The practice of Intermittent Fasting, or IF, has grown in popularity. It consists of eating and fasting windows and is regarded as an efficient way to lose weight that doesn't require exercise. This guide will go over the definition of intermittent fasting (IF), its types, its mechanisms, possible side effects, and precautions to follow when implementing IF.
What is Intermittent Fasting?
Intermittent Fasting (IF) is a diet routine that cycles between periods of fasting and eating. It is about reducing calories for short periods and not starving. The primary focus of intermittent fasting is on the timing of meals rather than the types of foods consumed. It also changes the body structure through fat loss, mass, and weight. The body’s main energy source is glucose, which is obtained from carbohydrates like sweets, fruits, vegetables, and grains. It is stored in the liver and muscles and released into the bloodstream accordingly.
Since ancient times, it has been utilized and existed as part of the major cultures. Even today, it is one of the world’s most popular health and fitness trends and is performed by many celebrities and health enthusiasts.
Types of Intermittent Fasting
Intermittent fasting patterns cannot be followed randomly. There are different types of intermittent fasting and people can follow what they want.
The 16/8 Diet
It involves eating food and drinking beverages within 8 hours of eating window per day. In the rest 16 hours i.e., fasting hours no food or beverages can be consumed excluding water. Intermittent fasting has gained popularity as it is easy to lose weight and burn fat.
To do this, one has to choose a time window. Increased weight loss and improved blood sugar control are benefits of this diet.
First, select your eating window time like 7 am to 3 pm, 9 am to 5 pm, 12 pm to 8 pm, etc., After you start for a few days you may experience side effects such as hunger, weakness, and fatigue until you get habituated to it. If you want to do it begin with doing twice a week.
The 5:2 Diet
This diet is also known as The Fast Diet. It includes five days of eating and two days of calorie restriction of 500-600 per day in a week. On these five days no need to think about calorie intake you can eat how much you want but on the other two days you can only eat 500 calories for women and 600 calories for men per day.
There are two patterns: Three small meals and two big meals. Focus on high-fibre, high-protein foods that make you full without eating many calories. On fast days soups are a great option. It's normal to feel weak and slow during this diet in the first few days. People with eating disorders, malnourished or underweight should avoid this diet.
In this diet, you have to fast 24 hours for 1 or 2 nonconsecutive days in a week. For the remaining days, you can eat whatever you want but try to consume healthy food like green leafy vegetables, fresh fruits etc, whole grains, etc., and ensure proper hydration. You can also consume calorie-free beverages like coffee or tea.
If you want to lose weight simply without any rules about food or calories choose this diet. The only rule is that 2 days you have to fast 24 hours in a week. It helps reduce calorie intake, shifts metabolism into fat-burning mode, and reduces weight.
The other name for this diet is The Every Other Day Diet. In this diet, you fast every other day and you can freely eat on nonfasting days. You are allowed to consume 500 calories or 20-25% of your energy requirements on fasting days. During fasting days you can drink calorie-free beverages like water, tea, unsweetened coffee, etc.,
The Warrior Diet
This diet starts with 20-hour fasting that starts overnight and continues into the next day with a 4-hour eating window. It got its name based on the eating habits of ancient warriors and modern soldiers. During the eating window choose nutritious foods. Drink plenty of water.
If you do it for three weeks, in the first week detoxification of the body takes place as you consume lots of veggies, whole grains, and some dairy. In the second week body’s ability to use fat for energy improves. In the third week carbs are used for energy. If you feel hungry drink water, coffee, or other low-calorie beverages. Adding raw fruits, vegetables, hard-boiled eggs, and dairy products is good for health.
How Does Intermittent Fasting Work?
To know how fasting works, you need to know that food was not abundant in ancient times and humans used to fast involuntarily. Due to this condition, humans adapted cycles of eating and fasting. Intermittent Fasting increases the production of brain-derived neurotrophic factor (BDNF), a protein that supports the survival of old neurons and enhances the growth of new neurons and synapses. This increase in BDNF levels through fasting can lead to improved cognitive function, learning, and memory.
- When you don't eat food your body utilises the stored sugar in the liver to continue to balance your blood sugar levels in normal range. Now you are in a breakdown state.
- After you enter the fasting state, the sugar gets utilised which triggers the liver to produce more glucose from noncarbohydrate sources. When carbohydrates are not consumed, the body creates its own from fat. This is the body’s transition into ketosis.
- In intermittent fasting, the body’s shift from using sugar to fat and ketones is done by the metabolic switch. Your body breaks down fat and stimulates the liver to create ketones from fat for energy. The metabolic switch occurs between 12 and 36 hours after eating.
