Green coffee extract has become a popular weight loss supplement over the past decade, though the hype has often outpaced the science. The active ingredient that interests researchers is chlorogenic acid, a polyphenol that gets destroyed during the roasting process that turns green beans into your morning brew.

I should be upfront: green coffee is not a miracle weight loss pill, despite what some marketing would have you believe. The evidence is mixed, the effects are modest at best, and it works primarily through the same mechanism as regular coffee (caffeine). That said, there are some interesting findings worth examining.

What exactly is green coffee?

Green coffee refers to raw, unroasted coffee beans. They look nothing like the dark brown beans you’re familiar with. Instead, they’re pale greenish-grey and have a grassy, slightly bitter taste rather than the rich flavour that develops during roasting.

The roasting process brings out the flavours we associate with coffee, but it also destroys most of the chlorogenic acid content. A typical roasted coffee bean retains only about 10-15% of its original chlorogenic acid. Green coffee extract supplements concentrate this compound, typically containing 45-50% chlorogenic acid by weight.

Chlorogenic acid itself is a family of compounds found in many plant foods including apples, potatoes, blueberries and artichokes. Coffee just happens to be one of the richest dietary sources. These compounds form when hydroxycinnamic acids (like caffeic acid and ferulic acid) combine with quinic acid.

The proposed health benefits of chlorogenic acid include effects on glucose metabolism, blood pressure, and body weight. Whether these translate to meaningful benefits at typical supplement doses is where things get complicated.

What does the research actually show?

1. Blood sugar regulation

This is probably the most promising area of research. A 2020 meta-analysis pooling 10 randomised controlled trials found that green coffee bean extract significantly reduced fasting blood glucose levels. The relationship between dose, duration and effect wasn’t linear, which suggests the mechanism is more complex than simply “more is better” [1].

Subgroup analysis found that insulin levels dropped most noticeably when participants took 400 mg or more daily. The proposed mechanisms include slowing glucose absorption in the intestine, reducing glucose production in the liver, and activating AMP-activated protein kinase (AMPK), an enzyme involved in cellular energy regulation.

For context, prediabetes affects roughly one in three adults in developed countries. The American Diabetes Association defines it as fasting blood glucose between 100-125 mg/dL, HbA1c of 5.7-6.4%, or glucose of 140-199 mg/dL after an oral glucose tolerance test. Without intervention, about 37% of people with prediabetes develop type 2 diabetes within four years.

That said, I wouldn’t rely on green coffee alone for blood sugar management. The effects seen in studies are modest, and lifestyle factors like diet and exercise have far more robust evidence behind them. Green coffee might be a useful addition for some people, but it’s not a substitute for proven approaches.

2. Weight management

Here’s where I have to be honest about the limitations. Green coffee became famous for weight loss after a small 2012 study showed dramatic results, but that study was later retracted due to serious methodological problems [2]. The researchers couldn’t verify their data, and the study design had multiple flaws.

More recent evidence is less exciting. A 2019 meta-analysis of 16 randomised controlled trials found that green coffee extract reduced BMI by a statistically significant but clinically modest amount (about 0.4 kg/m²). Body weight and waist circumference didn’t change significantly [3].

The effect was only meaningful in people who were already overweight (BMI over 25), and studies lasting less than four weeks showed no benefit at all. This suggests any weight loss effect requires consistent use over time and may only help people who have weight to lose in the first place.

The mechanisms are straightforward: caffeine increases metabolic rate and chlorogenic acid may reduce carbohydrate absorption. Neither is revolutionary. If you’re looking for substantial weight loss, diet and exercise remain the evidence-based approach.

3. Blood pressure

The blood pressure research is more encouraging. A 2019 meta-analysis of nine trials found that green coffee extract lowered systolic blood pressure by about 3 mmHg and diastolic by about 2 mmHg [4]. These aren’t dramatic numbers, but they’re clinically meaningful for population-level cardiovascular risk.

Interestingly, the effect was strongest in people with hypertension, at doses below 400 mg daily, and after four weeks of use. Higher doses and longer duration didn’t produce better results, which is unusual.

The mechanism likely involves chlorogenic acid’s effect on nitric oxide metabolism and blood vessel function. It may also reduce cortisol levels, though this needs more research.

For reference, hypertension affects about one in four adults worldwide. The NHS defines high blood pressure as consistently reading 140/90 mmHg or higher. Persistent hypertension is a major risk factor for kidney disease, heart disease, and stroke [5].

If you have high blood pressure, green coffee isn’t a replacement for medication or lifestyle changes. But it might offer modest additional benefit for some people, particularly those with borderline readings who want to try dietary approaches first.

4. Cognitive function

A single 16-week randomised trial in 38 middle-aged and older adults found that chlorogenic acid improved scores on tests of motor speed, psychomotor speed, and executive function [6]. Blood markers associated with early cognitive decline (apolipoprotein A1 and transthyretin) also improved.

I’d treat this with caution. It’s one small study, and cognitive function trials are notoriously difficult to replicate. The improvement could be partly due to caffeine’s well-known effects on alertness and reaction time. Whether chlorogenic acid specifically protects brain function long-term is unknown.

That said, the finding is interesting enough to warrant larger studies. Anything that might help maintain cognitive function as we age deserves investigation, even if the current evidence is preliminary.

5. Retinal health

This one surprised me. A small study in 18 patients with retinitis pigmentosa, a genetic condition causing progressive vision loss, found that chlorogenic acid supplementation improved peripheral retinal activity as measured by multifocal electroretinography [7].

Visual acuity, visual field and contrast sensitivity didn’t change, but the improvement in peripheral retinal function suggests chlorogenic acid might help slow degeneration at the outer edges of the retina.

Retinitis pigmentosa typically starts with night blindness and gradually narrows the visual field, eventually leading to legal blindness. It affects roughly 1 in 4,000 people. Any intervention that might slow progression would be valuable, but this was a single-arm study without a control group, so the results need replication in proper randomised trials.

Are there side effects?

Green coffee products contain caffeine, so they cause the same side effects as regular coffee in susceptible people: jitteriness, insomnia, increased heart rate, anxiety, stomach upset, and headaches. The caffeine content varies by product, but most green coffee supplements contain 20-50% of the caffeine you’d get from a cup of coffee.

At typical supplemental doses (480-600 mg of extract daily for up to 12 weeks), green coffee appears safe for most people. Higher doses or longer use haven’t been well studied.

There’s one metabolic concern worth mentioning: short-term high-dose chlorogenic acid intake may increase homocysteine levels [8]. Elevated homocysteine is associated with cardiovascular disease, though whether this represents a real risk from green coffee supplements isn’t clear. The effect may only occur with unusually high doses.

Some people report frequent urination with green coffee supplements, which makes sense given caffeine’s diuretic effect. If you have overactive bladder or similar conditions, caffeine-containing supplements might worsen symptoms.

Who should avoid green coffee?

Pregnant and breastfeeding women: Safety data is lacking. High caffeine intake during pregnancy is associated with low birth weight and other complications. The NHS recommends limiting caffeine to 200 mg daily during pregnancy [9].
People with anxiety disorders: Caffeine can worsen anxiety symptoms. If you’re prone to panic attacks or generalised anxiety, stimulant-containing supplements are generally a poor choice.
Those with bleeding disorders or taking blood thinners: Some evidence suggests green coffee might affect blood clotting. If you’re on anticoagulants, discuss any supplements with your doctor first.
People with diabetes: While green coffee might help blood sugar control in some people, it could also interfere with diabetes medications. Blood sugar effects can be unpredictable, so careful monitoring is essential.
Those with irritable bowel syndrome: Caffeine can worsen diarrhoea. If IBS is a concern, green coffee supplements may aggravate symptoms.
People with osteoporosis: Caffeine increases calcium excretion. If you have or are at risk for osteoporosis, keep total caffeine intake below 300 mg daily (roughly 2-3 cups of coffee, including any supplements).

The bottom line

Green coffee extract is neither worthless nor a miracle cure. The chlorogenic acid it contains has genuine biological effects on glucose metabolism, blood pressure, and possibly body composition. The evidence for most benefits is moderate at best, and effect sizes are modest.

If you’re considering green coffee supplements, be realistic about what they can do. They’re not going to transform your health or cause dramatic weight loss. They might offer small additional benefits for blood sugar or blood pressure management as part of a broader healthy lifestyle.

The featured image of raw green coffee beans is appropriate because green coffee extract is made from unroasted coffee beans, which retain the chlorogenic acid that’s largely destroyed during the roasting process.

References

Asbaghi O, et al. Effect of green coffee bean extract supplementation on glycemic indices: A systematic review and dose-response meta-analysis of clinical trials. Nutr J. 2020;19(1):32. PubMed
Vinson JA, et al. Randomized, double-blind, placebo-controlled, linear dose, crossover study to evaluate the efficacy and safety of a green coffee bean extract in overweight subjects (RETRACTED). Diabetes Metab Syndr Obes. 2012;5:21-27.
Gorji Z, et al. The effect of green-coffee extract supplementation on obesity: A systematic review and dose-response meta-analysis of randomized controlled trials. Phytomedicine. 2019;63:153018. PubMed
Tajik N, et al. The effect of green coffee bean extract consumption on blood pressure: A systematic review and meta-analysis of randomized controlled trials. Complement Ther Med. 2019;46:104-110. PubMed
NHS. High blood pressure (hypertension). NHS website
Saitou K, et al. Effect of chlorogenic acids on cognitive function: A randomized, double-blind, placebo-controlled trial. Nutrients. 2018;10(10):1337. PubMed
Iloki-Assanga SB, et al. Chlorogenic acid-enriched extract from Coffea arabica and its effect on ERG in patients with retinitis pigmentosa. J Clin Med. 2014;3(1):57-71. PubMed
Olthof MR, et al. Chlorogenic acid and caffeic acid are absorbed in humans. J Nutr. 2001;131(1):66-71. PubMed
NHS. Foods to avoid in pregnancy. NHS website