To our knowledge, this study is the first one that compares food intake and the development of body weight of seafarers at home and on board of merchant ships. According to the on-board examinations, foods and beverages consumed on merchant ships differed widely from seafarers’ diets in their home country. Burmese, Filipino and European seafarers equally reported higher fruit and vegetable and lower coke consumption at home and several culturally different changes among all other food and beverage groups. Based on the self-reported data of the online questionnaire, 45.8% of seafarers were overweight and 9.8% obese. Furthermore, 43.9% stated to have gained body weight over the course of their professional career. While European seafarers were more likely to be overweight and gain weight compared to their Filipino counterparts, it could not be determined whether the increase in body weight was more likely to occur at home or aboard ships.
Origin-related differences in BMI
When comparing the BMI of our study sample with the values of a corresponding general male population from a study of the NCD (non-communicable diseases) Risk Factor Collaboration [20], differences depending on the seafarers’ origin become apparent. More European seafarers are overweight (55.4% vs. 41.8%) but less obese (11.1% vs. 21.7%) than in the general Middle and Eastern European population. Furthermore, Filipino seafarers appear to be more likely to be overweight (30.8% vs. 21.6%) and obese (19.2% vs. 5.5%) compared to the Filipino general population. These figures are also reflected in average BMI, which is slightly lower for European seafarers (26.3 kg/m2 vs. 26.8 kg/m2) and higher for Filipino seafarers (25.3 kg/m2 vs. 22.9 kg/m2) compared to the respective general population. Thus, the occupational profile of the seafarer seems to have a greater influence on the BMI of Filipinos than of Europeans.
The food supply on board influences dietary pattern
Our results show that the food and beverage intake of seafarers depends on the living and working environment. The overall shift in eating habits from “at home” to “on board” involves disadvantageous changes. For example, a high consumption of fruit and vegetables would be beneficial for health, as is a decreased intake of foods high in sodium, like sausage, as well as beverages high in sugar, like coke [21,22,23]. The actual supply of food on board is impacted by many factors. Food availability depends on the delivery capacity and possible shortages of caterers, the port of supply, restricted storage space on board and the limited budget provided by the shipping company [24]. These factors affect all seafarers identically, nevertheless, we found fewer significant differences in food intake between home and on board for European seafarers than for Burmese and Filipinos. Foods and beverages supplied on board seem to be more oriented towards European standards, indicating a mismatch between seafarers’ food preferences and food orders. A culture-related optimisation of food orders is recommended to ensure the provision of commonly consumed food groups and thus also a diverse and sufficient supply of nutrients. Employing crews with seafarers of one nationality would simplify the provision of a culture-specific nutrition and health-promoting conditions on board but is difficult to implement in practice.
Seafarers’ overweight and weight development is more complex than overeating and unhealthy diet on board
So far, the nutritional status and weight gain have been attributed to frequent overeating and unhealthy diets among seafarers during stay on vessels [9, 24, 25]. On board of the merchant ships, meals are prepared by a cook and large portion sizes offered free of charge [25]. Hence catering on board represents a tempting eating environment which encourages overeating. This finding is consistent with the results for our study sample, as more than one-third of the seafarers with self-reported weight gain during their careers also reported gaining more body weight on board. However, it is further remarkable that for another third of the seafarers, weight gain was more likely to occur at home, suggesting that for more than two-thirds of seafarers, the environment plays a role in weight gain.
In general, overeating can be promoted by physical and psychological factors which might apply to seafarers as well, such as lack of sleep, poor hydration and stress [26,27,28]. According to the Pavlovian behavioural conditioning, the incentive of food increases and contributes to satisfaction, when the ingestion of foods is linked to a rewarding consequence [29]. The reward is an amplifying stimulus. As food is described as one of the few pleasures of the seafarers’ daily routine [7], cravings for food or eating can arise and thereby encourage overeating. In this context, food could also be understood as reward if the supply of culturally related food reminds seafarers of home.
