I don't think it would knock you out....in cd they used to say no due to the salt....making you retain water..leading to people getting disheartened when weighing in. If that's all you have tille you can get some marigold low salt....then if it were me i would have it and just drink a bit more water to flush the salt out
Well oxo cubes are meat-based aren't they? So its just like having meat and water. Also Bovril is made from meat juices. Marmite is vegetable in origin.
How much does a cube weigh? Basically it seems to me that what you'd have to do is make sure the carbohydrates contained in the portion you have fit in the total allowed under ketosis rules.