In the Lifestyle, Biomarkers and Atherosclerosis (LBA) study we have previously reported that the high prevalence (15%) of Swedish, young adults with unfavorable homeostasis model assessment of insulin resistance (HOMA-IR) raises concerns about future health [7]. The main findings from the present study were that subjects with a high intake of food rich in sweets had higher insulin resistance (HOMA-IR) values as compared to subjects eating less sweets. Young adults with a sufficient intake of fish and seafood on the other hand had lower HOMA-IR values compared to subjects not eating fish and seafood as recommended, and subjects with a recommended intake of fruit and vegetables had significantly lower HOMA-IR values and less body fat (%) as compared to subjects eating less fruit and vegetables.
Arts et al. have studied CVD risk in college students, 18–24 years, in the USA. Similarly to us Arts et al. have found a high prevalence of CVD risk factors. They highlight the importance of screening young adults for CVD risk, with regard to lifestyle factors such as dietary habits [21]. Most of young adults are unaware of their risk and are ideal targets for prevention since they are in the process of establishing lifestyle habits. Risk factors in the young adulthood strongly predict CVD risk. It is known that reaching middle age free from traditional CVD risk factors are associated with longer life expectancy, and lower risk of developing CVD later in life [21].
Body composition
As mentioned in the introduction Fernandes et al. have examined the influence of dietary habits on CHD risk in College students in the USA. They found that healthy dietary habits with sufficient intake of whole grain and reduced intake of sugar were associated with reduced CHD risk. They conclude that dietary habits and BMI are important indicators of CHD risk [12]. In the present study no association of healthy dietary habits to the body composition measures BMI or waist circumference was found in any of the seven examined food groups.
However, body fat (%) was significantly lower in women and men eating fruit and vegetables five times per day or more which means that they reached the recommended intake of 500 g per day. Equally, lower body fat (%) was seen in woman eating fish and seafood as recommended. The results indicate that body fat (%) is also a sensitive biomarker in this age group. Body fat distribution and adipose tissue dysfunction are key factors in the development of CVD and obesity-related insulin resistance, and better predictors of disease risk, compared to BMI and body fat (%) [22]. However, BMI and body fat (%) are both important determinants of metabolic health at the population level. The present study aimed to associate food habits to metabolic health at population level. A limitation, except for the lack of measurement on body fat distribution, was that a majority of the young subjects were women, see Table 1.
Reduced intake of food choices rich in sugar might in the long run reduce weight, and thereby contribute to a healthy aging process. Both women, and men with a higher than recommended consumption of sweets had higher HOMA-IR values but at this age no difference in BMI, body fat (%) or waist circumference as compared to subjects eating less sweets. The result was surprising to us but is supported by a number of epidemiological studies showing that sweets do not contribute much to body weight gain in normal-weight individuals [23].
In Sweden media have been supportive for a low-carbohydrate-high–fat (LCHF) diet and intake of carbohydrates have decreased in both genders [4]. A possible explanation for the low intake of bread (whole grain) and fruit observed in the present study may be changes in dietary habits, with less carbohydrate, and that fruit is perceived as an alternative rich in carbohydrates and sugar. In the present study on young adults only 6.9% answered that they were following a LCHF like diet and the majority of young adult’s participating in the LBA study chose unsaturated fat in cooking. The majority (89.2%) of the subjects were also following the recommendations on fast food and sausage.
HOMA-IR
The recommendations on whole grain and fish and seafood were hardest for the subjects to follow. Most of the subjects (88.6%) in the present study did not eat enough of fish and seafood to reach the recommendations. In the present study a recommended intake of fish and seafood was significantly related to healthy insulin resistance (HOMA-IR) values when women, and men were analyzed together. When split by sex no significance was reached. The lack of significance was most likely due to the low amount of subjects eating fish and seafood as recommended (11.4%), see Table 4 and Fig. 1.
In the present study the majority of the subjects had lower than recommended intake of fruit and vegetables. When women and men were analyzed together a recommended intake of fruit and vegetables were related to lower insulin resistance (HOMA-IR) values. But, when split by sex a significant difference was observed only in women. The lower number of men participating in the study, in combination with the low number of participants eating fruit and vegetables as recommended (15.4%), was most likely the reason for the lack of significance in the male subjects, see Table 4 and Fig. 2.
