Fasting was initially a ritual followed during many festivals. But if you see it in terms of nutrition it is a form of calorie restriction.
However, in this case, you don’t typically count the calories or decide what type of nutrient to include in your diet.
You just abstain from eating for a certain interval of time.
Intermittent fasting is a technique derived from the practice of fasting in order to regulate eating habits and induce the body’s metabolism to make efficient use of resources and stores.
Scientists are looking forward to this as a new weight loss tool.
However, this type of fasting does not mean that you have to starve yourself for some period. Let's find out more about this.
Table of Contents
- What is Intermittent Fasting?
- How does Fasting Work?
- Does Intermittent Fasting Work For Weight Loss?
- 1. Intermittent fasting burns fat rapidly in normal and overweight individuals
- 2. Fasting elevates the level of glucagon and growth hormone in order to get rid of body fat
- 3. Fasting alters glucose and fat metabolism
- 4. In alternate day fasting, the time of meal on fast day does not matter
- 5. Alternate day fasting with high-fat diet is as effective as alternate day fasting with a low-fat diet for weight loss
- 6. Intermittent fasting combined with calorie restriction improves weight loss and heart health in obese women
- 7. Intermittent fasting increases longevity and reduces the risk of other diseases
- Intermittent Fasting versus Dieting: Who wins?
- Different Techniques of Intermittent Fasting?
- What is the impact of Exercise on Intermittent Fasting?
- Does intermittent fasting affect performance or cognitive performance?
- Are there any drawbacks or precautions linked with intermittent fasting?
- Research Study
What is Intermittent Fasting?
A common definition you will find all over the net is: ‘Intermittent fasting is not a diet, it is a pattern of eating.’
And indeed that is the best part about this weight loss intervention.
You don’t have to literally count your calories you just have to observe the time you consume it.
Intermittent fasting involves severe calorie restriction ( 0-25% of individual’s daily calorie intake) for a period of 16-24 hours followed by a normal energy intake for 8-24 hours depending on the type of intermittent fasting you chose.
Intermittent fasting typically involves periods where you don’t eat food followed by periods when you are allowed to eat foods.
There is no such restriction of the type of food you eat but eating healthy food is always a plus point.
What this technique does is it makes your body utilize the food you consume efficiently.
Also since you are limiting the time you eat, you are in turn limiting your calories.
This puts your body in a calorie deficit which forces it to make use of stored fat.
How does Fasting Work?
It is pretty logical to think that if you are not eating anything you will lose weight eventually.
But a number of things occur simultaneously to give you that result.
We are typically going to investigate how the old school definition of fasting impacts our body.
An old study dated back to 1982 pretty much describes everything that goes on in your body during a fast.
In this study, the fast was to be conducted for 40 days with little or rather negligible calorie intake (we do not advise this We are quoting this study to explain the mechanism of fasting).
However, the individual completed 36 days of the fast at the end of which he started experiencing weakness.
At the end of 36 days he lost 22.9 % of initial weight.
The rate of weight loss initially was 0.9kg per day and gradually stabilised at 0.3 kg per day in the third week.
For the first 18-24 hours of fasting, liver glycogen is depleted.
Glycogen is the form in which we store glucose.
Protein constitutes 15% of total body energy stores and muscles have glycogen but they cant release glucose immediately into the blood stream.
Fat reserves, on the other hand, constitute 85% of the body’s total energy, thus making them the easiest accessible form of energy.
Initially the glucose levels drop and insulin levels drop correspondingly.
However, glucagon, a hormone that acts exactly opposite to that of insulin is raised. The change in form of energy occurs in three phases:
- Initial 6 to 24 hours: Glycogen reserves are broken down
- 2-10 days of fasting: Glucose is produced from protein precursors-amino acids
- Beyond 10 days of fasting: Fat reserves are used instead of proteins and ketones are produced.
You must be reminded of ketone bodies from low carbohydrate diets.
