Abstract
Growth and body composition in childhood are influenced by many factors. Some of these are modifiable e.g. dietary intake, while others may be less easy to influence. The hormonal regulation of growth and body composition during childhood is complex and the interrelationship between the numerous hormones involved has to be taken into account when studying the impact of individual
hormones. There is increasing evidence for a bidirectional relationship between bone growth and energy metabolism. Hormones coupled to the mineralization or demineralization of bones have been suggested to impact on energy metabolism and body fat deposition. The other way around overweight children seem to have an up-regulation of linear growth prior to puberty and a larger bone mass than their leaner peers, which may be partly due to the influence of adipokines or other hormones related to energy metabolism on bone growth or remodeling. Seasonal variations in growth and changes in body composition, if present, are of interest when trying to understand the regulation of growth. They may also be important to be aware of when assessing growth and body composition during shorter periods of time.
The overall aim of this thesis was to identify factors influencing or associated with growth and body composition of 8-11 year old children. Four specific research questions were specified:
1.) Does a school meal intervention based on the New Nordic Diet (NND) influence height, body mass index (BMI) z-score, waist circumference (WC), android fat mass divided by total fat mass (AFM:TFM), fat mass index (FMI) and fat-free mass index (FFMI) of 8-11-year-olds?
2.) Can fasting levels of leptin, ghrelin, adiponectin, insulin, insulin-like growth factor 1 (IGF-1), osteocalcin and intact parathyroid hormone (iPTH) predict changes in FMI and FFMI over a three to six months period in 8-11-year-olds?
3.) Can fasting levels of leptin, ghrelin, adiponectin, insulin, IGF-1, osteocalcin and iPTH predict changes in height, height-adjusted bone area (BAheight) and size-adjusted bone mineral content (BMCsize) over a three to six months period in 8-11-year-olds?
4.) Are there seasonal variations in changes in height, body weight (BW), BMI, FMI and FFMI of 8-11-year-olds?
In the school year 2011-2012 we carried out a large randomized, controlled cross-over study among third and fourth graders in 9 Danish schools. Children were provided school meals based on a NND for three months and for another three months they ate packed lunch brought from home (control).
At baseline, between the two dietary periods, and after the last dietary period children went through a number of investigations.
In paper I we showed that ad libitum school meals based on the NND increased WC, AFM:TFM in intention-to-treat analyses and in completers-analysis also FMI compared with control in 8-11-yearold children, while no effects were seen on height, BMI z-score and FFMI. Effects were not dependent of initial BMI, and adjustment for physical activity, pubertal status and parental education did not change the results. Despite the effect on abdominal fatness, the NND meals
decreased blood pressure, plasma triacylglycerol and insulin resistance. The main conclusion to be drawn from paper II was that baseline leptin was independently inversely associated with subsequent changes in both FMI and FFMI in girls, a finding which may reflect preserved leptin sensitivity in this predominantly normal weight childhood population. Results from paper III are
suggestive for the hypothesis that fat mass, osteocalcin, and in girls also IGF-1 act stimulatory on growth in bone size, while having no effect on bone mineralization. Apparent inhibitory effects on bone size of leptin and ghrelin in girls are contrary to theoretical growth stimulatory effects of leptin. From paper IV we concluded that there were substantial seasonality in growth and body
composition of contemporary Danish children. We did find the “classical” height velocity peak during spring, but unlike many earlier studies this was coincident with peaks in BW, BMI and FFMI velocities. Seasonal variation in physical activity may explain seasonal variations in BW and body composition velocities.
Taken together, the data presented in this thesis suggest that provision of ad libitum school meals based on an apparently healthy diet may have potentially negative effects on children´s body composition despite overall positive effects on risk markers of the metabolic syndrome. However, diet is not the only factor that may influence body composition and also bone growth in this age group. Leptin may be important in relation to prevention of BW gain (FMI as well as FFMI), but may at the same time be detrimental to bone health through an inhibition of gain in bone size. IGF-1 and osteocalcin could be important in stimulating gain in height and bone size, while ghrelin may decrease gain in bone size. Also the results on seasonal variations in growth and body composition add to the general understanding of regulation of growth and body composition, and may have practical implications in relation to analysis of growth data over shorter periods of time, and in planning of strategies to combat obesity.
hormones. There is increasing evidence for a bidirectional relationship between bone growth and energy metabolism. Hormones coupled to the mineralization or demineralization of bones have been suggested to impact on energy metabolism and body fat deposition. The other way around overweight children seem to have an up-regulation of linear growth prior to puberty and a larger bone mass than their leaner peers, which may be partly due to the influence of adipokines or other hormones related to energy metabolism on bone growth or remodeling. Seasonal variations in growth and changes in body composition, if present, are of interest when trying to understand the regulation of growth. They may also be important to be aware of when assessing growth and body composition during shorter periods of time.
