Considerations For The Optimal Timing Duration Frequency And Length Of An Intermittent Fasting Regimen For Health Improvement
1Intermountain Medical Center Heart Institute, Salt Lake City, UT 84107, USA Tel.: +1-801-507-4708 Fax: +1-801-507-4792
2Division of Cardiovascular Medicine, Department of Medicine, Stanford University, Stanford, CA 94063, USA
Intermittent fasting is a general term encompassing a variety of dietary regimens that vary based on the duration, frequency, timing, and length of fasting. While sometimes referred to as a lifestyle, intermittent fasting is usually practiced as a diet that leads to weight loss. Some regimens are attuned to rapid weight loss, including popularized versions such as alternate-day fasting , and twice-weekly fasting that utilize a duration of about one day in each fasting episode and a frequency of more than once per week. These regimens employ higher frequency and duration than other fasting methods, but the timing of fasting is not specified. Further, they may be difficult to maintain over the length of a year or more, as evidenced by substantial drop-out rates in controlled trials , which may bode poorly for fasting in actual-practice situations.
Timing of meals, thus, may have critical implications for metabolic health through mechanisms of glycemic control and via circadian clock mechanisms. Specifically, greater consumption of calories in the early part of the day appears to lead to better cardiac health and lower weight, likely in part because the bodys circadian clock influences glycemic control and cholesterol metabolism .
How To Do The 12
When following this IF method, in as much as the two meals are 12 hours apart, you must finish your last meal before the 12 hour fasting-eating interval. For instance, if your eating window is 8 a.m. to 8 p.m., you should eat breakfast at or after 8 a.m. finish dinner before 8 p.m. As you begin, you will have hunger pains, but your body will adjust with time.
Do not jump into the 12 hour intermittent fasting. Your body takes time to adjust to not eating, especially if you usually take three meals and two snacks a day. Begin by staying off some meals, then when you get used to staying without food for hours, increase the period slowly to the 12 hours optimal window. Ensure that you are comfortable staying for long without eating because 12 hour intermittent fasting should not make you miserable, but rather, you should enjoy doing it.
Is Intermittent Fasting Safe
Some people try intermitting fasting for weight management, and others use the method to address chronic conditions such as irritable bowel syndrome, high cholesterol or arthritis. But intermittent fasting isnt for everyone.
Williams stresses that before you try intermittent fasting , you should check in with your primary care practitioner first. Some people should steer clear of trying intermittent fasting:
- Children and teens under age 18.
- Women who are pregnant or breastfeeding.
- People with diabetes or blood sugar problems.
- Those with a history of eating disorders.
But, Williams says, people not in these categories who can do intermittent fasting safely can continue the regimen indefinitely. It can be a lifestyle change, she says, and one with benefits.
Keep in mind that intermittent fasting may have different effects on different people. Talk to your doctor if you start experiencing unusual anxiety, headaches, nausea or other symptoms after you start intermittent fasting.
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The 5 Stages Of Intermittent And Prolonged Fasting
Cahill conceptualized his fasting stages according to which energy source the body is predominantly using at any given time .
He distinguishes between two primary fuel sources:
- Glucose: a carbohydrate and sugar
- Triglycerides: stored body fat
While most cells can use both energy sources, the brain is an exception because it cannot use triglycerides.
Other cells, such as those in the liver, kidneys, muscles, or heart, can use both energy sources.
While the body stores fat as triglycerides, carbohydrates are stored in the form of glycogen.
This molecule consists of glucose chains and water. Glycogen is stored primarily in the liver and partially in skeletal muscle.
As soon as the body needs blood sugar, it splits the molecule into smaller glucose molecules and relieves them into the bloodstream.
When glycogen is no longer available, the body must draw on fat reserves. For this purpose, triglycerides from the fat cells enter the liver, where they are broken down.
In addition to fatty acid chains, glycerol is produced, which your body can convert into glucose for the brain.
Overeating And Potential Weight Gain
Restricting your intake to just 8 hours per day may cause some people to eat more than usual during eating periods in an attempt to make up for hours spent fasting. This may lead to weight gain, digestive problems, and unhealthy eating habits.
Interestingly, current research doesnt suggest that intermittent fasting leads to any more weight loss than typical diets that recommend overall calorie restriction. Both eating patterns may lead to modest weight loss .
If weight loss is your primary goal, you may therefore prefer to lower your calorie intake instead of fasting intermittently to prevent the overeating that may occur when restricting intake to a certain time window.
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Women And Intermittent Fasting
Intermittent fasting can cause hormonal imbalance in women if its not done correctly . Women are extremely sensitive to signals of starvation, and if the body senses that it is being starved, it will ramp up production of the hunger hormones leptin and ghrelin.
So when women experience insatiable hunger after under-eating, they are actually experiencing the increased production of these hormones. Its the female bodys way of protecting a potential fetus even when a woman is not pregnant.
So women have to set cunningly about it. And if you do so, you can get all the benefits of fasting.
