Fasting has been in vogue for some time now, and for what would seemingly involve refraining from putting anything in one’s mouth… it has become quite complicated! If you bear with me through some science, I promise to give you some great take-homes by the end! By Ryan Bonney.
This article is by no means exhaustive on the subject; and while adhering to the latest literature on fasting, I have kept it as straightforward as possible. I hope that reading this encourages you to get out of your comfort zone and perhaps try something you never thought possible.
Final caveat is that I am a Chiropractor, not a Dietitian. While I do have training in this field and am simply synthesising the research, this is still an opinion piece. I advise that you do your own homework, and if you have any conflicting health issues please consult with either a Medical Doctor or Dietitian who has a special interest in this area.
Fasting has been ubiquitous throughout history – either done voluntarily (health practices, medical treatment, religious teachings etc.) or involuntarily (famine, torture etc.).
Amongst our developed world food has become so ridiculously easy to acquire, that the most stress inducing time of the year is the Easter holiday when – God forbid – your partner forgot to buy the hot cross buns! In this supermarket-on-every-corner society, skipping a meal (or ten) might be perceived as a psychological shortcoming of some sort…
In the medical profession, fasting has been historically employed to help treat epilepsy (reducing episode frequency and consequent neuronal damage).
Fun fact: The longest medically monitored fast recorded was 382 days, over which time a Scottish man lost 120kg, and kept it all off!
In a non-medical setting, there are a number of proposed benefits that can be experienced by fasting. These benefits stem from the principle that while we are in a “fed state” (i.e. eating our three-square meals daily), our body is so busy processing food that it cannot prioritise the clean-up of our own cells. We begin to accumulate cells that are dead/dying or deteriorating (senescent cells) and put up with a fairly inefficient system; one that might be prone to cell mutations and consequently cancer if left unchecked!
When our body is deprived of nutrients and enters a state of nutritional deficiency for 16+ hours, it undergoes what we call autophagy. This is the body’s ‘garbage disposal and recycling system’.
Our lysosomes (garbage collectors) engulf these senescent cells and any parasitic bacteria, strongly bolstering the immune system and providing a neuroprotective effect.
Millions of years of mammalian evolution has fine-tuned our physiology to deal with stresses in a beneficial way. While we often think of stress as a negative thing to be avoided like the plague; we forget that stress is how we as humans adapt and grow.
Whether it’s your bulging bicep on the preacher machine in the gym, or enhanced ability to concentrate after meditating – stress is vital.
This form of beneficial adaptation to stressors is known as hormesis or eustress – stress arising to combat physiological challenges such as: hunger, thirst, extreme heat, extreme cold, acute pain, or exercise.
Hormesis, when applied tactically, can enhance the robustness of an individual. For a hormetic stressor (such as fasting) to be effective, it must sit in that sweet spot – not too little, not too much…
Interestingly, the hunger hormone ghrelin has been shown to operate on its own circadian clock. Most people would assume that while fasting, hunger levels build and build until one chews one’s own arm off.
Not so. Hunger instead seems to roll in waves, and often matches up with regular meal times. Most ‘hunger’ cravings are often just habitual desires- time of day, appetising smells, social eating calendars, boredom etc. It is important to recalibrate for ourselves what hunger really is!
What is Ketosis?
The body’s default fuel is glucose. And when food’s aplenty and all is well, this is our go-to for a quick hit of energy. While most people do okay with this way of fuelling, it keeps our blood sugar in a constant state of flux, and insulin receptors can develop resistance which (to state it very bluntly), has now been shown to promote auto-immunity, inflammatory conditions, and contribute to our obesity pandemic.
When glucose is eliminated/strongly limited, the body adapts (within 36 hours) – beginning to mobilise fat stores to provide a more constant energy source for our body and brain. Despite the lack of food intake, glucose is still produced (approximately 80g/day via gluconeogenesis) from amino acids and glycerol in our body. However, the vast quantity of fatty acids being drawn from our fat stores create what are called ketone bodies, in our liver. These are then sent to our muscles and brain, where they are a much more efficient fuel (by around 28%) than glucose.
The average person has 40,000 calories of fat on their body, and only 2,000 calories of sugar (glucose) at any one time. While the fat is analogous to a big log fire which will keep burning indefinitely, it is harder to access, and in fact can only be utilised once all the kindling (glucose) has been used up.
What happens when we fast (or practice an intermittently calorie restrictive diet)?
