Best to check what you're putting in your mouth when you're eating out, tucking in to a "bento" lunch box or the equivalent. Heaven forbid there's a fly or a cockroach in your soup, although a health ministry survey has found it happens quite often.

It looked at 14,000 or so instances of contamination of food reported to public health centers nationwide between April 2014 and November 2016. The results showed that in about 30 percent of cases, or 4,519 of the total, foreign objects were mixed in or most likely added when the meals were prepared at factories, restaurants and retailers.

The most common cause of contamination was insects, such as cockroaches and flies. In some cases, fragments of metal, bits of plastic and human hair were reported.

These instances mainly occurred in prepared food such as dishes served at restaurants and boxed lunches, followed by snacks, cooked rice and pre-sliced vegetables.

In 236 cases, consumers reported health hazards such as suffering a cut mouth or chipped tooth while eating prepared food, the survey found. About 90 percent of those injuries were due to the presence of bits of animal bone, plastic and metal.

In many of about 1,000 cases where hard objects were involved, the ministry team found that broken cooking utensils used while creating ready-to-eat meals, snacks and drinks were responsible.

The Ministry of Health, Labor and Welfare survey team contacted 142 local governments where public health centers are located last December for the survey and received responses from 127 local governments.

Kunihiro Kubota, who is with the National Institute of Health Sciences and works at the Division of Safety Information on Drug, Food, and Chemicals, said complaints about food contamination and its causes hovered at the same level each fiscal year.

Even so, he urged more caution on the part of the food industry.