Interesting calculator Bakari, hadn't seen that one before. Apparently I spend only 25% of the thrifty single female plan. Ha! Other girls like to eat out a lot more than I do I guess.
I'm not single and I don't know what food prices are like in Germany but here in South Jersey, I could eat very well on $100 a month(non-organic but fresh and in season and sales). In the summer that would drop to $50 a month since I would be harvesting from my backyard garden.
I average $300 a month for our family of 5. Hubby is the biggest expense since he eats the most meat and baked goods. The rest of us are flexitarian and prefer beans, grains, nuts, dairy, fruits and veggies the majority of the time. Chicken breast is our preferred meat when we do have meat and that regularly goes on sale here for $2lb. Our state grows a lot of food and our neighboring states provide a lot of dairy and meat so the food basics here are really reasonable. We only eat out if we're on vacation or if we have a gift card. We're all slim and eat to live, not live to eat.
So much depends on where you are and how you prefer to eat and how much you eat and how much of what you eat you will grow or prepare from scratch. Here in the US, a single adult could eat well and very healthy on $200 of groceries a month(organic, imported and finer items like high end seafood and the best cuts of meat).
Maybe the best plan for you is to monitor how much you are spending now and attempt to reduce it by 10% the next month. If that goes well try to bump it down another 10%. Shop in new places. Make more from scratch. Keep going until you reach your lowest comfort level.