- If you extend fast for more than 36 hours then the body stops using the sugars and metabolism slows down.
- When metabolism slows down you burn protein but not fat for energy.
How to Start Intermittent Fasting?
To start Intermittent Fasting there are a few steps:
Step 1-Choosing a fasting method
There are many methods like the warrior diet, 16/8 diet, 5:2 diet, alternate day and eat stop repeat fasting.
Step 2-Set goals
Whether you want to lose weight or improve your metabolism.
Step 3-Plan your eating window
If you choose 16/8 your eating window is 8 hours.
Step 4- Stay hydrated
Drink lots of water, herbal tea, or black coffee.
Step 5-Healthy food choices
Eat nutrient-rich foods and avoid processed foods.
Step 6-Listen to your body
When you are feeling hungry make sure to eat immediately don't wait.
Step 7-Avoid excessive consumption of coffee
More caffeine in coffee leads to disturbed sleep.
Step 8- Stay flexible
Don’t change your timings of feasting or fasting window as it may lead to irregularity and you cannot see any changes.
Potential Side Effects
Intermittent Fasting provides health benefits but also causes side effects such as hunger, headaches, malnutrition, poor sleep, etc. To reduce these side effects one has to plan his or her diet accordingly.
Hunger and Cravings
Hunger is a common side effect of intermittent fasting. When we decrease calorie intake, we tend to feel more hungry. The intake of protein-rich foods helps in maintaining blood sugar levels and controlling appetite.
Cravings involve snacking on unhealthy items, which can lead to weight gain. They are normal but depend on the type of food we choose to eat. Chronic stress, fatigue, and dieting can make you crave foods that stimulate your brain to eat more. To stop cravings, eat small meals and consume plenty of fibre to help you feel full.
Headaches can occur after prolonged fasting for 16 hours or more, and they are often associated with low blood sugar levels. The good news is that these headaches typically resolve within 72 hours if you resume eating. Fasting headaches can resemble migraines in some ways, and fasting can indeed trigger migraine attacks.
Fasting headaches are typically felt in the frontal region of the head, and the pain is usually nonpulsating. Dehydration can contribute to headaches during extended fasting periods because your fluid intake primarily comes from the food you consume.
Good quality sleep also is necessary during intermittent fasting. The time of the meals can disrupt sleep and trigger unwanted changes in body temperature, alertness, and mood.
Eating before bedtime can increase body temperature making it difficult to sleep.
Irregular eating schedules also affect the body’s circadian rhythms which make not to fall asleep. Fasting also causes a dip in melatonin which plays a key role in sleep patterns. It increases energy and adrenaline levels Create a sleep routine and environment that makes you sleep.
Intermittent fasting leads to digestive symptoms such as constipation, diarrhoea, nausea, and bloating. The reduction of food intake and dehydration cause constipation. Eating too much food at a time can cause diarrhoea as large amounts of food require more time to digest. This puts pressure on the gastrointestinal tract leading to improper digestion and constipation. Intake of less carbohydrates also causes constipation.
Bad breath also known as halitosis is a common symptom of fasting. When fasting ketones are released, the chemicals that are produced when fat breaks down into energy. When these ketones mix with bacteria in the mouth bad breath is caused. Dehydration also leads to bad breath.
During dehydration, the mouth becomes dry and causes the release of more ketones. Fasting also decreases saliva production. Saliva is essential to cleanse the mouth and prevent bacterial growth. Reduce the intake of foods like garlic and onion which give you a smelly mouth.
The feeling of tiredness or lack of energy is called fatigue. It is a common symptom of intermittent fasting which is experienced at the beginning of fasting. It is due to the body adapting to a new eating pattern. As you get habituated to fasting, there's a chance of increasing energy levels and to minimize fatigue it's important to get enough sleep, stay hydrated, and eat nutrient-rich foods.
At the beginning of intermittent fasting, individuals get irritated easily, and their mood changes within minutes. This is related to fluctuations in blood sugar levels and hunger. It takes time for an individual to get adapted to intermittent fasting. As we fast, serotonin levels decrease and cortisol levels increase causing continuous mood swings.
Less intake of nutritious food leads to malnutrition. The symptoms of malnutrition include reduced appetite, feeling weak, poor concentration, feeling tired all the time, etc., An individual should meet his calorie requirements every day to avoid malnutrition and plan your diet accordingly.
Changes in menstrual cycle
Extended fasting (36 hours or longer) may cause irregular periods; however, most women should be able to tolerate a shorter fasting window. Make sure your eating window is long enough for you to ingest enough calories to maintain optimal health if you practice intermittent fasting. For most women, a 16-hour fast is ideal since it allows you to feel the benefits of weight loss if that is your objective.
