Health Benefits of Intermittent Fasting

Scores of animal studies followed by human clinical trials have proven that intermittent fasting not only helps lose weight, it also modifies and improves our glucose regulation, increases stress resistance, and suppresses inflammation and prolongs life.

Muslims all over the world are close to the end of Ramadan, the month of fasting.

From the religious perspective, Muslims are commanded to fast just as believers in the past were ordained to do. The following two verses from The Quran are illustrative:

Oh, you who believe! Fasting is prescribed to you as it was prescribed to those before you, that you may learn piety and God consciousness” [Quran,2:183]

“The month of Ramadan [is that] in which was revealed The Quran, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast; and whoever is ill or on a journey – then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you, and perhaps you will be grateful.” (Quran: 21:85)

In contrast to people today, our human ancestors did not consume three regularly spaced, large meals, plus snacks, every day, nor did they live a sedentary life. Instead, they were occupied with acquiring food in ecologic niches in which food sources were sparsely distributed. Eating habits changed over time as the societies evolved.

To understand the impact of fasting on the metabolism, one needs to refresh our knowledge of the physiology. Glucose and fatty acids are the main sources of energy for cells of the body. After meals, glucose in the food is used for energy, and fats are stored in adipose (fatty) tissue. During periods of fasting when glucose is not readily available, the body uses the stored fat. Fats are broken down to fatty acids and glycerol, which are used as fuel to generate energy for the body functions. The liver converts fatty acids into ketones (ketone bodies). In the absence of glucose such as during fasting, the ketone bodies provide a major source of energy for many tissues, especially the brain. In the fed state, blood levels of ketone bodies are low. However, during fasting, as the fat stores are broken down, the level of ketones rise within 8 to 12 hours after the onset of fasting, reaching levels five times the normal. This leads to a significant reduction in the fat content in the body. This was discussed in a recent article published in a prestigious medical  journal. 

The researchers have conducted scores of studies in animals and humans to assess the physiological effects of fasting and/or calorie deprivation. These studies have shown that metabolic switching from liver-derived glucose to fatty tissue–derived ketones occurs daily or several days each week. This not only helps gradually melt away the fat and helps lose weight (Ketone Diets), it also modifies and improves the glucose regulation (diabetic control), increases stress resistance, and suppresses inflammation, all being important components of chronic diseases.

Additionally during fasting, the cells activate mechanisms that increase their defenses against oxidative and metabolic stress and repair or remove the damaged molecules. Such “housekeeping “functions may be the reason why fasting helps improve life span.

The following are the varieties of fasting that are reported in the medical literature:

Intermittent Fasting:

Complete alternate-day fasting:  Involves alternating fasting days (no energy-containing foods or beverages consumed) with eating days (foods and beverages consumed as desired). The minimum period of fasting ranges between 12-14 hours.

Modified fasting regimens:  Allows consumption of 20–25% of energy needs on scheduled fasting days; the basis for the popular 5:2 diet, which involves severe energy restriction (500-700 calories per day) for 2 nonconsecutive days per week and eat as you like in the other 5 days. (attach link)

Time-restricted feeding:   Allows ad libitum (as you desire) energy intake within specific time frames and regular, extended fasting intervals (10-14 hours).

Religious fasting:  

Variety of fasting regimens undertaken for religious or spiritual purposes

Ramadan fasting:   A fast from daybreak to sundown during the holy month of Ramadan; the most common dietary practice is to consume one large meal after sundown and one lighter meal before dawn. The feast and fast periods of Ramadan vary in length based on the time of the year in a given locale.

Other religious fasts:  Members of the Church of Jesus Christ of Latter-Day Saints routinely abstain from food and drink for extended periods of time. 

Some Seventh-day Adventists consume their last of two daily meals in the afternoon, resulting in an extended nighttime fasting interval that may be biologically important.

A very detailed review of the health impact of fasting was published in the Annual Review of Nutrition in 2017. 

There are many websites that provide actual diet plans for 500-700 calories daily intake. 

The take home points are that eating less helps prolong life and reduce chronic diseases. Having two meals a day, having smaller portions and avoiding snacks in between meals offers significant health benefits.

In the complete alternate day fasting (one of the intermittent fasting techniques), the metabolism switches from burning glucose to burning body fat as the source of energy. It also decreases the level of inflammatory and stress responses at the cellular level and increases the anti-oxidative processes.

If one cannot manage the complete alternate day fasting, then the 5:2 intermittent fasting regimen offers the most practical compromise. In this regimen, one reduces the energy intake to 500-700 calories per day on two non-consecutive days of the week and eats normally on the other 5 days. The best results have been noticed when the 5:2 intermittent fasting diets were adhered to at least 4 months.