Nutritional protein intake is associated with body mass index in young adolescents

Preventing and treating obesity has become a major public health concern. Obesity results from the imbalance of energy intake and energy expenditure. Energy intake has increased, energy expenditure has decreased in recent years. In addition, the proportion of macronutrient intake has changed with a substantial decline in the percentage of energy from nutritional fat, and an increase in energy from sweetened beverages. We focus on the interaction between body mass index and the recent population wide increase in protein consumption. 7182 three-day weighing and nutritional protocols and anthropometric data of the DONALD (Dortmund Nutritional and Anthropometrical Longitudinally Designed) Study from 1028 healthy children and adolescents, aged 2 to 18 years (51.3% girls, 48.7% boys), measured between 1985 and March 2006, were obtained and re-analyzed. Mean daily energy intake (r=0.060, p>0.1), and the absolute daily intake of fat (r=0.031, p>0.1), and carbohydrate (r=0.050, p>0.1) were independent from BMI standard deviation scores (BMI-SDS). However, a significant interaction between BMI-SDS and the mean absolute daily intake of all protein (r=0.143, p<0.0001), and animal protein (r=0.151, p<0.0001) was found. When expressing macronutrient intake as percentage of daily energy intake, the fat and carbohydrate correlations remained insignificant with r= -0.040, and r= -0.037, respectively, whereas the correlation between BMI-SDS and all protein (r=0.203, p<0.0001), and animal protein (r=0.163, p<0.0001) further increased. The correlation depended on age and reached maxima in the group of 10-12 year old boys (r=0.31, p<0.0001), and girls (r=0.36, p<0.0001). Protein intake explained up to 13% of the BMI variance in young adolescents. We strongly suggest reconsidering the recommended daily allowances of nutritional protein, to abstain from the popular very high protein diets, and particularly from adding the flavouring agent monosodium glutamate.