Along with the production of ketone bodies, degradation of fats or lipolysis occurs.
Basic calorie requirements of a man weighing 70 kg can be met only by utilization of fat reserves for 2-3 months.
Another noteworthy change is an increase in growth hormone levels.
Hunger is said to be an initial obstruction to the attempt to fast, but after 2-4 days of fasting a loss of appetite and sense of well being is reported.
What does this mean? In fasting initially glucose reserves are utilised followed by production of glucose from amino acids. Then fat reserves are utilised and energy derived from this is used to prepare ketone bodies which then replaces glucose as the primary form of energy. Drop in insulin while rise in glucagon and growth hormone is seen. Hunger which initially thwarts fasting attempt reduces with time.
Does Intermittent Fasting Work For Weight Loss?
Now intermittent fasting is not as rigorous as fasting continuously for a long period of time but it puts the body into a fasted state for a short interval of time repeatedly.
Gradually the same physical changes occur in your body and finally, your body gets used to the periods of fasting and eating.
A lot of active research is being conducted on intermittent fasting and it has revealed a number of facts to us.
1. Intermittent fasting burns fat rapidly in normal and overweight individuals
In this study, alternate day fasting (ADF) included a day where only 25% daily energy was consumed followed by a day where you were free to eat anything.
Body weight decreased by 5.2 kg and fat mass decreased by 3.6 kg within 12 weeks. Level of hormones that metabolize fat also improved.
It was concluded that ADF is an effective tool for weight loss and cardio protection in normal weight and overweight individuals.
A clinical trial investigating the effect of ADF on non-obese subjects demonstrated reported an average daily increase in fat oxidation of approximately 15g.
Weight loss of around 2.5% was observed.
A review of intermittent fasting protocols was conducted.
This review included alternate day fasting, whole-day fasting and time-restricted food consumption.
ADF trials lasting for 3-12 weeks were found to cause a weight loss of 3-7% and loss of 3-5.5 kg of body fat.
Whole day fasting trials lasting for 12-24 weeks reduced 3-9% of body weight and body fat.
Improvement in cholesterol was also observed with intermittent fasting.
Another review study covering all intermittent fasting trials conducted from 1975 to 2014 reported a weight loss ranging from 2-8% over 6 months increasing gradually followed by average weight loss of 8% after a month of weight maintenance.
Improvement in blood pressure and insulin sensitivity was observed in all trials. Attrition rates were lower than those seen in other weight management techniques.
What does this mean? Intermittent fasting brings about weight loss of around 2-8% of body weight much of which is body fat.
2. Fasting elevates the level of glucagon and growth hormone in order to get rid of body fat
Glucagon is a hormone secreted by the pancreas whose effect is opposite of that of insulin. It raises glucose concentrations.
Research shows that glucagon levels rise two folds and reaches its peak on 3rd day of fasting.
Glucagon stimulates the breakdown of fats and the production of ketone bodies during fasting.
Surprisingly growth hormone levels are proven to increase by a whopping 5 fold within 2 days of fasting.
What does this mean? Glucagon and growth hormone levels rise with fasting that stimulate breakdown of fats.
3. Fasting alters glucose and fat metabolism
A study demonstrated that varying duration of fasting alters glucose and fat metabolism with a 70% decline in insulin levels in 24 hours and a decrease in glucose.
Breakdown of fats was also observed and fat burning potential increases by 50%.
Fasting also activates genes that increase fat burning potential.
What does this mean? Studies show that fasting influences glucose and fat metabolism, reduces insulin resistance and activates genes that aid in breakdown of fats.
4. In alternate day fasting, the time of meal on fast day does not matter
Typically in alternate day fasting, on the day of the fast individuals consume their fast meal at lunchtime.
Researchers investigated whether change in time of this meal would affect the weight loss outcome.
Three groups were made were all followed alternate day fast but the meal times were either lunch or dinner or three small meals. (The last one typically voids the idea of a fast).
