Doctor's Note

For some of the most recent videos on refined grains:
If Fructose is Bad, What About Fruit?
Constructing a Cognitive Portfolio
Prostate vs. Plants

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. Also, there are 1,449 other subjects covered in the rest of my videos--please feel free to explore them as well!

For some context, please check out my associated blog post:  Plant-Based Diets for Metabolic Syndrome

  • Veguyan

    Dr. John McDougall says potatoes are the perfect food:

    I wish you guys would agree on things.

    • Michael Greger M.D.

      Have you seen Jeff Novick’s response to a similar question? He’s one of my favorite dietitians (And I think we can all agree that sweet potatoes are perfecter! :)

      • pk

        I’m also unhappy about these research results. Is this a single isolated study regarding white potatoes and cancer? What about the healthy Peruvians and Ecuadorians?
        As far as the potato skin, I have heard of people who survived starvation eating potatoes with their skins, while those who ate the potato alone did not survive. The implication was that there are good things we don’t necessarily know about in the skin.

        Is one study enough to condemn a food that has been widely consumed for hundreds of years?

        By the way, I love your site!

  • becochic

    I remember a study awhile ago that found that white potatoes are actually way healthier than we used to think because there are a lot of nutrients in the skin. Do you know about this?

  • Toxins

    im curious to the question above too

  • walfaro

    Certainly, there are nutrients in the skin of potatoes. But also there are toxins (called glycoalkaloids) produced by the tuber in response to the attacks of the potato beetle. ( The video shows a wonderful explanation about this issue. If you still want to eat white potatoes, please peel them or, even better, eat sweet potatoes as recommended in

  • WKing

    Ok so white potatoes aren’t very good but what about colored (I’m not referring to sweet potatoes, I understand they are very nutritious)? Is there a nutritional difference between colored potatoes? Are yellow fleshed, blue fleshed, or red fleshed potatoes more nutritious than white potatoes? I have read claims that some of the colored (flesh not just the skin) potatoes are more nutritious and intuitively based on the idea that vibrant color is an evolutionary sign of nutrition it would make sense to me, but I was curious if there is any research out there about it.

  • Matt

    i like white potatoes and sweet potatoes, pop them in the microwave 3 min… easy snack, and i like the skin in white ones…. so my question is: Would i have to eat a lot of skins or is just eating one on occasion enough to harm my health.

    • Nunya Biznez

      I wouldn’t microwave anything. Throw your microwave in the bin :-(

      • DStack
        • Nunya Biznez

          The nutritional content of the food is the least of my concerns with microwaves, LOL. Why don’t you check YOUR facts!?

          • DStack

            Please give a reason for your opinion or post a link to a reputable source! I did my research and decided the fear of microwaves was basically an unsubstantiated paranoia of technology.

          • Toxins

            Nunya, DStack is asking an honest and good question. Basically what he is asking, and what I am curious as well of, is what reason do you have to believe that microwaves are harmful? Do you have any studies to back these claims? You must understand, is very science based, so an evidence based approach is best.

          • Thea

            Nunya: Name calling is not allowed on this site. Respectful discourse only please.

  • veganinja

    Is there any way you could do a video on the yeast in bread and what effects, if any, it has on humans?

  • Grasshopperkitchen

    hello, could you comment on light spelt flour please? thank you

  • melliforte

    What about Russian black rye bread flavored with molasses?

  • Chiqlet

    So does this mean sprouted while grains bread is bad for you? Eg. Slver Hills

  • shoewasphone

    Interesting, because a similar study ( found something different:

     Poultry (OR = 0.74), processed meat (OR = 0.64) and vegetables (OR = 0.65) were inversely associated with RCC risk. No relation was found for coffee and tea, soups, eggs, red meat, fish, cheese, pulses, potatoes, fruits, desserts and sugars.

  • Fernando

    Hi Dr. Greger,

    My sister just met you in Marshall, TX over the weekend. She’s a huge fan of yours!

    I love tacos, and since going on a plant-based diet I’ve been eating vegan tacos from one of our local taco places: the Freakin’ Vegan: corn tortillas, black beans, pico de gallo and avocados. The Papadulce: sweet potato, roasted corn, pepitas (roasted pumpkin seeds), etc. They’re all delicious!

    However, I haven’t seen anything on your site about:

    – Tortillas, especially corn tortillas and
    – Cooking oils from a weight gain vs. weight loss perspective (although you’ve covered their shelf-life).

    Could you tell me how healthy corn tortillas are, and what is the best cooking oil if I’m trying to lose weight, avoid cancer, etc.?

    Finally, is it just bad all around to use a lot of oil when cooking? That’s the way I cook refried beans; put a bunch of onions and garlic in to hot oil and have them swim around in there until they’re translucent, then put the beans in there.



    • Nunya Biznez

      please make sure any corn products you buy are not made from genetically modified corn. :-(

  • Nunya Biznez

    was the study done on organic skin-on potatoes?

    • Nunya Biznez

      And how much potato? Even leafy greens can be dangerous at high amounts. That’s the problem with studies. :-(

  • DarylT

    This study didn’t find a correlation between renal carcinoma and potatoes.

    Is this going to be another one of those things like soy?

  • Borkent

    I am looking for a video on the nutritional value of fresh whole vs. pre-cut vegetables from the supermarket. Is it available?

  • William Dwyer

    I’m very skeptical of these association studies. Correlation is not causation, but in medical science, the two are often irresponsibly equated. Moreover, as one commentator noted previously, a similar study found (with one exception) entirely different food associations with renal cell carcinoma, viz. Int. J. Cancer: 120, 681–685 (2006) (c) 2006 Wiley-Liss,Inc.: FOOD GROUPS AND RENAL CELL CARINOMA: A CASE-CONTROL STUDY FROM ITALY. In this study,

    “A significant direct trend in risk was found for bread (OR 5 1.94 for the highest versus the lowest intake quintile), and a modest excess of risk was observed for pasta and rice (OR 5 1.29), and milk and yoghurt (OR 5 1.27). Poultry (OR 5 0.74), processed meat (OR 5 0.64) and vegetables (OR 5 0.65) were inversely associated with RCC risk. No relation was found for coffee and tea, soups, eggs, red meat, fish, cheese, pulses, potatoes, fruits, desserts and sugars.”

    I’m especially skeptical of the association with potatoes that the study cited by Dr. Greger claimed to have found. Potatoes (baked or boiled) have generally been considered a healthy carbohydrate. In fact, there’s enough vitamin C in a potato to cure scurvy. The idea that the consumption of (non-fried) potatoes are a cause of renal cell carcinoma strikes me as counter intuitive!

    • DarylT

      Likewise with me, especially since potatoes have formed the staple food of whole populations of people who appear to have thrived on them. I’d want more evidence and there’s already contradictions in the studies we have to hand.

  • Jenny

    Potassium a little raise – had kidney cancer – one kidney- information from doctor – eat white bread ,no sweet potatoes and a host of
    Other foods that are high in potassium .

    Your site seems to disagree. confused.

  • Paul Spring

    Did the study control for what people dump on white potatoes (butter, sour cream, bacon bits)??