It might seem surprising that there's such a strong connection, but when you learn about the physiology of the stress response, it makes a lot of sense. When you're stressed your body activates its "fight or flight" physiological response. Part of this response involves your body releasing blood sugar into your bloodstream so that you can use it immediately in an emergency situation. For example, if you were running away from a dangerous situation, you would need that quick energy provided by glucose in your blood. A problem occurs, however, when you're always stressed. When this happens, you get a constant blood sugar release, which causes more insulin to be released as well.

This high insulin state, called hyperinsulinemia, basically causes your body to try to force glucose back into cells. Insulin is also one of the hormones that signals to your body to store fat, which explains why people often gain weight during a stressful time in their lives—even if they don't change their eating habits.

If you were to look inside the body while all this is occurring, you would see the brain perceive stress or anxiety and release cortisol from the adrenals as a result. Then you would observe a message from the brain travel to the body to release blood sugar and increase liver gluconeogenesis—a process that regenerates glucose. Once the stressful event is over, the signal stops.

This is fine if it occurs infrequently, but for most of us, this is happening a few times a week, daily, or even hourly! It can leave your body really confused and with a lot of unnecessary glucose floating around in the bloodstream that the muscles and body do not actually need.