Indians are well versed in the art and science of fasting – be it a religious fast or the one simply to lose weight or a hunger strike. This particular article seeks to offer an in depth understanding about the ‘new kid on the block’ – intermittent fasting. Intermittent fasting is exactly as the name suggests – you fast for some time then you stop fasting for a time and begin this cycle again. The obesity epidemic has spawned a cottage industry of weight-loss schemes. All diets achieve weight loss through the same equation – you take in less food energy each day than your body burns during normal activity. But intermittent fasting has also piqued the interest of the scientific community as seen by ongoing research studies.
Intermittent fasting is not a new concept. It has evolutionary basis. Hunters and gatherers followed intermittent fasting as a part of their lifestyle due to scarcity and uncertainty of food. Intermittent fasting is also said to have its roots in ancient Indian culture and labeled as a secret behind the long lifespan of sages. In some religions, intermittent fasting is followed during particular days of the year. is an excellent example of intermittent fasting.
In recent years, intermittent fasting has gained popularity due to its simplicity and effectiveness in reducing weight. It came into limelight after some celebrities like Chris Hemsworth, Hugh Jackman, Halle Berry, Jennifer Lopez and Nicole Kidman who gave credit of their body transformation to intermittent fasting.
Intermittent fasting explained
Intermittent fasting is to have some set periodic breaks from eating. In intermittent fasting, meals are consumed at defined time within a day or week. Intermittent fasting has raised interest as it gives liberty to eat anything during the specified period. When one eats, the food is converted to glucose at the end of digestion and utilized for different bodily processes. Some part of the glucose is stored in the body.
When one fasts, the glucose stores in the liver start breaking down. Liver has stores equivalent to 150 to 200 grams glucose. It takes about 12 hours to utilize these stores. After depletion of these stores, body starts using fats as a source for energy. This process is called ‘metabolic switching’. Metabolic switching leads to fat loss and ketone bodies are produced as a by-product. Ketone bodies are ascribed to impart various health benefits. Along with fat loss and ketone body formation, Intermittent fasting produces various metabolic changes in the body which are
discussed further in this article. The popular 3 meals per day plan or so called ‘small frequent meals’ plan cannot lead to this metabolic switch. Therefore such plans don’t offer benefits other than weight loss.
Intermittent fasting methods
Intermittent fasting does not advocate omission or inclusion of any specific food group or nutrient. It simply modulates meal timings. There are different methods of intermittent fasting. Following are the common ones:
Time restricted feeding (TRF): Eating for 8 hours, fasting for 16 hours
The easiest way to follow the 16:8 diet is to choose a 16-hour fasting window that includes the time that a person spends sleeping. Food should ideally be consumed by early evening, as metabolism slows down after this time. People usually choose an 8-hour eating windows like 9 a.m. to
5 p.m. or 10 a.m. to 6 p.m. or noon to 8 p.m. Within this timeframe, people can eat their meals and snacks at convenient times. If you start eating at: 9 am, stop eating and start fasting at 5 pm. If you start eating at: 11 am, stop eating and start fasting at 7 pm. If you start eating at: 2 pm, stop eating and start fasting at 10 pm. Eating regularly is important to prevent blood sugar peaks and dips and to avoid excessive hunger.
Periodic prolonged fasting (PPF): Fasting for 24 hours once or twice in a week.
Alternate day fasting (ADF) This is generally called 5:2 pattern (5 days of normal eating, 2 days of fasting / consuming only 500 to 600 calories per day).
Alternate day fasting diet is eating normally every alternate day and fasting or taking only few hundred calories on alternate days. Beginners can start gradually and increase the fasting window over a period of several weeks from 10 hours with aim to achieve 16 to 18 hours of fast per day. In 5:2 or ADF pattern, fasting can be practiced once a week initially and when accustomed, it can be increased to twice or thrice a week. It gets easier over time. But consistency is the key.
Breaking the fast
Intermittent fasting involves alternate fasting and re-feeding states. It is important to have a well-balanced and nutritious diet in the re-feeding state (while breaking the fast). A nutritious diet will further improve functioning of cells which have undergone clean-up process during fasting. Break the fast with small portions of foods which are easy to digest. Do not take foods that are very high in fibre at this time. It may lead to bloating. In the later part of the feeding state, include plenty of vegetables, pulses, beans, whole grains and plant fat sources.
Don’t break your fast with sugary, fatty, starchy and refined foods. This will do more harm than good as it can lead to sugar spikes. Avoid packaged and processed foods. It’s very common to overeat after the fasting period. But one should be mindful while breaking the fast as overeating and eating junk foods can reverse the effects of intermittent fasting. It is also important to have a healthy lifestyle while following intermittent fasting. Smoking and alcohol consumption should be avoided.
Your cells and hormones
During intermittent fasting, insulin levels drop and body becomes more insulin sensitive. This leads to improved glucose profile in people with Diabetes and cuts the risk of developing Diabetes in those who are at risk. Lower insulin level benefits our body in many ways. It reduces inflammation in the body, helps protect against various cancers and signals autophagy. Autophagy is an important process in our body meant for cellular rejuvenation. It literally means ‘eating our own body parts’. During this process damaged cellular components including proteins are removed and recycled. Autophagy can protect the brain against some degenerative diseases.
