Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You have to learn the ふと portion of this word to be able to read it. Here's a mnemonic to help you:
You're getting fat so quickly that you can see your body expanding. You look down - at first you can see your foot (ふと) but then a second later you can't. You can't see your foot because you're getting fat, even when you stick your foot way out. What's going on?
I’ve gotten a little fat from overeating lately.
I envy people who don't get fat even though they eat a lot.
The fatter I get, the hungrier I become.