The 10 riskiest foods to eat, and how sick they can make you

Certain foods can carry toxins that can cause illness. Jeanette Wang takes a look at the preventive measures to reduce the risk

PUBLISHED : Monday, 06 April, 2015, 6:11am
UPDATED : Tuesday, 07 April, 2015, 7:25pm

Ever experienced a nasty case of food poisoning? There's a high chance you have: most of us will experience a food or waterborne disease at some point in our lives, usually relatively harmless and short-lived ailments with symptoms such as stomach pains, vomiting and diarrhoea.

More than 200 diseases are caused by unsafe food containing harmful bacteria, parasites, viruses, toxins and chemical substances, according to the World Health Organisation.

Some people may suffer more severe and long-term consequences, including kidney and liver failure, brain and neural disorders, reactive arthritis, cancer and even death.

Food-borne and waterborne diarrhoeal diseases kill about 2.2 million people annually, according to WHO estimates, most of whom are children. Pregnant women, the sick and the elderly are also particularly vulnerable to foodborne diseases.

In Hong Kong, there were 214 reported food poisoning outbreaks last year, affecting 1,009 people, according to statistics from the Centre for Health Protection. Nearly 70 per cent were victims of bacterial contamination.

The positive news is that these were the lowest figures for food poisoning since the earliest data available in 2000, but the reality is that most cases, as WHO director-general Margaret Chan put it, are "largely under-reported".

"Most people suffering from diarrhoea do not consult a physician. Diseases and deaths might be attributed to other causes, even when the food that people have eaten is the culprit," Chan said in a commentary in the Lancet medical journal last November.

Hong Kong's heavy reliance on food imports, coupled with the increasing globalisation of food production and trade, makes food safety more complex and all the more essential.

Just last year, many local food outlets were affected by the Taiwanese gutter oil scandal and the rotten meat from a Shanghai food supplier.

The arrival of warmer weather also increases food poisoning risk, since bacteria thrive in warm environments.

To raise awareness of the importance of food safety along the whole length of the food chain - from production and transport to preparation and consumption - the WHO has designated tomorrow's World Health Day theme as "Food safety: from farm to plate, make food safe".

Here, we highlight hazards in 10 common foods based on information from Hong Kong's Centre for Food Safety.

Leafy greens

They're essential for good health, but leafy vegetables are also a key culprit of food-borne illnesses. In the US, they're the largest source of food-borne contamination, accounting for about 23 per cent of the 9.6 million cases of food-borne illness each year, according to a study released in 2013 by the US Centres for Disease Control and Prevention.

Most of the US cases were caused by norovirus, which is spread to produce from water contaminated by faeces. This may be present from production and processing, or may occur through improper handling and preparation.

Leafy greens could also be contaminated with bacteria - most commonly Escherichia coli strain O157:H7 and Salmonella enterica - which can come from human or animal excrement; for example, from run-off from nearby farms, communities or from contaminated irrigation water.

Pesticides are another source of contamination. Pesticide residual problems are more commonly seen in leafy vegetables such as Chinese flowering cabbage, Chinese white cabbage, spinach, water spinach, garland chrysanthemum, matrimony vine and Chinese kale.

Prevention: soak and wash vegetables thoroughly; blanch vegetables in boiling water for one minute (cooking eliminates both E. coli and salmonella); eat organically-grown greens.


Most illnesses from eggs are linked to salmonella. The bacteria can be introduced to eggs via external faecal contamination of the shells, or from infected reproductive tissues of poultry prior to shell formation.

The tricky thing is that contaminated eggs may look normal. Proper egg handling and cooking should destroy most bacteria. However, the bacteria can multiply in raw or "runny" eggs, food items that contain raw eggs (such as mango pudding and mayonnaise), or egg dishes held at improper temperatures (such as scrambled eggs at a buffet).

Prevention: avoid eating raw or undercooked eggs and their products; refrigerate eggs; buy eggs from reliable sources.


