Infants’ diets are now receiving some long overdue attention. Interest stems from two major public health concerns. coronary artery disease and obesity. Until recently, most interest in these two hazards to health has focused on adults, since older members of our society are the ones who actually suffer most. However. evidence is accumulating that these disorders begin far earlier in life, perhaps in infancy. Recent studies of the blood of newborns from families with a disorder of fat metabo. lism leading to high blood fat levels has shown elevation of blood fat at birth.
Although there is no proof yet that this blood funding is predictive of later disease or that reducing the blood fat by special diets or drugs will help, the likelihood of these relationships is quite great. If important clues such as these are linked to the strong suspicion that the average American diet, particularly regarding its heavy use of animal fats, contributes significantly to the development of atherosclerosis, it is understandable that interest is being directed to the diet of infants.
Already, certain changes in infant feeding are occurring in keeping with this line of thinking. even though there is no conclusive evidence yet to prove their value. For example, there is a growing tendency to use low fat milk for older infants and children. More and more dairies are producing special milks with reduced fat content and added protein. These changes may be premature, however. Recent experimental work in rats has suggested that it may be desirable to expose baby rats to the animal fat of their own mother’s milk. Exposure to this fat during infancy may “accustom” rats to using these fats effectively so that they are not deposited as readily in arteries.
The blood cholesterol levels of human infants who are breastfed arc higher than those of infants fed commercial formulas with polyunsaturated fats. The long-range mean-ing of this observation is not known. Is this helpful or harmful? At present, we cannot answer this question. Accordingly, we cannot
Babies of today are undoubtedly larger and heavier as a group than those of thirty or forty years ago. It is reasonable to suspect a connection between this development and our national problem of obesity. An interesting experiment recently conducted in rats suggests an explanation for how obesity in infancy may set up a lifelong pattern. Infant rats in this experiment were fed average diets and then compared with other rats overfed to the point of obesity. When the rats were sacrificed and their fat analyzed, it was found that the ones overfed in infancy had more fat-containing cells. And the cells were bigger.
Rats made obese as adults, on the other hand. increased only the size, not the number of fat cells. The number of fat cells present at the end of infancy persisted throughout life, regardless of diet. Thus, the rats made obese by over-feeding as infants had more fat cells as adults. It appears that appetite is related to number of fat cells. If the number of fat cells increases, appetite may permanently increase. This increase in fat cells may be the way the food thermostat is raised by overfeeding in infancy. If the same situation applies to humans, it may explain in part at least why infants who become obese because of too many calories in their diet tend to remain so, why dieting to lose weight is often so difficult, and why a premium should be placed upon preventing obesity in infants when this is possible.
Why some babies are fat and others are thin is an intriguing question to which a satisfactory answer is not yet available. Paradoxically, thin babies consume more calories than obese ones under normal circumstances. The apparent explanation is that thin infants are very active and “burn up” energy, while chubby ones tend to be quieter, converting more of their caloric intake to fat. The basic appetite thermostat of a baby appears to he largely determined by his heredity. The number of calories that a baby is offered unquestionably plays a part, but probably more so for some infants than others. Variation in number of calories taken depends on the richness, calorically speaking, of the diet and the emphasis placed on food by parents.