If you want to do intermittent fasting, there are certain precautions so that you don't harm your body.
- Don’t fast for more than 24 hours as it leads to dehydration, mood swings, fainting, and fatigue.
- Eat a healthy and well-balanced diet during the eating window. Add complex carbohydrates like brown rice to feel full for a long time, fruits, and vegetables.
- Dont binge eat.
- Drink at least 8 cups of water every day for hydration.
- Patients with kidney problems, liver cirrhosis, low blood pressure, eating disorders, etc., are not allowed to do this fasting.
- Avoid pregnant or breastfeeding women.
Benefits of Intermittent Fasting that have been discovered so far through the study
Several studies when done on animals have shown that IF is linked to reducing stress, preventing obesity, lowering cholesterol levels, etc.,
All organ systems respond adaptively to intermittent fasting, which enables the body to overcome obstacles and regain balance. Frequent fasting exposure results in long-lasting adaptations that offer responses to various stresses. In response to periodic fasting, cells initiate a coordinated stress response that leads to increased expression of systems for DNA repair, antioxidant defence, protein quality maintenance, mitophagy, and autophagy. Consequently, an organism's cells operate better and withstand a variety of potential stresses, such as metabolic, oxidative, ionic, physical, and proteotoxic stress (Mattson & Arumugam, 2018).
Obesity and Diabetes
Studies on animals have shown that intermittent fasting improves insulin sensitivity and prevents obesity. On the island of Okinawa, people often follow a low-calorie, high-nutrient diet and engage in intermittent fasting. As a result, obesity and diabetes rates are low and life expectancy is high. In a similar vein, people who adhere to the CRON (Calorie Restriction with Optimal Nutrition) diet recommended by the Calorie Restriction Society have a lower incidence of diabetes, lower levels of insulin-like growth factor 1, and lower levels of oxidative stress and inflammation.
Daily calorie restriction improves cardiometabolic risk factors in non-obese people, according to multiple clinical trials. Studies conducted on adults who are overweight or obese over a brief time have shown that intermittent fasting is just as effective at helping people lose weight as regular diets (Fontana et al., 2004),(Most et al., 2017).
Intermittent fasting has shown positive effects on cardiovascular health in both animals and humans. It improves processes that include blood pressure, heart rate, cholesterol levels (HDL and LDL), triglycerides, glucose, insulin, and insulin resistance. Additionally, intermittent fasting helps reduce inflammation and oxidative stress linked to atherosclerosis (Harvie et al., 2013; Moro et al., 2016).
Studies have shown that intermittent fasting can enhance heart rate variability by boosting parasympathetic activity, benefiting both rats and humans (Mager et al., 2006), (Stein et al., 2012). The CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) study revealed that a 12% reduction in daily calorie intake over two years led to improved cardiovascular risk factors in non-obese individuals (Rochon et al., 2010),(Ravussin et al., 2015). Alternate-day fasting has been found effective for weight loss and heart protection in normal-weight and overweight adults. These cardiovascular health improvements usually manifest within 2 to 4 weeks of starting alternate-day fasting and tend to diminish over several weeks after returning to a regular diet.
Alternate-day fasting can delay the progression of diseases such as Alzheimer’s and Parkinson’s disease. Intermittent fasting increases neuronal stress resistance by boosting mitochondrial function, inducing autophagy, antioxidant ability, and DNA repair. It also improves GABA levels and prevents seizures. (Liu et al., 2019)
Asthma, Multiple Sclerosis, and Arthritis
Several health issues have shown promise when intermittent fasting is used. Over two months, obese asthmatic patients who adhered to an alternate-day fasting routine lost weight and experienced symptom improvement. Decreased oxidative stress indicators and inflammation were associated with this improvement. Periodic cycles of calorie restriction and alternate-day fasting enhanced outcomes and decreased autoimmune demyelination in a multiple sclerosis-modeling mouse.
Additionally, patients with multiple sclerosis who fasted intermittently reported a reduction in symptoms in as little as two months, according to recent pilot trials. There is evidence to support the use of intermittent fasting as a treatment for rheumatoid arthritis, as it has the potential to reduce inflammation (De Toledo H Müller, 2001).
Intermittent fasting is considered safe and offers various benefits, such as improving heart health, promoting weight loss, regulating blood sugar levels, and preventing neurodegenerative diseases. However, it also comes with side effects, including hunger, cravings, and headaches. It is essential to consume nutrient-rich foods during the eating window, including fruits, vegetables, and proteins, while avoiding packaged and processed foods. Several studies have shown that intermittent fasting can help prevent obesity, improve cardiovascular system function, and reduce inflammation.
