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PGdip Dietetics and Human Nutrition, MSc Clinical Nutrition and Food Science
During centuries, humans have fasted for religious reasons, spiritual discipline and as a pathway of purification. Fasting is the abstaining of food and/or drink for a certain period of time; either the whole day, alternate day or by time-restricted feeding also called intermittent fasting. This month Muslims worldwide are fasting from dawn to sunset. Fasting currently observed by during Ramadan, is considered as intermittent as it ranges between 10 and 20 hours followed by a few hours eating window. Renowned scholar Dr Tariq Ramadan wrote “during the fasting days, Muslims are called upon to abstain from eating, drinking and responding to our instincts, to help us turn inward, to our heart and the meaning of our lives. Fasting is a school of faith, spirituality, awareness & giving. Nothing less”. (1) Totally agree. Now, let’s reveal much more. Beyond the spiritual dimension, whether you fast for religious reasons of for health, scientists are just starting to understand how hugely beneficial Fasting can be for health.
You know food is vital to live, though eating can also kill you. Overconsumption of foods leads directly to metabolic complications and cardiovascular diseases. In the meantime, a good amount of scientific literature reports that fasting positively affects our cellular functions, body weight, inflammatory response, immunity and longevity. Definitely, fasting helps look after your heart by reducing cardio-metabolic markers! And now more exciting, latest research suggests that fasting can literally rewire the brain. Did you know that if you fast for long hours, you highly challenge it? In order to adapt to a food deprived state, perceived as biological stress, the brain reacts by stimulating much more the neurons. Anything from the capacity to control behaviour to learning activities pushes the brain to work at optimum capacity. This can dramatically improve brain performance and prevent cognitive decline, opening thereby new avenues to decrease the risk of neurodegenerative diseases like Parkinson or Alzheimer.
So, what science says?
Fasting can be a good strategy for weight loss and cardio-protection
There’s been compelling evidence on fasting and the benefits on body weight, glycaemia, immune response and cardio health. Fasting long hours is actually common for most animal species and primitive man who used to evolve in hostile and stressful environments with very little foods. From an evolutionary perspective, the human body has learnt how to adapt and function at a high level physically and cognitively in a food-deprived or fasted state. (2)
According to the American Journal of Nutrition, human studies showed that caloric restricted diet or intermittent fasting can help obese individuals to lose weight, improve body composition and lower cardiovascular disease risk. (3)
An Oxford University study reported that alternate-day or intermittent fasting for minimum 3 weeks appear to be effective at reducing body weight, body fat (weight loss 3 -5kg), total cholesterol and triglycerides, all risk factors associated with heart diseases. (4)
The mechanism behind is fasting helps stimulate the production and regulation of crucial hormones involved in fat burning and body metabolism, especially Insulin, Ghrelin and Growth Hormone, big players in regulating appetite as well.
Fasting helps normalize Insulin and regulate hunger hormone Ghrelin
Our nervous system sends different signals: hunger stimulating or hunger suppressing peptides which are hormones responsible for telling the brain if we need to eat or if we feel full.
Ghrelin the appetite-stimulating hormone- also called hunger hormone- starts to rise when you run low in energy and likely contributes to changes in food intake and body weight. High levels of circulating Ghrelin are linked with higher levels of hunger and appetite which lead us to eat beyond our caloric needs and then gain weight. Researchers found that fasting helps reduce levels of Ghrelin. (5)
Several studies show that dietary restrictions and intermittent fasting also change the secretion of Insulin, a vital hormone that helps keep your blood glucose stable (sugar levels). Sugar is a primary source of energy but if you consume too much, you can develop insulin resistance which leads to chronic diseases. People looking to control their weight often need to balance their blood sugar levels that directly affect appetite and satiety. Calorie restriction through intermittent fasting may be one of the most effective ways to improve insulin sensitivity and reset the body to use fat as primary fuel*.
“During the initial 14-16 hours of not eating, your body burns through almost all of your carb (glycogen) stores in your muscles and liver. Once those glycogen stores have been depleted, your body turns to fat stores for energy. Intermittent fasting teaches your body to efficiently burn fat for fuel”explained Dr Mercola.(6)
Researchers also discovered that Periodic cycles of fasting reprogram new pancreatic cells to replace dysfunctional ones, restore insulin production and stabilize blood glucose. (7)
All these mechanisms help not only to decrease body weight but may also reduce inflammatory markers (C-reactive protein levels, tumour necrosis factor, interleukin-6) linked with age-related ailments such as heart disease and cancer. Normalizing insulin and reducing inflammation put naturally the body in “repair and rejuvenation programming” and may prolong your life. Here Growth Hormone plays a key role.
