Just the thought of fasting may make you hungry. But going without food for a time — whether for health or religious reasons — can be good for you, says hepatologist Nizar Zein, MD.
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“There’s actually a range of ways to fast,” he says. “Sometimes, fasting means avoiding certain types of food, like carbohydrates or fats. Other times, it just means reducing calories overall. Then, there’s the type of fasting when you don’t eat (or sometimes drink) at all for a day or more.”
Many religions promote some form of fasting as a spiritual exercise. And medical literature indicates fasting, in general, can:
- Support weight loss.
- Decrease inflammation from chronic conditions like arthritis.
- Lower your blood pressure.
- Lower your cholesterol.
“There also are theories that periodic fasting may help you live longer, boost brain function and prevent neurodegenerative disease,” Dr. Zein notes.
What to know before you start fasting
If you’re planning a fast in which you don’t eat at all, Dr. Zein recommends these five tips for maintaining your health and energy level.
1. Ease into it
Cut back on food and drink gradually for several days — or even weeks — before your fast. Otherwise, abruptly beginning a fast will be a shock to your body.
“Don’t eat three full meals a day with between-meal snacks and then suddenly stop eating one day,” Dr. Zein says. “If your body is used to regular refueling, you may have a hard time maintaining energy levels during a fast.”
And keep your sugar intake low as you’re heading into a fast. Loading up on cookies and sweet tea before your fast isn’t a good idea. You may feel full and satisfied at first, but when your blood sugar plummets an hour or two later, you may become extremely hungry and weak. To have enough energy for the long haul, fill up on complex carbohydrates (like pasta, rice and potatoes) and protein (like meat and beans).
2. Drink plenty of water
Some religious fasts restrict all food and beverages, including water, as part of the observation. If, however, the guidelines for your fast allow for consumption of water, staying hydrated will help you avoid dehydration, maintain your energy levels and lessen side effects like headaches, cramps and irritability.
3. Cut down on activity
“It’s not a good idea to do intense exercise when you’re not eating or drinking,” says Dr. Zein. “If you’re not planning to replenish nutrients for a while, preserve your energy for vital daily activities.”
4. Plan ahead for medications
Before fasting, talk to your doctor about how to take your medications. Some medications — such as for seizure disorders — are essential, and you shouldn’t stop taking them while fasting. Other medications should be taken with food. “When people have adverse outcomes from fasting, it’s often because they didn’t take their medications correctly,” states Dr. Zein.
5. Ease out of it
At the end of your fast, replenish your calories gradually. Rather than going on an eating binge right away, spread those calories over your next two meals. This is better because it will help you avoid rapid changes in blood sugar and the fatigue associated with consuming a large amount of food.
Is fasting healthy?
“Overall, fasting can be a healthy practice that I recommend for many people,” says Dr. Zein.
Even when following these tips, too much fasting can be dangerous, though, and fasting for too long may cause dehydration, mental stress and disrupted sleep. Also, there are different health benefits and risks associated with various kinds of fasts, based on what restrictions you’re following and for how long.
Fasting for religious reasons
It’s customary in some religions to fast entirely for a day, for a portion of certain days or to abstain from certain foods for an extended period of time.
Is it safe? Research shows that religious fasting has potential benefits for improving cholesterol, reducing oxidative stress and balancing energy.
Fasting for health reasons
Some diets recommend eliminating certain foods or restricting eating at certain times, both of which can be done in a healthy way, Dr. Zein says.
Intermittent fasting, for example, encourages people to only eat during certain times of the day or to restrict eating on certain days. It’s an eating pattern that focuses on consciously cutting back on calories for certain time periods.
Certain restrictive diets, like the ketogenic diet (keto), approach fasting differently. Rather than fasting for a period of time, people who follow keto cut all carbs and sugars from their diets.
Is it safe? Studies have shown intermittent fasting and certain restrictive diets can be good for your heart health, help with weight loss and improve your cholesterol. However, researchers also caution that fasting diets can be difficult to maintain as a long-term lifestyle.
Who shouldn’t fast?
While fasting can be done safely for some people, it can cause problems for people with certain health conditions.
Many religions indicate certain groups of people may not be required to participate in fasting based on certain criteria. From a health perspective, Dr. Zein suggests those who shouldn’t fast from all food and drink include people who:
- Have diabetes and struggle with keeping blood sugar stable.
- Have chronic kidney disease.
- Are breastfeeding (chestfeeding).
- Are underweight.
- Are recovering from surgery or illness.
- Live with or are at high risk for an eating disorder.
Fasting may provide psychological and physical benefits when done in a healthy way. If you plan to make fasting a part of your routine, talk with a healthcare provider about any risks.