Medically reviewed by Dr. Shunmukha Priya, Ph.D. in Food Science and Nutrition
Humans have adopted the practice of fasting since time immemorial and religious fastings are a classic example of this. Many scientists and experts in the past have come up with various fasting methods too. Over time, with the help of several studies and results, we saw the emergence of intermittent fasting – a fasting method that is now widely followed.
In this article, you will learn all about intermittent fasting, the various fasting methods involved in it and how can it be implemented safely, its pros, cons and its health impacts.
Table of content
- What is intermittent fasting
- Intermittent fasting benefits
- Methods of intermittent fasting
- Effects of intermittent fasting
- Healthy Alternatives to Intermittent Fasting
- Intermittent fasting for weight loss
- Pros and Cons
- How long can one stick to intermittent fasting?
- Intermittent fasting results
What is intermittent fasting?
Intermittent fasting (IF) is a popular fasting method where an individual will abstain from eating for a particular period of time. This period is usually for 12 hours and the individual should manage their meals accordingly. The window period for eating is about 8 hours.
When you search the internet, you will find numerous articles about intermittent fasting and how effective it is when it comes to weight loss. However, the effectiveness of this fasting depends on each individual and their metabolic rate. A number of studies have been conducted by reputed medical schools and research centres to establish the effectiveness of intermittent fasting.
A study published by NCBI in the year 2018, deduced that intermittent fasting works great for short term weight loss goals. The study conducted four methods: Alternate-day fasting (ADF), ADF combined with exercise, ADF with two ‘feast’ days and very low-calorie diet.
Most of the researchers arrived at the conclusion that intermittent fasting is quite effective for significant weight loss. However, the study pointed out the disadvantage of low-calorie consumption in the long run. The study noted that continuous calorie restriction leads to increased hunger and abnormal eating.
It is noteworthy that the study did not report any adverse effects of fasting. It also observed that the participants continued to eat mindfully even after the study since they were accustomed to the ADF method.
Intermittent fasting benefits
For us, intermittent fasting is not a new concept. Across the globe, during certain occasions, fastings are being encouraged. Fasting is not only practised for religious purposes but for general wellbeing as well.
Here are the benefits of intermittent fasting.
1. Great for heart health
A study published by the US NLM – NIH after experimenting on laboratory animals revealed that after the animals were introduced to intermittent fasting, they showed an increase in longevity, improvement in neurological disorders and reduction in diseases.
The study also observed cardiovascular benefits among animals such as improved heart rate, blood pressure, good circulation of triglycerides and cholesterol and reduction in carotid intima-media thickness.
Though the study’s conclusion is based on research conducted on animals, the results are quite positive.
2. Prevention and management of Diabetes
Studies indicate that there will be significant changes in insulin levels when you fast. The studies also noted that intermittent fasting improves type 2 diabetes.
Four ways to show how Intermittent Fasting may help in managing type 2 diabetes
- Usually, fasting is observed for 12-16 hours. This ‘no-food’ period allows the body to use the glucose instead of storing it.
- Since fasting decreases the amount of food consumption in a day, sugar levels in the body drop. This increases the body’s insulin sensitivity pushing the excess sugar from the blood.
- When you are fasting, your pancreas secretes a lesser amount of insulin. This reduces insulin levels.
- Intermittent fasting has been shown to help weight loss. This plays a key role when you are trying to manage type 2 diabetes.
Note: Though intermittent fasting holds a number of benefits, diabetic patients must observe fasting only after consulting their diabetologist.
3. Therapeutic fasting improves body cells
Studies have shown that intermittent fasting can improve body cells. Fasting initiates autophagy – a process in which cells are cleaned.
During this process, the cells get rid of metabolising proteins that are accumulated in the dysfunctional and broken cells. This process is beneficial for Alzheimer’s disease and certain cancers. 
4. Belly fat reduction
Intermittent fasting has also known to have reduced belly fat. As per a review published in 2014, people who observed intermittent fasting for 3 to 24 weeks have demonstrated a reduction in their waist circumference by 4 to 7%. 
5. Improvement in brain health
A couple of studies suggest that observing intermittent fasting can improve overall brain health and how they benefit are listed below.
- Studies show that intermittent fasting plays a key role in reducing oxidative stress. This is immensely important for promoting brain health. 
- As per the experiments done on rats, intermittent fasting might promote the development of nerve cells. 
- Similarly, intermittent fasting has shown to increase derived neurotrophic factor (BDNF) – a brain hormone.
4 Popular methods of intermittent fasting
1. The Leangains Method
This method suggests women and men fast for 14 and 16 hours respectively. They can eat during the remaining 8-10 hours.
