Despite the enormous lifestyle changes experienced by Saudi society during recent decades, few researches have simultaneously been conducted on the physical activity, sedentary behaviors and dietary habits of Saudi adolescents. The present study reported on the prevalence of the above lifestyle factors among adolescents aged 14-19 years from three major cities in Saudi Arabia. The findings of this study provide evidence on the high prevalence of sedentary behaviors and the low level of physical activity, especially among females. Unhealthy dietary habits were also widely found among both genders. Furthermore, correlation analyses revealed that unhealthy behaviors, such as increased screen time and unhealthy dietary habits, appear to aggregate in this group of Saudi adolescents.
Although some health benefits can occur through an average of 30 minutes of physical activity per day , physical-activity guidelines for children and adolescents recommend that they should participate in at least 60 minutes of moderate to vigorous physical activity on a daily basis [13–16]. In the present study, we used 1680 METs-min per week as cutoff scores to correspond to 1 hour of daily moderate-intensity physical activity and 2520 METs-min per week as cutoff scores corresponding to 1 hour of daily moderate- to vigorous-intensity physical activity. Based on these cutoff scores, we found a considerably high prevalence of physical inactivity, especially among Saudi females. About half of the males and less than quarter of the females met the current recommendations of 1 hour daily of moderate-intensity physical activity. Such high rates of low physical activity levels represent an area of great concern because of the association of inactivity with increased cardiovascular and metabolic risk factors in children and adolescents [13, 15]. Previous local data using objective physical-activity measurement indicated that 60% of Saudi children and 71% of youth do not engage in health-enhancing physical activity of sufficient duration and frequency [24, 25]. Major factors that contribute to youth inactivity in Saudi Arabia include a reliance on cars rather than walking for short-distance travel, including trips to and from school , and limited quality physical education programs in schools, especially for girls.
It is well understood that a comparison between physical-activity studies should be made with caution since wide variations are observed in age range, representation and activity-assessment methods. In spite of that, it is important to provide comparative estimates of physical-activity levels in different countries to place our sample prevalence into perspective. Findings from the European Youth Heart Study using an accelerometer for physical-activity measurements showed that the great majority of 16-year-old boys (81.9%) and girls (62.0%) achieved current health-enhancing physical-activity recommendations . In the United States, results from the Youth Risk Behavior Surveillance indicated that only 18.4% of adolescents met these physical-activity guidelines . Furthermore, more than 52% of Greek-Cypriot children and adolescents met the physical-activity guidelines . In Finland, among 15- to 16-year-olds, 59% of boys and 50% of girls reported 60 minutes or more of total physical activity per day; however, when daily moderate- to vigorous-intensity physical activity was considered, lower proportions of the boys (23%) and girls (10%) were able to meet the recommended amount of daily physical activity . The Global School-based Student Health Survey (GSHS), which included data on physical activity and sedentary behaviors of schoolchildren in 34 countries, indicated that nearly 24% of boys and over 15% of girls across the countries met the physical-activity recommendations .
Females in the present study were found to be not just significantly more sedentary than males, but they were much less physically active too, especially with vigorous physical activity. Insufficient vigorous physical activity was shown to be a risk factor for higher BMI for adolescent boys and girls . Thus, our findings suggest that Saudi females may be a good target for physical-activity intervention. It is noteworthy that physical-activity levels of Arab females, irrespective of the region, have generally been reported to be much lower than those of males [6, 47, 48]. This could be due to the fact that females have generally limited opportunities compared with males to engage in physical activity, both in and outside school. Not many female schools in Saudi Arabia offer physical education classes. In addition, for cultural reasons, families may not encourage females to take part in physical activity. Elsewhere, males were found more likely than females to participate in sports and physical activity [43, 49].
Modern life has to a great extent systematically reduced total energy expenditure. Moreover, urbanization and related environmental determinants may also be considered an important risk factor for physical inactivity in developing countries undergoing economic transition . Before the recent economic growth surge, which started three decades ago, communities in major cities in Saudi Arabia were designed to support pedestrian travel in common daily activities. These traditional design settings facilitate walking and cycling, resulting in an increase in daily living activity. Walking and cycling to and from school was also common in the past. In contrast, major Saudi Arabian cities are now modernized, with large street networks and separate zoning for residential and commercial areas. This kind of design requires the use of automobiles for all trips and, therefore, totally discourages walking.
The prevalence of sedentary behaviors found in the present study among Saudi adolescents was remarkably high. The American Academy of Pediatrics (AAP) has expressed concern about the amount of time that children and adolescents spend viewing TV and has issued guidelines recommending that screen time not exceed 2 hours per day . Only 16% of adolescent males and less than 11% of females in the present study actually met the AAP recommendations on daily screen time. The implication of this finding is that there is a need to reduce the time spent by adolescents on TV viewing and computer use. Excessive TV viewing in adolescence appears to be related to an unfavorable cardiovascular risk factor profile . In addition, it is now recognized that sedentary behaviors are associated with harmful health outcomes that are different from those attributable to the lack of physical activity .
