Michael Greger MD

Michael Greger MD

Posted December 18, 2011

Published in Health

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Ask the Doctor: Q&A with Michael Greger, M.D. (Week 13)

Read More: AMD, baking soda, beans, fructose, fruit, gas, genetic engineering, GMO, lentils, neti pot, nosewashing, raffinose, vinegar

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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:

Mary Ellen commented on Nutrition education in medicine: A doctor a day keeps the apples awayPlease discuss GMOs and decreased nutrition in our foods.

For a discussion on how much the nutrient content of food crops has declined over the last 50 years please see my video Crop Nutrient Decline. In terms of GMOs, I’ve published a few papers on the inclusion of genetically modified animals in the food supply (for example herehere, and here), but the relative risks and benefits of genetic engineering in crop agriculture is less clear. Unfortunately, the latest review on the safety of plant GMOs is not freely available, but an earlier review is. If one is interested in the two extremes of the debate I’d suggest Health Risks of Genetically Modified Foods on the “anti” side and Why Genetically Modified Crops? on the pro.

Jessica asked on Is Vinegar Good For You? Are you familiar with research linking high glycemic foods with incidence of macular degeneration? (NY Times reported on a 7/07 study in The American Journal of Clinical Nutrition.) Is there any reason to believe that restricting high glycemic foods, adding in vinegar, or boosting antioxidants by eating lots of leafy greens would help prevent further development of severe macular degeneration?

I’m so glad you brought this up. Age-related macular degeneration (AMD) is the leading threat to eyesight among the elderly and responsible for millions of cases of blindness every year. The study you may be referring to is “Dietary glycemic index and the risk of age-related macular degeneration” available full-text here. As you’ll read, they conclude that “Low-glycemic-index foods such as oatmeal may protect against early AMD.” Eliminating refined carbs may also slow progression. A study published this year (and available full-text here) suggests that three simple lifestyle behaviors (a healthy diet “abundant in plant foods,” daily exercise, and no smoking) can eliminate most of our risk. See my video Egg Industry Blind Spot for a discussion of the best sources of eyesight-sparing nutrients.

dave23 asked on Are Dates Good For You?  Thank you for this fantastic, resourceful website. I’m a bit confused on how much fruit is safe to consume. The study you quote here says it’s healthy but there are other well known Doctors who say one should not consume more than 2 – 3 fruits per day. Apparently it can harm our liver and raise triglycerides? Thanks for clarifying.

The only thing I can imagine they’re thinking about is the relationship between rising fructose consumption and nonalcoholic fatty liver disease, but the fructose is coming from high fructose corn syrup (mostly from soft drinks) and table sugar, not fruit. See for example this recent article. Fruit may even have beneficial effects, for example this study on prunes and liver function. As far as I can tell, the best available science says that the more fruit the better.

Vegan Epicurean asked on Beans and Gas: Clearing the AirI recently heard that the reason humans produce gas after eating beans is because they contain raffinose which is a starch that is poorly digested due to a lack of the enzyme galactosidase. The MD claimed that adding baking soda to the soaking liquid reduced the raffinose. Have you heard anything about this?

Yes indeed, research dating back more than 25 years (“Effect of Processing on Flatus-Producing Factors in Legumes“) found that adding baking soda to the soak water of dried beans before cooking (about 1/16 teaspoon per quart) significantly decreases the content of the raffinose family of sugars. The study I profile here in Beans and Gas: Clearing the Air that concluded “People’s concerns about excessive flatulence from eating beans may be exaggerated” used canned beans, though, which I find to be much more convenient. If you have the time, though, it’s hard to imagine a better nutritional bargain than dried beans, peas, and lentils.

shellbelle asked on The risks and benefits of neti pot nasal irrigationDr Greger- I love your informative videos. Thanks so much. I have not missed a day of nosewashing since 1995. I rinse out my neti pots and have never had any trouble but perhaps I should clean them in the dishwasher ? I read an article about 2 deaths linked to a “brain-eating amoeba” called Naegleria fowleri in tap water used in a neti pot in the south. The article says that that amoeba is rare and usually found in the WARM fresh water lakes and rivers of the south – Florida and Louisana & around there. I’m in California – should I now boil my nosewashing water & let it cool?

I do recommend you effectively sterilize your neti pots using one of the two methods I describe in my Risks and Benefits of Neti Pot Nasal Irrigation video. In terms of Naegleria fowleri, it’s not really an amoeba but it does appear to eat brains. It apparently invades through the lining of the nose and climbs along the olfactory nerve fibers into the brain, causing a nearly invariably fatal meningoencephalitis (about 99% of reported victims die). Thankfully it’s extremely rare (only about 3 cases a year reported in United States). It is a thermophilic (warmth loving) organism, and indeed most cases are reported in the South, but there was a case up in Minnesota last year, so I agree with the new safety advisory that one should use only distilled or previously boiled (and cooled) water to irrigate one’s nose.

-Michael Greger, M.D.