The result is supported by several studies. In a large study, with results from different parts of the world, the importance of fruit and vegetable consumption, in relation to insulin resistance and diabetes have been pointed out [24]. Another example is a prospective Chinese study, 0.5 million Chinese adults were followed during 7 years to study the effect of fruit consumption on diabetes [25]. In China, and in many parts of the world, the relative high sugar content in fresh fruit have led to diminished fruit consumption in diabetic subjects. The findings of the Chinese study suggest that fresh fruit is beneficial for primary and secondary prevention of diabetes [25]. In a large study from Brazil, it was shown that among the dietary factors they studied a low intake of fruit, (< 300 g/day), was the largest contributor to cardiometabolic deaths. Next to fruit a low intake of whole grain and a high intake of sodium contributed most to cardiometabolic deaths [26]. In another Brazilian study on 4202 young adults, average age 23 years, a traditional Brazilian diet was compared to a diet based on processed food. The traditional diet showed generally healthier trends regarding CVD risk factors [27].
In Sweden, the importance of an adequate intake of fruit and vegetables are stressed by the Swedish national food administration [15]. It is also stressed in the Lifestyle recommendations for the prevention and management of metabolic syndrome [28].
The relation between high intake of fruit and vegetables, and HOMA-IR highlights the importance of increasing the intake of fruit and vegetables, with natural sweetening, fibers, vitamins and minerals, to prevent insulin resistance in young adults. It also highlights the importance of reducing the intake of sweet dietary choices, such as buns, candy and soft drinks.
The association of vegetable and fruit consumption with metabolic syndrome has recently been shown in a meta-analysis. A total of twenty-six observational studies were included and the evidence suggest that fruit and vegetable consumption is negatively associated with metabolic syndrome [29]. There are several articles on the topic and in another review 11 studies were included. All reported cross-sectional data. The majority of participants, with type 2 diabetes, were consuming less than the recommended amount of fruit and vegetables [30].
In the United States young adults have a high intake of sugar and saturated fat. The high intake of fat and sugar is aggravated by inadequate intake of fruit, vegetables and fibers [21]. More than half of the young American adults have at least 1 CHD risk factor. This greatly increases lifetime CHD risk [21]. In the present study the intake of sweets was high, only 40.1% of the participants were following the recommendations. Women and men following the recommendations had lower HOMA-IR values compared to women and men not following the recommendations on sweets, see Fig. 3. Unhealthy HOMA-IR values due to high intake of sweets were, as previously mentioned not reflected by increased body composition measures. BMI, body fat (%) and waist circumference were similar in subjects eating sweets as recommended and in subjects eating more sweets than recommended.
In the present study, only 11.4% of the participants had a sufficient intake of whole grain, but intake of whole grain was not associated to body composition measures or HOMA-IR values. Sufficient intake of whole grain gives an increased sense of saturation, and may thereby reduce snacking, and in the long run contribute to weight maintenance. It has been shown that whole grain reduces the risk of deteriorating glucose tolerance, including progression to prediabetes [31].
Lifestyle, and dietary habits have changed in Sweden [4] and worldwide [32]. A study on University students in Spain, similarly to the present study, shows that the majority of students, 96.1%, were recommended to improve the quality of their diets. The main deviations from a recommended diet, in the Spain University students, were a low intake of fruit and vegetables with a high intake of meat and diary products [33]. The observed association between less body fat (%) and lower insulin resistance (HOMA-IR) values in the present study, with dietary choices containing sufficient amounts of fish, seafood, fruit and vegetables gives support to the health beneficial effects of lifestyle interventions also in young adults [13].
Strengths and limitations
It is important to study dietary habits and the risk of diabetes. The strength of the study lies in the study population, young adults. Limitations are that it was hard to recruit men, and therefore the majority of participants were women. In addition, many of the participants studied medicine and had an interested in health, which may have affected the result. Finally, most of the participants studied at Örebro University. We believe that Örebro University, located in the middle of Sweden, reflects the Swedish University’s, but regional differences cannot be ruled out.
