Breast Fed Babies are in Ketosis
Breast fed babies have diet that's 50% fat and high in lactate. The fat is converted into ketones in the liver, and used for energy. The lactose and protein in the diet is used for growth.
The baby is in mild ketosis, ketones supply 80% of the energy needs, of the baby's brain. The baby's heart and muscles run on both fatty acids and ketones.
Glucose is made in the liver from protein, and conserved because ketones are available.
These few months are a major stage in the development of the human brain. The fact that nature ensures that babies are in ketosis, demonstrates that this form of metabolism, using lipids (fats) as fuel is quite normal and perhaps even preferred.