Newsletter #285: Effects of Green Tea & Coffee Polyphenols on GLP-1
Observational evidence suggests that consumption of tea, as well as coffee, are both associated with lower risk of developing type 2 diabetes. Interestingly, this effect appears to be at least partly independent of caffeine.
The reason for this probably has something to do with the bioactive plant compounds found in these beverages. Historically, many of these phytochemicals were characterized as "antinutrients" because they can restrict bioavailability of certain nutrients. Which at first sounds disadvantageous.
However, we now know that the story is a little more complicated than that. The impact that these chemicals have on digestion and absorption may be largely beneficial, especially in the context of the modern world. For instance, phenolic compounds in tea bind to digestive enzymes, which slows the breakdown of starch, and leads to improved glycemic control. These polyphenols may also boost levels of incretins, most notably glucagon-like peptide-1 (GLP-1), perhaps by binding to enzymes that break down dietary fats and thus slowing their digestion. When fat lingers in the intestine for a longer time, it promotes the release of various gut hormones that enhance satiety and blood sugar control, including GLP-1.
Notably, prior observational research has shown that drinking both green tea and coffee seems to provide the greatest metabolic benefits — and more appears to be better.
To gain some more insight into the specific compounds that might be responsible for these benefits, as well as the amounts needed to realize said benefits, a research team in Japan recently conducted two intervention studies that test the impact of catechins from green tea and chlorogenic acid from coffee on GLP-1, as well as on glycemic measures. Let's take a look.
This Week’s Research Highlights
A single dose of green tea catechins combined with chlorogenic acid from coffee alters the incretin response to a meal, and can also lower blood sugar levels.
Researchers in Tokyo recruited 18 healthy volunteers and put them through a series of different acute ingestion studies, with a one-week washout period between each test meal. The test meal to accompany all of the beverages was a cookie, containing close to 600 calories and 75 g of glucose.
Study 1 was designed to find the best dose of green tea catechins, combined with a fixed dose of coffee chlorogenic acids. To that end, participants were given, on three different occasions:
- 270 mg green tea catechins + 270 mg coffee chlorogenic acids
- 540 mg green tea catechins + 270 coffee chlorogenic acids
- 0 mg of green tea catechins + 0 mg coffee chlorogenic acids (placebo)
Study 2 was similar, but investigated the best dose of coffee chlorogenic acids, with a fixed dose of green tea catechins.
- 150 mg of coffee chlorogenic acids + 540 mg of green tea catechins
- 300 mg of coffee chlorogenic acids + 540 mg of green tea catechins
- 0 mg coffee chlorogenic acids + 0 mg green tea catechins (placebo)
So the idea here is they were looking at the acute effects of four different combinations of these polyphenols to identify the best dose for improving postprandial glucose metabolism. Worth noting that all of these beverages, including the placebos, contained the same amount of caffeine. After each meal, they took bloodwork to measure incretin responses as well as glycemic parameters.
After analyzing the bloodwork and comparing the various doses administered for the two studies, the researchers calculated that the minimum effective dose of green tea catechins for acutely promoting secretion of GLP-1 is 540 mg, while the minimum effective dose of coffee chlorogenic acid is 150 mg. To put that into perspective, a single cup of coffee might contain as much as 70–350 mg of chlorogenic acids (light roast higher than dark roast), while a cup of brewed green tea contains 50–100 mg of catechins (powder green tea, or matcha, contains more). The high doses of both polyphenols also led to decreased postprandial blood sugar, which makes sense given how these compounds affect digestive enzymes.
Consuming green tea and coffee polyphenols for three weeks increases postprandial GLP-1 and enhances insulin sensitivity.
To examine the longer-term effects of these combined phenolics, Yanagimoto and colleagues recruited 11 healthy men and put them through a double-blind, placebo-controlled crossover trial.
For three weeks, the men consumed a beverage enriched with 620 mg of green tea catechins and 373 mg of coffee chlorogenic acids, and containing 119 mg of caffeine. So this would be a little higher than the high doses that they tested for each of the polyphenols in the previously described acute trial.
For another three week period, the men drank a placebo beverage, devoid of catechins or chlorogenic acid, but that did contain 119 mg of caffeine, to control for the metabolic effects of the stimulant.
The effects of each treatment on incretin hormones and on glycemic markers were measured at the start and end of each study period, during which time the men were presented with the 592 calorie cookie to consume with their assigned beverage.
As you might expect, combined consumption of polyphenols from green tea and coffee led to significant improvements in whole-body insulin sensitivity, as well as a marked increase in GLP-1 secretion.
The researchers state, "These findings indicate that combined supplementation with dietary polyphenols from green tea and coffee may effectively prevent diabetes onset due to their synergistic beneficial effects compared to single-polyphenol supplementation.”
Random Trivia & Weird News
Kitagawa Farm, a pork farm in Shizuoka, provides their pigs with green tea, which they brew from one kg of green tea leaves infused in a 1-ton water tank. This is done, purportedly, for improved flavor and health benefits.
Podcasts We Loved This Week
- Stephen Morse: “Neurolaw” — Neuroscience and criminal law. Via Brain Ponderings.
- Mike Tipton: Cold water immersion — Kill or cure? A true expert speaks. Via Reason & Wellbeing.
Products We Like
Matcha is a powder made from finely grinding green tea leaves. Because you are consuming the whole plant, as opposed to an infusion like when you use tea bags, you wind up getting far more catechins.
If you’re trying to hit the threshold found in the acute dose-response study described above, you will want to consume 2-4 grams, which is a reasonable amount. I like this brand in particular because it has been third-party lab-tested for quality, safety, and polyphenol content.
humanOS Catalog Feature of the Week
The course takes a deep dive into phytochemicals in plants, where they are found, their powerful health effects, and how intelligently-devised smoothies can help optimize our intake of these compounds.
For more practical information on using smoothies to enhance nutrition, please refer to our How-to Guide for smoothies.