Michael Greger MD

Michael Greger MD

Posted October 9, 2011

Published in Health

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Ask the Doctor: Q&A with Michael Greger, M.D. (Week 4)

Read More: blue-green algae, bones, breast cancer, calcium, cannabis, dairy, fish oil, flax, lung cancer, lycopene, multivitamins, nutrient absorption, omega-3, phytoplankton, produce, spirulina, toxins, vegetables, yeast

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This is just a sampling of the 600 comments and questions I've responded to on the site (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 make sure you don't miss any:
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GrantMM77ni asked on Plant-Based Omega-3 Supplements: As you have reported, the effects of animal based omega-3 supplements can prove to be ironically, inflammatory. While you recommend utilizing algae as an alternative, is there concern over the neurotoxins (as you have discussed in other videos as present in spiralina), or are these only present in the blue-green algae?

All the algae-oil omega-3 supplements currently on the market are made from phytoplankton that are in an entirely different biological kingdom than the blue-green algae known to produce toxins (such as spirulina, detailed here:

sapire asked on Raw Food Nutrient Absorption: In regards to raw food nutrient absorption - Have there been any studies performed on blended raw vegetables versus raw vegetables (in their natural form) nutrient absorption. I'm advised that blended vegetables are more easily absorbed than eating the whole raw vegetable in its natural form. I suppose a lot has to do with how much blending (chewing) you do before swallowing the mouthful?

As you can see here, the heating itself seems to improve the bioavailability of lycopene. I would not be surprised if the blending helped too, though, so maybe you could blend and heat and have the best of both worlds?

Toxins asked on Long Term Vegan Bone Health: I thought dairy leaches calcium from the bones from its acidity?

The scientific nutrition community used to believe that the abundance of sulfur-containing amino acids in animal proteins would lead to a negative calcium balance, but that is outdated thinking. See for one of the later reviews.

Veguyan asked on Cannabis Receptors & Food: How can we believe in any study? It seems they can always refute each other.

Thank you for bringing up this important larger point. What does one do in the face of conflicting evidence? The answer is to look at the balance of evidence and ask yourself before making any decision "What does the best available evidence show right now?" Unfortunately, sometimes the media fails to put new study results in context and so you get this kind of intellectual whiplash back and forth. In terms of the purported link between smoking cannabis and lung cancer, although doubts have been raised, the latest review continues to raise strong concerns. It seems smoke inhalation is not good for your lungs, whether from a burning building or bogie.

David Schmidt asked on Fish oil in trouble waters: So is Flax oil the way to go?

I'd suggest the algae- or yeast-based long-chain omega 3′s:

Louis commented on Multivitamin supplements and breast cancer: I'm bit disappointed with your presentation, and I'm wondering why you exactly choose this multi vitamin study to underpin your conclusion in this video. The Swedish cohort was from 2010 and in April of this year a meta-analysis, which is scientifically stronger in terms of proof, concluded : "Multivitamin use is likely not associated with a significant increased or decreased risk of breast cancer, but these results highlight the need for more case-control studies or randomized controlled clinical trials to further examine this relationship." [...]

Thank you so much Louis for taking the time to contribute! It is such a relief to see that meta-analysis come out. This video was queued up from my volume 5 DVD, reviewing the peer-reviewed nutritional science published between Spring 2010 to Spring 2011, and so I must have just missed it (wasn't indexed by the National Library of Medicine until August 19!). I'll have to re-record the video now that there's a systematic review published on the subject.

Of course negative findings don't automatically "cancel" out positive findings. As one of my research preceptors once quipped: "if two people drill for oil in Texas and one finds oil and the other does not, one can't conclude that the question of whether or not there is oil in Texas remains undetermined." Similarly, the conclusion from the 2010 study profiled in the video is not necessarily invalidated: "These results suggest that multivitamin use is associated with an increased risk of breast cancer. This observed association is of concern and merits further investigation." But it's nice to know that if there is an effect it's not one that has been replicated!

The critical question remains: should women take multivitamins or not? That depends on the risks versus benefits like any other life decision. Since both the risks and the benefits appear equivocal (see for example the National Institutes of Health State-of-the-Science Conference Statement on multivitamins (PDF here) I agree with the Cleveland Clinic Journal article I featured and would recommend women take the money they would have spent on the pills and instead buy some produce with more proven benefits (see my Breast Cancer and Diet post). A similar recommendation can be made for men (as a similar meta-analysis likewise thankfully casts doubt on the multivitamin link there as well).

Until we know more, I agree with the conclusion from the meta-analysis you cite: "Until further studies assist in clarifying the association between multivitamin use and increased or decreased risk of breast cancer, health-care professionals should open discussions with their patients regarding multivitamin use and risk of breast cancer."