In a big bowl mix together the buttermilk, baking soda, salt, sugar and olive oil. Mix until mixture will rise (about 2-3 minutes).
Add the rye flour and 250g of whole wheat flour.
Mix everything together, then add about half of the 100g of whole wheat flour and keep mix it. I used a tablespoon. The dough will be sticky, don’t worry.
Spread the rest of the flour on the work surface and dump the dough. Use your hands to form a dough into cylindrical shape, then flatten the dough into about 1 inch thick.
Transfer the bread to a baking sheet, covered with parchment paper or Teflon sheet and make diagonal cuts on the top of the bread. Bake at 400 degrees for 35-40 minutes. Check for readiness with a wooden stick. Transfer the bread to the surface, cover with a kitchen towel and let it cool completely.