I was wondering what food should I buy for my spouse so that my toddler gets more volume of natural milk rather than supplementing with milk or formula produced by companies?
I appreciate you asked for advice on foods, but you may have more luck with environmental factors, which have more evidence behind them.
The advice from our midwife and the breastfeeding helpline was to make sure you're doing at least one night feed (2am-6am). Apparently early morning feeds have more influence over milk production than the daily feeds.
The other thing we learnt is that the mother's milk supply will increase to match demand, so if you want to increase supply, expressing milk via a breast pump or hand-expressing may help. At the same time, if you're using a bottle of formula, that's actually reducing the demand, so only do it once milk's properly established. The same principle applies to carefully scheduling the feeds, in that your body will see that as reduced demand.
One thing many people forget is water! You can load her up with loads of fresh vegetables and good quality meat (which is a good idea), but it she's dehydrated production goes way down. A good proportion of people are chronically dehydrated which is very easy to fix. At least 1.5 liters a day is the minimum, some doctors say 4-5 liters a day which sounds excessive to me as too much can hurt production and dilute her electrolytes. I'd say focus on 2 liters at minimum.
One recommendation I have seen repeated a lot is the use of Fenugreek supplements to increase breast milk supply.
There is at least one study that shows evidence of reasonable increase in breast milk production from Fenugreek:
The most popular herbal remedy used around the world for increasing milk synthesis is fenugreek. Fenugreek (Trigonella foenum gracen) is a seed product from the legume family that is commonly sold, since the dried, ripe seed and extracts are used as an artificial flavor for maple syrup. When used orally in amounts commonly found in foods, it has been granted GRAS status in the USA by the FDA (Generally Recognized as Safe). Although it is used by millions of women around the world to increase their milk supply, we have only one small case report which suggested it might actually increase the milk supply.
In this one study, the authors found an approximate 40% increase in milk production, although the study was not blinded, nor did they use a control population. For these reasons, we still do not know with certainty if fenugreek works as a galactagogue.
The general consensus I've heard is "it can't hurt", and it works for some breastfeeding mothers.
I think that in the end, it doesn't matter. As deworde states, the mother's milk supply is regulated by demand. If your baby tries to drink more, then the mother will produce more.
That being said, there are certain herbs that are considered to be helpful when breastfeeding, because they change the milk's flavour in a good way:
You can buy special breast feeding tea that is made from those herbs.
The only herb I know of that should be avoided is sage, because it has a negative impact on milk production.