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One of the wisdoms passed on early in my family is not to eat certain types of food raw, because they will cause bellyache. It is regarded common sense on par with not to touch a hot stove because it will cause a burn. As far as I can tell, my friends have been educated in the same way.

The foods are usually pointed out individually to the child, but now I think about it, they are all high in starch. A few examples are dough, batter, corn, starch slurry and potatoes. I don't think it is a concern about bacterial contamination - it isn't only said about cookie dough, but also about freshly made bread dough with no eggs in it. It is just that raw starch is considered indigestible.

Now I happened to read the question Is it safe to eat Raw Corn?. Given that the answer there is that it is safe to eat corn, I started wondering if starch is really so bad as to cause bellyache, or is it just a myth everybody believes because they heard of it before they had developed critical thinking. On the other hand, if a significant amount of starch starts its gelation process in the stomach, maybe it will cause unpleasant symptoms through dehydration or similar (although I don't see how it will gellate at body temperature).

So, is there a food safety concern in eating raw starch, or is this a widespread misinformation? And if it doesn't cause ill effects, does it get digested, or just pass through the digestive system unchanged?

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I'm inclined to think the issue is not the starch itself as much as specific vegetable compounds, particularly lectin and insect-hostile alkaloids. –  BobMcGee Aug 16 '11 at 16:17
    
I tend to believe that what a lot of folks may have been experiencing back when this myth started was probably intestinal problems related to gluten which weren't widely known/understood then but are much more understood now. –  Brendan Jan 9 '13 at 19:37
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@Brendan I doubt it. First, gluten intolerance symptoms are AFAIK equally strong between cooked and raw gluten - but nobody warned me against eating baked bread or cookies. Second, many of the foods I was warned against (corn, potatoes, peas) don't contain gluten. –  rumtscho Jan 9 '13 at 23:24
    
i was more commenting on how that type of myth may have come about more than suggesting what was actually the truth. –  Brendan Jan 10 '13 at 0:30
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4 Answers

There is no real ill effect from eating raw starch. Some people will suffer a bit of "gas" from excessive raw starch as our digestive system is designed to process cooked starches (rice, wheat, potato etc.) and doesn't do an efficient job, so lots of starch gets to the bacterial breakdown stage after being through the stomach, this usually makes "gas"

The energy loss from easting raw starch is huge, there is little point. Eat it cooked

Some starches can be rendered edible through chemical or catalyst processes

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"our digestive system is designed to process cooked starches" "The energy loss from easting raw starch is huge, there is little point." Really? This seems odd, as most of our evolution took place before we were able to cook food. Has our digestive system changed that much since? –  Jefromi Aug 15 '11 at 15:54
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@Jefromi: I'm not a fan of the "evolutionary" argument myself, but one might technically argue that our bodies didn't evolve to process any starch, since agriculture itself was invented long after most of our evolution. Cooked food is still easier to digest than raw because it's essentially semi-digested already. –  Aaronut Aug 15 '11 at 17:11
    
@Aaronut: I get why cooking is a big deal, but weren't there, I don't know, tubers and such around before we started growing them? In any case, I mostly meant my comment as a "citation needed" tag. –  Jefromi Aug 16 '11 at 5:36
    
@Jefromi - basic biology, some animals handle raw starch fine, we don't. It just is that way. We can store and and cook food to make it edible for our digestive system. Other wise we would be limited to digestible resources only. A human biology book should cover the problem with raw starch and other non/partially digestible food in the stomach –  TFD Aug 17 '11 at 10:34
    
Have a look at the book "Catching fire" by Richard Wrangham about eating uncooked food. bookdepository.co.uk/Catching-Fire-Richard-Wrangham/… –  No'am Newman Aug 18 '11 at 8:31
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We eat raw starch, in small to moderate amounts, almost every day without any obvious side effects.

It's difficult to find good figures, but bananas contain at least 1% starch (if ripe) and, I estimate, as much as 5% assuming only completely yellow bananas are eaten raw.

Fresh garden peas contain around 2% starch given that 40% of the sugars are converted to starch (estimated using the sugar content of snow peas).

Eating raw starch (in moderate amounts) is good for you

As the Wikipedia starch article states,

Digestive enzymes have problems digesting crystalline structures. Raw starch will digest poorly in the duodenum and small intestine, while bacterial degradation will take place mainly in the colon.

