As a part of Nature, mankind has been practising fasting throughout his existence; much before civilization and religion. Intermittent Fasting (IF) is the voluntary abstinence of food intake for a specified period of time and 3 most common applied methods are: alternate day fasting (fast on one day and then eat the next day), 5:2 intermittent fasting (fasting 2 days each week), and daily time-restricted feeding (fast, for example 16 hours, then eat all your calories in an 8 hour window). It is a well-known atavistic practice associated with many religious and spiritual traditions, although the methods vary considerably.
Ancient Eastern traditions, dating tens of thousands of years, lay much importance on fasting as an adjunct to a full-fledged life. In the world's oldest religion, Hinduism, fasting is one of the 365 Nandinatha Sutras (traditional ways to enlightenment) as an understanding of man and nature totally consistent with Vedic philosophy (Subramuniyaswami, 2004). Prominent Hindu scholars believe that purification of the body at the cellular level happens when the stomach is empty to allow the systemic functions of the body to resynchronise themselves.
Fasting in Hinduism would usually occur on designated days, such as the bimonthly Pradosham (13th day of every fortnight) and Ekadasi (11th lunar day) or for a period like the 10-day Kavadi Viradam among Tamil Hindus. In relatively recent Abrahamic teachings, 1.6 billion followers of the Islamic faith would fast by refraining from eating or drinking from Sahur (sunrise) to Iftar (sunset) for 28-30 days in the holy month of Ramadan. Islam views Ramadan as a way of practising self-discipline, self-control, sacrifice, and empathy for those who are less fortunate, thus encouraging actions of kindness and zakat (compulsory charity). Greek Orthodox Christians follow the 3 fasting periods, which are the Nativity Fast (40 days prior to Christmas), Lent (48 days prior to Easter) and the Assumption (15 days in August).
Science proves that each time we eat, excess glucose molecules obtained from food are converted to glycogen and stored in the liver. In an individual not exercising, the stores would usually last for 10-14 hours. Upon glycogen depletion, the body turns at our fat stores found in our adipose (fatty) tissue to release fatty acids. Our liver in turn converts fatty acids to ketones which are used as the major cellular fuel source to compensate for low availability of glucose. This process is termed as Intermittent Metabolic Switching or 'IMS'.
As an analogy, glucose can be compared to gasoline and ketones to a wood log in terms of the duration of energy production through the exothermic reaction when these energy sources are burned. Though, besides acting as an energy substrate, there is a whole remarkable complex and coordinated adaptations in relation to ketones production on the body to maintain or even enhance our bodily performances. Now, we will discuss on how our dietary patterns affect our delicate physiology and intricate functioning levels of our body at the molecular and cellular levels.
Does the brain work best when the stomach is empty?
Our everlasting interests in mechanisms of human cognition have led to the emergence of information on how dietary energy intake impacts our extraordinary brain circuits. To put it into perspective, let us roll back a few millennia, before the advent of food agriculture. Lack of food has been a major driving force for brain evolution, the main reason being that critical thinking and sharp decision-making occurred in individuals who navigated through a well-diversified environment for the search of food in a fasted state.
These selected individuals were skilled at conjoining to acquire and share food (Mattson et al., 2018). As mentioned above, the production of ketones led by IMS has many other remarkable properties, besides providing a source of body fuel. In one animal study, it was shown that mice which underwent intermittent fasting showed better working memory, strength, coordination and spatial navigation skills (Ingram et al., 1987). Another study by Witte et al. (2009) demonstrated IF resulted in better memory performance among elderly people. To find possible scientific explanations for these findings, exploration on the neuro-physiological effects of fasting is a pre-requisite.
At the molecular level, ketones are needed for the production of some crucial Neurotrophic factors or 'growth hormones for neurons (brain cells)', which in turn stimulate the production, consolidation and protection of new neurons and neural circuits (Vivar et al., 2013). In addition, the fasting state enhances the production of the 'hunger hormone' ghrelin by the gut. This hormone is known to optimise our hippocampus, which is a major structure of the human brain responsible for consolidation of information from shortterm memory to long-term memory and spatial memory. When the experimental evidence and knowledge of the human physiology are combined, we can support the evolutionary principle that the brain and body perform at remarkably high levels in the fasting state and can be sustained through long-term neuro-adaptations.
Can Intermittent Fasting enhance physical fitness and delay ageing?
Before addressing the effects of fasting on physical fitness and ageing, we should ask ourselves one critical question: did our human ancestors consume three regularly-spaced large meals, along with caloric-dense snacks whilst leading a sedentary lifestyle? This was highly unlikely because acquiring food in ecologic niches in which food sources were sparsely distributed required dedication of their physique and time. Over time, they got more creative through the enhancement of their physical and communication capabilities.
It has been postulated that repeated exposure to IMS led to long-term adaptations and resistance to challenges provided by Mother Nature. At the cellular level, there is a coordinated adaptive 'stress' response leading to an increase in stimulation of antioxidants, DNA repair, 'quality control' of proteins, genesis of mitochondria or 'powerhouse of cells', autophagy or 'auto-destruction of defective cells/proteins' and decrease in inflammatory cells and hormones (de Cabo & Mattson, 2019).
It is noteworthy that prominent Japanese cell biologist Yoshinori Ohsumi received the Nobel Prize in Medicine and Physiology in 2016 for his discovery of mechanisms for autophagy and its wonders on the human body. During the recovery period (eating and sleeping) from fasting, the resultant IMS leads to an increase in cell repair and growth through protein synthesis. But what are the effects of this myriad of cellular reactions?
