The Physiology of Stress
When the body senses stress, the sympathetic nervous system activates what’s commonly known as the “fight or flight” response. Hormones like epinephrine (adrenaline) and cortisol surge, preparing the body to use energy quickly. Glycogen stores release glucose into the blood, and fat cells begin breaking down triglycerides into fatty acids.
This shift in fuel availability is part of the reason stress can be both energizing and exhausting. The brain and muscles suddenly have more energy at their disposal—but when stress becomes chronic, the constant release of glucose and insulin can eventually blunt metabolic flexibility.
Stress and Ketone Production
While stress tends to raise blood sugar, it also triggers processes that favor ketone production, particularly when glucose is limited. Epinephrine encourages fat breakdown, providing the raw materials for ketogenesis—the conversion of fatty acids into ketone bodies in the liver.
In short bursts, this response is protective. During fasting, exercise, or low-carb conditions, mild stress can actually enhance ketone production and energy efficiency. But when cortisol remains elevated, the body’s ability to maintain ketosis can be disrupted, as excess glucose and insulin inhibit ketone synthesis.
The Balance Between Adaptation and Exhaustion
The key, Dr. Bikman explains, is balance. Acute stress can make the body more metabolically agile—it’s a built-in survival mechanism. Chronic stress, however, keeps the body stuck in a constant state of high insulin and poor fat utilization.
This is why many people who struggle with stress also struggle with weight gain, fatigue, and insulin resistance. The body simply loses its ability to toggle smoothly between glucose and fat as fuel.
Supporting Healthy Stress Responses
Understanding this connection highlights why lifestyle habits like quality sleep, daily movement, and time-restricted eating matter so much. They help restore metabolic flexibility—allowing stress hormones to do their job when needed, without causing long-term damage.
As Dr. Bikman summarizes, “Stress is not the enemy. It’s how frequently we face it, and how well our metabolism can respond, that determines whether it helps or harms us.”