Dark Chocolate Put to the Test for Peripheral Artery Disease

One of the problems with publishing research on chocolate is that the press jumps on it, oversimplifying and sensationalizing the message, and then the money starts rolling in from candy companies and the message is muddied even more. As a result, an important idea is lost in all the frenzy: The flavanol phytonutrients in cocoa appear to be beneficial, as I discuss in my video Chocolate and Stroke Risk. Though the sugar, fat, and excess calories in chocolate aren’t good for us, “natural cocoa powder can be a health food.” So, adding cocoa to a smoothie or oatmeal, for example, would be health-promoting. Try to use unprocessed, undutched cocoa, though. The beneficial flavanols are what give cocoa its bitterness, so manufacturers try to process cocoa with alkali to destroy them on purpose. Thus, when it comes to cocoa, bitter appears to be better.

In my previous video Dark Chocolate and Artery Function, you can see how high-tech angiography showed that dark chocolate could improve the function of coronary arteries in the heart within two hours of consumption, but there are some blood vessels you can visualize with your own eyes: the blood vessels in your eyes. Two hours after eating dark chocolate, as I show at 1:18 in my Chocolate and Stroke Risk video, you can observe a significant improvement in the ability of the little veins in your eyes to dilate.

What about the blood vessels in our legs? Peripheral artery disease (PAD) is atherosclerosis in the arteries feeding our limbs, which leads to claudication, a crampy pain in our calf muscles when we try to exercise, due to impaired blood flow. So, maximal walking distance and time were studied in 20 PAD patients two hours after subjects ate either dark chocolate with at least 85 percent cocoa or milk chocolate with no more than 35 percent cocoa. After eating the dark chocolate, the subjects could walk about a dozen more yards and about 17 seconds longer than before they had the dark chocolate. In comparison, after the milk chocolate, they weren’t even able to walk as far as baseline and not for a single second longer. So, there does seem to be something in cocoa that’s helping, but a few seconds here and there isn’t much to write home about. How about reversing the atherosclerosis, which we didn’t even think was even possible until 1977.

1977? Dean Ornish didn’t start publishing on heart disease reversal until 1979. In actuality, the first demonstration of atherosclerosis reversal with a cholesterol-lowering diet and drugs wasn’t on the coronary arteries going to the heart, but on the femoral arteries going to the legs.

What have researchers observed regarding the arteries going to the brain? There is a noninvasive way to measure arterial function within the brain using transcranial ultrasound. At 2:49 in my video, you can see a chart of what happens when we hold our breath. Once we start, our brain starts opening up the arteries to increase blood flow to compensate. If the arteries in our brain are stiffened and crippled by atherosclerosis, however, they’re unable to open as much and as fast as they should, and so are said to have a smaller “breath holding index,” which can be a risk factor for stroke. So, researchers designed an experiment in which they compared the results of a target food to something neutral, like oatmeal. What target food did they choose? A spoonful of cocoa powder or something? No. They chose a randomized crossover trial of oatmeal versus a deep-fried Mars bar.

Why a deep-fried Mars bar? The study was published in the Scottish Medical Journal, and, evidently, the “deep-fried Mars bar (DFMB) is a snack…strongly associate[d] with Scotland.” Really? Yes, really. Researchers phoned a total of 627 fish and chips shops in Scotland “to ascertain the delicacy’s availability.” More than one in five shops said they did carry deep-fried Mars bars and sold up to 200 a week. (Batter-dipped and deep-dried Snickers was evidently less popular.) The researchers “conclude[d] that Scotland’s deep-fried Mars bars is not just an urban myth. Encouragingly, [they] did also find some evidence of the penetrance of the Mediterranean diet into Scotland, albeit in the form of deep-fried pizza.”

Could this be contributing to Scotland having among the highest stroke rates in Europe?  Interestingly, there was a significant drop in men compared to women, which you can see at 4:29 in my video. Maybe men are from Mars and women are from Snickers? Regardless, what about chocolate that’s not deep-fried? There have been a few population studies that have followed people over time that found that those who ate chocolate appeared to have lower stroke rates, which has since been confirmed by another study. Is it possible, though, that chocolate consumption just happens to be related to other behaviors that are heart- and brain-healthy? Maybe people who exercise a lot have to eat more food, so maybe they eat more chocolate? Researchers didn’t see any evidence of that, but you can’t account for everything. To prove cause and effect, people would need to be randomized into two groups, with half eating chocolate and the other half not, and then followed for a decade or two. To this, one researcher replied that “it would be hard to gain consent from most people to the possibility of being randomized to a ‘no chocolate’ arm. How many people would agree to forego chocolate for a ‘sufficiently long follow-up period’?” Ten to twenty years without chocolate is a pretty long time.

