Sunday, February 1, 2015

The daily raw carrot is not antiseptic, it increases bacterial growth in the gut


Ray Peat's daily raw carrot is one of the most popular peatarian recommendations. Yet, it is among the recommendations that are the least questioned.
A daily raw carrot, shredded with a little vinegar and olive oil, can suppress bacteria. - Ray Peat
Sometimes having a daily carrot salad (grated, with salt, olive oil, and a few drops of vinegar) will stimulate (and disinfect) the small intestine enough to prevent fermentation. - Ray Peat

Where is the evidence for such claims?

When Peatarians are asked, they usually just quote 1-2 in vitro studies on the antimicrobial effect of carrots, such as this one. Although they sound convincing, caution should be applied when generalizing the evidence on much more complex systems such as the human gut with its microbiome and different compartments (i.e. stomach, small intestine, colon).

Interestingly, there is one older publication out there that tested the effects of raw carrots in humans. This one is also often quoted by Peatarians because it shows a cholesterol reducing effect of carrots, which is somewhat in line with Peat's observation of changes in estrogen/progesterone ratio (clear study data on that are lacking unfortunately).

Unfortunately, the second result of the study is only rarely discussed. The authors measured stool mass/fats and breath hydrogen, the latter being a marker for bacterial fermentation. This is what they found:

  1. The raw carrot more than doubled breath hydrogen, which is a marker for bacterial fermentation. This effect started to occur after around 10 days of starting the raw carrot.
  2. The excretion of fecal bile acids and fats was still increased 3 weeks after ending the carrot phase. 
Similar results have been obtained in another study. It compared the fermentation of different types of fibers in rats and man. Just like above, carrots seem to be fermented quite efficiently, similar to apples. Wheat bran in contrasts is one of the fibers that appears to be largely undigested. 


These studies show that the raw carrot is not "antiseptic" in the gut, but the opposite, that it increases overall bacterial mass when consumed regularly. The change takes several days to take place sugesting a slow adaption of the microbiome with a proliferation of bacteria that thrive on carrot-fiber. The change in microbiome may also explain the long lasting effect on fecal bile excretion.

By no means I am suggesting that eating the carrot is bad for you just because it favors microbial growth. The effect probably depends on how your microbiome reacts. I've heard from some people (2 of them with inflammatory bowel disease) that they got terrible stomach upset from eating the carrot. Here, the carrot seems to bring the microbial balance out of whack. In others, it might regulate things and lead to growth of beneficial bacteria while suppressing the "bad" ones.

In the light of these results, eating carrot fiber each day, but careful avoiding all other fibers doesn't make that much sense. Similar fibers such as from fruits or other vegetables could be equally beneficial (or deleterious, depending on the person). By the way, other fiber sources have also been shown to lower estrogens suggesting that the hormone regulating effects are not limited to the carrot but may apply to fiber in general.


  1. Anonymous17/3/15 17:18

    Hi, CB. Thanks for posting this. But to me, it's unlikely from this that Peat is wrong about the antiseptic effect of two medium size (120 grams) carrots, grated, with salt, coconut oil and vinegar.

    He's been experimenting with this for going on 50 years, and has more data than these studies.

    Moreover, I probably don't need to point out the flaws in the studies here, because you already know what they are, and wanted to make a strawman argument, as you like to say. :)

    Cheers, VoS.

  2. Anonymous26/3/15 18:45

    You have posted carrot does cause bacterial growth, yet have not explained why this bacterial growth has this beneficial effect on estrogen/progesterone that Ray measured on tens of people.

  3. I never saw the data Peat has, there are just his claims. He never published his study on the estrogen/progesterone ratio and carrot, I dont know his sample size or whether it was a controlled study. Hence I remain very very sceptical.

    Those other studies on the other hand clearly show that the carrot can be fermented, which is to be expected with everything organic put into our gut that is not absorbed.

    The estrogen/progesterone ratio could either be due to increased binding of estrogen within the enterohepatic cycle reducing its reabsorption or could be represent a chance finding.

  4. Anonymous29/5/15 21:21

    I believe the disinfectant property of the carrot is only intended to act on the small intestine, as in Peat's opinion the small intestine should be largely "sterile". I would hazard a guess that whatever fermentation is happening is happening in the large intestine.

    I would also guess that, although carrots are not entirely resistant to fermentation, they offer more resistance than other forms of resistant starch/fiber because they are technically root vegetables and imbued with mild anti-microbial properties. The addition of coconut oil and vinegar would be to compound the anti-microbial effect, as both are also anti-microbial.

