When there's a lot of insulin in your blood, it shuts down the body’s ability to break down fat even when epinephrine (the 'fight or flight' hormone) tries to tell it to.

This study found that insulin normally stops fat cells from breaking down fat, but in obese men, insulin doesn’t work as well at doing this — which means the claim that insulin suppresses fat breakdown is supported.

Even when insulin is high, epinephrine can still break down fat — but during fasting, insulin doesn’t work as well to stop it. So yes, insulin usually suppresses epinephrine’s fat-burning effect, but fasting makes it harder for insulin to do so.

The study found that when blood sugar is very high, insulin can’t do its job well at stopping the fat-burning effect of epinephrine — which means insulin normally does suppress epinephrine, but only when things are normal.