We’ve learned a lot about the effects of early influences on the physical characteristics of both animals and humans. One thing we know is that almost any kind of stimulation—either positive or negative—any stimulation of the young shortly after birth will affect their rate of growth as well as their resistance to stress. Daily handling—such as touching, hugging, and / massaging—can promote healthy growth and boost the immune system. Exposure to cold, on the other hand, can have negative effects and leave the young animal more vulnerable to disease.
Another thing we know is that malnutrition early in life can have lifelong consequences. If the food intake of the young is limited, this will decrease the rate of growth and the body size of the adult. Animal studies show some interesting results. For example, deer born during a period of food scarcity, or in a crowded population, will remain relatively small in size, even if their adult diet is adequate or the density of the population decreases. The effect of poor nutrition on deer can also extend to the following generation, as the offspring of small deer will also be small.
The eating habits acquired early in life tend to last throughout life, affecting eating behaviors. For example, rats that are used to eating a low-protein diet will continue eating it by choice, even if a more protein-rich diet is available to them later.
With humans, low protein intake or almost any other form of nutritional deficiency during early childhood will result in a slowing of growth, smaller body size, physical deformation, or tendency to get sick—characteristics that can last a lifetime.
Moreover, poor nutrition affects the mental development of children. Children who don’t eat well don’t learn well in school. They may have difficulty paying attention and may not be able to remember information. As a result, these children may develop negative attitudes toward school. Several behavioral problems in school children have been linked to poor eating habits.