Both are important. With low insulin levels the body cannot store fat. Not according to me, according to insulin researcher Ben Bikman. A little over 3 minutes long.

https://www.youtube.com/watch?v=gNqAdGvSvSQ
#mce_temp_url#

It is why type I diabetics (that make no insulin) who do not take insulin shots can eat 5,000 calories a day and never gain an ounce of fat. They wither up and waste away (and that is what happened to all type I diabetics before the invention of insulin shots to supply insulin to them).

So what is the ideal level of insulin? Bikman talks about 6.
https://www.youtube.com/watch?v=5mzc5zU47-Y&pp=ygUPSW5zdWxpbiBsZXZlbCA2
#mce_temp_url#
Under 4 minutes long.

Most doctors do not request a fasting insulin test during annual blood tests. They should. Fast 12 hours before.