You'd be fat, not strong. Breast milk is high in fat content and sugar content both.
The saturated fat content of a single cup of breast milk contains 24% of the recommended daily value, so twenty ounces is 60% of the day's total. You'd better be eating extremely low fat for the rest of your day.
It's also adding about 425 calories to your day's intake, and a pound of fat takes 3500 calories to gain. So every eight and a quarter days, give or take, you'd gain a pound.
Ever have cereal that you added a lot of sugar to, with regular milk (not reduced fat)? The milk left in the bottom of the bowl, sitting on a layer of grainy sugar, is what breast milk tastes like.