    Peat probably wants to avoid a fiber free diet, as this would probably result in lower digestive transit time, imbalanced gut flora, etc. However, he also wants to avoid the forms of fiber that come with a bolus of starch granules or other gut irritants, i.e. grains. So, he chooses the carrot: mildly anti-microbial, increases digestive transit time, perhaps helps to disinfect the small intestine by improving transit time, carries with it excess estrogen, and just generally serves as bulk matter to get the intestine moving. Not a perfect, gut-sterilizing solution, but definitely the less of the starch/fiber evils.

  5. Peat talks in terms of eating a raw carrot in terms of sterility of the upper gut, while this study looks at the result of the entire gut, upper and lower. I thought that fermentation products of resistant starch in the lower gut is nowadays thought to be beneficial? (A topic that Peat doesn't discuss and that this study's results seems to confirm, anyway?)

  6. Anonymous15/2/16 01:27

    I'm still neutral in this debate, but I'll add two Devil's advocate tidbits against carrots...
    - Almost every maker of ready to eat peeled and washed carrots in the U.S. has dipped them in chlorine before shipping them out! That weird slimy slippery feeling you feel on those carrots when they are a bit old and then wash them off and there's no more slimy feeling, you just washed off chlorine!!!
    - David Jubb: Banana and dates, and corn and wheat, and rice and carrots and beets, are composed symbiotically of a flora that really won't ecosterilize against mold, fungus, and yeast in nature. And they wreak havoc in the body and cause more mold, fungus, and yeast. / Carrots are not good because they are starchy.

    1. Anonymous25/6/16 01:08

      Did you really quote David Jubb?
      a quote from his wikipedia:
      "Jubbs was a raw foodist for over a decade before the late 90’s when he says he began eating only herbal tea with honey, gaining his nutrition from "intestinal flora and friendly yeast" and his own urine.[5] "The ancient ones wanted us to know it's no secret why death occurs, so they put eat in the middle," he said [5]"

      The man is a quack. The fact that you might believe that is worrying. I suggest you try to become educated in Science before you start drinking your own urine too.

      Wholegrain wheat and Bananas were shown to have pre-biotic effects.

      And beetroot is definitely not bad for you

      Ps. Fuck your bullshit. Bitch. (Memo et. al 2016)

  7. Anonymous4/2/17 06:04

    Interesting, but can you provide citations for wheat bran having any benefits? I am under the impression it scrapes and irritates the insides to a significant degree and may cause IBS.

  8. Anonymous9/3/17 05:41

    This comment has been removed by a blog administrator.

  9. In the rat and man study, it looks like the fiber prep was "Dried wheat bran, apple, cabbage and carrot were extracted twice for 3 h with hot aqueous methanol (850 ml/l water), then, after filtration, with acetone, and finally air-dried. The materials were ground, sieved and the particles retained between 0.5 and 1.4 mm sieves used for the feeding studies." Peat has mentioned that cooking carrot fiber ruins it's antiseptic properties. I suspect the preparation of the carrot fiber is not representative of a raw carrot.

  10. The hospital study is a specific population. Without knowing the conditions of the various patient's it's hard to understand the outcome. Also, the dietary content is not specific enough to know the main factors of what is going on. The diet is listed in terms of macronutrients, not foods

  11. It's good to be skeptical of any claim, but Ray has given me no indication of being anything but a humble and honest guy with brillant ideas. He's had decades to figure out if the carrot salad had a adverse effect. Additional fermentation would surely be accompanied by lowered transit times, gas and other gastro-intestinal symptoms. For most people who eat it properly with coconut oil, salt and vinegar, it's plain to see that it comes out the other end not digested, much like sweet corn. And it never seems to do anything but help bowel motility and digestion in general.

    Experiment, that's all there is to it really. Ray mentions wheat bran and oat bran often as good sources of fiber, which present other problems when taken long term. As other comments have alluded to, I presume that's why he recommends the carrot salad. In my opinion the coconut oil, vinegar and salt are also very important.

  12. It's so simple. Peat's diet is deficient in vegetables, i.e. fiber and plant nutrients. But to fit it into his let's say unusual paradigm, he has to make up some far-out-there story how it's really the opposite of what everyone else said. And boom magic.

    But seriously... eating raw vegetables (within reason) is good for you. Wow, that's news... just that it isn't. It's just conventional wisdom.