According to our results, there was a higher proportion of more ready-to-eat dietary patterns than we expected in Korean children and adolescents, particularly ready-to-eat dietary patterns with high consumption of white rice, wheat/bread, eggs, fish, and dairy products. The ready-to-eat dietary pattern seems to have unhealthy effects on children and adolescents due to its hypocaloric and nutrient-poor content. Moreover, HGS was lower in participants from the ready-to-eat group than those from the balanced and western-style fast-food groups. Further, following adjustment for potential confounders, HGSWR was higher in participants following a balanced or western-style fast-food dietary pattern rather than in those following a ready-to-eat dietary pattern. McNaughton et al. showed that a dietary pattern rich in fruit, salad, cereals, and fish might be associated with diastolic BP in 1,086 adolescents.(27) Moreover, recent studies showed that greater HGS is associated with longitudinal health maintenance and health improvements in adolescents(28); in addition, the author reported that low HGS could serve as a prognostic indicator of cardiometabolic risk and to identify adolescents who would benefit most from lifestyle interventions to improve muscular fitness.(28) Remarkably, our results agree with those of the aforementioned studies. However, in the present study, the additional evaluation of HGSWR deepened the investigation of muscle quality; besides, HGSWR seems to be also associated with dietary intake of adolescents, especially with the ready-to-eat dietary pattern.
Furthermore, the participants following a ready-to-eat or western-style fast-food dietary pattern showed a lower consumption of carbohydrates, fibers, calcium, and vitamin C compared to those following a balanced dietary pattern. The ready-to-eat dietary pattern implies a high intake of eggs, fish, processed products, and refined carbohydrates — such as white rice, flour, and bread — as well as a low intake of vegetables and fruits, which is rather common for foods from convenience or street-food stores. By contrast, the balanced dietary pattern is crucial for adolescents, especially when active physical and emotional development is considered. Nevertheless, Korean adolescents seem to prefer simple meals such as bread, sandwiches, and cereals, and the frequency of convenient dietary patterns is increasing.(29) In addition, the data from The Korean Student Health Examination and the Korean Youth Risk Behavior Web-based Survey showed that the consumption of healthy foods such as fruits and vegetables tended to decrease while the consumption of foods such as fast food and ramen increased.(30, 31) According to the Korean Youth Risk Behavior Web-based Survey (n = 62,276), 39.3% of the Korean adolescents consume convenient food more than once or twice a week, whereas 26.0% more than thrice a week. High-school students had a higher intake of convenient food than middle-school students. Adolescents who consumed convenient food more than thrice a week had a lower intake of recommended foods such as fruits, vegetables, and milk as well as higher intakes of fast food, snacks, and soda than the rest of the adolescent population. However, this is not only a problem of Korean adolescents: in fact, the food consumption patterns of Indian adolescents have also shown to imply inadequate dietary intakes, including lower consumption of vegetables and higher consumption of energy-dense snacks.(32) Cutler et al. reported increases in fast-food consumption patterns in older boys and girls.(33) In the United States, fast food is consumed by one-third of children each day and by two-thirds of children every week.(34) In summary, the adolescents’ preference for ready-to-eat dietary patterns seems to be a problem worldwide.(35)
The participants following a balanced dietary pattern ate a lot of whole grains, potatoes, beans, nuts, vegetables, mushrooms, fruits, eggs, fish, seaweed, and dairy products, as the name balanced suggests; notably, their HGSWR was significantly higher than that of the participants following either a ready-to-eat dietary pattern. Western-style fast-food dietary patterns, which were based on wheat, bread, noodles, sugars, meats, oils, sodas, and seasonings, were not associated with decreased HGSWR compared to balanced dietary patterns in this study. This may be due to the inclusion of unique Korean eating patterns in the definition of the western-style fast-food pattern group. Remarkably, kimchi — a traditional Korean food — was consumed in all groups; this may deviate from the traditional western-style diet as we know it. In this study, we defined the western-style fast-food dietary pattern as based on wheat/bread, noodles, sugar, meat, oils, sodas, and seasonings. However, other studies defined the western-style diet as based on poultry, eggs, mayonnaise, fast foods, pizza, pies, and fried potatoes.35 As a consequence, further studies are still necessary in order to find an association between the western-style diet and HGSWR.
Interestingly, high BMI and low socioeconomic status are known to be associated with decreased muscle strength.(36, 37) However, in this study, a reduction of HGSWR was observed in association with the ready-to-eat group rather than with the balanced group, even with adjustments for BMI and socioeconomic status. Therefore, the results of this study show that dietary patterns could independently play an essential role in muscle quality.
Robinson et al. showed an association between nutrition and sarcopenia and insisted that efforts to prevent muscle strength should be started earlier in life with the optimization of diet and nutrition.(38) Moreover, unhealthy diets are well-known risk factors for several pathologies.(39) Fiber intake, fat, physical activity is introduced as a distal risk factor in chronic disease prevention model, and specific strategies are underway by several countries for the prevention of chronic diseases. Reduction in HGS and HGSWR by participants following a ready-to-eat dietary pattern indicates that Korean adolescents are also experiencing problems due to nutritional imbalance. Further, adolescents need to learn the importance of following a balanced diet and reducing the intake of fast food or ready-to-eat food in early life. In addition, an appropriate environment would be required for the spread of balanced dietary customs. National efforts on nutritional policies are needed for reducing ready-to-eat dietary customs and the overall environment related to nutritional imbalance.
Nonetheless, this study has several limitations. Firstly, errors might occur in the 24-hour dietary recall method in face-to-face interviews even when examinations are performed by trained interviewers. Secondly, many common types of food might not be represented in the questionnaire. Thirdly, this is a cross-sectional study, and a longitudinal study might instead be a better method for detecting an association between food intake and HGSWR.
Despite these limitations, this is the first study to investigate the association between HGS, HGSWR, and dietary intake in adolescents.