"Cortisol is the stress hormone, which basically leads to people eating more, sleeping less, and it may affect insulin resistance," Dr. Arad explained. "It's probably the most important hormone in that regard because insulin tells the body to store and build rather than to burn," he said. If you become very insulin resistant (the cells in your muscles, fat, and liver don't respond well to glucose in your blood), you can have a lot of metabolic repercussions, he explained.
"It can affect your ability to oxidise fat and to oxidise sugar. When you develop insulin resistance, it's a state of metabolic disaster because it means that your body is not communicating well," Dr. Arad said. "For each person, it manifests differently, but it means that you may not be burning fuel when you need to, you may not be storing fuel as you need to . . . you're certainly going to be storing much more than you need."
According to Dr. Arad, insulin resistance means that your body isn't able to adapt to the various energy fuel sources. "In a healthy body, people can make an excellent adaption in fuel use to whatever is available. A healthy body can adjust the use for energy based on what's available," he explained. For example, a healthy person can eat a diet high in fat and as a result, their body will burn more fat. If the same person ate a diet high in sugar, their body would still be able to use the sugar efficiently, Dr. Arad explained. Conversely, people who become insulin resistant and are overweight lose the ability to be flexible when it comes to burning fuel sources and as a result, their body will end up storing more.