By Meera Senthilingam

CNN

(CNN) -- Underneath its spiky exterior, the fruit is smooth, juicy and beautifully sweet.

The spikes of the lychee fruit -- also known as litchi -- may be a deterrent for some animals, but for humans willing to break it away, it's an exotic and tasty treat. And often, just one is not enough.

But if eaten too early, particularly by someone who missed their evening meal or by a child in a malnourished state, this seemingly sweet fruit can be toxic and sometimes fatal, as shown recently by a mystery illness that affected the town of Muzaffarpur in India -- the country's largest lychee-producing region.

Each year, hundreds of children in India alone may be hospitalized with fever, convulsions and seizures. A recent report revealed they are probably due to toxins from unripe lychees. Combined with low blood sugar or malnourishment, these toxins can result in even lower blood sugar, or hypoglycemia. They block the body's production of sugar, which becomes especially dangerous when we sleep and our blood sugar levels naturally fall.

This could lead to an encephalopathy, a change in brain functioning, said Dr. Padmini Srikantiah of the Centers for Disease Control and Prevention office in India, who led the investigation in Muzaffarpur.

"Naturally occurring toxins in the lychee fruit are associated with toxicity that led to this encephalopathy," she said. "It's quite possible that when glucose metabolism is disrupted, you get buildup of other metabolites that could have some toxic affects as well." When the victim is young and malnourished, the impact is greater.

But lychees are not the only produce with the potential to poison us if eaten too early or unprocessed.

"The idea that all natural things are good for you is rubbish. ... We are eating (fruits and) vegetables that potentially contain bad things," said Peter Spencer, professor of neurology and occupational health sciences at Oregon Health and Science University.

"(Many) plants were not put here for our benefit but to protect themselves from predators," he said.

When ackee is an enemy

The unripe ackee contains the same poison as the lychee, known as hypoglycin, Srikantiah said.

The toxic nature of the ackee fruit is well-understood in Jamaica and West Africa, where the plant is grown. It's native to West Africa and was brought across the Atlantic Ocean during the slave trade.

As the national fruit -- and national symbol -- of Jamaica, it is a key part of the country's national meal: ackee and saltfish. But locals know not to go near an unripe or even uncooked fruit. It is eaten boiled and as a savory dish.

"It's well-known in Jamaica that if your child eats an unopened or unripened ackee fruit, you better get ready to take them to the hospital or give a spoon of sugar to increase glucose," Spencer said.

The most affected demographic is again children, he said, particularly malnourished ones, who are less able to restore the sugars blocked by toxins. He hypothesizes that this may "relate to body mass," meaning children "might require a smaller dose."

"A common theme you see is young children who don't know the unripe fruit can be harmful," Srikantiah said.

Be careful with cassava

Well-known in Africa, South America and parts of Asia, cassava is the third most important source of calories in these regions after maize and rice, according to the World Bank, feeding more than 600 million people globally each day.

Also known as yucca, it is a root vegetable that is delicious fried, boiled or baked, harnessing a gummy, starchy texture. It's also ground into a flour.

But the staple can be poisonous if not processed properly.

The plant naturally contains hydrogen cyanide, Spencer said, and is the subject of strict regulations regarding its processing and production to diminish concentrations of this poison.

"It feeds millions across the world," Spencer said. "But if you're very poor and don't have time to process it, then you come down with disease."

Processing involves a mix of fermentation, peeling, drying and cooking to detoxify the tubers. Eating the root raw or unprocessed means eating cyanide and metabolizing it, which in turn can affect thyroid hormones and damage nerve cells in the brain relating to movement, Spencer said. The tuber's toxins can also cause sudden, irreversible paralysis, according to the National Institutes of Health.

The neurological disorder causing paralysis is known as konzo and is prevalent in certain developing regions, including the Democratic Republic of Congo, where drought, famine and conflict can increase the likelihood of people eating the crop unprocessed.

Spencer fears that this problem may increase in other parts of Africa, Asia and Latin America as climates change and droughts increase.

Staying away from starfruit

This fruit originates in Asia and gets its name from its shape.