Mattson, M. P., & Arumugam, T. V. (2018). Hallmarks of brain aging: adaptive and pathological modification by metabolic states. Cell metabolism, 27(6), 1176-1199.
Fontana, L., Meyer, T. E., Klein, S., & Holloszy, J. O. (2004). Long-term calorie restriction is highly effective in reducing the risk for atherosclerosis in humans. Proceedings of the national Academy of Sciences, 101(17), 6659-6663.
Most, J., Tosti, V., Redman, L. M., & Fontana, L. (2017). Calorie restriction in humans: an update. Ageing research reviews, 39, 36-45.
Harvie, M., Wright, C., Pegington, M., McMullan, D., Mitchell, E., Martin, B., ... & Howell, A. (2013). The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. British Journal of Nutrition, 110(8), 1534-1547.
Kroeger, C. M., Klempel, M. C., Bhutani, S., Trepanowski, J. F., Tangney, C. C., & Varady, K. A. (2012). Improvement in coronary heart disease risk factors during an intermittent fasting/calorie restriction regimen: Relationship to adipokine modulations. Nutrition & metabolism, 9, 1-8.
Mager, D. E., Wan, R., Brown, M., Cheng, A., Wareski, P., Abernethy, D. R., & Mattson, M. P. (2006). Caloric restriction and intermittent fasting alter spectral measures of heart rate and blood pressure variability in rats. The FASEB Journal, 20(6), 631-637.
Stein, P. K., Soare, A., Meyer, T. E., Cangemi, R., Holloszy, J. O., & Fontana, L. (2012). Caloric restriction may reverse age‐related autonomic decline in humans. Aging cell, 11(4), 644-650.
Rochon, J., Bales, C. W., Ravussin, E., Redman, L. M., Holloszy, J. O., Racette, S. B., ... & Kraus, W. E. (2011). Design and conduct of the CALERIE study: comprehensive assessment of the long-term effects of reducing intake of energy. Journals of Gerontology Series A: Biomedical Sciences and Medical Sciences, 66(1), 97-108.
Ravussin, E., Redman, L. M., Rochon, J., Das, S. K., Fontana, L., Kraus, W. E., ... & CALERIE Study Group. (2015). A 2-year randomized controlled trial of human caloric restriction: feasibility and effects on predictors of health span and longevity. Journals of Gerontology Series A: Biomedical Sciences and Medical Sciences, 70(9), 1097-1104.
Liu, Y., Cheng, A., Li, Y. J., Yang, Y., Kishimoto, Y., Zhang, S., ... & Mattson, M. P. (2019). SIRT3 mediates hippocampal synaptic adaptations to intermittent fasting and ameliorates deficits in APP mutant mice. Nature communications, 10(1), 1886.
Müller, H., de Toledo, F. W., & Resch, K. L. (2001). Fasting followed by vegetarian diet in patients with rheumatoid arthritis: a systematic review. Scandinavian journal of rheumatology, 30(1), 1-10.
1) Does Intermittent Fasting Work?
Yes, Intermittent fasting works when taken with the right amount of nutritious food, and with IF one can lose weight easily up to 2kg a month. It is more effective and uses fat for energy. It preserves muscle mass while targeting fat loss and leads to healthy eating habits.
2) Can you drink water during fasting?
Yes, you can drink water during fasting. A minimum of 8 glasses of water should be taken. Our human body is made up of 60-70% water, so drinking and staying hydrated is crucial for better physical and mental performance, digestion, and kidney functions.
3) Can IF be combined with specific diets (e.g., keto)?
It is possible to combine intermittent fasting (IF) with particular diets, including the ketogenic diet (keto). When combined, these two dietary strategies can strengthen one another and possibly provide some advantages. Reduced appetite, increased energy levels, reduced fatigue, more nutrition, etc., are some of the advantages of combining IF with other diets.
4) How long should one follow IF to see results?
It takes around 2 to 4 weeks to see or feel any results. In this period, your body switches from using glucose for energy to using fat for energy. It will take your body a while to get habituated to this eating pattern. One can easily shed up to 3 to 5 kilos by following the diet properly for some time.
5) What to eat and what to avoid during fasting and eating windows?
In the fasting window, you are allowed only to drink water and black coffee. In the eating window, you can eat the following:
Fruits - apples, bananas, berries, oranges, pears, etc.
Vegetables - broccoli, cucumbers, green leafy veggies, cauliflower, etc.
Whole grains - barley, quinoa, rice, oats, etc.
Healthy fats - olive oil and avocados
Protein sources - eggs, legumes, meat, poultry, seeds, nuts, etc.
Avoid processed foods like snacks, deep-fried foods, and sugary beverages.