One study of healthy young women found that a 10-hour eating window had an anti-stress effect, lowering cortisol and increasing parasympathetic* activity .
*) The parasympathetic nervous system is the âbrakeâ that causes the body to calm down, and which is active when we relax, sleep, eat and meditate.
So if you are a woman or trying fasting for the first time, you might benefit from modified or crescendo intermittent fasting.
This is a more gentle approach that helps the body more easily adapt to fasting. Not all women need crescendo fasting, but it will ensure success in most.
Fast on 23 non-consecutive days per week
On fasting days, do yoga or light cardio.
Ideally, fast for 1216 hours.
Eat normally on your strength training/HIIT workouts intense exercise days.
Drink plenty of water.
After two weeks, feel free to add one more day of fasting.
Listen to your body.
Fasting May Improve Brain Health
The Warrior Diet is promoted as a way to improve brain health.
There may be some truth to that based on scientific studies on intermittent fasting.
Intermittent fasting has been found to benefit the regulation of inflammatory pathways that affect your brain function.
For example, animal studies have shown that intermittent fasting reduced inflammatory markers like interleukin 6 and tumor necrosis factor alpha , which may negatively impact memory and learning (
However, research in this area is ongoing and more human studies are needed to determine the benefits of intermittent fasting on brain health.
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How To Stay Focused
With so many resources pertaining to intermittent fasting, not all the information you find online can be trusted. Poorly informed or false sources can give IF a bad rep, which Krystal felt firsthand.
The biggest challenge is probably other peoples perceptions of fasting and overcoming the idea that not eating is dangerous or an eating disorder, said Krystal. Ive found that having information about why I do what I do helps me stay focused.
Intermittent Fasting Decreases Metabolism Less Than Continuous Calorie Restriction
When you lose weight, your metabolic rate goes down. Part of this is because losing weight causes muscle loss, and muscle tissue burns calories around the clock.
However, the decrease in metabolic rate seen with weight loss cant always be explained by the loss of muscle mass alone .
Severe calorie restriction over a long period can cause your metabolic rate to drop, as your body enters so-called starvation mode. The scientific term for this is adaptive thermogenesis.
Your body does this to conserve energy as a natural defense against starvation .
This has been demonstrated dramatically in a study of people who lost large amounts of weight while participating in The Biggest Loser, a reality show on TV.
Participants followed a calorie-restricted diet and intense exercise regimen to lose large amounts of weight .
The study found that 6 years later, most of them had regained nearly all of the weight they had lost. However, their metabolic rates had not gone back up and remained around 500 calories lower than you would expect for their body size.
Other studies investigating the effects of calorie restriction on weight loss have found similar results. The drop in metabolism due to weight loss can amount to hundreds of calories per day (
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How To Get Started
Getting started is simple.
In fact, chances are youve already done many intermittent fasts before. Many people instinctively eat this way, skipping morning or evening meals.
The easiest way to get started is to choose one of the intermittent fasting methods above and give it a go.
However, you dont need to necessarily follow a structured plan.
An alternative is to fast whenever it suits you. Skipping meals from time to time when you dont feel hungry or dont have time to cook can work for some people.
At the end of the day, it doesnt matter which type of fast you choose. The most important thing is to find a method that works best for you and your lifestyle.
The easy way to get started is to choose one of the methods above and give it a go. Stop immediately if you experience any adverse effects.
Best Intermittent Fasting Schedule For Men
For most men, in my experience, it is possible to start directly with a 16/8 fasting plan. Finally, you will unlearn appetite in the morning in less than two weeks.
In addition, 24- or 36-hour fasting is also excellent for men, as they find it easier on average to fast for more extended periods at a time.
Those who are athletes and do not like to restrict themselves in everyday life are best served with 36-hour fasting. Because two nights lie in the fasting period, this method is feasible weekly and effective for health goals.
Men who have been engaged in intermittent fasting for a long time also tend to use more extreme methods more often.
People who travel a lot or have a physically active working day can optimize their health by skipping lunch.
So 16/8 becomes a 20/4 or OMAD fasting schedule. In any case, the daily routine must fit to increase the fasting window from 16 hours to 20 or more.
I practice OMAD, especially when I want to maximize productivity and free time. There is no question that lunch brings losses in concentration. Still, it has social benefits and may reduce stress on your working day.
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How Do I Do Intermittent Fasting
There are multiple ways to do intermittent fasting:
The Benefits Of Fasting Don’t Kick In At The Same Time For Every Person
Experts agree that your personal habits will play a role in when exactly certain health benefits will kick in. “There are very few definites here,” says Vincent Pedre, M.D., an integrative physician and gut health expert who frequently recommends intermittent fasting diets to his patients. “Where you start seeing those benefits depends on what you eat, how healthy your gut health is, what kind of physical activity you’re doing, etc.”
For example, letting calories slip into your fasting window, overeating calorie-dense foods like pizza during your eating window, not prioritizing sleep or physical activity, or making one of these intermittent-fasting mistakes could all delay or counteract the benefits of intermittent fasting.
