When it comes to reducing body weight, dark roast coffee is more effective than light roast coffee. If you drink non-paper-filtered coffee, such as boiled, French press, or Turkish coffee, you should know that the amount of cholesterol-raising compounds in the lightest roast coffee beans may be twice as high as in very dark roast coffee beans, as you can see at 0:07 in my video Which Coffee Is Healthier: Light vs. Dark Roast. It appears some of the cholesterol-raising compounds are destroyed by roasting, so, in this case, darker is better. (Alternatively, as I described in Does Coffee Affect Cholesterol?, you can use a paper filter and eliminate 95 percent of the cholesterol-raising activity of coffee regardless of the roast.)
You may be familiar with another video of mine—Friday Favorite: Does Adding Milk Block the Benefits of Coffee?, which showed that dark roasting may also destroy up to nearly 90 percent of the chlorogenic acids, the antioxidant, anti-inflammatory phytonutrients purported to account for many of coffee’s benefits. In that case, light roast would be better, as you can see at 0:39 in my video. However, dark roasting can wipe out up to 99.8 percent of pesticides in conventionally grown coffee and more than 90 percent of a fungal contaminant called ochratoxin, a potent kidney toxin found “in a wide range of unprocessed and processed food including coffee”—foods that can get moldy.
What about the polycyclic aromatic hydrocarbon (PAH) products of combustion that are suspected to be carcinogenic and DNA damaging? As you can see in the graph below and at 1:16 in my video, darker roasts may have up to four times more than light roasts. “Thus, roasting conditions should be controlled to avoid the formation of PAHs due to their suspected carcinogenic and mutagenic properties.” To put things in perspective, benzopyrene is considered to be “the most toxic and the most carcinogenic” of these compounds, and even the darkest roast coffee might only max out at a fraction of a nanogram of benzopyrene per cup, whereas a single medium portion of grilled chicken could have over 1,000 times more, as you can also see in the graph below at 1:39 in my video.
Overall, you don’t know if light versus dark roast is better until you put it to the test. A study found that “dark roast coffee is more effective than light roast coffee in reducing body weight” and even said so in the paper’s title. Folks were randomized to a month of drinking two cups a day of light roast coffee or dark roast coffee, roasted from the same batch of green coffee beans. In normal-weight participants, it didn’t seem to matter—there were no significant weight changes either month—but overweight study participants ended up about six pounds lighter drinking dark roast coffee than light roast coffee, as you can see at 2:05 in my video. They lost more than a pound a week just drinking a different type of coffee.
What about light versus dark in relation to blood sugars? We’ve known since 2015 that even a single cup of coffee can affect the blood sugar response. As you can see at 2:33 in my video, after drinking a cup of coffee with more than a dozen sugar cubes in it, which is about a quarter cup of sugar in one cup of coffee, blood sugar spikes higher over two hours compared with the spike from the same amount of sugar in just plain water. “What is not known is whether this statistically significant increase in blood glucose [sugars] is physiologically relevant,” clinically meaningful. After all, coffee consumption does not seem to increase the risk of diabetes, and if you compare drinking light roast coffee with dark roast coffee 30 minutes before “a 75-g oral glucose tolerance test,” that is, drinking about 20 teaspoons of sugar, there didn’t appear to be any difference. Perhaps the take-home message is that regardless of whether the coffee is light or dark, maybe we shouldn’t be adding 20 spoonsful of sugar to it.
How Much Added Sugar Is Too Much? Check out the video!