Leangains Intermittent fasting table:
|Meals||Food To Eat|
|Early morning||Warm water with lemon juice|
Apple cider vinegar and warm water
Watermelon and lemon detox water
Green tea without sugar.
|Breakfast||One bowl of wheat flakes with milk|
Two pieces of lightly buttered wheat bread, milk, and one boiled egg white.
|Pre Lunch||An apple or an orange|
Raita or buttermilk
|Lunch||Two medium sized chappati with vegetable curry|
Fish curry, one bowl or rice, and salad
|Evening Snack||Green tea with two digestive biscuits.|
|Dinner||Two chapatis and one medium-sized bowl of daal.|
Two chapatis and chicken stew.
|Before Bed||A bowl of curd or a glass of warm milk.|
2. The Eat Stop Eat Method
In this method, you can take up fasting for 24 hours once or twice a week. During this fast, you will abstain from eating for 24 hours. However, you can consume calorie-free drinks in between. Once the fast is over, you can eat normally.
Submitted by: R Sindhu Vas
3. The Alternate-Days fasting
This method too suggests 24-hour fasting. Here, you will fast for 24 hours and resume eating for the next 24 hours.
4. The Warrior Diet
The Warrior Diet suggests fasting for 20 hours every day and having one large meal for dinner.
Ori Hofmekler, who was the brainchild behind the Warrior Diet suggests that the meal should consist of healthy fat, fibre-rich vegetables and protein-rich foods. If you are still not satiated you can include good and healthy carbohydrates.
The 14:10 and 5:2 intermittent methods have also gained immense popularity. In the 14:10 method, you should refrain from snacking post-dinner and skip breakfast the next day. On the other hand, the 5:2 method allows normal eating for five days but limits calorie intake to 500-600 for the other two days in a week.
Another most famous intermittent fasting schedule is 8 hours of eating and the 16 hours of fasting. This can either be followed in a go or can be spaced out throughout the day.
Diabetic patients, pregnant and breastfeeding women, people recovering from anorexia or bulimia and patients with cardiovuscular diseases must observe IF only under medical supervision.
Effects of intermittent fasting
Just like exercising and dieting, our body responds to fasting as well. When you fast, a number of things happen inside the body and these are listed below:
1. Breaking down of sugar
Your body breaks down the glycogen and stores glucose for energy.
2. Reaching the ketosis stage
Five to six hours after commencing the fast and depending on the glucose level in the blood, the body will reach a stage called ketosis which is a metabolic state. During this state, the energy levels in the body are supported by the ketone bodies that are present in the blood.
3. Uric Acid and cholesterol clean-up
Once the ketosis process begins, the body releases uric acid and cholesterol into the bloodstream. This is a part of the body’s detoxification process.
4. Giving rest to the digestive system
Since there is very little to no food intake during fasting, the body’s digestive system takes a little rest. However, the digestive system never stops from fully working. It rests a little only during prolonged fasting.
5. Detox to the mind and emotions
Six hours post the commencement of fasting, you will feel hungry and probably overwhelmed because of food deprivation. This feeling might give way to emotions like frustration, anger and even sadness.
However, it is important to tackle these emotions in a mature manner and remind yourself about the health benefits you will be gaining from intermittent fasting.
Intermittent fasting is mostly observed by people who are looking to reduce their calorie intake and reduce weight. Since fasting is about consuming food during certain hours and refrain from eating during the rest of the hours, this regulates unhealthy eating habits while allowing you to eat your daily calories during the eating period.
6 Healthy Alternatives to Intermittent Fasting
Though there are positive study results pertaining to intermittent fasting, anything in excess is bad.
If you are apprehensive about going without food for straight 16 hours, try these following methods instead.
1. Take it slow with calories
By dramatically cutting down the calories, you deny your body the much-needed minerals, proteins, vitamins and essential fatty acids. This can seriously damage your health.
It is important to provide the body nutrition-rich foods so it can function properly and have a good blood supply. Therefore, gradually cut your calorie intake.
If you are used to eating 2500 calories a day, bringing it to 2000 calories the next week. Ensure that you consume enough micronutrient-rich foods to get all the essential vitamins and minerals.
2. Include protein
A healthy diet should be rich in protein; it promotes weight loss and keeps the stomach full. Since protein satiates the stomach, you can avoid unhealthy snacking and eat a lesser portion of food for the next meal.
3. Abstain from refined carbohydrates and sugars
Refined carbs have the ability to raise the body’s blood glucose level quickly since they are simple carbohydrates. Refined carbohydrates, along with sugar causes bloating since they can retain water. Cutting out refined carbs and sugar can improve this. Likewise, avoiding fried foods can benefit your health as well.
4. Indulge in exercising
Exercise contributes to the body’s overall wellness and improves metabolism. Indulge in exercises that you love. It could be dancing, doing yoga, Pilates, cycling or brisk walking. Another important factor is sleeping well. Sleep rejuvenates your mind and restores the body and its cells.
5. Keep your body hydrated
Drinking plenty of water is important for body hydration. Water absorbs and transports nutrients to the body and maintains body temperature. It also promotes digestion.
6. Include red peppers
A study has revealed that red pepper has the ability to decrease hunger. Also, red peppers are rich in vitamin C and antioxidants. 
Intermittent fasting for weight loss
Studies have revealed that intermittent fasting has the potential to benefit people who are looking to lose weight in a healthier way.
