It's quite normal for some of the lentils, carrots and peas to come out the other end looking just the same as how they went in! This is often because our furry friends don't chew their food in quite the same way as we humans do, so that initial stage of mechanical digestion is skipped and most of the food is often swallowed whole.
As dogs have a shorter digestive tract than humans, this means there's less of a journey for the vegetables and so there's less time for it to be broken down in the gut. But don't worry - once in the gut, all the useful vitamins and minerals will still be absorbed. Think of it like a sponge - even after all the water (nutrients) has been squeezed out, the sponge is still the same shape.
The bit left over is classed as the insoluble fibre. This is what helps to provide bulk to your dog's poo and keeps everything moving through their gut. It also provides the colon with lots of friendly bacteria.
So rest assured, these bits aren't just passing through without offering any nutritional value, it's all providing lots of the good stuff. Most pet parents do notice an improvement the longer their dog eats Butternut, as the gut flora begins to adapt.