Eat whole foods early.
"Collective evidence from human studies supports a beneficial effect of exposing infants to a varied diet in the developmental stage," says Dr. Anna Nowak-Wegrzyn, a pediatrician at Mount Sinai. One 2013 study found that babies who ate homemade whole foods developed fewer allergies than those whose diets relied on processed and commercial baby food. And a recent study published in Science suggests why: Eating a diet of whole macronutrients instead of the basic elemental stuff (a.k.a. commercial baby goop) can stimulate the cells that give the immune system its tolerance. So if your kid can already swallow lumpy food (usually at four to six months), try to introduce a wide variety of solid meals taken from your own plate, like fish, fruits, poultry, and veggies. These have a more "protective" effect than commercial baby fare because they expose infants to a wide range of proteins, carbs, fats, and fiber — and a diet stripped of such diverse nutrients could contribute to an underdeveloped immune system.