I’ve been on the 5:2 since January and lost 3kilos which has I’m happy about but am hoping to lose faster on the BSD5:2 method. Regarding bread, how safe is sourdough which contains no sugar?
On another related matter, I realise that commercial bread may have lots of sugar but when I make my own bread there is one teaspoon of sugar in the entire loaf. Is this harmful?

You don’t say how big the loaf is so it is hard to know how bad a teaspoon of sugar is. I presume that it is to ‘feed’ the yeast (I’m not a baker or food scientist so I’m guessing) so maybe it is partially consumed.

The bigger problem will be the flour you are using. All the sourdough breads I have eaten seem to contain refined white flour. Is this correct? If so that would be a problem on this diet. Whole grains only, rye bread seems to be okay if it uses whole grain. Others might know of other breads.

Examine your flour.