One of them is to robustly improve survival and delay ageing, proved by data obtained after nearly a century of research. In one study conducted among 34 resistance-trained male athletes, the latter were put on a 2-month IF regimen. The results showed a decrease in fat mass while their muscle mass and maximal strength were maintained. On an interesting note, studies on rats have shown that a 10-week period of IF increased glycogen stores in their muscles, which led to better strenuous exercise performances like swimming (Sakamoto & Grunewald, 1987). With regards to the major effects to ageing, it has been shown that fasting causes a decrease in some specific types of growth factors associated with accelerated ageing (Fontana et al., 2015). A recent Harvard Health Publishing article recognised that the anti-ageing effects of IF are at their finest when IF is combined with a plant-based diet (Tello, 2019).
Can IF play a key role in curbing the global burden of major illnesses?
When viewed from an evolutionary perspective, it is unnatural to thrive when consuming three energy-rich meals plus snacks every day. Does that mean the nutritional dogmas we have been raised with are now outdated? Indeed - in our present-day civilization, hunger can be mistaken as pleasure-seeking behaviours which encourage the consumption of a large amount of food, caloric-dense processed ones resulting in immediate, yet short-term, gratification. The collateral damage caused by these eating patterns includes the emergence of obesity, obesity-related morbidities such as hypertension, diabetes and ischaemic heart disease, autoimmune conditions and even cancer.
Compared to our ancestors, we have undergone a form of 'self-domestication' owing to easy access to food across most parts of the world. Interestingly, there has been an approximate 10% reduction in brain volumes in humans during the past 10,000 years, which correlates with the agricultural revolution and the consequent effortless ways of obtaining food. Also, overeating in children initiated by their over-nourished parents has been associated with declining cognitive functions, possibly due to a reduction in the size of the hippocampus and low levels of important brain growth factors needed for brain maturation. In fact, USA states with the highest prevalence of childhood obesity also have the lowest percentages of high school and college graduates.
"...did our human ancestors consume three regularly-spaced large meals, along with caloric-dense snacks whilst leading a sedentary lifestyle?"
Recent findings suggest that IF can be clinically applied to the prevention and management of diseases that socio-economically impacts the world. Since IF does improve our cells' sensitivity to the insulin hormone, some studies have shown that it can decrease the risk of diabetes. Furthermore, one study among Okinawans has effectively proved that fasting and low-calorie diet has a positive impact on weight loss. In another one year observational study of 1,422 subjects with pre-existing diseases who underwent a fasting regime, significant reductions have been seen in weight, abdominal circumference, blood pressure and blood glucose, along with a significant improvement in emotional well-being.
IF leads to a depletion of your fat tissue to produce fatty acids, which helps in weight loss. The decrease in blood pressure in fasted individuals is due to the optimization of our autonomic nervous system, which plays a critical role in regulating our blood pressure. The improved emotional health can be attributed to a decrease in the stress hormone cortisol in the fasted subjects. Yet, adverse effects were seen in less than 1% of the participants. Since fasting plays a key role in down-regulating inflammation, one study showed that an elevated level of ketones and low levels of inflammatory markers alleviated asthma symptoms (Johnson et al., 2007).
Strong evidence has also shown that fasting can delay the onset of neurological conditions such as Parkinson's disease, stroke and Alzheimer's disease through the plethoric benefits of fasting on our brain function: de- creasing inflammation risks in the brain, stimulation of brain growth factors and destruction of damaged brain cells (Arumugam et al., 2010). IF can decrease the amount of certain notorious growth factors, which grabbed the attention of scientists involved in cancer research. Studies, dating nearly a century, have proved the beneficial effect of fasting on cancer by reducing its spontaneous occurrence and suppressing its growth.
Scientists believe that IF might jeopardize the energy metabolism in cancer cells, which can eventually render them susceptible to available interventions (e.g. chemotherapy). There have been case studies documented, where scientists observed patients with gliobastoma (an aggressive form of brain tumour) put on a regimen of IF. The tumourgrowth was suppressed whilst survival was extended (de Cabo & Mattson, 2019). There are currently ongoing trials on IF in patients with breast, ovarian, prostate, endometrial and colorectal cancers.
Ancient practice as a new way ahead?
Fasting has a solid spiritual, metaphysical and religious significance - and the non-exhaustive list of scientifically proven benefits is phenomenal. Notwithstanding its applicability might be impeded owing to our counterintuitive habit of eating three meals with snacks every day and the unfortunate lack of training of doctors in medical schools. In the midst of the current lockdown due to the unprecedented Covid-19 pandemic, haven't we obtained a finer opportunity to rewire our way of thinking by exposing ourselves to evidence-based literature on the correct eating habits? In addition to its health benefits, this cost-effective intervention could help in developing better strategies to counteract the socio-economic effects of chronic diseases and their current, possibly contentious pharmacotherapeutic strategies. And the best news is anyone can consciously practice IF, for it does not cost money and time.
This article is for general informational purposes only. It should not be used to self-diagnose and it is not a substitute for a medical exam, cure, treatment, diagnosis, and prescription or recommendation. It does not create a health practitioner/patient relationship between the author and you. You should not make any change in your health regimen or diet before first consulting your doctor and obtaining a medical exam, diagnosis, and recommendation.