Michael Greger MD

Michael Greger MD

Posted December 25, 2011

Published in Health

  • digg
  • Delicious
  • Furl
  • reddit
  • blinklist
  • Technorati
  • stumbleupon

Ask the Doctor: Q&A with Michael Greger, M.D. (Week 14)

Read More: amia, cancer, garlic, gooseberries, kale, nutrients, onions, vitamin B12, vitamin C, vitamin D

Get VegSource Alerts Get VegSource Alerts

First Name


Email This Story to a Friend

This is another sampling of the more than 750 comments and questions I’ve responded to on (so far!).

Please feel free to leave any follow-up questions here or on any of the hundreds of videos on the more than a thousand topics covered on

And remember, there’s a new video posted every weekday, so to make sure you don’t miss any:

Michelle Rowe asked on #1 Anticancer VegetableAwesome video, Dr. Greger! I am left with the question of the anticancer effects of raw vs. cooked garlic and onions. I know cooking reduces some of the nutrients but have raw and cooked alliums been tested in regard to the anti-cancer effects? In other words is it important to try to consume these raw notwithstanding their very strong flavors?

The secret to maintaining the anti-cancer effects of garlic is to either eat it raw (think salsa, homemade dressings, pesto, etc) or crush the garlic first, wait ten minutes, and then cook it. You know those chemical flares? You bend them, two chemicals mix and a light-emitting reaction takes place? The same kind of thing happens in garlic. Floating around in the cytoplasm of garlic cells is a compound called alliin and packed away in tiny intracellular storage compartments (called vacuoles) is an enzyme called alliinase. When the garlic tissues are crushed, the two mix and alliinase turns alliin into allicin, the phytonutrient thought to be responsible for many of garlic’s health benefits. Cooking destroys the enzyme, though, so even if you crush your garlic, if it’s thrown immediately into the pan, little allicin may be produced. Allicin is relatively heat stable, though, so if you chop your garlic and wait 10 minutes for the allicin to be formed, you can then cook it (the enzyme has already done its work) and presumably maintain many of the benefits.

Cherie Perkins asked on Latest in Nutrition vol. 7 DVD now available (proceeds to charity)I got volume 7  yesterday and plugged it in. Great stuff. Do you know if Amla be used in baked goods without sacrificing the health benefits? Thanks so much for your efforts!

Ooh, great question! Indian gooseberries (Phyllanthus emblica, or “amla”) are so astringent (and sour and bitter and fibrous and overall nasty-tasting) that they are typically processed in some way (dried, pickled, or made into jam). So one would expect to find lots of good data on the effects of cooking, but I could find only one single paper. And all they looked at was the decline in vitamin C levels (amla is one of the most concentrated sources–nearly 1% of their weight). After boiling for an hour a 27% drop in vitamin C was noted. As per all all the other antioxidant phytonutrients, we simply don’t know. As I detailed in my video Best Cooking Method, the nutrition of some fruits and vegetables declines with cooking, others remain just as healthful, and a few actually become healthier.

vfayes asked on Vitamin D supplements may be necessaryDr. Greger — have you heard about the new vitamin D3 spray? What is your opinion — helpful? Harmful? Waste of money? Thanks!

Based on their current pricing, supplementing with that product would cost hundreds of dollars a year. Given the fact that at the preferred daily dosing D2 and D3 appear to be equivalent, I would suggest choosing a less expensive option (D2 is easily 10 times cheaper). Just think about how much kale you could buy with all the money you save!

David tunison asked on Vegan epidemicI have followed you for years and purchase your tapes. Met you in Ann Arbor at the food co- op. Is it true Cyanocobalamin b12 ( which you recommend for us as vegans) turns into cyanide and the best b12 to take is hydroxycobalamin? Per Raymond Francis MIT scientist. That’s what his website shows anyway. His comments were it is man made , not natural, and not well utilized. What is absorbed is turn into cyanide. Could you please clarify, help.

Let me guess: Mr. Francis sells hydroxycobalamin supplements? It’s like the whole coral calcium scam. Calcium is cheap as chalk–in fact it is chalk! So how are you going to bilk people out of lots of money? You sell some sort of special calcium. Same with B12 supplements. They are so cheap to produce that supplement manufacturers try to come up with all sorts of fancy ways to “add value” to products so they can charge $30 a bottle. Unless you’re a smoker, have kidney failure, or base your diet around cassava root, cyanocobalamin should be fine.

patmcneill asked on Heart attacks and cholesterol: Purely a question of dietThis study might also be of interest to you and your other readers: As always, your comments and insights would be most welcome.

Thank you Pat! The Lancet is one of my favorite journals. Sponsored by the World Health Organization, the INTERHEART study you point out was indeed a monumental undertaking, trying to tease out modifiable risk factors for heart attacks across populations in more than 50 countries on every inhabited continent. They concluded that more than 90% of the risk of our #1 killer is attributed to things we can do something about, like eating fruits and vegetables every day. The most important risk factor by far was cholesterol–twice as important as exercise–followed by smoking. The designated discussant at the European Society of Cardiology Congress, where the results were first reported, lamented “mankind is doing a good job of killing himself.” Their follow-up study, called INTERSTROKE, published in 2010 concluded that 90% of strokes were preventable as well.

-Michael Greger, M.D.