Should a Diet Containing High Protein and High Glycemic Load Be Blamed for the Epidemic of Overweight and Obese Children?

The escalating prevalence of overweight and obesity in children is a challenge for the medical community as well as health authorities. According to the World Health Organization (www.who.int/topics/obesity), approximately 1.6 billion adults (>15 years of age) worldwide are overweight, and 400 million are obese. Recent prevalence figures for children from different European countries show worrisome numbers, especially in western and southern Europe, where 20% to 35% of 7- to 11-year-olds are overweight or obese (1). In the United States 31% of children between 6 and 19 years old are at risk for being overweight (ie, body mass index [BMI] >85th percentile for age) and 16% are overweight or obese (BMI >95th percentile) (2). Hence, we may experience a health disaster during the several next decades, with large numbers of early-onset type 2 diabetes mellitus, hypertension, and cardiovascular diseases among adolescents and young adults (3,4). Already adolescents are described as having these obesity-related disorders (5). What is the cause of this epidemic of obesity? During the last decades the focus has been on reduction of fat intake. Despite this, a dramatic increase in overweight children and adults has occurred (6–8). The abundance of “junk food” and processed food with a high content of fats and carbohydrates surrounds our children, who have difficulty resisting the temptation. Furthermore, information and communication technologies also compete with children's play and physical activity, which has always been a natural part of a healthy childhood. Thus, should we blame a lowfat diet with high content of carbohydrates and proteins for the overweight epidemic? Do parents and other adults in the children's environment really know what a healthy diet is for the children and are the nutritional recommendations from the local health authorities followed? Even if the recommendations of energy intake are followed, the diet may still be wrong. In this issue of the Journal, Verduci and coworkers (9) meritoriously describe a cohort of healthy Italian children that have been prospectively studied from birth through their first 10 years of life for dietary energy and macronutrient intake. This is an admirable achievement that is rarely seen in clinical pediatric research. The dietician, in particular, who interviewed the mothers throughout the investigation, should be highly commended. In the study anthropometrical measurements and dietary habits of 61 children were recorded at birth and at age 1, 5, 8, and 10 years. The dropout rate reached 25% after 10 years (82 children at start), which is acceptable during such a long study period. Apart from anthropometrical measurements and dietary questionnaires, overall glycemic index (OGI) and glycemic load (GL) were calculated. These parameters may be of importance when understanding the overweight and obesity epidemic because they are measures of postprandial blood glucose response to carbohydrate intake. Glycemic index represents the relative rate of entry of glucose into the bloodstream compared to a reference carbohydrate, whereas GL represents both the quality of the carbohydrate containing food and the quantity consumed (6). The dietary OGI is the weighted average of the GL values of all carbohydrate-containing food consumed during a day (6). The authors found a high protein intake at all measurements, a high lipid intake from age 5 onward, and a high energy intake at age 5. At age 10, almost 25% of the children were overweight, which is rather alarming, but is actually lower than earlier reported from Italy, where 36% of 7- to 11-year-olds were reported to be overweight or obese (1). Hence, Italy, the home of pasta and pizza, has among the highest prevalence figures in all of Europe. The overweight in the majority of children (80%) developed between ages 1 and 5. Thus, chubby toddlers and preschool children should not be overlooked. Instead, early overweight may predict obesity late in life, perhaps throughout the lifespan. However, the association between a high BMI during childhood and the development of adult obesity has yet to be proven (10). Consequently, the dissemination of dietary information should be intensified and begin early in life, which is practical when parents are more susceptible and easily informed at infant and pediatric health clinics. There are many known risk factors for childhood obesity. In the study by Verduci et al (9), having an overweight parent seemed to be a risk factor because 35% of the parents of overweight children were overweight themselves as compared with only 12% in the nonoverweight group. Overweight or obese mothers tend to have a shorter duration of breast-feeding of their offspring compared with normal-weight mothers (11) and breast-feeding has been suggested to be inversely associated with childhood obesity (12). Although 82% of the mothers in Verduci and associates' study were reported to breast-feed their children, duration and BMI status of breast-feeding mothers were not mentioned. A total of 12% of the mothers smoked during their pregnancy, which is a high figure, but this may be more of a reflection of the Italian lifestyle. There is some evidence that maternal smoking during pregnancy may be a risk factor for childhood overweight or obesity (13). Smoking may also denote less educated parents, which is another risk factor for childhood obesity (14). Smoking during pregnancy is another area where information should be improved to reduce obesity risks for their offspring. The relevance of high intake of carbohydrates with high GI for the development of overweight and obesity in otherwise healthy children is uncertain. A low GI diet is recommended mainly for patients with diabetes. Carbohydrates with high GI are rapidly digested and cause a shorter term of satiety in obese children (15). At least for obese children, a diet with low GI will decrease the BMI and the weight as compared with the children on a lowfat diet (16). In contrast, in a Danish study consisting of 10- and 16-year-old children, an association between dietary GI and body fatness was found only for the 16-year-old boys as compared with the 10-year-olds and the 16-year-old girls (17). Verduci and coworkers did not find any statistically significant difference of OGI or GL between overweight and nonoverweight children (9). Hence, apart from already overweight or obese children or children with diabetes mellitus, the benefits of a low GI diet need to be studied further. Excess high protein intake will enhance the secretion of insulin and insulin growth factor 1, which may increase adipogenic activity as well as decrease lipolysis and secretion of growth hormone (18). This early adiposity rebound has been associated with an increased risk of childhood obesity (19,20). However, in a group of healthy Danish infant boys who were re-evaluated at age 10, no association was found between protein intake in infancy and body fat measurements at the outcome age (21). This finding has been confirmed by others (22). To further evaluate the early protein hypothesis (ie, that an excess protein intake in early life will increase the risk for obesity in later life), the European Union childhood obesity programme (www.childhood-obesity.org) has initiated a prospective cohort study. From 2002 to 2004, 1150 non–breast-fed infants were included and blindly randomised to a lower or higher protein formula. The children will be followed up until school age (18). This study may provide important answers to many of the questions regarding protein intake in infancy and risk for obesity later in life. To better understand the epidemic of overweight and to find instruments for the prevention of obesity-related diseases, more prospective longitudinal pediatric studies are warranted. These studies are expensive and need to be financed by national health authorities. One such promising study is the US children's study in which 100,000 US-born children will be studied prospectively for 21 years. Different environmental risks and individual susceptibility for obesity and other diseases will be examined (23). Finally, the focus should not only be on the children's diet but also on physical activity. Hence, the 2004 Nordic Nutrition recommendations integrate nutrition with physical activity by recommending 60 minutes each day of physical activity for all children and adolescents (24). The study by Verduci and coworkers (9) is a small but important piece of the puzzle in understanding the role of diet in the epidemic of childhood overweight and obesity.