*Geek alert. Please skip ahead if you don’t really care*
12-24 hours: Our glucose drops by 20% and liver glycogen is almost totally used up.
Two days in: Liver glycogen has been depleted. Human Growth Hormone may increase up to 5-fold, with adrenergic upregulation.
Three days onwards: Glucose drops a further 30%, insulin sensitivity enhances, IGF-1 drops by 50%.
Other findings: Pro-inflammatory cytokines (TNF-a, IL-1b, IL-6) are reduced; Increased production and signalling of BDNF and GDNF (brain/glial derived neurotrophic factor); Upregulated heat shock proteins (HSP-70), glucose regulated proteins (GRP-78); Tumorogenesis and mutated cell proliferation has been shown to become stunted; Leptin (pro-inflammatory) reduces; Insulin sensitivity and adiponectin (anti-inflammatory) increases; Short term increase in circulating corticosterone, with a down-regulation in glucocorticoid receptor activation; Mineralocorticoid receptors are maintained.
What does this all mean?
*Please resume reading if you didn’t really care earlier*
While fasting, we may expect to experience: rapid fat loss while preserving muscle mass; protection against neurological diseases such as Alzheimers, Parkinsons, and Huntingtons; a slowing/stunting of cancer cell growth; improvement in memory, learning ability, and cognitive performance; improved coordination; a reduction in systemic inflammation which may assist conditions such as Rheumatoid Arthritis and/or Asthma; reduced blood pressure; bone density preservation; AND reduction in general physiological markers of aging.
So, how do I start?
There are juice fasts, water fasts, fat fasts, fasting-mimicking diets, the 5:2… the list goes on. The purpose of this article is not to provide you with a road map for how to fast. There are a bunch of great resources out there that are much more comprehensive and instructive in this respect.
What I will suggest, is that the best fast is the one that suits your lifestyle. What can you manage that is going to promote eustress, and not result in distress!
I think one of the most important benefits of fasting (that you don’t need a Science degree to understand) is that it helps you re-establish a healthy relationship with food. Learn to experience actual hunger again and know that this is probably benefitting you.
Don’t eat dinner just because the clock says it’s 7pm. Realise that you can actually go without food.
You’ll survive, and probably thrive.
Be like the penguin, who fasts up to 5 months every year!
1. Effects of intermittent fasting on body composition and clinical health markers in humans.
Tinsley GM1, La Bounty PM2.
Nutr Rev. 2015 Oct
2. Spontaneous 24-h ghrelin secretion pattern in fasting subjects: maintenance of a meal-related pattern.
Natalucci G1, Riedl S, Gleiss A, Zidek T, Frisch H.
Eur J Endocrinol. 2005 Jun
3. Energy intake, meal frequency, and health: a neurobiological perspective.
Annu Rev Nutr. 2005
4. Short-term fasting induces profound neuronal autophagy
Mehrdad Alirezaei et al
2010 Aug 14
5. Fasting: Molecular Mechanisms and Clinical Applications
Valter D.Longo1Mark P.Mattson23
Volume 19, Issue 2, 4 February 2014, Pages 181-192
6. Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women
Nutrition and Metabolism. 2004
Volek, JSl; Sharman, MJ et al
7. Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake
Anson, M; Guo, Z et al
8. A periodic diet that mimics fasting promotes multi-system regeneration, enhanced cognitive performance, and health span.
Cell Metabolism. 2015
Brandhorst, S; Choi, IY et al.
9. Caloric restriction and intermittent fasting: Two potential diets for successful brain aging
Ageing Res Rev. 2006
Martin, B; Mattson, M et al
10. Very low carbohydrate diets and preservation of muscle mass
Nutrition and Metabolism 2006
11. The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus
Nutrition and Metabolism, 2008
Westman, E; Yancy, W et al.
12. Fuel Metabolism in Starvation
Harvard Medical School. 2006
13. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.
K Y Ho, J D Veldhuis et al
J Clin Invest. 1988 Apr
14. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings.
Barnosky AR1, Hoddy KK2, Unterman TG1, Varady KA3.
Transl Res. 2014 Oct
15. Beneficial effects of mild stress (hormetic effects): dietary restriction and health.
Kouda K1, Iki M.
J Physiol Anthropol. 2010
16. The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting
Jason Fung, 2016
17. “Fasting Decoded” E-book
Ben Greenfield – Get Kion