In comparison with our findings on the prevalence of screen time among adolescents, much less prevalence of TV viewing was reported for Saudi adolescents in the city of Abha, where 38% of the participants watched TV for more than 3 hours per day . The Abha sample, however, included only boys with a wider age range (11-19 years) located in southwestern Saudi Arabia. In addition, watching TV was found to be the predominant leisure time pursuit among 14- to 16-year-old adolescents in the United Arab Emirates, with an average of 2.5 hours per day . Elsewhere, more than half (52.4%) of Greek-Cypriot adolescents met the recommendations of the AAP on TV viewing . Among adolescent Finns, 48% of boys and 44% of girls reported watching TV more than 2 hours per day . The prevalence of 2 hours or more screen time per day for Chinese boys and girls aged 13-18 years was 44.3% and 34.7%, respectively . The proportion of US youth who met the TV-viewing guideline of 2 hours or less per day ranged from 65% to 71% . Among Canadian youth, 41% of girls and 34% of boys in grades 6-10 watched TV 2 hours or less per day; but when the total screen time was considered, only 18% of girls and 14% of boys met the 2-hours guideline . The mean daily time spent on TV viewing by Italian youth was reported as 2.8 hours , which is very similar to what was found in the present study. However, much less time, with an average of 4.7 hours per week, was spent on all sedentary activities by Hungarian youth aged 13-19 years . From the preceding comparison, it appears that the prevalence rate of screen time among Saudi adolescents exceeds that of adolescents in many countries and is comparable with the prevalence rate observed among adolescents in the United States and Canada.
The females in the present study spent, on average, more screen time than the males--a finding that is supported by some previous studies [43, 54, 56]. However, not all studies found such a gender difference . Contrary to our findings, male high school students from Turkey had higher screen time than females . Females in the present study were found to be much less active than males, and compared with males they had less opportunity to engage in physical activity; this would suggest that females may substitute physical activity with sedentary activity. However, examining the association between sedentary behaviors and physical activity in our sample did not reveal any significant relationship between the two variables, indicating that other independent factors may be responsible for this gender difference in screen time.
The majority (ranging from 66.85 to 80.4%) of adolescents in the current study did not daily consume breakfast, fruit, vegetables and milk, while a considerable proportion frequently showed unhealthy dietary habits. The WHO Global Strategy for Diet and Physical Activity recommendations call for achieving an energy balance, limiting the energy intake from fats, reducing the intake of free sugars and increasing fruit and vegetable consumption . It is worth noting, though, that the food-consumption pattern has changed dramatically in Eastern Mediterranean countries during the past four decades. During the period from 1970 to 2005, the intake of animal products and refined sugar increased while the intake of fruit and vegetables and complex carbohydrates decreased .
Presently, unhealthy dietary habits are not uncommon in youth. The results from the 2009 National Youth Risk Behavior Surveillance of the United States indicated that during the 7 days preceding the survey, about 78% of high school students had not eaten fruit and vegetables five or more times per day and 29.2% had drunk soda or pop at least once per day . In the present study, the prevalence of daily fruit and vegetable consumption by both genders was noticeably low, and it was slightly lower than what was previously reported for Saudi adolescents in Jeddah, which amounted to 27.6% and 26.4% for fruit and vegetables, respectively . However, our sample prevalence is much lower than the 50.8% and 62.4% prevalence reported for fruit and vegetable intake by Saudi adolescents from Abha . Moreover, fruit and vegetable consumption more than three times per week among adolescent males and females in the United Arab Emirates was reported to range from 49% to 69% . This figure is higher than the average prevalence of fruit (32%) and vegetable (48%) consumption more than three times per week found in the present study. Skipping breakfast is another unhealthy dietary habit and was found to be very common in the present study. Breakfast skipping was reported to be 49% among Saudi adolescents from Abha , about 15% among Saudi secondary school students from Jeddah , and about 10% among adolescent males and nearly 19% among females in the United Arab Emirates . Skipping breakfast was also shown to be prevalent in the United States and Europe, ranging from 10% to 30%, depending on age-group, population and definition .
The overall weekly frequency of fast-food intake in the present study was significantly higher in males than in females (2.90 versus 2.63). This may be due to the fact that for cultural reasons, adolescent males in Saudi Arabia have more opportunity than females to go outside to fast-food restaurants. Irrespective of the difference between males and females, such frequency is much lower than the average frequency of fast-food intake of 4.5 times per week recently reported for adolescents in Riyadh  and higher than the average frequency that was reported for Saudi adolescents in another study . In addition, daily consumption of fast food by adolescents in the present study (9% for males and 6% for females) is not much different from that reported for Saudi secondary school boys in Riyadh , but it is much less than the 30% that was recently reported for adolescents in Abha . The proportion of adolescents in the present study consuming fast food more than three times per week was 30.2% and 24.9% for males and females, respectively. These percentages are lower than the rate of fast-food intake reported recently for Emirates adolescents .
