This root vegetable is both a nutritious superfood and a potentially lethal poison

By Anastasia Climan, RDN, CD-N | Fact-checked by Barbara Bekiesz
Published June 18, 2024

Key Takeaways

  • Cassava is a resilient, starchy tuber that is a primary source of calories and nutrition for people across the globe.

  • Cassava flour is naturally gluten-free, and cassava leaves are nutrient-dense.

  • Natural cyanide compounds in all parts of the cassava plant pose an acute and chronic health risk, which can be drastically reduced through proper food processing.

Cassava is a staple crop in Nigeria, Brazil, the Philippines, and many other countries around the world. For people in the Congo, cassava supplies 1,000 daily calories per person.[] It’s easy to grow and versatile, with starchy roots and nutritious leaves. But there’s just one problem: it’s poisonous. 

Cassava contains neurotoxins that can wreak havoc on the central nervous system, especially with long-term high exposure.[] So, how does the world’s fourth most popular agricultural food prevail against this fatal flaw? It’s all about how you prepare it.

Cassava’s nutritional contributions

Cassava is a tuber that’s often boiled, fried, toasted, or processed into a naturally gluten-free flour. Cassava is also used to engineer food additives like tapioca and sorbitol.[]

Cassava roots are an important food because they’re so hardy and resilient.[] They can be left in the ground and harvested when other crops aren’t available. Cassava is tolerant to a range of rainfall levels and can thrive in substandard soil. Cassava leaves are less calorie-dense but more rich in nutrients than the roots. They contain vitamins B1, B2, and C, along with beta-carotene.

Cassava is higher in insoluble fiber but lower in total protein than many other cereal grains. It's also a poor source of the essential amino acids lysine and methionine, and as it is often grown on land with low nutrient content, it may be lacking vitamin A, iron, and zinc.

Acute and chronic cyanide poisoning

Acute cyanide poisoning from improperly prepared cassava flour has been reported, including a 2017 case in Uganda that sickened 98 people and caused 2 fatalities.[] Illness set in within a few hours of ingestion and continued for a few days afterward.

The most noted signs and symptoms include the following (listed in order of highest prevalence).

  • Vomiting

  • Diarrhea

  • Malaise

  • Dizziness

  • Tachypnea

  • Syncope

  • Tachycardia

  • Fever

Patients were treated for cyanide poisoning with injectable cobalamin (vitamin B12) along with IV antibiotics and oral rehydration salts.

According to an article in the Journal of Water Process Engineering, “The continuous ingestion of cassava and its by-products, when processed incorrectly (without cooking, drying or fermenting properly), brings a series of problems to human health [...] or even death."[]

As a result, regulating bodies around the world (including the European Union, World Health Organization, and Environmental Protection Agency) have established maximum permissible limits of cyanide in cassava foods.[]

While some levels of toxins remain, there’s less concern when the cassava comes from reputable sources and is consumed in moderate amounts rather than as a primary source of calories.

Safe ways to prepare cassava

The main cyanoglycosides in cassava are linamarin and lotaustralin. They’re present in all parts of the plant.[] Fortunately, both free and bound cyanide in cassava can be processed out through various methods, such as drying, boiling, and fermentation.[]

In fact, sun-drying cassava tubers and leaves decreases their free cyanide content by 90% (for six days at 82.4 degrees Fahrenheit). Oven drying is another option, but slightly less effective. Another way to reduce free cyanide by 90% is by boiling cassava chips for 15 minutes, or soaking or fermenting cassava before cooking. Ultimately, using multiple processing methods is the most effective way to minimize cassava toxins.[]

Insufficient processing time for cassava can lead to an unacceptable reduction in toxins. In addition, the use of wild cultivars is particularly problematic, as they have a high cyanogenic content.[]

Wild cultivars are not recommended for human consumption. The fact that wild cultivars are resistant to pests and produce high-yielding crops makes them a desirable product for irresponsible or untrained farmers. One sign of wild cultivars is the pure white color of their flour, rather than a cream color. Farmers and food regulators can use a rapid and inexpensive test to determine the cyanide content in cassava flour. The recommended safe level is <10 ppm.

What this means for you

Cassava appeals to people who prepare it in traditional recipes or as part of a gluten-free diet. It’s safe to eat as long as it’s from a reputable source and properly processed. However, caution is warranted for those who obtain cassava from unregulated farmers or who consume it in large quantities over long periods of time.

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