All grains and cereals are starches, as products made from them - e.g. bread - also potatoes and parsnips.
All starches tend to spike blood sugar, if you have blood sugar issues.
So, you'd still lose weight on the 800 cals even with starches, but maybe less of that weight is the fat around liver & pancreas that you need to shift, to improve your insulin metabolism and reduce T2 risk.
It is a compromise between sustainability and the ideal BSD.
If you just want to lose weight quickly and are not at risk of T2, then starches are much less of an issue.
Many low carbers are ok with oatmeal or oat bran, about 40g portion. However, I'd play safe and just have it with cinammon, not fruit.
Carrots are starchy veg, but so healthy that I'd keep them.
Squashes are quite starchy veg, about double the carbs of say broccoli in the same volume. However, also quite healthy, so I'd keep them too.
If you have the above, then that's already quite a lot of carbs, so I recommend leaving out grains & cereals, at least in the 8-week phase.
Swap to beans, lentils, peas instead, to fill you up but with higher nutritional value.
To me, a BSD garnish is 1 level tbsp, btw.
The original paper and human trials by Prof Taylor excluded starches completely. Mosely seems less hardcore in his 8 weeks.
The longterm maintenance or the 5:2 BSD is more relaxed:
For this, DrM says restrict starches to a side dish, e.g. in Webchat he said about 1 slice of wholegrainbread some days, which I understood to be a daily total for starches.
A typical slice wg is about 28g and 12g carbs, which would be the carbs in a half-cup (120ml) of butternut squash or â…› cup of cooked wg pasta. Not much !