Chapter 4 endnote 30, from Lisa Feldman Barrett.
Some context is:
Cortisol is released whenever you need a surge of energy, which happens to include the times when you are stressed.
Cortisol is a steroid hormone (a glucocorticoid). It is mistakenly called a “stress” hormone because it is almost always released during stressful events (i.e., events where your body is making a large withdrawal from its energy budget). Cortisol functions primarily to provide a quick increase in blood sugar and aid the metabolism of carbohydrates, fats, and proteins. During times of stress, your body needs a quick boost of glucose.