Want more chocolate? See:

For more on stroke prevention, check out:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:


Who Should Avoid Coffee?

Do coffee drinkers live longer than non-coffee drinkers? Is it “wake up and smell the coffee” or don’t wake up at all? I discuss these questions in my video, Coffee and Mortality.

The largest study ever conducted on diet and health put that question to the test, examining the association between coffee drinking and subsequent mortality among hundreds of thousands of older men and women in the United States. Coffee drinkers won, though the effect was modest, a 10-15% lower risk of death for those drinking six or more cups a day. This was due specifically to lower risk of dying from heart disease, respiratory disease, stroke, injuries and accidents, diabetes, and infections.

However, another study that amount of coffee was found to increase the death rate of younger people under age 55. It may be appropriate, then, to recommend that you avoid drinking more than four cups a day. But if you review all the studies, the bottom line is that coffee consumption is associated with no change or a small reduction in mortality starting around one or two cups a day, for both men and women. The risk of dying was 3% lower for each cup of coffee consumed daily, which provides reassurance for the concern that coffee drinking might adversely affect health, or at least longevity.

A recent population study found no link between coffee consumption and symptoms of GERD, reflux diseases such as heartburn and regurgitation. If you actually stick a tube down people’s throats and measure pH, though, coffee induces significant acid reflux, whereas tea does not. Is this just because tea has less caffeine? No. If you reduce the caffeine content of the coffee down to that of tea, coffee still causes significantly more acid reflux. Decaf causes even less, so GERD patients might want to choose decaffeinated coffee or, even better, opt for tea.

Coffee intake is also associated with urinary incontinence, so a decrease in caffeine intake should be discussed with patients who have the condition. About two cups of coffee a day worth of caffeine may worsen urinary leakage.

A 2014 meta-analysis suggested that daily coffee consumption was associated with a slightly increased risk of bone fractures in women, but a decreased risk of fractures in men. However, no significant association was found between coffee consumption and the risk of hip fracture specifically. Tea consumption may actually protect against hip fracture, though it appears to have no apparent relationship with fracture risk in general.

Certain populations, in particular, may want to stay away from caffeine, including those with glaucoma or a family history of glaucoma, individuals with epilepsy, and, not surprisingly, people who have trouble sleeping. Even a single cup at night can cause a significant deterioration in sleep quality.

We used to think caffeine might increase the risk of an irregular heart rhythm called atrial fibrillation, but that was based on anecdotal case reports like one of a young woman who suffered atrial fibrillation after “chocolate intake abuse.” These cases invariably involved the acute ingestion of very large quantities of caffeine. As a result, the notion that caffeine ingestion may trigger abnormal heart rhythms had become “common knowledge,” and this assumption led to changes in medical practice.

We now have evidence that caffeine does not increase the risk of atrial fibrillation. Low-dose caffeine—defined as less than about five cups of coffee a day—may even have a protective effect. Tea consumption also appears to lower cardiovascular disease risk, especially when it comes to stroke. But given the proliferation of energy drinks that contain massive quantities of caffeine, one might temper any message that suggests that caffeine is beneficial. Indeed, 12 highly caffeinated energy drinks within a few hours could be lethal.

To learn more about various health aspects of coffee, see my videos Coffee and Cancer, What About the Caffeine?, Preventing Liver Cancer with Coffee?, and Coffee and Artery Function.

What else can we consume to live longer? Check out Nuts May Help Prevent Death, Increased Lifespan from Beans, Fruits and Longevity: How Many Minutes per Mouthful?, and Finger on the Pulse of Longevity.