It is used as a herbal remedy for a range of ailments in certain parts of the tropics, but if consumed by someone with kidney disease, it can be fatal.

Starfruit contain toxins that affect the brain and can cause neurological disorders, says the National Kidney Foundation in the US. These are processed and removed in people with healthy kidneys, but people with chronic kidney disease can't detoxify the fruit, leaving the toxins and the potential for serious harm or even death.

"(It's) a risk for anyone with renal disease," Spencer said. Recent studies have found a few cases in which people used it to treat other conditions, as a herbal remedy, and developed kidney disease or failure after excessive or prolonged consumption.

Symptoms of starfruit poisoning include hiccups, confusion and seizures.

Sugar cane's fatal fungus

The sugar cane crop itself is not harmful to eat, but leave it for too long, and its impact won't be very sweet.

Eating moldy or dated sugar cane comes with a risk of poisoning courtesy of a common fungus that grows on the plant when it's stored for more than a few months.

"If a child eats that fungus, it can cause death or lifelong neurological disease," Spencer said. The toxin is harmful to all ages, though children and young people are more commonly the victims.

The fungus, called artbrinium, produces toxins that can cause vomiting, staring to one side, convulsions, spasms and coma, according to the World Health Organization (PDF).

Concerns over cycad plants

One more popular product of the cycad plant is sago, a starch extract obtained from the inner stem of the sago palm tree and eaten in various forms. Perhaps you have fond memories of sago pudding.

Cycad plants -- including the sago palm -- are ancient plants widely grown throughout the world, according to Spencer, and are a common source of food and medicine. But like cassava, they require extensive processing to remove a range of toxins that they naturally contain.

"This is an ancient plant, but is one of the most toxic plants on the planet," Spencer said. "It's strongly implicated in the induction of neurodegenerative disease." It might play a role in Guam disease, a common neurological disease resembling motor neuron diseases such as Alzheimer's and Parkinson's on the island of Guam, where the plant originates.

Two toxins, known as cycasin and BMAA, within the plant must be removed before any part can be safely eaten. The process of detoxifying varies by region but can include washing, fermentation, cooking and aging.

This need for extensive processing led to the plants having reduced commercial value. They are commonly known as a famine food, as they thrive in drought conditions. Spencer worries that cycads could be another cause for concern, as climates change and droughts become more common, for people living in the most affected parts of the world.

Today, an estimated one in nine people goes to bed on an empty stomach, and one in three suffers from malnutrition, according to the World Food Programme.

"With strict control of food supplies into the US and Europe, we have little to worry about here," he said. "But we need to think about the rest of the world."

A pause over potatoes

It may not come as much of a surprise that a beloved food favorite, the potato, can be poisonous, particularly when they have sprouted or are green in color.

Their toxin, solanine, is found throughout the plant but poses a greater risk in green or spoiled potatoes and within the spouts, according to the National Institutes of Health.

Symptoms of poisoning include vomiting, stomach pain, hallucinations and even paralysis.

Red kidney beans raise red flag

Many species of beans contain the toxin phytohemagglutinin, but concentrations are particularly high in raw red kidney beans. Levels are reduced significantly in cooked beans. As few as four or five raw beans can cause symptoms, according to the US Food and Drug Administration.

Within one to three hours, people can develop nausea, vomiting and diarrhea, which can develop into stomach pain. The impact is less severe than with exposure to the toxins found within foods such as cassava or starfruit. People are likely to recover quite rapidly: within three or four hours after symptoms begin. However, some victims have been hospitalized, the FDA reports.

Be informed about the risks

Srikantiah believes that everyone, not just public health officials, needs to be made aware of the risks posed by foods containing toxins detrimental to our health, with greater surveillance of outbreaks of disease to help officials make better lifestyle recommendations.

"There are unanswered questions," she said, referring to the recent lychee-based epidemic in India and the chance of related clusters of disease. "Are these outbreaks happening elsewhere and we're just not detecting it?"

In the meantime, be sure to check what you're eating -- and how well it's been processed.