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Fasting has a long history in human evolution. In ancient times, people did not have regular access to food, which led to sporadic meals and natural periods of fasting. Many religions also include fasting as a form of spiritual cleansing or to enhance spiritual focus. Research shows that the human body is capable of sustaining short periods with little or no food.
A person can survive for approximately 3-4 days without water, but more than 3 weeks without food!
While complete fasting is not sustainable long-term, intermittent fasting has become a popular trend in the health and fitness world. Some claim it can help with weight loss, as well as manage blood pressure, blood sugar, cholesterol, and more. But is it really that effective?
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What is Intermittent Fasting?
Intermittent fasting is an eating pattern that involves alternating eating and fasting for a few weeks or a few months. Intermittent fasting is not considered as a “diet” since it isn’t about what to eat, but about when to eat it.
There are several different types of intermittent fasting:
1) Alternate-Day Fasting
Alternate-day fasting is to rotate days of eating and fasting. On eating days, people eat meals like usual. On fasting days no food or beverages with calories are allowed, only non-caloric drinks such as water, black coffee and tea are permitted.
2) Modified Fasting
Modified fasting refers to eating very little on fasting days, usually 20-25% of our daily caloric need, or less than 500 calories daily.
The “5:2 Diet” is the most common form of this and is widely used in Europe and the US. This entails eating as usual on 5 non-fasting days, then on the 2 following days, usually weekends, fasting occurs where men eat 600 calories, women eat 500 calories.
3) Time-restricted Fasting
Time-restricted fasting refers to fasting during certain hours of the day.
The fasting hour can range from 8-12 hours. Usually people eat normally throughout the day and start fasting from night until the morning of the next day. This pattern limits the night-time eating and could also help improve sleep quality. Time-restricted fasting also fits the circadian rhythms where the body changes in biology and behavior though 24-hr light-dark clock cycles, which may lead to better management of metabolism.
Certain religions will include a daytime fast of 8-16 hours which, in fact, may actually drop metabolism.
If you would like to try intermittent fasting, here is what you need to know:
1) Make sure you do not have any medical condition that makes you unsuitable for intermittent fasting.
2) When eating, choose more fruits, vegetables, whole grains and lean proteins to make sure you get all the vitamins and minerals you need daily.
Stick to healthy foods on an intermittent fasting diet—it doesn't give you a free pass to indulge in everything during non-fasting periods.
3) Consider choosing time-restricted fasting, which is a simple form of intermittent fasting. Limit food intake for 8 to 12 hours per day and continue to eat a healthy, balanced diet the rest of time.
Takeaways
Intermittent fasting is currently not a recommended treatment for weight loss and chronic disease management. Research is limited with small sample size, short duration, unrepresentative sample populations and various eating patterns. More studies will be needed to determine how it actually works, who it is best suited for, and long-term impacts.
Intermittent fasting may be helpful for certain populations that we don’t yet know about, but it is not suitable for pregnant or breast-feeding women, people with diabetes (especially people that are taking insulin), people with eating disorders or have history of eating disorders, people are in risk of malnutrition, people that takes certain medications, and others.
Talk to your doctor or dietitian first before you start a diet like this, and let us help to guide you. If you are fasting for religious reasons, discuss this with your doctor to better adjust medications during the fasting period.