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Pros and Cons of Intermittent fasting


Fasting is simply a period without consuming calories. Intermittent fasting does not include a prescription of specific foods to eat when not fasting, nor does it control the number of calories consumed when not fasting.


Intermittent fasting is romanticized in the nutrition blogosphere and sometimes viewed as the way to improve health and body composition.


Intermittent fasting has come to mean many different things to many people. Here is a general summary:

  • Fasting is simply a period without consuming calories. Note that it is intermittent fasting; the name implies infrequency.
  • Not eating for an extended period is a stress. Fasting is a stress whose severity is dictated by the length of the fast, but stress itself is not inherently good or bad.
  • Intermittent fasting does not include a prescription of specific foods to eat when not fasting, nor does it control the number of calories consumed when not fasting. The term “time-restricted feeding” is sometimes used to specify fasting without a caloric deficit.


Many different proposed protocols can be used with intermittent fasting; it is not a one-size-fits-all method. As one example, a 15-hour overnight fast means finishing dinner at 8 p.m. and abstaining from any calories until 11 a.m. the next day (non-caloric liquids are permitted, except when containing non-caloric sweeteners). The actual fast length and frequency of fasts can be modulated (knowing that more of either variable is a greater stress).


A few of the potential benefits include improved:

  • Body composition (metabolic flexibility).
  • Health (hormonal control).
  • Psychological effects.

As with most aspects of nutrition, every benefit can become a detriment depending on each person’s approach.


Body Composition (Metabolic Flexibility)



Intermittent fasting might improve body composition. Because the practice compresses the “feed window” on a selected day, it is likely people will eat less than their usual volume unless they are tracking their intake. It is harder to eat your daily caloric load in a shorter period, so intermittent fasting might indirectly reduce total consumption, resulting in weight loss.


Intermittent fasting also generally promotes more fat burning, even in the presence of the same daily caloric load. At rest, the body preferentially uses fat for energy, especially in the periods not directly after a meal. As the length of these periods increases (to a degree), the body becomes better able to access and use stored fat (instead of carbohydrate) for energy.



Intermittent fasting does not improve body composition when the body is starving. For someone who is under eating—intentionally or not—the body shifts more to muscle catabolism versus fat burning. Chronic stress, such as starving, increases cortisol. Chronically elevated cortisol can elevate blood sugar and in turn elevate insulin, which ultimately shifts the person away from fat oxidation.


Health (Hormonal Control)



Intermittent fasting brings some potential health benefits via better hormonal control—particularly insulin sensitivity. Suppose a regular coffee drinker consumes four cups of coffee a day. It is unlikely he or she notices a significant difference from caffeine with the last two cups. However, by removing caffeine from the diet for a month, he or she will likely notice the effects of smaller doses. By exposing oneself to periods of low insulin during a fast, the body becomes better at detecting small increases. This is relevant for health because insulin resistance is present with many chronic diseases (e.g., heart disease, diabetes)



Depending on a person’s current hormonal status, intermittent fasting might add too much stress. Someone who already has high cortisol does not need to be fasting; it will only make things worse


Psychological Effects



As someone who came from typical mainstream fitness before CrossFit, We found intermittent fasting brought freedom from food. Missing meals was freeing, and the body is not so sensitive that skipping a meal occasionally will result in disastrous metabolic shifts.



For those who have struggled with diagnosed eating disorders, or even undiagnosed but disordered eating patterns, intermittent fasting is not recommended. It promotes restricting eating that can lead to increased obsession about food “rules.” For someone who has these tendencies, intermittent fasting will likely not create healthy habits.


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