Ketone bodies are also produced during intermittent fasting indicating that fat is being used as a fuel. Ketones serve as an alternate energy source for brain in the fasting period. It is observed that ketone bodies in mild concentration are linked to alertness, positive mood and mental clarity!
Ketone bodies and ghrelin (hunger hormone) together promote growth hormone production inside the body.Growth hormone further preserves muscle mass and prevents fat deposition. It also has connections with repair mechanism, longevity and cardiovascular wellbeing.
Intermittent fasting and weight loss
Studies show that intermittent fasting initiates and accelerates weight loss. The mechanism is simple. Due to specific periods of fasting, total
daily calorie consumption is reduced leading to weight loss. Whereas due to the metabolic shift, the body uses the fat as fuel resulting in fat loss.
Intermittent fasting leads to a reduction in insulin secretion and an increase in the secretion of growth hormone as well as norepinephrine.
These hormonal changes aid fat loss. Further, fasting also triggers secretion of a protein called fasting induced adipose factor (FIAF) by liver and gut bacteria. FIAF also signals fat burning process.
Health benefits of intermittent fasting
Apart from weight and fat loss, intermittent fasting offers following health benefits:
It is found to control blood sugar levels due to improved insulin sensitivity.
It increases resistance to stress, intermittent fasting improves longevity.
It suppresses inflammation and oxidative stress.
It improves blood pressure and blood cholesterol levels within 2 to 4 weeks.
Intermittent fasting also improves resting heart rate.
It improves memory and brain health by elevating levels of brain derived neurotrophic factor (BDNF). Intermittent fasting is found to delay the onset and progression of Alzheimer’s disease and Parkinson’s disease in animal models.
It improves cancer treatment. Cancer cell particularly survive on glucose and cannot utilize proteins for energy. Therefore intermittent fasting inhibits growth of cancer cells. These cancer cells can be easily killed during chemotherapy or radiation if the person is fasting.
It has been found to modulate gene expression related to immunity and longevity resulting in prolonged lifespan in animals.
Intermittent fasting is not for those who are grossly underweight as it can lead to further weight and fat loss. Children, pregnant and breastfeeding women and endurance athletes should also avoid intermittent fasting. These populations have increased nutritional requirements and intermittent fasting can be restrictive.
Intermittent fasting has been found to be associated with eating disorders like bulimia nervosa. Therefore those at risk of developing eating disorders (with family history of eating disorders etc) should avoid intermittent fasting.
Elderly, people taking treatment for Diabetes (insulin or oral hypoglycaemic agents) and those who are on any other medications need to be more careful while following intermittent fasting. Some medications need to be taken with food. Anti-diabetic medications like sulfonylureas
may cause hypoglycaemia if food is not taken on particular time. Therefore, it is advisable to consult a doctor and a certified dietician before starting intermittent fasting and check whether any change in medications is required. Routine health check-ups are also recommended for
people with Diabetes, hypertension, kidney or thyroid problems while following an intermittent fasting diet plan.
While switching from regular or multiple meals diet to intermittent fasting, most of the people will experience symptoms like severe hunger, hyperacidity, headache, irritability, tiredness and lack of concentration. However these initial symptoms fade away within a month. Other
side effects include disturbed sleep pattern and overeating during feeding periods. The person intending to follow intermittent fasting regimen should be made aware of these facts. It is also advisable to start intermittent fasting gradually over a period of several weeks. Time window for eating period can be gradually reduced and that of fasting period can be gradually increased.
This helps the person cope up with hunger issues. Breakfast has been considered the most important meal of the day. It is believed that skipping breakfast results in excessive hunger and food cravings. Though it might be true for children and teenagers, breakfast is not essential for healthy adults. Controlled studies have found no association between breakfast and weight reduction.
Can liquids be taken during the fasting period?
During the fasting state, many face strong hunger pangs especially in the first few days of initiation. During such times, water can be taken abundantly. Experts advocate if one keeps calorie intake below 50 calories during fasting state, he can still avail benefits of fasting. So some non caloric or minimal caloric beverages can be consumed during fasting state. Green tea, green coffee, black coffee – ideally these beverages should be consumed without sugar and milk. In case of excessive hunger, small amount of milk (preferably almond or coconut milk) or a
teaspoon of coconut oil/butter/cream can be added. Other permissible fluids include diluted apple cider vinegar, lime water, water) mint water, clear vegetable broth or bone broths. Though fat in cream or oils or bone broths break the fast, they will still allow the person to remain in ketosis. Beverages with artificial sweeteners are best avoided as they are found to evoke insulin response.
Are supplements required with an intermittent fasting regime?
Nutrient deficiencies are less common during intermittent fasting as this regime does not recommend any restrictions on food choices. If the fasts are prolonged and restrictive, deficiencies can be seen and supplementation is needed. While choosing supplements, one must be careful. Some supplements contain sugar and calories. They can break the fast. Protein powders or BCAA supplements can trigger insulin response and oppose autophagy. Some supplements are better absorbed when taken with food, so should be avoided in the fasting state. It is always better to consult a nutritionist to know whether you need any supplements, right type of supplements and appropriate time to take the supplements while on intermittent fasting.
