6 Tips for Fasting Safely

Just the thought of fasting may make you hungry. If you’re planning to go without food for a time, whether for health or religious reasons, there are a few important tips to help you stay healthy throughout it.

What is fasting and how does it work?

Fasting means abstaining from food and/or drink, whether entirely or partially. But it’s not always that straightforward.

“There’s actually a range of ways to fast,” says hepatologist Nizar Zein, MD. “Sometimes, fasting means avoiding certain types of food, like carbohydrates or fats. Other times, it 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.”

• Religious fasting: Many religions promote some form of fasting as a spiritual exercise.
• Intermittent fasting: There are different types of intermittent fasting, eating patterns that focus on consciously cutting back on calories for certain time periods. You intentionally alternate between periods of eating and fasting (sometimes described as “patterns” or “cycles” of fasting).
• Restrictive diets: On the keto diet, for example, people who follow keto cut all carbs and sugars from their diets.
• Fasting before a medical procedure: Your healthcare provider might instruct you to fast before undergoing surgery or certain types of blood tests, imaging tests or diagnostic procedures.

Talk to a healthcare provider before starting any sort of ongoing fasting, like for weight loss.

How to fast properly

If you need to fast for a short-term reason, like a religious holiday or an upcoming medical procedure, here’s a hot tip: Preparation is key!

“Putting in some extra work ahead of time will help make things easier on your body,” Dr. Zein says. He shares six tips for maintaining your health and energy level during a fast in which you don’t eat at all.

1. Ease into it

Abruptly beginning a fast is a shock to your body. Instead, cut back on food and drink gradually for several days — or even weeks — before your fast.

“Don’t eat three full meals a day with between-meal snacks and then suddenly stop eating one day,” Dr. Zein warns. “If your body is used to regular refueling, you may have a hard time maintaining energy levels during a fast.”

2. Cut back on sugar ahead of time

Keep your sugar intake low before you head into a fast. Loading up on cookies and sweet tea may feel satisfying (and filling) in the moment, but when your blood sugar plummets an hour or two later, you’re likely to end up feeling hungry and weak.

Another possible side effect? Feeling hangry — that combination of hungry and angry that ruins your mood and can spill over into your interpersonal relationships.

To give yourself enough energy for the long haul, plan your pre-fasting meals accordingly to fill up on complex carbohydrates (like whole-grain pasta, brown rice and potatoes) and protein (like meat, beans and legumes).

3. Plan ahead for medications

Before you begin any type of fast, talk to your healthcare provider about any prescription medications that you’re taking.

Some medications need to be taken with food, while others, like those taken for seizure disorders, are essential and shouldn’t be stopped abruptly. In these cases, you’ll need your healthcare provider’s guidance on how to safely fast or modify your fast.

“When people have adverse outcomes from fasting, it’s often because they didn’t take their medications correctly,” shares Dr. Zein.

4. Drink plenty of water

Some religious fasts, like for the Muslim month of Ramadan and the Jewish holiday of Yom Kippur, restrict all food and beverages, including water. In these cases, it’s especially important to hydrate ahead of time to help prevent dehydration.

If the guidelines for your fast allow for water consumption, stay hydrated so you can maintain your energy levels and lessen any possible side effects like stomach cramps, irritability and the aptly named hunger headaches.

5. Cut down on physical activity

Don’t let the word “fast” fool you: When you’re going without food or drink, it’s best to take things slow.

“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.”

6. Ease out of it

You might feel ready to chow down when your fast comes to an end, but resist the urge. Instead, replenish your calories gradually rather than eating a huge meal right away.

“It’s better to spread those calories over your next two meals,” Dr. Zein advises. “This will help you avoid rapid changes in blood sugar and the fatigue associated with consuming a large amount of food.”

Is fasting safe?

Diets that recommend eliminating certain foods or restricting eating at certain times can be done in a safe and healthy way, though you should only do them under the guidance of a healthcare provider like a dietitian.

“Fasting can be a healthy practice, and it’s one that I have recommended for many people,” Dr. Zein says. “Studies have shown that intermittent fasting and certain restrictive diets can be good for your heart health, help with weight loss and improve your cholesterol. There are also theories that periodic fasting may help you live longer, boost brain function and prevent neurodegenerative disease.”

Research also shows that religious fasting may have potential benefits like reducing oxidative stress and balancing energy levels, but there’s not enough research to say for certain.

Risks of fasting

Even when you follow tips for safe and healthy fasting, doing it too much or for too long can cause issues like:

• Dehydration.
• Disrupted sleep.
• Mental stress.

There are different health benefits and risks associated with various kinds of fasts, based on what restrictions you’re following and for how long. 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 serious health problems for people with certain conditions. Many religions indicate that people who can’t safely fast are exempt from participating in fasting rituals.

From a health perspective, Dr. Zein says that you shouldn’t fast from all food and drink if you:

• Have diabetes and struggle with keeping your blood sugar stable.
• Have chronic kidney disease.
• Are breastfeeding (chestfeeding).
• Are underweight.
• Are recovering from surgery or illness.
• Have or are at high risk for an eating disorder.

“When it’s done in a healthy way, fasting may provide psychological and physical benefits,” Dr. Zein says, “but if you plan to make fasting a part of your routine, talk with a healthcare provider about any risks.”