What is fasting?

Fasting is the voluntary restriction of food and drink for a certain period of time. In other words, the person practises abstinence from food and drink for a chosen time duration. There are several health benefits of fasting. Individuals may practise fasting for health or religious reasons. Owing to this there are several different types of fasting one may choose to practise.

History of fasting

Fasting is now a fashion but it is with evolution that we have been consuming three meals a day. However, fasting has been a part of human life for several decades. In terms of fasting from an evolutionary perspective, it has been in practise for several years. It is practised for religious rituals, diets and political protests. Many faiths believe that sacrificing food and water for hours, days or weeks at a time contributes immensely to self-reflection and self-discipline. Animals also fast during times of stress or illness as it is said to be natural instinct to conserve energy and take rest, especially during critical conditions.

Types of fasting

The current definition of fasting is defined as avoiding food and drink for at least 8-12 hours each day. This means that we are all technically fasting between dinner and breakfast. Here are some of the different types of fasting followed:

Impact of fasting on human metabolism

1. Lipid metabolism
   During fasting, the body shifts from using glucose as the primary source of fuel to the lipids stored in the body. This is because the stored fat is metabolised when glycogen is depleted after 12-36 hours of fasting.
   
   This speeds up the rate of lipid breakdown (lipolysis) in the body. The free fatty acids are converted to ketones in the liver which act as the provisionally preferred source of fuel for several tissues. The brown fat is the key mediator of energy homeostasis and thermogenesis. It helps in increasing energy expenditure and helps in the reversal of hyperlipidaemia. 

1. Glucose metabolism
   Fasting can benefit an individual’s glucose metabolism based on the individual’s body composition/BMI, fasting window and duration of fasting. A study conducted on the effect of a 2-day severe intermittent energy restriction followed by 5 days of normal eating for 12 weeks revealed that the participants who had diabetes/obesity had better HbA1c levels.

1. Protein metabolism
   Amino acids are the building blocks of proteins. Proteins support biological function and activity. During fasting, proteins are broken down and used as a source of fuel for the body. Fasting may alter the amino acids based on it’s type and duration of fasting.
   
   An animal study revealed that fasting decreased the concentration of the amino acids – Arginine, alanine, serine, threonine, aspartic acid, and aspartic acid and proline etc. After 6 hours of fasting, the concentrations of lysine, leucine, isoleucine and taurine were the lowest. The concentration of these amino acids was recovered after 12 hours of fasting. In comparison, the effect of fasting on essential amino acids was greater than that of non-essential amino acids.

Impact of fasting on psychological health

Studies on the effect of short-term fasting on psychological health revealed contradictory results. This is possible because:

• Fasting is related to self-control. Completing fasting periods can increase feelings of self-control. 
• Fasting due to strong religious beliefs can contribute to positive physical and psychological health.

Relationship between blood glucose and emotional self-control: The major fuel of the brain’s functions is glucose. Food restriction directly influences the amount of energy available for the brain’s use. Usually, low blood glucose levels are related to poor mood. 

• Emotions are strong determining factors of mental health
• Emotions are sensitive to glucose
• Coping with strong emotions requires a high amount of glucose
• Hypoglycaemia influences emotions to a great extent. It may cause anxiety, irritability, nervousness etc.
• People with poor glucose control have poor emotional control

General health benefits of fasting

• Maintaining body weight – Overweight and obesity is usually triggered by the consumption of a high-caloric diet and a sedentary lifestyle. Fasting helps cut down the energy consumed drastically and can be helpful in weight loss or weight management in short-term and long-term practise.
• Blood pressure – Studies suggest, fasting (specifically known as arterial fasting) can be followed as a part of anti-hypertensive intervention. Fasting can lower the systolic and diastolic blood pressure levels but not to the extent of hypotension. This is possibly due to the secretion of catecholamines during fasting that help reducing sympathetic nerve impulse. 
• LDL level – Fasting can significantly lower the serum LDL levels. Due to the change in the meal pattern of individuals. The period of fasting between meals necessitates the need for the body to utilise the stored fat for energy in the absence of glucose.

• Vascular wall – Fasting significantly improves cardiovascular health. Conditions associated with the vascular wall are the key cause of atherosclerosis. It restricts vasodilation leading to an imbalance between vasodilation and vasoconstriction. Fasting increases the serum Nitric oxide which helps improve vascular health and elasticity.
   

Circadian health and fasting

• The basic evolutionary principle of an organism is to restrict activity to the day and wind down as the sun sets. Circadian health helps in integrating metabolisms and energies. 
• The biological clock of mammals is influenced by the suprachiasmatic nuclei (SCN) of the hypothalamus. It is sensitive to light and dark stimuli.
• There are clock oscillators located in the peripheral tissues like the liver.
• The imbalance between the 2 clocks – SCN and peripheral circadian clocks, has the ability to cause energy imbalance leading to chronic diseases.
• Fasting or time restricted feeding improves the diurnal food intake (body’s need for meals at different times of the day).
• This is said to help in weight regulation and energy metabolism.

Fasting and gut health

• The functions of the gut also work on circadian rhythm/sleep wake pattern.
• Gastric emptying and blood flow are greater during daytime than the evening. The blood glucose load is slower in the evening.
• Fasting improves gut health significantly. It helps in changing the composition of gut bacteria from an obese microbiota to a lean microbiota in individuals with obesity.
• Thereby it may be a cause of preventing systemic inflammation.

Contraindications of fasting

• Diabetic individuals – Individuals with Diabetes might find it challenging to maintain stable blood sugar levels during fasting as they are at a high risk of hypoglycaemia.

• Pregnant or breastfeeding mothers – The energy requirement is considerably higher during pregnancy and lactation. Fasting may limit the the total energy consumed by the mother and may affect maternal and child health.

• Individuals with low bone density – Fasting may reduce the bone mineral content. This makes the individual vulnerable to fracture, osteoporosis and osteopenia.

• Individuals with a history of eating and behavioural disorders – Though fasting is very effective. It may trigger relapse of eating disorders or obsession about food.

• Individuals with immune diseases – Individuals with compromised immune systems need a continuous supply of energy. Energy restriction during starvation can worsen their condition.

Though fasting has several health benefits. It is important to understand that, one needs to consult a physician and dietitian before beginning any diet.


Mayuri,
Dietetic Researcher, Simplyweight