Many researchers say that obesity and other adult diseases are getting common as we eat more western food.

obesity 是名词，由形容词 obese（肥胖的）加上名词后缀 -ity 构成，表示"肥胖的状态或状况"。这个词根来自拉丁语，-ity 是常见的将形容词转化为名词的后缀。