Is a raw sweet potato toxic? Unlike a raw carrot, it turns out that eating one may actually be bad for you. Uncooked sweet potatoes contain a trypsin inhibitor. In other words, they interfere with your body's ability to use trypsin, which is an enzyme we use in digestion for breaking down many types of different proteins (1). Classifying this as a toxicity would be a bit extreme, but it certainly is not healthy for you.
Fortunately, this trypsin inhibitor is sensitive to heat so the act of cooking - whether it be boiling, baking, or microwaving - will dramatically if not entirely deactivate this compound.
Stomach aches after eating a raw sweet potato, or other symptoms of indigestion such as bloating, cramps, and gas, should be expected. If symptoms are severe, it likely isn't the trypsin inhibitor but rather food poisoning from one of the common molds which can be found on raw root vegetables. It's not always the mold or fungus which is directly responsible, but rather when they attack this plant, as a result it may generate phytoalexins which are a class of toxins. In mice and livestock, that has been found to cause or worsen severe respiratory issues including pneumonia (2). In cattle, the acute respiratory side effects were so severe as to cause fatalities resulting from asphyxiation (3). Studies of regularly or frequently feeding mold-laced potatoes to humans have not been conducted for obvious reasons and therefore, it is unknown whether our immune system's response is comparable, more, or less severe than the animals studies conducted. That being said, it confirmed that these compounds, ipomeanine and 4-ipomeanol, are also toxic to humans (4).
Whether it's raw or not, those with certain medical conditions should consult their doctor if they plan on making sweet potatoes a regular part of their diet. Why? Like spinach, sweet potatoes have a lot of oxalate content. Some people can suffer very adverse health effects from oxalates - an estimated 1 to 3 people per 1 million have a disease called primary hyperoxaluria, which can be either acquired or inherited (5). Having it causes excessive excretion of oxalates and as a result, recurring kidney stones. Even for those without this diseases, oxalates have been associated with increased risk of developing kidney stones, particularly those who don't get enough magnesium or citrate in their diet (6).
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010