previous 3-month period), increased blood levels of insulin, and reversed alterations of sugar producing enzymes found in the diabetic rats. The most prominent effects were found in the group who received the combination regimen.
Bassoli et al  looked at the effect of CGA on blood glucose levels and glucose tolerance testing in rats. They found no significant reduction in blood glucose after an intravenous infusion of CGA, but there was a significant reduction in peak plasma glucose in an oral glucose tolerance test (OGTT).
In human studies, Olthof et al  found that CGA improved insulin responses (compared to placebo) in an oral glucose tolerance test performed on 15 overweight, but otherwise healthy men. Ahrens and Thompson  used Emulin™, a patented blend of chlorogenic acid, myricetin, and quercetin, in a study of 40 subjects with confirmed T2DM.
Four groups: placebo/no medication, Emulin/no medication, placebo/metformin and Emulin/metformin) were evaluated. At the end of 1 week, fasting blood glucose, 2 h post meal glucose, and OGTT were determined. “The placebo-only group had a large (5%-13%) increase in all parameters.
The Emulin group and those on metformin performed similarly with reductions between 1% and 5%, with Emulin slightly outperforming the medication-alone group. The most significant reduction occurred in the Emulin/metformin group, with decreases in the parameters by up to 20%.”
Johnston, Clifford, and Morgan  did a 3-way, randomized, crossover study. Nine healthy fasted volunteers consumed 25 g glucose in either 400 mL water (control) or 400 mL caffeinated or decaffeinated coffee (equivalent to 2.5 mmol chlorogenic acid/L).
Blood samples were taken frequently over the following 3 h. They found that CGA increases cell insulin secretion. They concluded: “Differences in plasma glucose, insulin, and gastrointestinal hormone profiles further confirm the potent biological action of caffeine and suggest that chlorogenic acid might have an antagonistic effect on glucose transport.”
GCE shows some promise as a biologically active phytonutrient for the balance of blood sugar. Some of this effect is due to caffeine, and some to CGA. However, there are not, currently, enough large-scale placebo-controlled clinical trials to confirm the effect in humans. More research is needed.
Does It Have Anti-Aging Effects?
The extension of a healthy lifespan, or healthspan, has become an exciting and very active area of research over the past several years. The primary goal of aging research is to delay or prevent the development of age-related diseases.
A great deal is now known about the biochemistry of aging, through the work of researchers such as Dr. David Sinclair. And some experts, such as Dr. Nir Barzilai, even believe that an anti-aging drug may be right around the corner.
Proponents of GCE as an anti-aging compound point to its antioxidant properties. However, most modern research no longer focuses on antioxidants but rather on restoring youthful levels of substances like NAD or NMN that make mitochondria work better.
(Mitochondria are the “powerplants” within our cells.) In fact, it’s now known that having too much antioxidant in our systems can actually be detrimental to some essential immune functions and helping our bodies fight cancer.
There are no scientific papers in PubMed related to green coffee extract and aging or anti-aging. This is one paper  which looks at the effect of green coffee supplements on mitochondrial function.
Lang and colleagues isolated several chemicals (carboxyatractyligenin derivatives) that had an inhibitory effect on mitochondrial function. This is the opposite effect one would be looking for in an anti-aging compound.
There is no evidence that green coffee extract has anti-aging properties.
Does It Improve Focus or Mood?
There is a fair amount of research done on the effect of caffeine on mood and cognitive performance. A review by Ruxton  states that “Caffeine is believed to impact on mood and performance by inhibiting the binding of both adenosine and benzodiazepine receptor ligands to brain membranes.
As these neurotransmitters are known to slow down brain activity, a blockade of their receptors lessens this effect. Caffeine intake also causes changes to a variety of other neurotransmitters, including noradrenaline, dopamine, serotonin, acetylcholine, glutamate and gamma-aminobutyric acid.
Lieberman et al  found that as little as 32 mg of caffeine (about the amount in a single service of a cola drink) improved auditory vigilance and visual reaction time, without any adverse behavioral effects.
Does the CGA component of GCE have any effect on focus or mood? There are a few studies done in laboratory animals, and even fewer in humans. Camfield et al  divided 60 healthy older adults (≥ 50 years old) into 3 groups: 1. 6 grams of a decaffeinated green coffee blend (GB), 2. 540 mg of pure CGA, or 3. a placebo.
Using a double-blind acute cross-over design, subjects underwent cognitive and mood assessments pre-dose, 40-mins and 120-mins post-dose. CGA did not induce any significant improvements in cognitive function, however those who received the green coffee blend significantly improved sustained attention, reaction time performance and alertness compared to placebo.
This suggests that there may be some other component involved in focus/mood effects.
Cropley et al  divided 39 healthy older volunteers (53-79-yr-old) who were considered “light coffee drinkers” (i.e. no more than 8 cups/week) into four groups: 1. Decaf coffee with regular CGA (224 mg) and 5 mg caffeine (“Regular CGA Decaf”) 2. Decaf coffee with high CGA (521 mg) and 11 mg caffeine (“High CGA Decaf”) 3.
Caffeinated coffee with regular CGA (244 mg) and high caffeine (167 mg) (“Caffeinated Coffee”) 4. A placebo drink with coffee flavor and color (“Placebo”).
They found that “Compared with the decaffeinated coffee with regular chlorogenic acid and placebo, caffeinated coffee showed a robust positive effect on higher-level mood and attention processes.
To a lesser extent, the decaffeinated coffee high in chlorogenic acid also improved some mood and behavioral measures, relative to regular decaffeinated coffee.”
Although coffee might keep you alert and temporarily improve your mood, the evidence for GCE is thin at best. Larger scale, double-blind, placebo-controlled studies are needed.
Is Green Coffee Bean Extract Safe?
Green coffee extract appears to be well tolerated, but its safety has not been rigorously studied. Reported adverse effects include headaches and urinary tract infections .
The caffeine naturally present in green coffee beans acts as a stimulant and can cause adverse effects, depending on the dose and whether it is combined with other stimulants.
For healthy adults, the FDA and the European Food Safety Authority (EFSA) state that up to 400 mg/day caffeine does not pose safety concerns. Caffeine can cause sleep disturbances and feelings of nervousness, jitteriness, and shakiness. Caffeine can be toxic at doses of 15 mg/kg (about 1,000 mg for a 150-lb adult), causing nausea, vomiting, tachycardia, seizures, and cerebral edema.
There is not enough reliable information about the safety of taking green coffee if you are pregnant or breast feeding. Stay on the safe side and avoid use under these conditions.
Although there is some evidence that green coffee extract has components with potential health benefits, it is not the weight loss panacea touted by the supplement industry.
Overall, most studies done in animal models and human studies are few, often with only a small number of participants in each arm of the trial. Much larger, double-blinded, placebo-controlled trials in humans are needed before CGE can be recommended.