The Ethical Committee of the National Institute of Public Health approved the study design (NIPH-IBRA#12302). All participants provided informed consent for data collection and storage. Written informed consent for study participation was obtained at the time of registration. In cases where participants were aged 18 years or younger, a consent screen was displayed to obtain permission from their parents or guardians. The web-based questionnaire survey was conducted by an authorized survey company in compliance with personal information protection regulations. After the questionnaire survey was completed, we obtained anonymized data from the company.

This study was conducted as a cross-sectional survey in January 2021 as a web-based panel survey. Initially, a screening survey was conducted among monitors registered with the panel survey company to recruit participants for this study. The research company randomly sampled registered participants aged between 15 and 79 years and emailed them regarding their interest in participating in our survey. When the number of participants in each group (eg, sex and age) reached the target sample size (103), the subject registration for this study was closed. Subsequently, participants were asked to answer a questionnaire on the web-based survey screen. Upon completion of the survey, participants received a small cash reward.

In this study, a custom-designed questionnaire survey was developed in collaboration with an expert in food defense research. A preliminary pilot survey was conducted involving 15 individuals (representing approximately 1% of the total sample size for the questionnaire) to assess the questionnaire’s completeness, clarity, and consistency. Adjustments were made to the questionnaire based on the pilot test findings to enhance its coherence. The web-based survey screens were created by a dedicated survey company.

Age, sex, household income, and residential area were recorded during the survey panel monitors’ registration. In this survey, participants responded to items related to food safety, food defense, awareness of food protection, and actions to be taken in 3 cases of abnormalities, such as contamination of foreign substances, bad smell of purchased food, and extra items which the customer had not selected. For the 3 cases, respondents were asked whether they would take the suggested actions. The questionnaire items shown in Textbox 1 were analyzed in this study. For each item (with some exceptions), the respondents were asked to answer on a 6-point Likert scale: 1=strongly disagree, 2=disagree, 3=somewhat disagree, 4=somewhat agree, 5=agree, and 6=strongly agree.

We combined the data into 2 binary values: “disagree” for 1=strongly disagree, 2=disagree, and 3=somewhat disagree, and “agree” for 4=somewhat agree, 5=agree, and 6=strongly agree.

To estimate the relationship between the actions that the respondents selected and the items of the questionnaire, a stepwise linear regression analysis was conducted. The dependent variable included the answers “agree” or “disagree,” while the independent variables included categories such as sex, age, household income, residential area, personality, and temperament of participants (eg, diligent, sociable, cooperative, and honest, or having a strong sense of responsibility or morality), and what is important when purchasing food (eg, price, brand, manufactured domestically, reputation or word of mouth, and safety) as determined from the questionnaire.

Statistical analyses were conducted using SPSS (version 27.0; IBM). The level of significance was set at P<.05.

A total of 1442 respondents (103 men and 103 women in each age group) who answered all questions were included in the analysis. Of the respondents, 53.5% were married and 51% (n=735) had children. The regions of residence were as follows: Hokkaido, 4.6% (n=66); Tohoku, 5% (n=72); Chubu, 16.5% (n=23); Kanto, 40.2% (n=58); Kinki, 19.1% (n=275); Chugoku, 4.4% (n=63); Shikoku, 2.1% (n=30); and Kyushu, 8% (n=115).

The responses to the questionnaire item “The following are important for you when buying food,” showed that more than 93.6% (n=1350) of the respondents tended to place importance on safety, with 37.7% (n=544) strongly agreeing, 33.6% (n=735) agreeing, and 22.3% (n=322) somewhat agreeing. The recognition of each term was as follows: 95.2% (n=1373) for “food security and safety,” 95.6% (n=1379) for “food hygiene,” 17.6% (n=254) for “intentional contamination of food,” 46.3% (n=668) for “food terrorism,” and 17.1% (n=247) for “food defense.”

The results of the questions “The frozen food you purchased is contaminated with foreign substances (metal, hair, etc.). You...” were as follows: 9.1% (n=131) for “eat it without worrying,” 77.6% (n=1119) for “contact the manufacturer,” 66.7% (n=962) for “contact the shop from where you purchased it,” 12% (n=173) for “upload it on SNS [social networking site],” and 69.8% (n=1007) for “dispose of it.” The majority of respondents answered “contact the manufacturer,” while “eat it without concern” was less than 10%. Interestingly, about 12% of the respondents indicated that they would “upload it on SNS.”

The results of the questions “The frozen food you purchased has a bad smell (rotten, chemical, etc.). You...” were as follows: 4.8% (n=69) for “eat it without worrying,” 78.4% (n=1131) for “contact the manufacturer,” 73.6% (n=1061) for “contact the shop from where you purchased it,” 12.6% (n=182) for “upload it on SNS,” and 74.8% (n=1079) for “dispose of it.” The trend of results was similar to that of contamination with foreign substances (eg, metal, hair).

The results of the questions “You find extra item(s), which you had not selected, in the food parcel delivered to you. You...” were as follows: 30.7% (n=443) for “eat it without worrying,” 75.6% (n=1090) for “contact the shop from where you had ordered it,” 7.3% (n=105) for “upload it on SNS,” 13.1% (n=189) for “dispose of only the extra item(s),” and 7.6% (n=110) for “dispose of all the items.” Interestingly, compared to the previous two questions, the percentage of respondents answering “eating it without worrying” increased. On the other hand, the percentage of respondents indicating that they would “upload it on SNS” decreased.