Can I work out while fasting?
Fasting and workouts may sound incompatible but with right planning, intermittent fasting and workouts can be clubbed together. Workouts can accelerate the most important benefit of intermittent fasting – ‘fat burning’. At the same time, workouts would help preserve muscle mass.
It is recommended that obese people following intermittent fasting can schedule their workouts (especially low intensity cardio workouts) during fasting period. This will facilitate fat loss but in such a scenario there is a chance to lose some muscles too. Exercising empty stomach also affects energy levels and performance. If the exercise is planned in the fasting state, it is better to plan it at the end of the fasting window. This allows the person to have post workout meal (as a first meal in feeding window) leading to better recovery. For those who are following intermittent fasting but are not obese, it is recommended to plan workouts during feeding window. This takes care of bothpre and post workout meals. Best bet is to plan cardio sessions in the fasting window and weight lifting sessions in the feeding window!
Dehydration is common during workouts if the person is on intermittent fasting. Therefore it is very important to stay hydrated during exercise sessions. Lime water with little salt is a better option than plain water to have during workouts. Listen to the body. If workouts in fasting state lead to symptoms like light-headedness, dizziness, fainting etc, take a break. Have carbohydrate electrolyte drink followed by a meal. If symptoms recur or persist, it is recommended to change workout time and intensity with proper guidance.
Will fasting lead to muscle loss?
Studies show that intermittent fasting helps maintain the muscle mass. Some studies have reported that intermittent fasting causes similar weight loss as other calorie restriction methods but with less impact on muscle mass.
Will fasting slow down metabolism?
It is believed that eating boosts metabolic rate. This is true. When a person eats, there is slight increase in the metabolic rate (thermic effect of food). This is attributed to energy expenditure that occurs during digestion, absorption and assimilation of food. On an average, thermic effect of food accounts for 10 per cent of daily energy expenditure. It has been seen that thermic effect depends on total energy consumed throughout the day and not on number or frequency of meals. So, intermittent fasting does not affect thermic effect and metabolism as far as the person is taking similar calories. Fasting of up to 48 hours has rather shown positive impact on metabolism. Fasting for longer than 48 hours can slow down metabolism.
What scientific research says
Intermittent fasting has broad spectrum benefits for many health conditions, claims a latest review in the. The health conditions listed range from obesity, Diabetes, cardiovascular disease to cancers and neurological disorders. Intermittent fasting improves multiple indicators of heart health, including blood pressure, resting heart rate, levels of high-density and low-density lipoprotein (HDL and LDL) cholesterol,triglycerides, glucose, insulin and insulin resistance. In addition, intermittent fasting reduces markers of systemic inflammation and oxidative stress that are associated with heart disease. Preliminary studies have shown that people who have asthama, multiple sclerosis and rheumatoid arthritis may benefit with intermittent fasting. Intermittent fasting, when done correctly, could benefit people but it is not an easy dietary pattern to adopt. We are told since childhood that breakfast is the most important meal of the day. An eating culture of 3 to 4 meal in a day is so ingrained that changing this meal pattern is rarely perceived as helpful by anybody. Often intermittent fasting regimen may result in hunger pangs, irritability and a reduced ability to concentrate during periods of food restriction. Doctors and dieticians rarely advise intermittent fasting. The usual advice is to eat less more frequently.
Review of research highlights that the studies conducted on intermittent fasting so far focus primarily on obese and middle aged adults. So these findings should be taken with a pinch of salt especially while generalizing to other populations.
Intermittent fasting can be considered as a potential approach along with physical activity and healthy food choices to improve health and well-being. But one must remember that one size does not fit all. Intermittent fasting may work for some individuals excellently and may not work
that effectively for others. Nutrition is all about individualisation. So, take guidance from qualified experts, experiment, evaluate and learn what works best for your body! While the intermittent fasting diet plan does not restrict any foods, diet should mainly include healthy foods and limit or avoid junk foods. A balanced diet focuses primarily on:
Fresh fruits and vegetables.
Whole grains like whole wheat, brown rice and millet like ragi and varai.
Lean protein sources, such as poultry, fish, beans, lentils, tofu, nuts, seeds, low fat cottage cheese and eggs.
Healthy fats from fatty fish, olives, coconut, avocados, nuts and seeds.
Note : It is best practice to seek expert advice and consult your doctor and dietician before starting or modifying eating patterns. If you have any health condition like Diabetes, hypertension, heart or kidney disease, etc then routine health check-ups are recommended. These check-ups should also assess for nutritional deficiencies. Ensure that you undergo routine health check-ups to maintain your quality of life. Speak with your doctor to find out if you can switch to intermittent fasting based diet. It is best to consult a registered dietician to understand the daily nutrient requirement to best suit your health parameters. Dieticians can also provide guidance with food substitutions or supplements to suit your personal preferences and lifestyle. If you are pregnant or planning a pregnancy, it is best to consult a doctor prior to modifying your diet or changing eating patterns. For growing children and elderly consult a doctor and dietician before switching diets.