Ask the Doctor: Q&A with Dr. Greger

Answers to featured health and nutrition questions provided by Michael Greger MD and the NutritionFacts.org volunteer moderator team.

Questions are taken from the video and blog comments throughout the site. Join in the discussion and get your question featured!


Q: Where can doctors go to supplement their nutrition knowledge?

Where to supplement nutrition training

I’m afraid I’m one of those guilty docs who never filled in the nutrition knowledge gap that medical school left me with. NutritionFacts.org has been such an eye-opener, and I am already seeing some quasi-miraculous changes in some of my more motivated patients. Where else would you suggest I...

Q: Does caffeine impair endothelial function in our arteries?

Positive Health Benefits of Caffeine

Hello Dr. Greger. Latest in nutrition Volume 8 was a fantastic DVD. It was very informative and applicable to my lifestyle. I especially liked the healthy ice cream idea, I’m going to try that! I don’t want to pester you with an email, so I thought I'd post it here. In regards to creatine, you...

Q: What about the oxalic acid in beets?

Oxalic Acid in Beets

What about the oxalic acid in beets? Is it good for you to take in large amounts? veggie4every1 / Originally posted in Priming the proton pump Answer: As noted in my video about the oxalates in turmeric versus cinnamon (Oxalates in Cinnamon), it’s not just the amount that matters but also...

Q: Is hempseed oil beneficial to adults with eczema?

Is hempseed oil helpful to adults with eczema

I’d be interested in your opinion of this study I found online at http://www.finola.com/FinolaOilandAtopy.pdf. This is regarding hempseed oil, not necessarily for children but for adults with eczema. Have you seen other studies looking at hempseed oil and eczema? Is it ok to take so much oil...

Q: What is the healthiest potato?

The Verdict on gold, red, & purple potatoes

What’s the verdict on gold, red & purple potatoes? Ionestamot / Originally posted in Toxins in Cooked Potatoes? Answer: The healthiest potatoes are probably sweet potatoes (see my video about sweet potatoes), but if you are going to eat plain potatoes, the varieties with colored flesh...

Q: Should we avoid celery to prevent colon cancer?

Celery for Colon Cancer Prevention

Class participant heard that celery should be avoided for colon cancer patients. Only thing I’ve read about celery is to consume only ‘organic’ as conventional grown veggie is extremely high in pesticides. Do you know any other reason it should be avoided? Thanks. Joanne Irwin / Originally...

Q: Should we avoid canned tomatoes and non-organic root vegetables?

Avoiding Canned Tomato and Non-Organic Root Vegetables

I’ve seen a number of blog posts about some food scientists stating that if you avoid ANY food, canned tomato products and non-organic root vegetables should be at the top of your list?  Do you know anything about these statements? Is it just the opinion of a few researchers or is there a lot of...

Q: Should we take algae supplements for astaxanthin?

Algae as Astaxanthin Supplement

Is any research available on astaxanthin which seems to be touted as a wonderful antioxidant? MarkB / Originally posted below Dragon’s blood Answer: Astaxanthin is the reason flamingos are pink (or at least flamingos in the wild; in the zoo they may be fed artificial dyes like farmed...

Q: The dangers of fluoride (tap water fluoridation)?

Fluoride in Tap Water

Dr. Greger, I have heard some talk about the dangers of fluoride. When I research this all I stumble upon are propagandists websites without scientific backing. Is there any truth to these claims that fluoride in our water supply and toothpaste is damaging our health? Toxins / Originally asked...

Q: What about pepper plus turmeric in V8 juice?

Powerful Pepper + Turmeric

I stirred 1 teaspoon of powdered amla into my daily glass of V8 juice, along with a sprinkle of black pepper and 1/2 teaspoon turmeric – tasted OK. soupy / Originally posted below Amla: Indian gooseberries vs. cancer, diabetes, and cholesterol Answer: That’s an even better idea than you...

Q: How much cinnamon is too much?

Toxicity from Cinnamon

Does the anti-oxi value decrease with age of spice (or berry)? If so, how much? Second, how much is “toxic”? I heard taking more than 1-2 tbsns of cinnamon a day could be toxic. Is one hurting oneself if one takes 2 tbs of all the above mentioned spices a day? Evan Brand / Originally...

Q: Sulfite sensitivity from sulphur dioxide in dried fruits?

Sulfite Sensitivity from Dried Fruits

I eat dried fruits (prunes, raisins, apricots and now apples) daily. Please tell me your thoughts about what may be the cumulative effects on an aging body of sulphur dioxide preservatives used in processing fruits for drying. rosaleah / Originally posted below  Dried apples versus...

Q: Would too much hibiscus tea be toxic due to iron content?

Hibiscus Antioxidants and Iron Absorption

According to the USDA Database, an 8 fl oz (237g) serving of hibiscus tea has 20.48 mg of Iron, while the RDA for a male is 8 mg with an upper limit of 45 mg. Furthermore, apparently the Vitamin C in the drink itself or added to increase the antioxidant content tends to increase the absorption of...

Q: Are there foods that protect teeth and gums?

Food to protect teeth and gums

Do you have any advice on which plant foods or beverages can help prevent cavities and gum disease? OmarLittle / Originally asked on the NutritionFacts.org facebook page Answer: Normally we just hear about things to avoid to protect our teeth and gums (like candy, acidic juices, smoking,...

Q: Can tea with meals hinder iron absorption?

Tea and Iron Absorption

This is a bit unrelated, but I eat a plant-based diet. I’m also a 20-something year old woman of child bearing age who runs, so making sure I’m getting enough iron from plant sources is important to me. I’ve heard that tannins in coffee, tea, and chocolate can hinder the adsorption of iron...

Q: What are the best sources of vitamin K?

Vitamin K in Leafy Greens

I have read in a magazine that there are several types of vitamin K. According to the article, Vitamin K1 is found in vegetables. Vitamin K2 mk7 is found in meat, fish and eggs. The article also said that Vitamin K1 is stored in the liver for only one hour, time not enough to perform all its...

Q: Any resources for vegan pregnancy, infancy, and childhood?

Vegan Pregnancy, Infancy, and Childhood

I feel our family has a healthy and complete diet (in no small part thanks to you!) but do you have any specific recommendations or guidelines for those who would like to follow a vegan diet through pregnancy, infancy and childhood? Is the most important thing (apart from healthy, whole foods)...

Q: Dairy and ear infections: is there an association?

Dairy and Ear Infections

Hi doc. Any research studies on dairy consumption and ear infections in children. My friend’s child had numerous ear infections and I recommended soy milk instead of cows milk plus to eliminate cheese, ice cream, etc. She asked a chief pediatric ENT at a big hospital who of course said there is...

Q: Is moringa (Moringa oleifera) good for you?

The Health Benefits of Moringa

A booth at our farmers’ market is selling moringa. It is a nutrient based plant, exceptional supplementation. It is touted to be “nature’s perfect food.”. Opinions please. Judy0520 / Originally asked on the NutritionFacts.org facebook page Answer: I had to look that one up! I assume...

Q: Might flax seeds (ALA) increase prostate cancer risk?

Flax and Prostate Cancer Risk

There are a lot discussions and articles online about the supposed connection between flax seeds (ALA) and prostate cancer – suggesting that more flax consumed = increase chance of prostate cancer. I haven’t found this issue addressed on your website (sorry if I missed it). Can you comment?...