Intermittent Fasting: 6 Ways to Do It and Proven Health Benefits
Written by Nadira MaharaniUpdated on May 19, 2023
Medical reviewed byAmy Rogers, MD MPH FACPM
Preventive Medicine, Public Health, Lifestyle Medicine, Pandemic Response, Global Health
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Intermittent Fasting (IF) is a diet which alternates between fixed fasting and eating windows. Unlike other diets, it doesn’t tell you what you eat, but rather when to eat. The diet draws its inspiration from times when humans needed to survive during periods of scarcity.
Intermittent fasting essentials
Intermittent fasting is a fairly easy routine to follow since it is about managing your eating pattern rather than worrying too much about foods and calories. The key is to get a correct balance between macronutrients, and an understanding of how timing and weight loss works.
Calorie intake and macronutrients
An important thing about intermittent fasting is to have a good macronutrient balance. Macronutrients are your main source of energy and include carbohydrates, protein and fats. These also perform other important bodily functions.
As you can see, the recommended intermittent fasting intake is higher in protein, moderate in fat, low in carbohydrates, and overall fewer calories.
How weight loss works
In the beginning of intermittent fasting, you’ll probably first burn off excess carbohydrates. Ultimately, the goal is to hit the timeline where your body starts burning fat stores instead of easily available sugars. This is when you can start to lose weight.
Generally, after fasting for 10 to 16 hours, the body will start to burn stored fat. Fatty acids or ketones will be released into the bloodstream.
Getting your timing right
To guarantee success with intermittent fasting, you need to reach a state of nutritional ketosis. This is when your body switches from burning carbohydrates or glucose to fats.
For better understanding, we need to take a closer look at the feed-fast cycle which is the process the body goes through. Each stage results in different changes in metabolism and hormone levels (5(5):
- The feed state - up to 3 hours after eating. Glucose and insulin levels increase and energy is readily available.
- Early fasting state - from 3 to 18 hours after your last meal. Insulin levels drop, initiating fat burning.
- The fasting state - from 18 to 36 hours of not eating. Insulin levels keep decreasing, fatty acids and ketones become the main energy source, fat-burning is accelerated. Protein catabolism, or loss of muscle can also result.
- The starvation or long term fasting stage - from 36 or 48 hours of fasting after eating. Insulin decrease further, breakdown of amino acids slows down. Levels of beta-hydroxybutyrate or B-OHB from ketosis rise.
As can be seen, after 18 to 36 hours of fasting, the body switches from glucose energy to fatty acids and ketones. This is the key target and why timing is all-important for intermittent fasting.
6 Types of intermittent fasting schedules
There are several ways to do IF, each with a different intermittent fasting eating pattern. Here are six popular methods to choose from:
1. The 18.8 method: 16 Hours fasting
The 18.8 method—formulated by Martin Berkhan in 2008. It simply means you fast for 16 hours and your eating window is the remaining 8 hours (11).
For a simple plan, your first meal is at 12 noon or 1 p.m. and accounts for around 25% of your calorie intake. The second eating window is at 4 or 5 p.m. with a similar calorie intake as your first meal. Then, your final and largest meal is at 8 or 9 p.m. in the evening.
2. The 5:2 method: 2 Days restricted calories
The ‘Fast Diet’ by Michael Mosley uses the 5:2 method. In this case, you eat normally for 5 days in a week. Then, you restrict your calorie intake to 500 calories for women or 600 calories for men on the other two days of the week.
This is based on a quarter of the 2,000 and 2,400 calories recommended calorie intake for women and men respectively.
3. Eat stop eat diet: Full day fasting
The Eat Stop Eat Method by Brad Pilon is a very flexible plan which requires a full-day fasting period, one or two days a week. Unlike the 5:2 method, you will completely starve your body of all calories and not eat anything for a full 24 hours.
4. Alternate-day fasting
With the alternate day intermittent fasting pattern, you will be restricting your calorie intake one day, then feast the next. It will go consecutively every day making a fast-feast cycle. Similar to the 5:2 method, during the fast day you will only consume a quarter of your recommended calorie intake (14)
5. The warrior diet
The warrior diet, by Ori Hofmekler, suggests we should embrace the primal habits of early human cultures. The classical warrior diet mode is that of working and eating sparingly during the day, with your main eating window at night (15).
6. Spontaneous meal skipping
Meal skipping is a very easy type of intermittent fasting. Basically, you just skip a meal from time to time if you don’t feel hungry, or when you don’t feel like cooking. For example, if you wake up feeling full, skip your breakfast and just eat lunch and dinner.
There are six popular intermittent fasting patterns. Some restrict eating to a fixed pattern of feeding hours. Others restrict calories on alternate days or designated days such as the Alternate Day method and the 5:2 method. One method actually requires a full-day fast once or twice a week.
Tips for intermittent fasting to lose weight
When people feel intermittent fasting is not working, it could be that they are not doing it properly. To ensure you get the best possible results, here are some dos and dont's for IF:
- Watch what you eat - avoid processed foods and choose wholefoods.
- Keep hydrated - drink plenty of liquid but stick to water to avoid calorie loading.
