Interaction between physical activity and nutrition early in life and their impact on later development.

It has been rare to find studies of the influence of nutrition on growth that have incorporated careful measurements of physical activity. This paper reviews interactions between physical activity and nutrition in early life and finds that such interactions have a significant influence on growth and later metabolism.Young animals are generally characterized by a high level of spontaneous motor activity that contributes to a high rate of energy turnover in early life. Such activity varies greatly between species and individuals and can be increased by reduced (but not extreme) dietary intake especially of protein, with consequent effects on growth rate (slower), body composition (leaner), eventual body size (smaller), lifespan (longer), cardiac resistance to toxic substances (increased) and changes in body lipids. Most studies have been conducted with laboratory rats but the much smaller literature concerning human beings is also reviewed here.In rats, exercise during pregnancy results in offspring that are smaller and leaner and there are later improvements in cardiac microstructure, cardiac resistance to toxic substances and lower plasma cholesterol and triacylglycerol concentrations.In industrialized countries in recent years, children's fitness, especially of the cardiorespiratory system has not developed at the same pace as body size, or has deteriorated, whereas average body mass index (BMI) and the overall prevalence of obesity have increased. This is partly accounted for by reduced levels of physical activity but there is some evidence that higher intakes of dietary proteins in early life are also implicated. Much recent research has focused on the influence of nutrition in the prenatal and early postnatal period on later health. This review has also underlined the importance of exercise and its interaction with diet beginning with the pregnant mother and continuing through childhood. Development and wider use of simple but reliable methods for the evaluation of physical activity and fitness in young children is now an important priority.