At the end of 8 weeks, the weight loss was similar in all groups- the highest being in the dinner group (4.1kg ).
Reduction in fast mass, visceral mass and improvement in cholesterol was seen.
It was concluded that since weight loss was similar in all groups, flexibility in meal timing can increase adherence to alternate day fasting.
Combining fasting with weight loss diets results in better weight loss results.
What does this mean? In alternate day fasting, you do not have to be rigid with meal timings. Research states that meals whether consumed at lunch or dinner or as three meals on fast day delivers similar weight loss results.
5. Alternate day fasting with high-fat diet is as effective as alternate day fasting with a low-fat diet for weight loss
In this study obese individuals were randomly split into high-fat group (45% fat) or low-fat group (25% fat). Results were almost similar but the high-fat group fared slightly better.
The best outcome was that both diets resulted in approximately 7 cm decrease in waist circumference within 8 weeks!
What does this mean? Alternate day fasting combined with low fat or high fat diet improves weight loss outcomes. The high fat diet option is slightly better.
6. Intermittent fasting combined with calorie restriction improves weight loss and heart health in obese women
Fasting already restricts calories; imagine an additional calorie restriction!
Sounds crazy right!? In this study intermittent fasting meant severe calorie restriction for 1 day where calorie intake was in the form of liquid or food.
Body weight decreased more with IF and liquid diet (3.9kg) in comparison to IF with food based calorie restriction (2.5kg).
Also, a greater reduction in visceral fat was seen in a liquid diet (0.7 kg) compared to food based diet (0.3kg).
For those who are brave enough to try this out, yep IF combined with calorie restriction and liquid diet indeed helps to lose more weight.
What does this mean? Intermittent fasting combined with only liquid meals on fasting days in a way that calories are under control results in better weight loss.
7. Intermittent fasting increases longevity and reduces the risk of other diseases
Modified versions of fasting are proven to be effective in treating rheumatic diseases, high blood pressure, metabolic syndrome, inflammatory and degenerative conditions as well as brain related disorders.
What does this mean? Apart from weight loss, IF improves cure rate in cancer, inflammatory conditions as well as brain related disorders.
Intermittent Fasting versus Dieting: Who wins?
A review study was conducted to examine the effectiveness of dieting and change in the pattern of eating or intermittent fasting.
3-12 weeks of IF resulted in 4-8 % loss of body weight and daily calorie restriction resulted in a weight loss of 5-8%.
Even fat loss was better with IF (11-16%) compared to dieting (10-20%).
According to researchers, these findings suggested that both techniques were equally effective for weight loss but IF even preserved lean mass.
Weight loss was around 6.4 kg for IF and 5.6 kg for daily calorie restriction. Improvement in metabolic parameters was also observed and they were greater in IF group.
If definitely proves itself as a great alternative to dieting.
A study was conducted to compare IF with carbohydrate restriction and daily calorie restriction.
IF with carbohydrate restriction regimen involved 600-650 calories a day with less than 40g of carbohydrate for 2 days every week. Daily restriction involved 25% calorie reduction.
Another IF diet with carbohydrate restriction and zero restriction on protein and fats was also studied.
Weight reductions in IF groups were far better than daily energy restriction and improvement in insulin activity was also observed.
What does this mean? Intermittent fasting is as effective as regular dieting when it comes to losing weight.
Different Techniques of Intermittent Fasting?
Variations in intermittent fasting are available and you can take a pick from these. There are three basic types:
- Daily intermittent fasting: You fast for 16 hours and eat within 8 hour window period. The best time to eat is around 1pm to 8pm so that it doesn’t hamper your social life and you can fast for the rest of the day.
- Weekly intermittent fasting: You can do this once or twice a week. Lunch can be your last meal on Monday and your next meal is on Tuesday at lunch time. This is only for 1 or days of the week.
