I just need to say something, because reading so much nonsense in various places is driving me mad.
The carbohydrate in breastmilk is Lactose. Lactose, lactose, lactose. There are minimal amounts of oligosaccharides, galactose, fructose and glucose. But on the whole infants get their energy from Lactose, and so the vast majority of babies can digest lactose.
Lactose intolerance develops in early childhood, not infancy. Primary lactase insufficiency is incredibly rare, and babies born with it become very sick within days of birth, and die within a week unless given special formula.
Many babies are, however, intolerant to other things. The most common ingested allergen is cow's milk. The protein in cow's milk, not the lactose.
And this is why unregulated sale of specialised formulas is dangerous. No baby should be being put on lactose-free formula or Soy formula without medical advice because the vast majority of babies do not need it. The fact that lactose free formula even exists is questionable.
But reading that people have their breastfed babies being topped up with lactose free formula is mind bogglingly silly. Waste of money, spreading misinformation and rotting their teeth for no reason.