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The quickest, easiest, and most fun way to learn what nutritional studies say about a particular health subject is to visit, the science-based nonprofit founded and run by Dr. Michael Greger.

If you’re wondering, say, what the latest view may be on whether or not coffee is healthy, all you have to do is go to and type “Is coffee healthy?” in the search bar. Several video results will pop up, and the latest, “Do the Health Benefits of Coffee Apply to

Everyone?” is vintage Greger.

The video takes you on a head-spinning tour of coffee-related studies. On the positive side, some studies show that coffee drinkers appear to be reducing their risk of Parkinson’s disease, prostate cancer, liver cancer, type 2 diabetes, cirrhosis of the liver (maybe because they’re drinking coffee instead of alcohol?), and overall mortality, while reducing risk of depression in women. Another study shows that coffee drinkers live longer than non-coffee drinkers, with those who drink four cups per day being the longest-lived coffee drinkers! Coffee appears to help people with chronic Hepatitis C, as well to reduce symptoms of Parkinson’s disease. Coffee even seems to improve athletic performance and male sexual performance.

But wait! Another study shows that the benefits associated with coffee drinkers may just be the result of “confounding factors.” Maybe coffee drinkers have lots of energy as a result and exercise more, for example? And yet another study refutes the mortality benefit associated with drinking coffee.

But wait! Then there’s a study on “Interindividual Variability” in coffee drinkers. In other words, some people respond better to coffee, while others respond worse. Yet another study reports that, in some individuals, heavy use of caffeine provokes—wait for it—sleepiness! Could their health be improved by perversely getting more sleep from drinking more coffee? Those with a gene that impairs their ability to metabolize caffeine have an elevated risk of high blood pressure from drinking coffee, especially if they are heavy coffee drinkers. But for the rapid caffeine metabolizers, their risk of hypertension is reduced with coffee consumption.

How could this be? Dr. Greger suggests the theory that caffeine, even if counterproductive to human health, is just one of many compounds in the coffee bean. So if you can metabolize caffeine quickly and get it out of your system, you stand to benefit from the

polyphenol antioxidants and other healthful compounds in the bean. Whether coffee is healthy or not would seem to depend on whether or not you have the gene to metabolize caffeine quickly.

In another video, Dr. Greger presents studies that show that decaf coffee improves arterial function while caffeinated coffee has a deleterious effect; this is contradicted by yet another study showing a positive effect of caffeine on arterial function, raising the question of

whether there’s another compound in caffeinated coffee that harms the endothelial cells lining the arteries. Dr. Greger concludes that we may fare better by obtaining our caffeine, if we’re seeking it, from green tea.

The back-and-forth, inconclusive, and seemingly contradictory evidence presented in many of Dr. Greger’s most entertaining videos speak to the limitations of nutritional studies. Confounding factors abound. Are participants in the coffee studies putting milk or cream or sugar in their coffee, for example? That will surely affect health outcomes. The type of coffee beans used, whether or not they were grown organically, and whether or not the coffee is filtered may all play a role.

Most nutritional studies, therefore, need to be reviewed with a skeptical eye, and the same caution applies to studies of medical procedures, and doctor recommendations premised on them. Virtually all conventional doctors will recommend that patients between ages forty-five and seventy-five be screened for colorectal cancer once every ten years. While there are different ways to approach that task, the colonoscopy is often recommended. And this recommendation is based on real science. One study of 12,000 people who got the procedure found that it reduced the risk of colorectal cancer by 31% and the risk of dying from that cancer by 50%. That’s significant.

On the other hand, there are risks to colonoscopies. You could get a reaction to the sedative. Your colon may be inflated during the procedure and that could cause cramping or discomfort. Sometimes cutting off a polyp will burn or inflame tissues. You can get an infection from colonoscopy tools. Worst of all, you could get a perforated colon, a life-threatening condition which requires immediate surgery. These risks are considered small when compared to the benefit. But the risk/reward ratio has been studied only in the general population—the meat-eating, cheese-eating, sugar-eating, overweight American population.

There are no studies determining whether the benefits of a colonoscopy outweigh the risks for people eating a whole-food, plant-based diet. It is highly unlikely that such a study will ever be conducted. And so we are all left to make personal health decisions by intuition as

much as by science.

As I’ve practiced a whole food, plant-based diet for decades, I’ve come to the conclusion, rightly or wrongly, that a colonoscopy just isn’t worth the risk.



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