- Alternate day fasting: Dinner on Monday night is your last meal and then you eat nothing till Tuesday night. Then on Wednesday you consume food normally and again begin the fast after dinner.
Nutritionists and researchers have developed different meal plans and workout schedules based on these techniques to suit everyone’s day to day life.
Let's go over them one by one.
This is started by Martain Berkhan, a Swedish personal trainer and nutrition writer. This plan is suitable for those who hit the gym regularly.
Fasting is around 14 hours for women and 16 hours for men. Food consumption is in 3 meals during the 8-10 hr window period.
On exercise days, meals should include protein, vegetables, and carbohydrates; on non-exercise days, meals should include protein, vegetables, and fat.
If a workout is scheduled for that day, then it should be before the first meal which should be a high protein meal.
What are the advantages and disadvantages of this plan?
The idea of splitting the feeding period into 3 meals gives you flexibility and avoids the pain of consuming extra large meals to meet calorie requirements. However, there is a lot of restriction on what to eat and what not to eat.
2. Eat Stop Eat/ Periodic Fast
This plan is covered by Brad Pilon and also described by Dr. John Berardi in his article. It is a 24 hour fast done typically 1-2 times a week.
Brad refers to the fast as a ’24 break from eating’.
No food is to be consumed but calorie free beverages are permitted.
This plan limits our calorie intake and prepares our body to make use of fat reserves as form of energy.
If resistance training is combined the plan will definitely reap success.
What are the advantages and disadvantages of this plan?
The advantage of this plan is that you can increase the fasting phase gradually till it reaches 24 hours. Also, there are no food restrictions. The disadvantage is that going without food for 24 hours is likely to cause irritation, fatigue, headaches etc. So you need to exert self control.
3. 5:2 Intermittent fasting
This one has been described by Dr. Michael Mosley in his book, The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting.
It involves eating normally for 5 days a week and reducing calorie intake for 2 days.
This is kind of similar to the above plan. On fasting days calorie intake should be around 600 calories for men and 500 for women.
What are the advantages or disadvantages of this plan?
The 500-600 calories on fasting days can be split up into different meals or can be enjoyed at one go.
This makes the plan psychologically attractive. However, a restriction on carbs should be exercised and this plan might just interfere with your social life.
4. The Warrior diet
This one is started by Ori Hofmelker. It is a strict plan for highly devoted individuals who have a good sense of self-control.
This plan is said to be in sync with the human body clock.
Warriors are trained to fast for 20 hours and eat one large meal at night.
During the 20 hours, fast servings of raw fruit, vegetables, and even protein are permitted.
The four hour window period helps the body recuperate and assimilate nutrients for growth and repair.
This plan stimulates hormones that cause fat burning.
What are the advantages and disadvantages?
This plan permits healthy snacks within the 20 hour fast but eating large meals at one go and especially at night might become difficult for some.
5. Alternated Day Fast/ UpDayDownDay
This technique is majorly exploited in clinical trials.
On one day you consume only 25% of your daily calorie requirements and the next day you consume your regular calories.
On low calorie days you can start initially by consuming meal replacement shakes which can be sipped throughout the day.
But that is just for the beginning later you have to start consuming low calorie foods.
What are the advantages and disadvantages of this plan?
6. Fat loss Forever
This plan combines the advantages of most of the above mentioned IF plans. This plan incorporates different fasting protocols over the week with one day’s rest.
However that one day of freedom is followed by a 36 hour fast! It also incorporates workouts for better results.
What are the advantages and disadvantages?
A scheduled timetable provided with this plan helps us develop a structured approach towards fasting thus delivering great benefits.
However, one day of freedom needs to be utilized with caution.
What is the impact of Exercise on Intermittent Fasting?
A practical thought process would be that can exercising in fasting state be possible?
Already your body is coping up with the deficit so would it actually permit exercise or any other training?
Now there is mixed evidence available on this one.