This is not necessarily a bad thing since undigested starch, or resistant starch as it is known, is a source of insoluble dietary fiber. Upwards of 80% of any raw starch consumed will remain undigested. This overview notes that there is 'also limited evidence for a prebiotic effect of some starches that resist digestion'.

Counter-indications

The same article referred to above states that '[m]ost resistant starches [...] are thought to be fermentable'. And foods fermenting in the gut will produce gas so you might want to avoid eating excessive amounts of raw starch to avoid uncomfortable digestion problems.

This article from a raw food site warns against possible toxicity problems,

Neither salivary amylase (ptyalin) nor pancreatic amylase can commence digestion of the starch until it is released from its globule. These starch-containing globules are, therefore, not digested at all and must be eliminated from the body as so much debris. Undigested materials such as these are toxic in the body and pose an eliminative burden without providing energy or other value.

I haven't yet found any scholarly literature to corroborate this, and the fact that this article fails to mention the, well established, role of resistent starch as dietary fiber makes me suspect its accuracy.

TFD's answer above states,

The energy loss from easting raw starch is huge, there is little point. Eat it cooked.

Although I haven't attempted to verify this, I can't see how energy loss counts against eating raw starch if you are getting enough calories from the rest of your diet. It doesn't seem to count against eating celery. The raw food article has another explanation for why we choose not to eat very starchy foods raw,

Most starches just don't taste that good in their raw state.

Carrots, sweet potatoes and yams are notable exceptions, however, because these tubers, in addition to containing starches, also contain enough sugars to give them a sweet flavor.

It seems clear from this article that at least some people enjoy potatoes raw. It also suggests that it is, for the most part, safe to eat them although the resistent starches, as I also indicate, might cause you some gastro-intestinal discomfort.

Another answer here seems to suggest that raw potatoes contain more toxins than cooked. This is incorrect unless the potatoes were cooked at temperatures over 170°C (340°F). The toxins in potatoes are low to begin with unless they are allowed to develop green patches, in which case cooking at normal temperatures won't help.

It is worth noting that, while eating raw starch is probably not going to give you any big problems, you should check that there are no other problems related to eating raw foods that you are not accustomed to.

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Thank you for the well-researched answer. I doubt the rawfood article too - both because it suggests that undigested materials are toxic per se (many non-nutritive materials are neutral as opposed to toxic), and because I remember biology experiments in school where student-donated ptyalin digested raw starch in small amounts. But the other sources seem sound. –  rumtscho Jan 10 '13 at 14:30
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I know raw potatoes contain a toxin, and that the green ones are more likely to have it: http://en.wikipedia.org/wiki/Potato#Toxicity

"Glycoalkaloids may cause headaches, diarrhea, cramps, and in severe cases coma and death" Although they suggest that poisoning is rare, and the green potatoes contain a higher concentration than the white. Raw potatoes are not particularly delicious, so I'm in favor of just avoiding the issue all together.

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Plenty more tubers need cooking to reduce toxins, Cassava is 100% inedible before cooking due to a poisonous cyanide compound. The starch itself is 100% OK though :-) –  TFD Aug 19 '11 at 1:01
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There is plenty of anecdotal evidence about eating raw rice on the web. The best answer however I found was here; http://www.livestrong.com/article/415189-what-are-the-effects-of-eating-raw-rice/

In summary; "...when rice is uncooked or undercooked, this strain of Bacillus cereus produces a toxin called cereulide, which can lead to vomiting and nausea within 24 hours of ingestion"

"Lectin is a protein that serves as a natural insecticide with a strong affinity for carbohydrates. Found on uncooked rice and beans, this protein is one of the top 10 causes of food poisoning and can lead to nausea, diarrhea and vomiting when eaten in abundance."

"Pica is a disorder defined by an insatiable desire to eat non-foods, such as hair, paint and sand, or food ingredients, such as flour, salt and raw rice."

Anecdotally most commentators seem to believe that raw rice will swell in the stomach, so consuming large amounts may cause discomfort, or in extreme cases a burst stomach.

Personally I've never heard of bread, or cookie, dough being a problem. While raw, milled, flour contains some of the hygroscopic properties of rice, dough already contains water. The gas from the dough rising is, well, just gas.

Of course if you eat enough of anything (even water) it's dangerous, but there doesn't seem to be a lot of scientific evidence that raw starches in general are bad for you.

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