The consumption of raw tomatoes has been linked to a number of salmonella outbreaks. The bacteria can enter tomato plants through roots or flowers and can enter the tomato fruit through small cracks in the skin, the stem scar, or the plant itself.

Ensure sushi and sashimi arrive chilled on your plate - and polish them off quickly

Prevention: avoid buying bruised or damaged tomatoes; consume cut tomatoes as soon as possible, refrigerate leftovers promptly and throw away those kept at room temperature for more than two hours.


The toxins involved in mushroom poisoning are produced naturally by the fungi, and most mushrooms that cause human poisoning cannot be made non-toxic by cooking, canning, freezing, or any other means of processing.

Prevention: don't pick and consume wild mushrooms; don't buy mushrooms that show signs of spoilage; wash and cook mushrooms thoroughly before consumption.

Soy sauce

Flies are attracted to the odour of fermented food such as soy sauce. A bottle of soy sauce that's not properly covered is an open invitation to flies to lay eggs on the liquid. In 2006, the Centre for Food Safety received a number of complaints from the public regarding the presence of larvae inside bottled soy sauce.

Prevention: close the lid tightly and clean the soy sauce bottle thoroughly after use; store opened soy sauce properly.

Sushi and sashimi

A favourite food of many Hongkongers, these Japanese food items have a very short shelf-life. Bacterial contamination can come in various forms: Vibrio parahaemolyticus is commonly found in seafood, whereas Staphylococcus aureus and salmonella species may be introduced into food by cross-contamination or improper handling during food processing.

Vibrio parahaemolyticus can breed exponentially in room temperatures of 18 to 22 degrees Celsius in just a few hours. Symptoms of poisoning include diarrhoea, vomiting, mild fever and abdominal pain, usually within one to two days of being infected.

Prevention: the bacteria can be destroyed by heating at or above 75 degrees Celsius for 30 seconds. Obviously, that's not ideal for most sushi and sashimi, so your best bet is to ensure they arrive chilled on your plate - and polish them off quickly.


Commonly sold in summer, the fruit may be treated with chemicals to prolong shelf-life. Sulphur dioxide, for example, is used to prevent skin browning and post-harvest disease. Some people may have an allergic reaction to the chemical.

Prevention: buy longans from reputable shops; store separately from other food to prevent cross-contamination; refrigerate and consume within two weeks; wash thoroughly before eating; avoid biting the husk of the fruit; consume the flesh as soon as possible and discard any left at room temperature for more than two hours.

Chinese preserved meats

Known locally as laap mei, these meats come in sausage, pork and duck versions. Among their ingredients are nitrites, which inhibit the growth of Clostridium botulinum and its toxin production.

However, nitrites may react with other substances found in meat and form nitrosamines, which are carcinogenic. Consuming a significant amount of nitrite can also cause methaemoglobinaemia, whereby red blood cells lose their ability to bind oxygen, resulting in hypoxia. The condition is characterised by headache, weakness and breathlessness, and a bluish discolouration of the skin and mucous membranes.

Infants and young children are more susceptible to this condition as their digestive and methaemoglobin reductase systems are still immature.

Prevention: buy lap-mei from reliable retailers; avoid excessive consumption; restrict intake among young children.


Raw beans - soya, green and red kidney - contain a natural toxin called lectin, which acts as a natural insecticide. If the beans are not cooked properly, it can cause symptoms such as extreme nausea, followed by vomiting and diarrhoea.

Prevention: soak and cook dried beans thoroughly.

Fruit seeds

There's a reason why we don't eat the seeds of most fruit: apart from being hard and difficult to digest, the seeds of many fruit also contain natural toxins.

Apple and pear seeds contain cyanogenic glycoside, and release toxic hydrogen cyanide when chewed or digested. Similarly, the seeds of stone fruits such as apricots, plums, prunes, peaches and cherries should not be consumed.

Prevention: avoid eating seeds; remove them before making juice; restrict consumption in young children, who are more sensitive to cyanide.