Friday Favorites: Does Adding Milk Block the Benefits of Coffee?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

This is a graph of mortality versus coffee consumption, suggesting coffee drinkers live longer than non-coffee drinkers. This may be because “[C]offee [may have beneficial effects on] inflammation, lung function, insulin sensitivity, and depression.” This may be in part because of a class of polyphenol phytonutrients found in coffee beans called chlorogenic acids, proven to have favorable effects with studies like these, where they just give it alone in pill form and can show beneficial effects—such as “acute blood pressure-lowering” activity, dropping the top and bottom blood pressure numbers within hours of consumption. Okay, so which coffee has the most? We know how to choose the reddest tomato, the deepest orange sweet potato, since many of the plant pigments are the antioxidants themselves. How do you choose the healthiest coffee?

More than a hundred coffees were tested, and different coffees had different caffeine levels, but the chlorogenic acid levels varied by more than 30-fold. “As a consequence, coffee selection may have a large influence on the potential health potential of coffee intake.” So, all those studies that show that “one cup of coffee” does this or that; what does that even mean when coffee can vary so greatly? Interestingly, “[t]he major contributor to [the] wide range [was the coffee] purchased from Starbucks which had an extremely low [chlorogenic acid] content,” averaging 10 times lower than the others. Maybe it’s because they roast their beans too dark. The more you roast, the less there is. They appear to be partially destroyed by roasting. Caffeine is pretty stable, but a dark roast may wipe out nearly 90% of the chlorogenic acid content of the beans.

The difference between a medium-light roast and a medium roast were not enough, though, to make a difference in total antioxidant status in people’s bloodstreams after drinking them—they both gave about the same boost. Other factors, such as how you prepare it, or decaffeination, don’t appear to have a major effect. What about adding milk?

Longtime fans may remember this ancient video, where the “addition of milk” was shown to prevent the “protective effects of tea” on artery function. Drink black tea, and you get a significant improvement in vascular function within hours, “whereas addition of milk completely blunted the effects of tea.” Here’s the big boost in artery function you get drinking tea, but drink the same amount of tea with milk, and it’s like you never drank the tea at all. They think it’s the casein to blame—one of the milk proteins binding up the tea phytonutrients. Bottom line, this “finding that the tea-induced improvement in vascular function is completely attenuated after addition of milk may have broad implications on the mode of tea preparation and consumption.” In other words, maybe we should not add milk to tea, or put cream on our berries. Appears to have the same effect on berry phytonutrients, or chocolate—check this out. Eat milk chocolate, and nothing much happens to the antioxidant power of your bloodstream. But eat dark chocolate, and get a nice spike within an hour of consumption.

Yeah, but is that just because the milk in milk chocolate crowds out some of the antioxidant-rich cocoa? Milk chocolate may only be like 20% cocoa, whereas a good dark chocolate may be like 70% or more cocoa solids. No, it’s not just that. Here’s how much of this cocoa phytonutrient you get into your bloodstream eating dark chocolate compared to milk chocolate. Eat that same amount of dark chocolate, but with a glass of milk, and it blocks about half.

Okay, that’s cocoa beans; what about coffee beans? “When milk was added to the coffee [in like a test tube], antioxidant activity decreased” by more than half with just a splash of milk, and down like 95% in a latte, or something with lots of milk.

Okay, but what happens in a test tube doesn’t necessarily happen in a person. You don’t know…until you put it to the test. And indeed, over the course of a day, significantly fewer chlorogenic acids made it into people’s bloodstreams drinking coffee with milk compared to black—cutting absorption by more than half.

What about soy milk? In a test tube, coffee phytonutrients do appear to bind not only to dairy proteins, but also egg and soy proteins. You can see how they did this computer modeling, showing how these coffee compounds can dock inside the nooks and crannies of dairy, egg white, and soy proteins, but what happens in a test tube or computer simulation doesn’t necessarily happen in a person. Eggs haven’t been put to the test, so we don’t know if having omelets with your black coffee would impair absorption, and neither has soy milk… until now.

Yeah, either way soy milk has some inherent benefits over cow’s milk, but does it have the same nutrient-blocking effects? And the answer is…no. No significant difference in the absorption of coffee phytonutrients drinking coffee black or with soy milk. What seemed to be happening is that the soy proteins do initially bind the coffee compounds up in the small intestine, but then your good bacteria can release them so they can be absorbed down in the lower intestine. So, “considering the reversible nature of binding,” as opposed to the dairy proteins, “it seems not to be as relevant” as to whether or not you add soy milk.

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Image credit: StockSnap via Pixabay. Image has been modified.

Motion graphics by Avocado Video.