Intermittent fasting helps weight loss using these 3 ways:
1. Upping the HGH function:
Our body can burn fat naturally since it is bestowed with fat-burning hormones and intermittent fasting plays a vital role in promoting the functions of these hormones, especially the Human Growth Hormone (HGH).
HGH burns body fat and derives energy that will be used for regular body fictions. Studies indicate that fasting promotes HGH by 2000% and 1300% in men and women respectively.
2. Bringing balance to the insulin levels:
As mentioned previously, intermittent fasting promotes a balance in insulin levels. These balanced insulin levels play a key role in weight loss. Insulin stores fat cells and prevent its release for energy.
However, this situation is altered during fasting. Since there is no new food consumed, the body has no choice but to use the stored fats in order to get energy. This paves way for weight loss.
3. Helps in reducing hunger:
During intermittent fasting, our body recognises the eating-period and somehow learns to deal with the fasting period. This has shown to reduce hunger pangs.
Intermittent fasting and body metabolism
Studies related to intermittent fasting and body metabolism had so far shown positive results. A study published by NCBI based on Energy Intake Metabolic unit had observed that modified and alternate fasting has reduced energy intake (food consumption) in adults. However, the studies are very limited and cannot draw a definite conclusion on how far intermittent fasting alters body metabolism.
Intermittent fasting pros and cons
The studies related to intermittent fasting that was done so far on humans had shown positive results. It is also important to bear in mind that these studies are limited and the studies that champion intermittent fasting were predominantly done on rats.
It is also worth mentioning that a blog published in ‘Harvard Health Publishing’ observed that food taken between 7 am to 3 pm and 10 am to 6 pm while fasting throughout the evening and night had better results. The article also insisted that one must refrain from snacking and eating in the evening to enjoy the full benefits of this fasting.
Here are some of the pros and cons that should be considered before intermittent fasting.
- Aids in weight loss since in intermittent fasting, the body uses the stored up fat cells for energy.
- Prevents diabetes and can reduce insulin resistance.
- A number of participants have reported a reduction in hunger and mindful eating.
- Prevention of cardiovascular diseases among other benefits.
- One of the major cons of intermittent fasting is, many indulge in unhealthy eating habits during the ‘feed days’. This reduces the effectiveness of the fast.
- Since intermittent fasting should be observed for at least 8 hours.
- The results did not indicate any benefits beyond the already existing ones that are gained from regular dieting.
How long can one stick to intermittent fasting?
The success of any weight loss plan depends on how long one can follow it in order to see any results and intermittent fasting is no different.
However, since it involves not eating for an extended period of time, following it on a regular basis can be challenging. While studies have indicated that it is safe to fast for a maximum of 24 hours, it is very important to take baby steps if you are a beginner.
Start by fasting for just 8 hours and slowly extended the time. Allow the body to adjust to your new eating habits and lifestyle.
Intermittent fasting results
Any kind of calorie reduction and diet method will help in weight loss and prevention of obesity. Similarly, cutting down snacks post-dinner will definitely have a profound effect on your health.
It is important to keep in mind that intermittent fasting should be done mindfully and one should not indulge in unhealthy foods during the feed days. This will nullify the effects of fasting.
Since there are no extensive studies on intermittent fasting with regard to humans, one cannot be sure about how feasible it’s in the long run. Nevertheless, healthy persons can adopt this fasting once a week for overall wellness.
Note: Before following any diets or taking up any fasting methods, we strongly suggest consulting a physician or nutritionist.
Q: How long should I do intermittent fasting?
A: If you are a healthy person and not on any medication, you can fast for maximum 24 hours with only consuming healthy liquids like water, tea/coffee. However, it is always best to talk to a nutritionist or physician before taking up fasting.
Q: Does intermittent fasting work for weight loss?
A: Yes, intermittent fasting helps in losing weight.
Q: Why am I not losing weight on intermittent fasting?
A: You may not see results if you binge on unhealthy food during your ‘eating hours’ and ‘feed days’. This makes intermittent fasting ineffective. Eat healthy, whole some foods to see better results. Changing the fasting methods can also help. Likewise, talking to an expert will help you figure out what you are doing wrong and rectify it.
Q: Can I do intermittent fasting every day?
A: Too much of anything is not good. It takes immense will power and determination to abstain from eating for more than 8 hours every day. This may lead to too much cravings. Also, while fasting, the body will be low on energy. It is better to talk to an expert to know how safe it is to take up intermittent fasting every day.
Q: Is intermittent fasting (IF) dangerous?
A: IF is not dangerous per se, but people with conditions like diabetes, cardiovascular diseases, pregnant and breastfeeding women should not observe fast without a doctor’s supervision.
Q: Is intermittent fasting good for health?
A: Fasting is generally good for adults. However, it is recommended that elderly people, people who are underweight and children avoid it.
Q: Can I lose weight by fasting?
A: Fasting restricts the overall calorie intake will help in weight loss. However, to observe a safe a healthy fasting, it is important to first discuss it with a doctor before taking up any fasting method.