For commoners in Feudal Japan, it would’ve been unpolished/brown rice, refining rice was labor intensive/expensive. When accessibility of white rice spread due to automation making it much cheaper, in the 1800s, it caused a huge epidemic of beriberi, which had once been a rich man’s disease, and killed a huge number of people.

the biggest problem with white rice is the lack of fiber, the somewhat high glycemic index, and it has the same problem all processed grains have: lacking potassium, iron and magnesium. these days though white rice and other processed grains all come with added b-vitamins (before that started at the turn of the century, there were massive b-vitamin deficiencies popping up everywhere). white rice has less protein than most grains but at 9% of calories, that's still not bad though some variety wouldn't hurt.

don't get me wrong, white rice isn't the worst thing in your diet but i think it's great to diversify with some whole grains and lots of beans (a real superfood), many of which can be had for 2$ to 3$ per 2k calories.

Err (150kg)(3500kcal/kg) = (5.25E5 kcal/E_koku)/(365 days) = ~1500 kcal/day. So not great working in the field or fighting for the average guy. But I feel like this is one of those things where the average lord didn't count how many fish you caught or what have you. So I bet if you had miso, fish, and like some vegetables from the outside your house, you would probably survive alright.

EDIT: the actual point is that it's probably not literal. Ease of quantifying and transporting dried rice over long distances without refrigeration probably had a lot of how they ended up with a Koku as useful measurement.

Supplement with the 50lb bag of beans that sits 20 feet away from the rice at my Costco and you are pretty much there.

weevils