Breast milk is a storehouse of all vital nutrients. You should focus on consuming a nutrient and calorie-dense diet. If you consume a deficit diet, your own body reserves will start depleting. The body consumes 1100-1200kcal/d energy in milk production. Make sure your food is energy-dense too.
There are certain foods that enhance milk production called LACTOGENIC FOODS.
Some most common foods are:
Fenugreek and fennel seeds
Whole grains like oats, barley
Yellow and red, orange root vegetables like pumpkin
Nuts.
Green leafy vegetables.
Oils and Ghee.