Fasting helps stimulate Growth hormone involved in tissue repair, fat loss and strong immunity
Our nutritional state is a major determinant of spontaneous rhythmic Growth hormone (GH) secretion. Growth hormone is vital for healthy growth and development of all our internal organs including the brain. During childhood It helps stimulate bones, muscles and cartilage; little GH result in slow growth of long bones and short stature. In adults, it is needed to maintain muscle and bone mass and for tissue repair. Growth hormone also helps regulate fat burning in the body by accelerating the breakdown of fatty tissue (lipolysis) which results in free fatty acids release used directly as source of energy, depleting naturally body fat.
Studies showed that fasting at least 12 hours resulted in increased Growth hormone secretion, concentration and peaks frequency. (8) This can directly promote the synthesis of lean muscle, while preserving muscle tissue and decreasing stored fat, resulting on effective weight loss.
Growth hormone also helps to regulate the immune response by stimulating T cell proliferation, important immune cells that protect the body from harmful invaders (bacteria, virus, parasites...).
In the meantime, fasting is believed to trigger autophagy, a vital process when basically the “body begins to eat itself” to clean up damaged cells and reduce the inflammatory response. (9)
Fasting may also prevent oxidative damage to cellular proteins, lipids, and nucleic acids associated with aging and disease. This may explain why people fasting claim to have a better skin and feel more energised. (10)
Fasting can improve cognitive functions and may prevent neurodegenerative diseases
Researcher and professor of neuroscience Mark Mattson (Johns Hopkins School of Medicine, US) explained that fasting is neurochemically a challenge to the brain and when the brain is challenged, either by cognitive and learning tasks, physically or by caloric restriction, the body produces specific chemicals that not only “strengthen existing neural connections and increase the production of new neurons but also have an anti-depressive effect”*. (11)
The fasted state increases the production of a protein called BDNF (brain-derived neurotrophic factor) critical for optimal brain function. When BDNF is released, new neurons and connexions form in the brain and support cognitive function including mood, productivity and memory performance. BDNF is also responsible for the survival of neurons and prevents apoptosis (brain cell death). During evolution, BDNF played a crucial role in increasing synaptic plasticity to stimulate alertness, focus and motivation. A part from calorie restriction and learning, exercise is another way to produce higher levels of BDNF and turn the brain on.
Now, because memory is basically formed by wiring of new neural network, BDNF stimulation may decrease the risk of neurodegenerative diseases like Parkinson and Alzheimer*. Matson also explains that fasting long more than 10 hours depletes our glucoses reserve stores (glycogen). Once there is no glucose available as source of energy for all cells, the body starts to burn fats. This mechanism explains again the weight loss results observed after fasting, but above all, the process of burning stored fats produces specific acidic chemicals called ketones bodies which are directly used by the neurons and are actually the preferred source of energy for the brain.
Ketones promote positive changes in the structure of synapses important for learning, memory, and overall brain health. This also explains the feelings of inner peace and emotional healing reported by people during fasting. Research is still ongoing but this can definitely generate novel prevention strategies to stimulate positive neuro-pathways and maintain healthy cognitive functions. (12)
Fasting is definitely a school and we still have a lot to learn. Increased difficulty and struggle always lead to more learning isn’t? Fasting is no exception and does shape your brain and your heart! Now, do not ruin all your fasting health benefits by eating afterwards processed foods and sugary drinks. Eat smart and hydrate yourself with a lot of filtered water to replenish all the nutrients your body needs. Practice mindful nutrition and mindfulness. Remember you are what you eat, what you drink but above all, you are what you digest, nutrients AND emotions. Challenge yourself, get out of your comfort zone, build the brain you want. In other words, take care of your overall health because in health there is freedom. And as Albert Camus wrote, freedom is nothing but a chance to be better.
*Caution: This article is not intended to diagnose, treat, cure or prevent any disease. We remind that if you suffer from a health condition especially diabetes, hypoglycaemia, chronic adrenal stress, cancer please always consult your physician before fasting.