Obesity is a complex chronic disease characterized by excessive accumulation of body fat. It has been declared a global pandemic by the World Health Organization (WHO) [1
]. Its prevalence is high among children, adolescents, and adults in developed countries [2
]. Obesity is considered a dangerous disease because it causes or worsens many health problems independently or in connection with other diseases. The WHO defines obesity as body mass index (weight—kg divided by the square of height—m2
; body mass index—BMI) of over 30 kg/m2
]. Among Asians, obesity is defined as a BMI of ≥25 kg/m2
]. BMI is a person’s weight in kilograms divided by the square of height in meters. BMI is an inexpensive and easy screening method for weight categories, such as underweight, healthy weight, overweight, and obesity. Obesity has negative effects on health, such as type 2 diabetes, hypertension, cardiovascular disease, and premature death. It is also highly related to social and psychological problems as well as a social and economic burden [6
]. Since such obesity-related costs impose a large economic burden on society [10
], rapid intervention and treatment for obesity are required.
In particular, it has been reported that the prevalence of obesity is higher among people with intellectual disabilities than among the general population [11
]. According to a study on people with intellectual disabilities in Australia, the prevalence of obesity (23.8%) and being overweight (22.5%) was higher in this population than that in the general population [12
]. In the UK, the prevalence of obesity and being overweight among adults with intellectual disabilities is 20.7% and 28%, respectively [11
]. This indicates that obesity is a more serious problem among people with intellectual disabilities than among the general population [14
On the other hand, it has been reported that the number of people with intellectual disabilities is the highest in low- and middle-income countries [16
]. Currently, there are 2.59 million people with disabilities in South Korea, accounting for 5% of the total population, of which 212,936 have intellectual disabilities. The proportion of people with intellectual disabilities among the population with disabilities consistently increased from 6.9% in 2009 to 8.2% in 2015, to 9.0% in 2018 [17
]. Although it may seem that the prevalence of being overweight and obese among people with intellectual disabilities is higher in South Korea than in Western countries due to social and environmental problems, studies examining such prevalence are limited.
Obesity is caused by a variety of factors, including environmental and genetic factors [18
]. In particular, it has been reported that decreased physical activity, decreased physical fitness, inadequate nutritional intake, and a sedentary lifestyle are risk factors of obesity [19
]. In this regard, people with intellectual disabilities are limited in their physical activities due to limitations in language development, cognitive function, and cognitive impairment [20
]. It has also been reported that many of them lead a sedentary lifestyle [21
]. In addition, as they have a stronger desire for food intake than the general population, the prevalence of obesity is also higher [22
]. Their lack of physical activity leads to a decline in their fitness level, which, in turn, causes various diseases such as obesity, hypertension, type 2 diabetes, and cardiovascular disease, thereby decreasing the health of people with intellectual disabilities [23
]. Previous studies have shown that people with low fitness levels have a higher risk of becoming overweight or obese than those with high fitness levels [24
]. Other studies have also shown that obese or overweight individuals have lower physical fitness levels than do people with a normal weight [26
], and that physical fitness and body fat are negatively correlated [27
It can be assumed that higher physical fitness levels among people with intellectual disabilities are associated with better body composition. However, little is known about the relationship between health-related physical fitness factors and obesity-related factors in this population. In addition, while the prevalence of intellectual disabilities and obesity is increasing in middle-income countries such as South Korea, no survey data have been reported on the obesity rates of teenagers to adults in their 40 s or the relationship between obesity and health-related physical fitness factors. Therefore, we aimed to investigate the prevalence of obesity among people with intellectual disabilities in South Korea and examine the relationship between health-related physical fitness and obesity-related factors. Elucidating the physical factors associated with obesity in people with intellectual disabilities could lead to the development of new intervention programs to promote a healthier lifestyle in this population. Our results can help researchers, clinical experts, and trainers develop intervention strategies for the treatment of obesity and further motivate policymakers and decision makers to prioritize the treatment of people with intellectual disabilities.
