The role of diet composition in childhood overweight, obesity and health

Background for OPUS

There is a pressing need to develop strategies to facilitate dietary changes that will tend to reduce caloric intake, and to increase levels of physical activity.

 

Although the cause of childhood weight gain and obesity is a complex interaction between genetic, intra-uterine, social, familial, behavioural and environmental factors, it is well recognised that nutrition, physical activity and inactivity (Astrup 2008), and perhaps impaired sleep, play a significant role in the development of overweight and obesity (Chaput et al. 2008).

We know that nutrition plays an important role in optimal health and disease prevention and treatment, but the evidence is often based on systematic reviews of the literature, combining evidence from observational, mechanistic, and smaller interventional studies.

 

Large-scale, long-term trials with dietary interventions are mostly lacking due to difficulties in obtaining the requisite funding.

 

Exceptions are the GISSI trial with 11,000 participants (Gissi-Investigators 1999), and the GISSI-HF (Gissi-Hf Invetigators 2008) trial with 7000 participants, showing that n-3 fish oil supplementation reduces morbidity and mortality in patients with ischemic heart disease and heart failure, respectively. Other examples are the Finnish and American diabetes prevention trials showing that diet and modest physical activity can produce a modest weight loss, and reduce the incidence of type 2 diabetes by 58% in overweight individuals with impaired glucose tolerance (Tuomilehto et al. 2001, Knowler et al. 2002).

 

Intervention studies are normally required to obtain an evidence-based fundament for modification of prevention and treatment guidelines, and the lack of solid evidence is a barrier to the implementation of changes to dietary recommendations.

 

The lack of convincing evidence also leaves the way open for unsubstantiated alternative diets, for example claiming that dairy and gluten-rich foods are the major dietary components responsible for obesity, allergy and behavioural disorders in children.

 

Larger intervention trials that document the effect of diet on body fatness, risk factors for type 2 diabetes and cardiovascular disease, and “softer” end-points such as behaviour, learning, performance, mood and quality of life, are needed to build positive cases to convince health professionals, teachers, parents and others of the importance of the establishment of healthy, early dietary habits.

There is evidence from intervention studies that the modification of diet and physical activity may attenuate increased fatness among children (Lobstein 2006, Brown et al 2007, Brown & Summerbell 2008). Focus has been on a more healthy diet that modifies the intake of fat-rich fast-food, sugar-rich soft drinks, fruit and vegetables.

 

A large body of evidence has demonstrated that a reduction in dietary fat content under ad libitum conditions can produce a modest but clinically important weight loss in 6-12 months in adults (Astrup et al. 2000), and make a small contribution to prevent weight gain in adult women (Howard et al. 2006).

 

However there is a growing interest in the impact of the amount and composition of other macronutrients in weight management.

 

A fat-reduced diet with a high contribution of simple carbohydrates has been shown to be just as effective in producing a minor weight loss as a comparable diet with a high contribution of complex carbohydrates (Sarie et al. 2000).

 

However, there is accumulating evidence to suggest that sugar in drinks exerts a weaker effect on satiety and may play an important role as an obesity promoting factor (Raben et al. 2002). Other factors are the dietary fibre and whole grain content of the diet, i.e. fruit and vegetables, and whole grain foods.

 

Moreover, increasing the dietary protein content from 10-15 to 20-25% of total energy may offer an additional strategy to low fat, high carbohydrate diets, and have the potential to enhance satiety (Paddon-Jones et al. 2008, Astrup 2005).

 

The effectiveness of low-carbohydrate, high-protein diets on weight loss (relative to low-fat diets) had, until recently, only been studied in the short term, but newer studies in adults show that a low carbohydrate/high protein diet led to greater weight loss than a low-fat diet over a two-year period with a more favourable impact on some metabolic outcomes (Nordmann et al. 2006).

 

However, it is questionable as to what extent findings from weight loss trials can be translated into prevention of weight gain, and to what extent findings in adults will be effective in children. We have recently participated in the large-scale EU-funded dietary intervention study "Diogenes".

 

Diogenes is a pan-European, randomised, controlled dietary intervention study investigating the effects of dietary protein and glycemic index (GI) on weight (re)gain and cardiovascular risk factors in obese and overweight families in 8 European centres (Larsen et al., Moore et al. to be submitted).

 

Eight hundred and twenty two eligible families with at least one overweight/obese parent were enrolled, and the obese/overweight adults followed an initial 8-week Low Calorie Diet (LCD). If minimum one parent attained a weight loss of ≥ 8%, the family was randomized to one of five ad libitum (no restriction on total energy intake), low fat (25-30 E%) diets for 6 or 12 month: Low Protein [LP]/Low GI [LGI]; LP/High GI [HGI]; High Protein (HP)/LGI; HP/HGI and Control (CTR), which implied eating according to official current local dietary guidelines.

 

At two of the 8 centers the participating families were provided with free foods from specially designed supermarkets for a period of 6 months, followed by another 6 month period with dietary instruction only. At the remaining 6 centre the families received dietary instruction only for a single period of 6 months.

 

Special attention was paid to minimising the burden for the children and to the potential risks associated with a high protein diet in children in particular, with respect to growth and metabolism.

 

The complete analysis of results is pending, but in the two supermarket centres the weight loss during the 8 week LED was 11±3%.

 

Subsequently, 263 adults (106 men, 157 women; initial body weight 99.8±15.6 kg, BMI 33.5±4.3 kg/m2) were randomized to the 5 ad libitum diets for 6 months, and 205 subjects (78%) completed the 6-month intervention.

 

Weight regain across diets was 2.1±3.9 (LP/LGI), 2.8±3.5 (LP/HGI), 0.8±4.3 (HP/LGI), 0.3±6.4 (HP/HGI), and 1.9±4.3 kg (control). Factorial ANOVA with BMI, gender and initial weight loss as covariates showed a significant main effect of protein content, but no main effect of GI or interaction between protein and GI.

 

The results regarding the children are still being analysed, and the outcome of the study will contribute with valuable information about the potential of GI and protein to prevent weight gain among children, and to induce a safe fat loss in overweight children. All these results will be available before the end of 2009, and will be used, together with information from the available literature, to design the optimal diet composition for the intervention studies in OPUS. 

 

The role of meals for obesity, health and performance

 

(Published on foodoflife.dk)