Even if you’re formulating the rest of your diet and lifestyle perfectly, it’s important to understand that the different health benefits associated with intermittent fasting will likely kick in at different durations of fasting. For example, weight loss may be triggered by a relatively short fasting window, while entering ketosis or triggering autophagythat “self-cleaning” cellular process that boosts brain functioning and maybe even longevitymay take significantly longer.
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Foods List And Meal Plan
To maximize the potential health benefits of your diet, its important to stick to nutritious whole foods and beverages during your eating periods.
Filling up on nutrient-rich foods helps round out your diet and supports a healthy weight. Try balancing each meal with a wide variety of whole foods, such as:
- Fruits: apples, bananas, berries, oranges, peaches, pears, tomatoes, etc.
- Veggies: broccoli, Brussels sprouts, cauliflower, cucumbers, leafy greens, etc.
- Whole grains: barley, buckwheat, quinoa, rice, oats, etc.
- Healthy fats: olive oil and avocados
- Protein sources: eggs, fish, legumes, meat, poultry, nuts, seeds, etc.
Drinking calorie-free beverages like water and unsweetened tea and coffee, even while fasting, also helps control your appetite while keeping you hydrated.
Its best to avoid ultra-processed foods like packaged snacks, deep-fried items, sugary drinks, and most frozen meals. These negate the positive effects of 16/8 intermittent fasting and may harm your health.
To begin 16/8 intermittent fasting, choose an 8-hour window and limit your food intake to that time span. Be sure to follow a balanced diet based in whole foods.
Animal and human studies suggest that intermittent fasting may increase weight loss, improve blood sugar levels, and extend longevity.
Week Three Phase Three
This is known as the concluding fat loss week or the high-carb high-protein cycle. During this week, your food consumption should be as follows :
- 1 to 2 days high in carbs
- 1 to 2 days high in protein and low in carbs
- one to two days high in carbs
- 1 to 2 days high in protein and low in carbs
1. Undereating window Eat the same foods that you had been eating during the first week.
2. Overeating window Break your fast with the same salad that you have been having. The next large meal or smaller meals should consist of cooked vegetables, some animal protein, and one main source of carbohydrates like corn, rice, potatoes, whole-wheat pasta, barley, or oats.
High-Protein Low-Carb Days
1. 20-hour Underfeeding window The same foods and drinks that you have been having throughout the previous weeks.
2. 4-hour Overfeeding window Break your fast with the same salad, and the next meals should have 227 to 454 grams animal protein and some cooked, non-starchy vegetables.
3. Fruit While you should not consume grains or starchy veggies during these days, you can have some fruit if you are still hungry at the end of the night.
Once you have completed this 3-week phase, you are supposed to start it all over again. If this suggestion does not appeal to you, just stick to the undereating rules set for the 20 hours and then consume healthy, high-protein meals in the 4-hour overfeeding window.
What Is 16/8 Intermittent Fasting
The practice of 16/8 intermittent fasting involves limiting your intake of foods and calorie-containing beverages to a set window of 8 hours per day. You abstain from food for the remaining 16 hours, though youre still allowed to drink water and other no-calorie beverages, like plain coffee or tea.
You can repeat this cycle as frequently as youd like from just once or twice per week to every day, depending on your preference.
The popularity of this fasting method has grown widely among those looking to lose weight and burn fat. 16/8 intermittent fasting is also believed to improve blood sugar control and enhance longevity.
While other diets often set strict rules, 16/8 intermittent fasting is easy to follow and may provide measurable results with minimal disruption to your diet. Its generally considered less restrictive and more flexible than many other diets and works with most lifestyles.
With 16/8 intermittent fasting, you restrict your food intake to an 8-hour window and fast for the remaining 16 hours. This practice may support weight loss, improve blood sugar, and increase longevity.
It is simple, safe, and sustainable to do 16/8 intermittent fasting.
Frequently Asked Questions Concerns And Complaints
Im a woman. Should I do anything differently?
I havent worked with women on implementing an intermittent fasting schedule, so I cant speak from experience on this one.
That said, I have heard that women may find a wider window of eating to be more favorable when doing daily intermittent fasting. While men will typically fast for 16 hours and then eat for 8 hours, women may find better results by eating for 10 hours and fasting for 14 hours. The best advice I can give anyone, not just women, is to experiment and see what works best for you. Your body will give you signals. Follow what your body responds favorably to.
Also, if youre a female, there is an allfemale page on Facebook that discusses intermittent fasting. Im sure you could find a ton of great answers and support there.
I could never skip breakfast. How do you do it?
I dont. Breakfast foods are my favorite, so I just eat them at 1pm each day.
Also, if you eat a big dinner the night before, I think youll be surprised by how much energy you have in the morning. Most of the worries or concerns that people have about intermittent fasting are due to the fact that they have had it pounded into them by companies that they need to eat breakfast or they need to eat every three hours and so on. The science doesnt support it and neither do my personal experiences.
I thought you were supposed to eat every 3 hours?
Hereâs why this was a popular idea for a brief period of time:
Hereâs the problem:
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