One study demonstrates that fasting prior to resistance training will increase the potential of subsequent carbohydrate or protein meal in developing muscle mass.
However long term endurance training is likely to be affected by fasting.
Does intermittent fasting affect performance or cognitive performance?
One thing that is likely to pop up in your mind is that probably not eating for so long is going to affect your mood or disturb your work performance.
And this does stand true because hunger is a feeling that makes you irritable.
But in case of intermittent fasting, this rage of appetite control occurs in the initial days after which your body eventually gets used to it.
Interestingly animal studies prove that intermittent fasting improves cognitive performance.
A clinical trial demonstrated that short term fasting, which in this case was little or no food for 24 hours, did not affect attention or immediate memory.
Another study demonstrated that even 2-day calorie deprivation does not seem to affect cognitive performance, activity, sleep or mood.
Actually its the other way round..Intermittent fasting is proven to reduce the risk of cardiovascular diseases, metabolic syndrome and even improves brain function.
However there a few things you should keep in mind:
- If you are suffering from diabetes or metabolic diseases, consult a doctor before fasting.
- Nursing and pregnant women should not even think about this.
- Elderly as well as adolescents should not attempt fasting.
- Intermittent fasting is all about watching when you eat. However if you don’t keep an eye on as to what you eat, fasting is not going to help.
- Results differ for men and women. So if you are a female go for a wider eating window.
Fasting, a regimen that was earlier mistaken for starvation, has been recently gaining popularity in the field of weight management.
However, this type of fasting does not involve long periods of abstinence from food.
It is a different pattern of eating called intermittent fasting. One of the most popular forms of intermittent fasting is alternate day fasting.
Fasting every alternate day seems like a task but this study proves to you that this weight loss technique actually works.
What happened in this study?
32 individuals were recruited for this study and were assigned to alternate day fasting group or control group.
Those in the fasting group ate only about 25% of their regular energy intake on fasting days and on the other days they were permitted to follow regular eating patterns at home.
Additionally, they were allowed to consume energy free drinks, tea, and coffee etc. The control group individuals followed regular eating patterns at home.
This lasted for 12 weeks.
What were the results?
Body weight decreased by 5.2kg in the alternate day fasting group and a decrease in body fat was about 3.6kg.
Improvement in cholesterol levels and hormones involved in fat metabolism was observed. No decrease in muscle mass was observed.
How did this occur?
When fasting every alternate day, firstly you are reducing your calorie intake, thereby reducing your chances for weight gain.
This calorie deficit forces your body to look for other forms of energy, fat is the most accessible one.
Your body is then shifted to a metabolism where you start burning fat and this translates into quick weight loss.
What does this mean?
Researchers concluded that alternate day fasting is a good weight loss strategy for those wishing to lose around 5-6 kg of weight in a short time period such as 12 weeks.
Also, it was found to be healthy for the heart.
This eating pattern seems to be a favorable strategy for quick weight loss and you can improve weight loss outcomes by avoiding calorie dense foods on non-fasting days.
Read full paper here: http://www.ncbi.nlm.nih.gov/pubmed/24215592
The thing about fasting is that it does not work for everyone. In that case, strictly adhering to old rules should help you.
There are different techniques for intermittent fasting and it definitely does not mean that you have to starve yourself. Find one that suits you and make it a habit.
The idea of intermittent fasting disrupts some traditional rules like ‘Dont skip breakfast!’ , ‘Eat three meals a day!’, ‘Eat frequently and regularly to curb hunger’ etc.
It does not mean that these rules do not apply anymore, they still do.
If you want some information on these two good reads are The Fast Diet by Micheal Mosley and Eat Stop Eat by Brad Pilon.
Our articles are written by writers with a deep domain understanding of the topic and usually hold Bachelors / Masters degrees. The articles are peer-reviewed before being uploaded on the website. Our writers spend 10s of hours researching and writing articles which are factual and comprehensive. Check out about our team in About Us section.