In recent years, high-energy food snacks have become readily available for the majority of Saudi children and adolescents. In the present study, among unhealthy dietary items consumed more than 3 days per week, the highest were sugar-sweetened beverages (67.2% and 57.4% among males and females, respectively) and candy and chocolate (37.3% and 52.6% among males and females, respectively). Previous local studies reported a proportion of daily consumption of soft drinks by Saudi adolescents ranging from as little as 33.4%  to as high as 62.4% . Furthermore, the average soft drink and candy intake more than three times per week among adolescents in the United Arab Emirates was found to be 63.2% and 62.9%, respectively .
Relationships amongst lifestyle factors
We observed a significant negative association between breakfast intake and BMI in the adolescent males and females. Previous reports indicated that breakfast intake was negatively related to overweight in adolescents [7, 60]. However, the inverse relationship found in the present study between females' BMI and the intake of fast foods, sugar-sweetened beverages, French fries and potato chips, and cakes and donuts cannot be really explained. In an international comparative study involving youth from 34 countries, Janssen et al.  observed a significant negative relationship between BMI categories and candy consumption in 91% of countries, while no association between the consumption of non-diet soft drinks and being overweight was found.
In the present study, breakfast, fruit and vegetable consumption showed significantly positive correlations with physical activity in males and females and significantly inverse relationships with screen time in females. Ample evidence shows that high physical-activity levels are associated with healthy dietary habits. Among adolescents from Riyadh, Collison et al.  found that exercise was positively correlated with fruit, vegetable and cereal intake in both genders. In French adolescents, it was reported that physical activity positively correlated with the consumption of fruit and vegetables . Adolescents from the United States participating in high school sports were also more likely than nonparticipants to report fruit and vegetable consumption the previous day . In addition, Kremers et al.  showed that a low frequency of fruit consumption was associated with low physical activity among Dutch adolescents. In a study conducted on Iranian adolescents, it was shown that the most active adolescents consumed fruit, vegetables and dairy products more frequently than their less active peers. . Fruit, vegetable and milk intake was shown to inversely relate to fast-food intake among Saudi adolescents in Riyadh . It is worth noting, however, that the most consistent determinants of fruit and vegetable consumption in children and adolescents were identified as age (younger children), gender (being a girl), socioeconomic status, preference, parental intake and availability .
The present study did not find any significant association between sedentary behaviors as measured by total screen time and total or vigorous physical activity (r value ranged from -0.01 to 0.04). Research on the relationships between sedentary behaviors and physical activity has produced contrasting results. Some studies have shown an association [44, 66], but other studies have failed to show any relationship between the two variables [21, 57]. Findings from a study on French pre-adolescents indicated that sedentary behaviors and physical activity are considered distinct behaviors . According to Gordon-Larson et al. , physical activity and sedentary activity were associated with very different determinants: physical activity was associated with environmental factors while inactivity was most associated with sociodemographic factors. The implication of the absence of a relationship between screen time and physical activity found in the present study is that both physical inactivity and sedentary behaviors must be targeted when implementing any program for the purpose of promoting physical activity and reducing sedentary behaviors.
The findings that screen time and fast-food intake in the present study both exhibited a significantly positive relationship with consumption of French fries and potato chips, cakes and donuts, sugar-sweetened beverages, candy and chocolate, and energy drinks indicates clustering effects of unhealthy dietary habits. Platat et al.  reported a significant positive association with the intake of French fries and potato chips and sweetened drinks and a negative association with the high consumption of fruit and vegetables. In our study, screen time was also inversely related to the intake of fruit and vegetables (p > 0.01). The results of a systematic review indicated that screen time in adolescents was associated with unhealthy dietary habits, including lower fruit and vegetable intake and higher consumption of energy-dense snacks, drinks and fast foods . Furthermore, a recent study on Saudi children aged 10-19 years has also reported a positively significant correlation between sugar-sweetened beverage consumption and poor dietary habits .
Strength and limitations
The findings of the present study should be seen in the light of their strengths and limitations. This is a novel study in Saudi Arabia that collectively examined several lifestyle factors in a large and representative sample of Saudi adolescents, using a validated and comprehensive physical-activity questionnaire, employing metabolic equivalents for calculating energy expenditure from physical activity. The information stemming from this study should add to existing knowledge about the lifestyle factors in a society experiencing a nutrition transition. One of the limitations of this multicenter epidemiological study was that the information was based on self-report, although we made every effort to minimize any possible over- or under-reporting by the participants. Because this is a cross-sectional study, the temporality of the associations between sedentary behaviors, physical activity and dietary habits cannot be certain; however, many of the observed associations conform to biological plausibility. In addition, dietary information provided by the adolescents in the present study was based on the frequency of consumption of food items without much regard to quantity or portion size. This could have influenced the information relating to dietary habits and their associations with other variables.