What Is Metabolic Flexibility? Why You Need and Want It

We all know that girl or guy who can eat velvety twirls of pasta carbonara, gooey cinnamon rolls dripping with vanilla icing, and gargantuan burritos stuffed with guacamole, fries, and steak but never seems to gain weight. Rather than throw green monster side-eye shade at him or her, consider why this can happen. It's because that person has metabolic flexibility.

He may be young and sporty with a “fast” metabolism. She may be a long-distance runner who eats calorically dense foods to fuel her demanding training schedule. But what explains this concept from a physiological perspective? 

Metabolic flexibility describes the ability to adapt the demand for fuel with what’s available. A metabolically flexible person can switch between burning carbs or using fat as an energy source to fuel everyday tasks, exercise, or merely to think and breathe. 

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What Is Impaired Metabolic Flexibility?

Impaired metabolic flexibility implies the inability to use fats stored in muscle cells for fuel. If your body can’t burn the excess glucose (stored as fat) in your muscle cells but you have a large fat supply in your body, you’ll continue to store fat you can’t burn, leading to insulin resistance ¹. Over time, insulin resistance can lead to obesity and prediabetes².

Why You Need Metabolic Flexibility

Who doesn’t want to be able to stress less about how many carbs they eat? Metabolic flexibility provides exactly what it promises—flexibility and freedom from diet micromanagement.

• Metabolically flexible people can tap into different fuel sources to power activity without difficulty. Going for a morning run? That mushroom farro you ate for dinner last night will provide the glucose you need. Don’t have time to eat breakfast and don’t feel hungry anyway? No problem, the glucose stored in your muscles will fuel your activities until you get hungry and decide to eat.
• Metabolic flexibility implies optimal mitochondrial function. The powerhouses of cells, mitochondria make energy for the cells from the food we eat. Mitochondrial dysfunction is shown to be a precursor to the onset of chronic diseases indicated by the inability to match fuel preference (glucose first if available, fat second) to demand(3). If your mitochondria struggle to function properly, you likely store excess energy that your body doesn’t burn. This difficulty in burning fat leads to weight gain, insulin resistance, and chronic health problems associated with metabolic disorders.

So does this mean you can eat all of the carbs and “get away with it” if you have metabolic flexibility? Sorry to disappoint. 

Metabolic flexibility is a state to strive for as a sign of a healthy, high-functioning body. Enjoying roasted chickpeas on a salad or sinking your fork into a puddle of mashed sweet potatoes and using the glucose to power an evening walk should be the goal. Prioritize whole-food sources of macronutrients most of the time and that occasional processed treat won’t have such a domino effect on your health. 

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Related reading: Using Metabolic Workouts to Boost Your Metabolism

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