Walnuts are good for the fetus in the third trimester for the following reasons: first, the fetus has a temporary peak in development during the third trimester, which is a critical period for the development of the fetus’ nervous system, requiring a large amount of protein and nucleic acid as well as vitamins necessary for brain development, and the supplementation of walnuts at this time is more conducive to the development of the fetus’ brain; second, the third trimester is also the peak period for the development of the fetus’ immune system. The development of immune cells cannot be achieved without vitamins and proteins, and walnuts are more nutritious. Third, the fetus’ bone development is also at a temporary peak, so if the mother’s nutrition is insufficient, taking walnuts at this time can supplement the nutrients that the mother cannot supply.