Intermittent Fasting

Written by Dr. Akeel Salahudeen, MD

The rising incidence of obesity and its associated health conditions have become a global cause of concern. This has also increased awareness and popularity of the various weight loss techniques and alternations in the diet. One such alternation, which has been a topic of particular interest to experts worldwide, is intermittent fasting. Studies have found that this diet is not only associated with weight loss and improved metabolic health, but it may lead to several other health benefits – longevity. (1) (2) (3)


What is Intermittent Fasting?

Intermittent fasting is a type of unique eating pattern which is associated with several health benefits. The types of intermittent fasting that individuals most popularly adopt all over the world include:

  • Intermittent Caloric Restriction: In this fast, the individual fasts for an entire day, once or twice a week. They can consume food freely, without restrictions on the remaining days of the week. (4)
  • Time-Restricted Feeding: As the name suggests, time-restricted feeding is a form of intermittent fasting where the individual may consume food only during certain hours of the day while they are supposed to remain in a fasting state during the remaining hours. The time pattern commonly adopted by individuals is the 16/8 intermittent fast. This includes the individuals consuming food for only 8 hours of the day, while the remaining 16 hours are spent in a fasting state. (5) (6)
  • Alternate Day Fasting: Alternate days fasting is an intermittent fasting plan where the individual may spend one-day fasting and the next day eating freely. However, every health expert has different beliefs regarding this fasting method. While some recommend that individuals have no caloric intake on the fast days, others recommend intake of foods that fulfil up to 25% of the energy needs. (5)

What Are The Benefits of Intermittent Fasting?

The common benefits of intermittent fasting include weight management and promoting metabolic, heart, brain, gut, and mental health.

Weight Loss

Studies have shown that individuals practising intermittent fasting undergo some weight loss. The range of weight loss that may be associated with intermittent fasting lies between 2.5 to 9.9%. (6) One such study was conducted on 16 individuals who were in good health and had an average body mass index. During the study, the individuals practised Alternate day fasting for 22 days, after which their measurements were taken. The study showed these individuals to have a 4% reduction in their body fats 2.5% reduction in body weight. At the same time, an increase in oxidation of fats was also seen. (6)

Another study, which was conducted on 32 overweight females, also showed similar results. When these females underwent alternate day fasting for eight weeks, they significantly reduced their weight, fat mass, and waist circumference. When the weight loss in the females undergoing alternate day fasting compared to those who did not, these females were found to have a 6.5% greater weight loss. (7)

Metabolic Health

Intermittent fasting is also associated with increased metabolic health due to the lower glucose levels and higher insulin sensitivity seen in practising individuals. This was further investigated in a study that included 48 overweight individuals divided into four groups based on the interventions they would be given. The study showed that the individuals who underwent calorie restriction had a 60% improvement in their insulin sensitivity after 6 months. (8)

Heart Health

Experts believe intermittent fasting can have cardio-protective effects and promote overall heart health by protecting the myocardium from inflammation and ischemia-associated damage. (9) This was further proven in a study on ten healthy individuals with a Body Mass Index of between 25 to 45 kg per m2. Caloric restriction in these individuals was found to have a reduction in their cardiometabolic risk by altering the risk factors associated with heart diseases. (10)

Cognitive Health

The cognitive improvement induced by intermittent fasting and caloric reduction over time has been a common topic of many recent studies. Research suggests that intermittent fasting may delay cognitive decline, often seen in ageing individuals. Results of the studies have shown intermittent fasting to be associated with improved biomarkers, lower oxidative stress levels, and enhanced memory. (11) Alternate-day fasting is also found to make the neurons more resistant to injuries. (12)

What Breaks A Fast?

During the fasting period, the individual is recommended to avoid all forms of calories, whether large or small. This is because the intake of these calories results in the disruption of the fasting process and the therapeutic changes taking place in the body. While most experts agree that no foods are to be consumed during the fasting period, the drinks that may be permitted have been a topic of debate. Some experts allow caffeine intake during the pasting hours, while others debate that it may break the fast. The experts who allow caffeine recommend its intake to be limited to 200 mg daily, as consuming it at this concentration does not raise any health concerns. Studies have found its consumption increases thermogenesis and fat oxidation in the body, leading to weight loss. (13) Moreover, caffeine is recommended to be consumed only in the form of coffee and no other forms like sweetened caffeinated beverages. The individuals are also recommended to increase their total water intake during the fasting period to stay hydrated. (14)

The Bottom Line

Intermittent fasting is linked to several health benefits, including improved metabolic health, weight loss, and prevention of cognitive decline. It also protects the heart tissues from inflammatory and ischemic damage. However, individuals are still advised to consult a licensed expert before starting their intermittent fasting routine. This allows the experts to evaluate if intermittent fasting may suit them in accordance with their current health status. The experts may also be able to guide them regarding the forms that may be ideal for them.


  1. ReferencesWithrow, D., & Alter, D. A. (2011). The economic burden of obesity worldwide: a systematic review of the direct costs of obesity. Obesity reviews: an official journal of the International Association for the Study of Obesity12(2), 131–141.
  2.  Cornier, M. A., Dabelea, D., Hernandez, T. L., Lindstrom, R. C., Steig, A. J., Stob, N. R., Van Pelt, R. E., Wang, H., & Eckel, R. H. (2008). The metabolic syndrome. Endocrine reviews29(7), 777–822.
  3.  Malinowski, B., Zalewska, K., Węsierska, A., Sokołowska, M. M., Socha, M., Liczner, G., Pawlak-Osińska, K., & Wiciński, M. (2019). Intermittent Fasting in Cardiovascular Disorders-An Overview. Nutrients11(3), 673.
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  6.  Collier R. (2013). Intermittent fasting: the science of going without. CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne185(9), E363–E364.
  7.  Cui, Y., Cai, T., Zhou, Z., Mu, Y., Lu, Y., Gao, Z., Wu, J., & Zhang, Y. (2020). Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis. Frontiers in nutrition7, 586036.
  8.  Heilbronn, L. K., Smith, S. R., Martin, C. K., Anton, S. D., & Ravussin, E. (2005). Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American journal of clinical nutrition81(1), 69–73.
  9.  Klempel, M. C., Kroeger, C. M., & Varady, K. A. (2013). Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet. Metabolism: clinical and experimental62(1), 137–143.
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