Metabolic flexibility is a term used to describe the body’s ability to respond and adapt between fed and fasted states. Good metabolic flexibility allows your body to ease between metabolizing carbohydrates and fats efficiently with change in diet, exercise and in rest.
In the same way that calorie restriction and exercise help with improving health span and potentially preventing age-related diseases so does metabolic flexibility. Disrupted metabolic flexibility or metabolic inflexibility is associated with metabolic syndrome, type 2 diabetes, and cancer. (1)
Metabolic flexibility is an essential process for maintaining the balance between food intake (energy input) and energy expenditure and allows you to access all the types of fuels the body uses both smoothly and interchangeably in response to changing environment.
The key benefits of metabolic flexibility are:
- Helps to stabilize blood sugar levels
- Excellent satiety between meals
- No longer hangry (hungry and angry)
- Fasting periods with little to no difficulty
- Prolonged ability to exercise in a fasted state for up to 2 hours
Research suggests that intermittent fasting is a useful aid in the fight against continuously elevated blood sugar.
Intermittent fasting (IF) also known as time restricted eating has become a popular health trend and involves alternating cycles of feeding and fasting.
Research show that reducing the number of hours you spend eating not only benefits weight loss but can help to stabilize blood sugar levels, improve insulin sensitivity, and support long-term health.
Fasting drives the body to switch between burning glucose (carbohydrates) for fuel and using stored fat for energy in a similar way that exercise does. When blood glucose levels are raised, insulin levels will be elevated which prevents us using our fat reserves for energy.
Studies have shown IF can support cardiovascular health, reduce inflammation, combat obesity, and enhance brain function. (2)
It takes on average at least 12 hours of continuous fasting for the health benefits to trigger and for the body to switch to a fat burning state. Regimes that promote this metabolic switch have the potential to help reduce weight in obese individuals and for those of normal weight to improve their energy and overall health.
Several methods of IF regimes exist with periodic fasting being the most popular and easiest regime to follow. IF permits an 8-hour nutritional window in which to consume foods followed by 16 hours of fasting.
Periodic fasting permits eating normally for several days followed by days of consuming very little or zero food. The most popular periodic regime being the 5 days of eating normally followed by a couple of days of fasting. Fasting days normally are zero calories or a reduced food intake to below 500 calories.
It typically takes 2 -4 weeks of sticking to a fasting regime to see the benefits to blood sugar. When you return to normal eating these positives quickly disappear.
Fasting is a valuable tool and can improve insulin sensitivity allowing blood sugar to swiftly return to normal after eating. Keeping blood sugar low is vital in the fight against cardiovascular disease and diabetes. (3)
- Smith et al. Metabolic flexibility as an adaptation to energy resources and requirements in health and disease. Endocrine Reviews, 2018; 39 (4): 489-517.
- Anton et al. Flipping the metabolic switch: understanding and applying health benefits of fasting. Obesity, 2018, 26 (2): 254-268
- Furmli et al. Therapeutic use of intermittant fasting for people with type-2 diabetes as an alternative to insulin. BMJ Case Rep, 2018: bcr2017221854.