Intermittent fasting is an eating pattern in which adherents rotate between periods of eating and fasting. Many experts claim that intermittent fasting has health benefits such as weight loss and improved brain function.
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What is Intermittent Fasting?
Intermittent fasting is a popular diet plan that does not dictate which foods dieters can consume. It is simply an eating pattern that cycles between periods of eating and fasting. There are many variations of the intermittent fasting diet, with some even allowing low caloric intake during periods of fasting.
Intermittent fasting is achieved by skipping meals throughout the day, and dieters can choose their eating windows. Instead of focusing on calorie restriction, intermittent fasting is a purposeful approach to consuming foods that can improve health, increase life expectancy, reduce inflammation, and improve brain function.
Common intermittent fasting diets involve 16-hour or 24-hour fasts on 2 days out of each week. In the Leangains protocol, participants alternate fasting for 16 hours and eating for 8 hours. In the 24-hour method, also known as the “eat-stop-eat” method, participants fast for 24 hours once or twice per week. A third approach is the 5:2 diet, in which participants have a modified fast on 2 non-consecutive days each week. On fasting days, participants are restricted to consuming 66 to 500 calories. For the remaining 5 days, participants eat normally.
The Science Behind Intermittent Fasting
During fasting, many changes occur at the cellular and molecular levels. After eating, the body digests the food for 3 to 5 hours. During digestion and absorption, insulin levels increase and the body does not metabolize fat. Around 4 to 6 hours after eating, the body is in a fasting state. After 8 to 12 hours without food, insulin levels decrease, and fat is metabolized for energy.
Other hormonal changes also occur during intermittent fasting. For instance, human growth hormone levels increase as much as 5-fold to stimulate fat loss and muscle gain. Sensitivity to this growth hormone is elevated and decreases only gradually until stored fat is metabolized. Low insulin levels allow for improved accessibility to metabolize stored fats during this time as well.
Intermittent fasting is also a time for cellular repair. During fasting, cells digest and eliminate old, faulty proteins that build up intracellularly. Lastly, the genes responsible for protection against disease and longevity undergo changes during fasting.
Is it Healthy and Safe?
Intermittent fasting has been practiced for thousands of years. However, its importance has gained increased attention during the last 2 decades. Studies have shown that skipping meals and intermittent fasting are associated with weight loss and improved metabolic health. Moreover, recent studies show no apparent harms associated with this diet.
In addition to helping people lose weight, intermittent fasting can improve blood pressure and fat metabolism. A small study published in the British Journal of Nutrition compared weight loss between two groups of overweight participants: one group decreased daily calorie intake and the other group ate normally for 5 days per week but restricted intake to 600 calories on 2 non-consecutive days per week. Although participants in both group lost weight, those in the 5:2 intermittent fasting group lost weight faster. Moreover, those in the 5:2 intermittent fasting group metabolized fat more rapidly after each meal and had a 9% decrease in their systolic blood pressure.
Intermittent fasting has also been shown to reduce the risk for some cancers, increase energy levels, improve mental focus, increase the speed of fat metabolism, improve memory, strengthen neural connections, improve mood, combat diabetes, and favor the production of brown fat, which helps reduce excessive weight.