And, for more on controlling acid reflux, see Diet and GERD Acid Reflux Heartburn and Diet and Hiatal Hernia.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Chocolate is Finally Put to the Test

Botanically speaking, seeds are small embryonic plants—the whole plant stuffed into a tiny seed and surrounded by an outer layer packed with vitamins, minerals, and phytochemicals to protect the seedling plant’s DNA from free radicals. No wonder they’re so healthy. By seeds, using the formal definition, we’re talking all whole grains; grains are seeds—you plant them and they grow. Nuts are just dry fruits with one or two seeds. Legumes (beans, peas, and lentils) are seeds, too, as are cocoa and coffee beans. So, finding health-promoting effects in something like cocoa or coffee should not be all that surprising. There is substantial evidence that increased consumption of all these little plants is associated with lower risk of cardiovascular disease.

Of course, much of chocolate research is just on how to get consumers to eat more. While it didn’t seem to matter what kind of music people were listening to when it came to the flavor intensity, pleasantness, or texture of a bell pepper, people liked chocolate more when listening to jazz than classical, rock, or hip hop. Why is this important? So food industries can “integrate specific musical stimuli” in order to maximize their profits. For example, purveyors may play jazz in the background to increase consumers’ acceptance of their chocolates. Along these lines, another study demonstrated that people rated the oyster eaten “more pleasant in the presence of the ‘sound of the sea’ than in the presence of ‘farmyard noises.’”

You’d think chocolate would just sell itself, given that it’s considered the most commonly craved food in the world. The same degree of interest doesn’t seem to exist as to whether or not Brussels sprouts might provide similar cardiovascular protection. So, it’s understandable to hope chocolate provides health benefits. Meanwhile, despite their known benefits, Brussels sprouts don’t get the love they deserve.

One of the potential downsides of chocolate is weight gain, which is the subject of my Does Chocolate Cause Weight Gain? video. Though cocoa hardly has any calories, chocolate is one of the most calorie-dense foods. For example: A hundred calories of chocolate is less than a quarter of a bar, compared to a hundred calories of strawberries, which is more than two cups..

A few years ago, a study funded by the National Confectioners Association—an organization that, among other things, runs the website voteforcandy.com—reported that Americans who eat chocolate weigh, on average, four pounds less than those who don’t. But maybe chocolate-eaters exercise more or eat more fruits and vegetables. The researchers didn’t control for any of that.

The findings of a more recent study published in the Archives of Internal Medicine were less easy to dismiss and there were no apparent ties to Big Chocolate. The researchers reported that out of a thousand men and women they studied in San Diego, those who frequently consumed chocolate had a lower BMI—actually weighed less—than those who ate chocolate less often. And this was even after adjusting for physical activity and diet quality. But, it was a cross-sectional study, meaning a snapshot in time, so you can’t prove cause and effect. Maybe not eating chocolate leads to being fatter, or maybe being fatter leads to not eating chocolate. Maybe people who are overweight are trying to cut down on sweets. What we need is a study in which people are followed over time.

There was no such prospective study, until now. More than 10,000 people were followed for six years, and a chocolate habit was associated with long-term weight gain in a dose-response manner. This means the greatest weight gain over time was seen in those with the highest frequency of chocolate intake. It appears the reason the cross-sectional studies found the opposite is that subjects diagnosed with obesity-related illnesses tended to reduce their intake of things like chocolate in an attempt to improve their prognosis. This explains why heavier people may, on average, eat less chocolate.

To bolster this finding came the strongest type of evidence—an interventional trial—in which you split people up into two groups and change half their diets. Indeed, adding four squares of chocolate to peoples’ daily diets does appear to add a few pounds.

So, what do we tell our patients? In 2013, researchers wrote in the American Family Physician journal that “because many cocoa products are high in sugar and saturated fat, family physicians should refrain from recommending cocoa….” That’s a little patronizing, though. You can get the benefits of chocolate without any sugar or fat by adding cocoa powder to a smoothie, for example. Too often, doctors think patients can’t handle the truth. Case in point: If your patients inquire, one medical journal editorial suggest, ask them what type of chocolate they prefer. If they respond with milk chocolate, then it is best to answer that it is not good for them. If the answer is dark chocolate, then you can lay out the evidence.

Even better than dark chocolate would be cocoa powder, which contains the phytonutrients without the saturated fat. I’ve happily (and deliciously) created other videos on cocoa and chocolate, so check out Update on Chocolate, Healthiest Chocolate Fix, A Treatment for Chronic Fatigue Syndrome, and Dark Chocolate and Artery Function. 

Whether with Big Candy, Big Chocolate, or some other player, you always have to be careful about conflict of interest. For more information, watch my Food Industry Funded Research Bias video.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: