Among the list of useless supplements Dr. Oz has promoted is green coffee extract. I’ve seen it in drinks, and even tried a green coffee drink once and felt nothing from it, thus have kept on drinking a good ‘ol cup of joe or two a day for a while now.
In this post I will simply share the results of one small pilot trial involving 18 participants. It’s just one study, but guess what? A trial is far more relevant to us for drawing conclusions than talking about mechanisms. When you read a supplement company’s research, they most often will cite laboratory research that discusses mechanisms. Mechanisms and theories are useless until they’ve been proven in human subjects.
So this study, published in Biomed Research International, gave eighteen healthy participants either four cups a day of green coffee or black coffee a day for two weeks in a crossover design. That means each subject switched to the other type of coffee and served as his or her own control. It looked like this:
- Participants are randomized to green or black coffee.
- Participants drink 4 cups/day of green or black coffee for fourteen days.
- One week washout period ensues.
- Participants switch groups and drink the other type of coffee for fourteen more days.
The researchers measured the following variables at the start and end of each fourteen day period.
- Anthropometric variables: Height, weight, BMI, body fat percentage, and waist circumference.
- Cardiovascular: blood pressure and pulse wave velocity (PWV).
- Antioxidants: the polyphenol content of the participants’ urine.
- Urinary cortisol and cortisone (a test of 11-β HSD activity–will be explained below).
Body fat percentage declined with green coffee and black coffee similarly. Body weight and BMI declined significantly only in the green coffee group. Systolic blood pressure declined slightly more, enough to reach statistical significance, with green coffee. However, statistically green coffee did not reduce systolic blood pressure anymore than black coffee.
I know that’s confusing but basically it’s important to test if the difference was different between groups. You could have a statistically significant result, like here with green coffee, but it may not be statistically different over the other group (black coffee). But it’s statistically significant compared to baseline. This same trend occurred with pulse wave velocity. It went down significant with green coffee, but also went down with black coffee nonsignificantly, but the difference between the two were not significant.
Diastolic blood pressure was significantly reduced in both groups. Urinary levels of antioxidants were similar in both groups.
The only thing that was drastically different was cortisol. It went down with green coffee, but remained unchanged with black coffee. But in both the black and green coffee groups the cortisol/cortisone ratio declined, but it declined significantly more with green coffee.
As far as black coffee raising blood pressure, it did the opposite in this study. Both black coffee and green coffee reduced blood pressure by 2-3 points. Participants seemed to lose a bit more weight in the green coffee group, but since this type of thing can stall pretty quick, a crossover design may not be the best way to assess this. Once the participants lose some fat, it might be harder later. In any case, linear weight loss may not occur.
But as far as cortisol, that result motivates me to even try green coffee. I don’t want to keep my cortisol high as that’s exactly what I need to not do to heal my own metabolism 100%. However, black coffee did decrease the cortisol/cortisone ratio. Cortisone is the inactive precursor to cortisol, and the enzyme 11-β hydroxysteroid dehydrogenase (11-β HSD) catalyzes the conversion.
Chlorogenic acids (CGAs) are polyphenols present in coffee, and occur in higher concentrations in green coffee than black coffee. CGA inhibits 11-β HSD, which most likely explains why the ratio decreased in both groups.
Green coffee is not better than black coffee for weight loss or for reducing blood pressure. If it is, it’s by a tiny bit. But the fact that it reduced cortisol here is fascinating. This could help with long term weight loss potentially over black coffee because cortisol rises with fat loss. The hormonal changes that occur with fat loss, involving cortisol and leptin, predispose us to rebound weight gain. That being said, I do not recommend any particular supplement for weight loss considering that my main focus is understanding how metabolic adaptations to weight loss are unfavorable for our long-term health.