The results of the logistic regression analysis are presented in Tables 1-3. Male participants and the younger generation were more likely to respond that they would “eat it without worrying” in case of “contamination with foreign substances” (Table 1), “bad smell” (Table 2), or “extra item(s)” (Table 3) in the purchased product. A similar trend was observed for “upload it on SNS,” although the tendency for “extra item(s)” was characteristically higher among “I am sociable” and “brand-conscious” respondents.

This study revealed that awareness of food defense as a term is very low compared to that of food hygiene. In addition, the percentage of respondents who answered that they would eat their purchased food without worry despite knowing there was something wrong with it was higher among the younger generation, especially male respondents. Similarly, the percentage of respondents who said they would post an article on SNS if something was wrong with the food they had purchased was also higher among the younger generation, especially respondents. Although businesses that manufacture or sell food have recently begun taking food defense measures (ie, protecting food from intentional contamination), the results of this study indicate that if food that has been intentionally contaminated with a foreign substance is sold and delivered to consumers, those consumers could eat it and suffer from health problems. In particular, the results showed that 30.7% (n=443) of the respondents answered that they would “eat without worrying” even if there were products in the package other than those they had purchased. This finding indicates it might be better to assume not only food hygiene issues with the manufacturer but also food defense issues in widely available food delivery services. Our study also demonstrates the importance of food protection measures in food delivery businesses, as well as the consumers’ role in ensuring safety. Promoting consumer education and awareness regarding food defense can contribute to enhancing food safety throughout the food chain.

To protect consumers from health hazards caused by food, food safety has been a matter of concern [8]. Food safety mainly deals with issues such as food poisoning, food additives, and pesticide residues, which can be prevented by avoiding system errors. In other words, food safety can be maintained by creating and following rules for the prevention of food poisoning and additives. In Japan, introducing the hazard analysis and critical control points system has helped maintain and improve food sanitation management throughout the food supply chain. Hazard analysis and critical control points–based hygiene management has become mandatory for all food businesses as of 2021 [16]. In recent years, food hygiene measures have been implemented not only by food manufacturers and sellers but also by consumers at home. For example, the World Health Organization [17] advocates the following core messages as the “Five Keys to Safer Food”: (1) keep clean, (2) separate raw and cooked, (3) cook thoroughly, (4) keep food at safe temperatures, and (5) use safe water and raw materials.

In light of recent incidents of intentional contamination of food with foreign substances, food manufacturing companies must implement food defense measures [10,13-15,18]. In addition to food manufacturing companies, businesses that serve food directly to consumers, such as restaurants and stores, are likely to be targets of intentional contamination by foreign substances. Intentional contamination in restaurants and other food service businesses is characterized by the fact that food is prepared in the kitchen and delivered to consumers immediately. If a foreign substance is intentionally mixed into the food provided by a restaurant, although the possibility of a widespread health hazard is not high, the possibility of health damage is high because the foreign substance is mixed into the food just before it reaches the consumer. Therefore, restaurants and stores must implement food safety measures. Home delivery of food products has recently become a common practice. Businesses that provide home delivery of food products must also consider measures to ensure the safety of food products during home delivery as an aspect of food defense.

Our study showed that young people, especially young men and boys, are more likely to eat their purchased food even when something is wrong with it. In addition, younger generations, especially young men and boys, are more likely to eat even if they receive extra food they did not order. Unfortunately, health hazards are more certain when foreign substances are intentionally mixed during food delivery because it occurs just before the food reaches a consumer. In addition, there is a possibility of individuals causing health hazards for consumers by replacing legitimate finished products with those contaminated with foreign substances or adding a finished product with a foreign substance to a legitimate finished product during food delivery. Therefore, food delivery companies must adopt food defense measures, and strengthen them through the establishment of rules. For example, it is necessary to ensure that delivery personnel do not leave food unattended, even temporarily, during the delivery process. In Japan, home delivery services for prescription drugs were also implemented during the COVID-19 pandemic. Although this study was conducted on food products, the participants’ response of “ingesting without concern even if there is an extra item” indicates a risk for delivery services in other industries. In addition, consumers also need to protect themselves and their families from food-related health hazards by thoroughly checking whether the purchased food has any abnormalities or if its condition is different than usual. Consumers, as well as food manufacturers and sellers, need to be aware that they play a role in preventing health hazards caused by intentional food contamination.

This study has several limitations that must be acknowledged. First, it should be noted that this survey was conducted on the web. This may have influenced respondents’ tendency to answer “upload it to SNS” in case of foreign material contamination. The data were collected only from respondents registered with an web-based panel company, thus, there may have been bias. Nonetheless, panel-based surveys have been widely used in recent years [19-23]. Second, because the participants in this study were recruited using an equal allocation of men and women by age group, they may not be representative of the country’s population by age group or place of residence as a whole. Third, the timing of the survey may have been influenced by the fact that it was conducted during the COVID-19 pandemic state of emergency. Fourth, the participants received a small cash reward for responding to the survey, which may have affected the randomness of the sample. However, since the research firm built the panel for the survey based on large enrollment, bias is expected to be minimized.

The findings of this study indicate that if food intentionally contaminated with a foreign substance is sold and delivered to consumers, it is possible that consumers will eat it and experience health problems. Therefore, it is crucial for not only food manufacturers but also food delivery service providers to consider food defense measures. Additionally, promoting consumer education and awareness regarding food defense can contribute to enhancing food safety throughout the food chain.