The 5 PM Energy Crash Explained
Many people feel an unmistakable dip in energy late in the day. You feel foggy, motivation drops, and the urge to grab something sweet kicks in. We call it the 5pm crash.
So what is going on?
While stress, poor sleep, or large meals can contribute, another reason may be how your body handles energy.
A concept known as metabolic flexibility.
Your body runs primarily on two fuels. Glucose comes from carbohydrates, and fatty acids come from stored fat. A metabolically flexible system shifts between them easily.
When you eat, insulin rises, encouraging your cells to use glucose. Between meals or during light activity, insulin falls, and your body gradually burns more fat for energy.
When this switch happens efficiently, you achieve a state called metabolic flexibility. You can switch between fuels.
So when your blood sugar drops a few hours after eating, your brain and muscles sense the shortage.
If you are feeling tired, it isn’t because energy is absent, it is because your body could not make the switch to fat.
Research shows that physical inactivity, excess refined carbohydrates, chronic stress, and inadequate sleep can all impair metabolic flexibility.
Obviously, exercise, especially steady-state aerobic activity like walking or cycling and resistance training, improves your ability to use fat for fuel.
You can also help by focusing on whole, unprocessed foods that combine protein, fiber, and healthy fats. Over time, these habits train your mitochondria to use both fuels more efficiently.
Sleep and hydration matter. Dehydration and elevated stress hormones like cortisol make your body cling to glucose metabolism, worsening fatigue.
Personally, I try to finish my last meal by 6 pm and allow 12 to 14 hours before the next. This isn’t deprivation. It is giving your body the space to recalibrate.
Metabolic flexibility isn’t about perfection. It’s about teaching your body to adapt. To shift between fuel sources, stay calm, and sustain energy naturally through the day.
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