The overall aim of this thesis was to identify factors influencing or associated with growth and body composition of 8-11 year old children. Four specific research questions were specified:
1.) Does a school meal intervention based on the New Nordic Diet (NND) influence height, body mass index (BMI) z-score, waist circumference (WC), android fat mass divided by total fat mass (AFM:TFM), fat mass index (FMI) and fat-free mass index (FFMI) of 8-11-year-olds?
2.) Can fasting levels of leptin, ghrelin, adiponectin, insulin, insulin-like growth factor 1 (IGF-1), osteocalcin and intact parathyroid hormone (iPTH) predict changes in FMI and FFMI over a three to six months period in 8-11-year-olds?
3.) Can fasting levels of leptin, ghrelin, adiponectin, insulin, IGF-1, osteocalcin and iPTH predict changes in height, height-adjusted bone area (BAheight) and size-adjusted bone mineral content (BMCsize) over a three to six months period in 8-11-year-olds?
4.) Are there seasonal variations in changes in height, body weight (BW), BMI, FMI and FFMI of 8-11-year-olds?
In the school year 2011-2012 we carried out a large randomized, controlled cross-over study among third and fourth graders in 9 Danish schools. Children were provided school meals based on a NND for three months and for another three months they ate packed lunch brought from home (control).
At baseline, between the two dietary periods, and after the last dietary period children went through a number of investigations.
In paper I we showed that ad libitum school meals based on the NND increased WC, AFM:TFM in intention-to-treat analyses and in completers-analysis also FMI compared with control in 8-11-yearold children, while no effects were seen on height, BMI z-score and FFMI. Effects were not dependent of initial BMI, and adjustment for physical activity, pubertal status and parental education did not change the results. Despite the effect on abdominal fatness, the NND meals
decreased blood pressure, plasma triacylglycerol and insulin resistance. The main conclusion to be drawn from paper II was that baseline leptin was independently inversely associated with subsequent changes in both FMI and FFMI in girls, a finding which may reflect preserved leptin sensitivity in this predominantly normal weight childhood population. Results from paper III are
suggestive for the hypothesis that fat mass, osteocalcin, and in girls also IGF-1 act stimulatory on growth in bone size, while having no effect on bone mineralization. Apparent inhibitory effects on bone size of leptin and ghrelin in girls are contrary to theoretical growth stimulatory effects of leptin. From paper IV we concluded that there were substantial seasonality in growth and body
composition of contemporary Danish children. We did find the “classical” height velocity peak during spring, but unlike many earlier studies this was coincident with peaks in BW, BMI and FFMI velocities. Seasonal variation in physical activity may explain seasonal variations in BW and body composition velocities.
Taken together, the data presented in this thesis suggest that provision of ad libitum school meals based on an apparently healthy diet may have potentially negative effects on children´s body composition despite overall positive effects on risk markers of the metabolic syndrome. However, diet is not the only factor that may influence body composition and also bone growth in this age group. Leptin may be important in relation to prevention of BW gain (FMI as well as FFMI), but may at the same time be detrimental to bone health through an inhibition of gain in bone size. IGF-1 and osteocalcin could be important in stimulating gain in height and bone size, while ghrelin may decrease gain in bone size. Also the results on seasonal variations in growth and body composition add to the general understanding of regulation of growth and body composition, and may have practical implications in relation to analysis of growth data over shorter periods of time, and in planning of strategies to combat obesity.
| Originalsprog | Engelsk |
|---|
| Udgivelsessted | Copenhagen |
|---|---|
| Forlag | Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen |
| Antal sider | 183 |
| ISBN (Trykt) | 978-87-7611-860-0 |
| Status | Udgivet - 2014 |
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