Our study aimed to investigate the prevalence of obesity and physical fitness factors affecting obesity among people with intellectual disabilities in South Korea. Our results show a high prevalence of overweight and obesity among people with intellectual disabilities in South Korea. The prevalence of overweight and obesity among people with intellectual disabilities was similar between male and female subjects. This shows a tendency to increase with age. In addition, there was a significant correlation between health-related physical fitness factors (muscular endurance) and obesity factors (BMI and body fat percentage) among people with intellectual disabilities in South Korea. Moreover, the muscular endurance factor had a significant effect on the body fat percentage (Figure 2
Obesity is a negative body change that degrades the quality of human life, regardless of the presence or absence of a disability, and requires continuous and systematic management. As people with intellectual disabilities tend to have low levels of physical activity and indulge in excessive nutritional intake, they are prone to having an unbalanced body, being overweight, and having impaired body functions, which eventually leads to obesity [28
The prevalence rates of overweight (17.6%) and obesity (34.3%) among people with intellectual disabilities in this study were similar to those of other countries. For example, in an Australian study of 206 subjects, approximately 22.5% of subjects were obese, and 23.8% were overweight [12
]. A study in the UK also reported that the prevalence rates of obesity and overweight were 20.7% and 28.0%, respectively, whereas subjects that fell in the normal range of weight accounted for 32.7% [11
]; a study by Hsieh et al. [36
] on people with intellectual disabilities in the United States reported prevalence rates of 28.9% for overweight and 38.3% for obesity. The prevalence of overweight and obesity is higher among people with intellectual disabilities than in the general population [12
]. This may be because people with intellectual disabilities have decreased income levels in an environment where they have difficulty engaging in economic activities, which leads to a lack of opportunities to participate in physical activities and exercise programs [20
]. At this rate, obesity among people with intellectual disabilities is expected to increase more rapidly in the future, thereby increasing the morbidity rate as well. Therefore, it is necessary to pay closer attention to obesity treatment interventions for people with intellectual disabilities.
In our study, there was no significant difference between the ratio of being overweight (male 16.0% vs. female 21.2%) and the prevalence of obesity (male 34.7% vs. female 33.3%) according to sex. This is supported by a meta-analysis on adults with intellectual disabilities, which showed no difference in sedentary behavior between genders [40
]. However, it is necessary to prioritize interventions for women with intellectual disabilities, given that the following studies: the study in [40
] showed a significantly lower physical activity level in female, compared with male, subjects with intellectual disabilities, and Hsieh et al. [36
] suggested that women have a higher risk of becoming severely obese than men with intellectual disabilities.
It has been reported that overweight and obese people have lower physical fitness than those with normal weight. However, to the best of our knowledge, few studies have analyzed the relationship between health-related physical fitness factors and obesity factors among people with intellectual disabilities. Our results showed an inverse relationship between muscular endurance and BMI as well as the body fat percentage of people with intellectual disabilities (BMI, r = −0.306; body fat percentage, r = −0.402). In addition, through multiple regression analysis, we found that muscular endurance had a significant effect on body fat percentage among people with intellectual disabilities (β = −0.218, p = 0.000).
Although it is difficult to make a direct comparison, several studies on people without disabilities have shown a negative relationship between obesity factors and physical fitness [26
]. A previous study by Fogelholm et al. [27
] in normal adolescents showed a strong negative relationship between muscular endurance (sit-ups) and being overweight. A similar result was found in a study by Lee and Oh [43
], who examined male Korean adolescent subjects without disabilities (n
= 3047) and found that muscular endurance is a significant factor affecting obesity. These results suggest that exercise programs that improve muscular endurance should be considered during interventions for people with intellectual disabilities who are overweight and obese.
Muscular endurance refers to the ability to use the muscles continuously for a certain period of time [44
] and can be improved by strength training. The exercise method that can improve muscular endurance in a population with a low physical fitness level is as follows: perform 10–15 repetitions of an exercise with an intensity of one repetition maximum of 40–50% or less, one to two sets per muscle area, and with short breaks between each set [44
]. Although aerobic exercise for cardiorespiratory fitness may be important for people with intellectual disabilities, it may be wise to focus instead on improving muscular endurance, because low muscular endurance can limit aerobic exercise performance [47
Meanwhile, muscular strength and flexibility were not shown to significantly affect obesity-related factors in intellectually disabled people. These results are similar to those of previous studies, which found a static correlation between weight and muscle strength [48
]. Muscular strength is defined as the ability of a muscle to exert maximum contractile force at once, against resistance [50
]. Muscular strength can be important for everyday life, in intellectually disabled people [53
]. However, our results suggest that muscular strength is the next consideration in exercise programs to mediate obesity. Regarding flexibility, many previous studies have reported no significant association with obesity [55
]. Although flexibility does not significantly affect obesity factors, it is believed that some participation in exercise could help in the daily lives of intellectually disabled people. This is because lack of flexibility is associated with musculoskeletal damage and back pain [55
Given the small sample size of our study, it is difficult to generalize our results. Future research should include a larger number of subjects and investigate the relationship and determinants of various obesity-related physical fitness factors in order to promote health among people with intellectual disabilities.