An opposing example of overeating was described for Kiribati seafarers. For them, the westernised food environment on board represents something long desired, where food is offered that is not available in their home country [12]. This demonstrates that most importantly the seafarers must be satisfied with the food offered, so that cravings arise for daily meals on board [29]. Since 98.4% of cooks in study II were of Asian origin, it stands to reason that Filipino seafarers might be more satisfied with the meals offered than European seafarers. This goes along with the results of Zyriax et al. [9] who reported that more than 60% of the European seafarers would appreciate better trained cooks. The dissatisfaction with served meals on board could lead to overeating back home, which would explain why significantly more Europeans than Filipinos reported weight gain at home. Furthermore, the westernised calorie-rich food offered on board is not available for the Asian seafarers when staying at home. Finally, the change between both locations itself could also be another influencing factor for weight development. Seafarers might be at risk to adapt to a high energy intake on board and transfer this eating pattern to at home where the individual energy needs are lower.
The impact of psychological and physical factors needs further investigation
Seventy percent of all seafarers who had lost weight, reported that weight loss occurred on board. It is likely that other factors than food intake contribute to weight change in seafarers as well. One of these factors certainly is the total daily energy expenditure. Considering the fact, that physically demanding work should support to maintain a normal body weight, it is almost surprising that large proportions of seafarers are overweight or obese [30]. Due to high levels of physical strain during working-hours, it is likely that seafarers expend more energy on board compared to their free-time at home which could favour weight loss on board. However, the amount of physical strain depends on the occupational profile of the seafarer and no in-depth studies have yet been carried out to investigate the differences in physical activity and energy consumption on board and at home. Also, psychological components caused by the work situation on board, such as social isolation and loneliness, were frequently described among seafarers [31] and could play an important role in eating habits and weight development [32, 33]. Furthermore, many seafarers work in shifts, which has been linked to overweight and obesity for other occupational groups [34]. To learn more about the underlying factors of seafarers’ weight development, more detailed tracking of body weight and further in-depth research on eating behaviour including psychological aspects are required.
The cook at the Centre of a holistic nutrition intervention
Our results show the need for sustainable changes in the supply system on board merchant ships in order to make the catering on board more demand-oriented, culture-specific and overall healthier. By instrumentalising cooks as a gatekeeper for nutrition, Hjarnoe and Leppin [7] reported that promotion of a healthy diet at sea is possible but needs to overcome the occupational challenges of the maritime industry. Such changes are both large and small-scale and need to address not only the cook but also all other levels involved in maritime nutrition, such as legal guidelines as well as its implementation by the shipping companies. Practical methods for cooks to practice on board were already explored in an intervention study with ship cooks [7]. In addition, Westenhöfer et al. [12] suggested to use the principles of nudging, e.g., to offer fruits and vegetables as appetiser, as a promising strategy to influence seafarers’ food choices and consumption. However, when developing such an intervention, it should also be questioned how health promotion can support the seafarers to prevent the development of overweight at home.
Limitations
Surveys on merchant ships are of course subject to limitations. The versatility of seafarers concerning origin, religion, culture, socioeconomic status, the different types of jobs and working conditions, as well as the prevailing living conditions on board merchant ships reflect a variety of difficulties for scientific investigations of seafarers’ nutrition and health. The merge of European seafarers of different countries as one group was necessary in order to enable evaluation, thus cultural differences among various European nationalities may bias the results for this group. Secondly, European seafarers were associated with the rank officer and Filipinos with crew ranks. Mixing of findings regarding cultural differences and socioeconomic status cannot be ignored along with genetic factors. Thirdly, since in study I the data of Burmese seafarers was exclusively gathered on the bulk carrier of one shipping company and the data of Filipino seafarers exclusively from container ships of another shipping company, it cannot be ruled out that differences between these groups arose due to the type of ship or shipping company guidelines. For study II, however, Filipino seafarers on merchant ships of all types were included in the survey. Fourthly, findings and conclusions are limited to male seafarers of the investigated nationalities. Fifthly, it needs to be mentioned that the small study population for study I divided into three groups only allowed finding significant differences in group comparisons that were at least of medium effect size. Small effect sizes remained statistically insignificant. For that reason, also a more detailed analysis, for example, among crew ranks, was not possible regarding the small dataset. Lastly, this study is based on a cross-sectional approach which excludes the possibility of cause-effect interpretations.