- Ease yourself into it - pick a more flexible regimen that fits your schedule.
- Be consistent -stick to a program for at least two to three months.
- Avoid overeating - don’t eat too much during feeding periods.
- Limit rigorous activities - save your energy while you are fasting.
What to drink during a fast
It’s important to remember that during fasting periods, you need to avoid calorie intake. This means only water, or zero-calorie drinks such as plain tea and black coffee.
For water, you can drink a standard 8 glasses of water, or around 2 to 3 liters a day. This will keep your metabolism going and your body hydrated throughout fasting periods.
Keep in mind tea and coffee are diuretics (32)(32), so keep the count to around two to three cups of coffee or five cups of tea per day balanced with water in between.
Health benefits of intermittent fasting
Some studies have shown that intermittent fasting can benefit your health, for your metabolism, brain, and cardiovascular conditions. Here are some of the highlights of these positive impacts.
Type 2 diabetes
Although studies are limited, there are promising results that intermittent fasting may be able to help type 2 diabetes. Specifically, it can aid in weight loss and improve glycemic variables (16)(16).
It has also been found that intermittent fasting can increase SIRT6 protein levels. This protein may help in stabilizing glucose levels and reverse insulin resistance. Long term research studies, however, are still needed (17)(17).
Brain health
Some research suggests that intermittent fasting may benefit neuroplasticity, or how the brain grows and changes, thus affecting mental health. Intermittent fasting, as well as vigorous exercise, seem to improve sensory-motor function. The mechanisms involved, however, are not clearly understood (18)(18).
Heart health
There are more promising results regarding intermittent fasting and heart health. Intermittent fasting seems to have positive impacts upon risk factors of cardiovascular diseases such as blood pressure, as well as HDL (good cholesterol) and LDL (bad cholesterol) cholesterol levels.
One study suggested that people had an average reduction of blood pressure after 5 weeks of fasting using 18 hour-periods. (2323) HDL and LDL, or lipid values showed positive response after 12 weeks of alternate day fasting combined with exercise (1919).
Cancer
Intermittent fasting has also been studied as an adjunct to cancer therapies. Autophagy, the process of clearing out and recycling dead cell material, may be triggered or supported by intermittent fasting. This in turn may lessen the side effects of cancer therapies such as chemotherapy or radiation therapy (20)(20).
Weight loss
A review of research involving one of three different, intermittent fasting protocols (alternate day fasting, 5:2 dieting, and time-restricted eating) showed positive results for weight loss. Participants managed to lose weight in mild to moderate amounts, or 3-8% their base weight over 8 to 12 weeks. This is similar to traditional dieting (21)(21).
Neurological disease
Animal studies show clear mechanisms by which IF has positive effects on brain-related disease models while clinical studies are mostly still at infancy. IF does not lead to any short-term benefits for cognition in healthy people, but there are indications that IF might be protective of developing neurological disorders (22)(22).
Inflammation
The most promising benefits of IF concern the management of type 2 diabetes and improving general heart health. Preliminary results are also positive for weight loss, and improving inflammation markers. Other benefits for cognitive functions are not so well understood.
Debunking popular myths
One myth about intermittent fasting is that fasting could lower your bodies metabolism (or ability to lose weight) over the long term.
Another myth is that intermittent fasting causes overeating during the feeding period.
Lastly, some people believe intermittent fasting will cause the body to burn muscle. It turns out that while we burn a little bit of protein at the beginning of hour 18, we quickly switch to burning fat as a source of fuel (5)(5).
Dangers of intermittent fasting
Although intermittent fasting is safe for the most part, there are side effects that you need to be aware of. A few of these can include headache, lethargy, mood swings, dizziness, and polyuria (31).
The most common issue is lethargy, often due to dips in glucose levels before ketosis kicks in. Therefore, choose a proper time to start you fast which won’t disturb your productivity or plans.
1. How long can you do intermittent fasting?
There’s a lack of comprehensive and reliable data on intermittent fasting, but 8 to 12 weeks is a good window for results.
2. How much weight can you lose in a month of intermittent fasting?
According to some research, an 8 to 12 week period can lose around 3 to 8% of baseline weight. Based on that, a month could see around a 1.5% to 4% weight loss. If you weigh 200 lbs, that 3 to 8 lbs weight loss.
3. What activities should be avoided during fasting?
It’s best to avoid high-intensity exercises that burn too many calories which can lead to lethargy. Time your training to avoid strenuous workouts during the fasting window.
4. Does sleep count as fasting?
Yes, because you aren’t consuming any calories for 6 to 8 hours—which is why when you wake up you need to break (your) fast. Make sure your sleeping times are balanced since oversleeping can be just as bad.
5. Is intermittent fasting a healthy diet for everyone?
Although intermittent fasting appears beneficial, it’s best avoided by children or teens under the age of 18 and pregnant or breastfeeding women. Also people with eating disorders and type 1 diabetes on insulin should always consult a healthcare provider.
Summary
Intermittent fasting plan
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Medical reviewed byAmy Rogers, MD MPH FACPM
Preventive Medicine, Public Health, Lifestyle Medicine, Pandemic Response, Global Health
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