Hmmmmm! This question was asked several years back and I think my response was that everything today makes you fat. Seriously though, this question is very pertinent in the alcohol world. All booze is "fattening." It's that simple. There is no low cal alcohol that you can gravitate to like a diet soda. Sure there are low carb beers etc but these are all still highly caloric compared to good old-fashioned water.
Drinking, as I like to say, is a luxury. It's a way to reward or celebrate or express ourselves after the daily grind. It's also a wonderful form of exploration. But it does come at a cost. It's not great for our "weight." Yes, there are lots of studies that express the benefits of low doses of alcohol in our systems that thin the blood and lead to longer lives. I personally love those interviews with 95 year-old women who get asked, "how did you do it?" and they reply that they consumed a daily glass or wine or drank their martini to keep the engine running.
Ah! But back to the specific question.
Here are some stats prepared by a US based sake brewery:
In a 3.3oz pour:
In the same size pour (3.3oz) of sake there are 5 grams of sugar, the Fat is less than 0.1 grams, and there is 0.5 grams of Protein.
I guess the silver lining is that sake has a little higher alcohol content than beer so you do not have to consume as much. I also feel that sake is cleaner than wine and hard alcohol as the final product is 80% water.
So, in answer to the question of "Will sake make you fat" that answer is comes down to one simple word - moderation.