The explanation is simple
Breast milk is the most healthy food you can find out there. It has all the nutrients you could ever need, even vitamin C, so you could literally live with only drinking breast milk. However, it doesn't contain iron, that's the only thing it lacks. But, you could easily find iron in dirt, and guess what, Fauna is mother nature. So, you could have the healthiest lifestyle possible by eating a handful of dirt from Fauna then chugging it down with some of her breastmilk and be fed for the day, and eventually have a high chance of living a long life due to your healthy lifestyle and meals.