Fasting, in general, is not a new concept and is an important part of many religions like Islam. Hippocrates is known as the first person to apply fasting to treat illnesses in the 5th century BC.
Fasting has many benefits, ranging from weight loss to promoting healthy living in various areas. Therefore, if you have decided to try IF, you can better understand its features and get tips for success by using this scientific guide.
Intermittent fasting is an approach that does not have a long list of rules, unlike other diets. According to RDN Heather Bauer, the founder of Heather Bauer Nutrition, the IF approach is entirely about “restricting or avoiding eating entirely or partially for a certain period.”
So, IF involves intermittent pauses in eating. While some people enjoy IF, it is noted that it may not be the right diet for everyone.
How Does Intermittent Fasting Work?
You get to choose how you want to do IF by deciding on which days of the week you will fast. On fasting days, you will likely be following a significant calorie-restricted diet or not eating at all. You can also choose to fast for a specific period each day. As a result, this leads to fewer calories consumed throughout the week, and some experts, including RDN Caroline Susie from the Academy of Nutrition and Dietetics in Dallas, say that this calorie reduction sometimes leads to weight loss and potentially provides additional metabolic benefits.
Frequently Asked Questions and Answers
Is Intermittent Fasting Safe?
Generally, yes. However, if you are pregnant or breastfeeding, have a low body mass index, or have a history of an eating disorder, you should not try this diet. Also, if you are over 70 years old, do not attempt intermittent fasting. If you have diabetes or take time-sensitive medication, talk to your doctor first to see if it is safe for you.
How Long Should You Do Intermittent Fasting?
It’s up to you. Some people prefer to set an 8, 10, or 12-hour eating window. Others choose to fast every other day or one or two days a week. Alternatively, you may prefer a 24-hour fast where you eat dinner one day and then fast until dinner the next day.
How Much Weight Can You Lose with Intermittent Fasting?
If you follow a time-restricted eating style (like 16:8, which involves a 16-hour fast and an eight-hour eating window), you can lose one to two pounds per week. More stringent styles like alternate-day fasting can help you lose twice that amount.
What Are The Rules of Intermittent Fasting?
The rules only apply to when you eat, not what you eat. Either you will set a specific eating window during the day, or commit to fasting (or eating only 500 calories) for a certain number of days per week.
Why Do You Urinate More While Fasting? If you drink more fluids like water, coffee, or tea to feel fuller during fasting, you may naturally urinate more. Also, when you significantly reduce carbohydrates during fasting, you can lose water weight resulting in more urination.
Types of Intermittent Fasting
There is no single standardized way to implement IF. According to PhD Krista Varady, a nutrition professor and researcher on intermittent fasting at the University of Illinois in Chicago, “Intermittent fasting is an umbrella term for three different types of diets.” Here’s what you are most likely to encounter, she says:
Alternate-Day Fasting For the most common type of alternate-day fasting, you eat 500 calories every other day. On the fasting days, you can eat whatever you want.
Time-Restricted Eating You choose a designated eating window (feasting) during which you can consume meals and fast for the rest of the day. One popular setup is the 16:8 method, where you fast for 16 hours and have an 8-hour window for eating. For example, you can set your eating window from noon to 8 pm every day (also referred to as skipping breakfast).
Potential Health Benefits of Intermittent Fasting Susie, in general, says that rigorous, long-term research on intermittent fasting is still limited, and most of the findings you will come across online are based on animal studies. It is not clear whether any type of IF is truly safe or effective in the long run. So proceed with caution. With that in mind, here’s how IF can potentially benefit you:
Prevention of Heart Disease
While more research is needed, a review has found that intermittent fasting (IF) shows promise in improving cardiovascular health by reducing cardiovascular risk factors such as obesity, high blood pressure and cholesterol, and diabetes. Researchers note that it is currently unclear which type of IF is best for heart health.
Type 2 Diabetes Treatment IF may be a promising treatment for type 2 diabetes.
Fasting helps with weight loss, reduces insulin resistance, and positively affects hormones released by fat cells that impact appetite and inflammation levels. However, if you have diabetes, you should not try IF without first consulting your doctor.
Get Rid of Alzheimer’s Disease and Stroke
While research continues, some studies have found that intermittent fasting may help reduce the risk of stroke and Alzheimer’s disease. However, much of this understanding comes from animal studies, and it is unclear when IF should be started to reduce neurological risks. Moreover, despite claims that IF improves cognitive abilities such as focus, it does not appear to be a short-term brain booster.
Improve Non-Alcoholic Fatty Liver Disease
A systematic review and meta-analysis of six studies found that people with non-alcoholic fatty liver disease (a liver disease seen in people with obesity, diabetes, and metabolic syndrome) who practiced IF showed an improvement in liver function tests compared to those who did not. The authors concluded that this was due to IF leading to weight loss. However, researchers note that larger randomized trials are needed before specific recommendations can be made.
Weight Loss Effects of Intermittent Fasting
During IF, whether it’s eating fewer hours in the day or having fewer eating days, you eat within a shorter period of time. “In our research, we found that time-restricted feeding naturally reduced a few hundred calories per day,” says Dr. Varady. She observed that this resulted in roughly one to two pounds lost per week. It’s similar to a daily calorie-restricted diet but with the added benefit of not having to count calories.
One study found that people who reduced their eating window to eight hours consumed about 300 fewer calories and lost approximately 3% of their body weight over 12 weeks. On the other hand, alternate-day fasting can help reduce a person’s daily calorie intake by 25% to 35% (over the course of a week) and lead to weight loss of 4% to 6% of body weight over 12 weeks. Another review of 11 meta-analyses concluded that IF, especially intermittent fasting, helps overweight or obese adults reduce their body mass index (BMI), a measure of body weight, better than a regular diet.
“Weight drops twice as fast with fasting for a full day,” says Varady. The issue is that compared to time-restricted eating, many people find it harder to sustain alternate-day fasting and fit it into real-life scenarios, she says. According to Varady’s research, 30% to 40% of people have dropped out of alternate-day fasting studies. Conversely, time-restricted eating has only a 5% dropout rate, according to Varady’s research.
However, longer-term data (based on following people for one to two years) is needed. Most of Varady’s published research has lasted no more than six months.
Side Effects of Intermittent Fasting
Before fully transitioning to a new way of eating, be aware that there may be some side effects, says Susie:
- Headaches
- Fatigue
- Low energy
- Irritability
- Hunger
Susie says all of these can occur because you’re not eating. While they’re normal, they can be bothersome and affect your daily well-being. Some people will realize they’re not good trade-offs and choose to stop IF. That’s completely okay. This isn’t for everyone.
A note: Varady says to expect hunger to peak during the first 10 days, then taper off as your body adjusts to the new eating schedule.
Health Risks of Intermittent Fasting Bauer says don’t try intermittent fasting if you’re pregnant or breastfeeding. Similarly, if you have a low (underweight) BMI or a history of an eating disorder, IF is not right for you. Varady also warns against fasting for adults over 70, as it can lead to muscle loss critical for protection in advanced age.
Additionally, if you have any type of diabetes, talk to your doctor before trying IF; skipping meals can lead to low blood sugar that can cause dizziness, fainting, and falls. If you’re taking any medication that needs to be taken at a specific time and with food, you’ll also need to check with your doctor.