Intermittent fasting: Does it work and can it be done safely?

One popular version of intermittent fasting concentrates on limiting eating to an eight-hour window each day.

Many people change their eating habits to take better care of their health and feel their best. Recently, intermittent fasting has become quite popular — as many as one in 10 Americans have tried it, according to a recent survey. If you're curious about intermittent fasting, it's helpful to understand what it involves, how it works and any potential side effects.

What is intermittent fasting?

Intermittent fasting (often called IF or time-restricted eating) is an eating approach that can help with weight loss. It's also linked to benefits like lower blood pressure, reduced inflammation, improved cholesterol and triglyceride levels, better sleep, clearer thinking, eased arthritis symptoms and a lower risk of Type 2 diabetes and heart disease.

It may even offer some protection against Alzheimer's disease.

Unlike most diets that focus on what you eat, intermittent fasting focuses more on when you eat. While this method can offer benefits for many, there are also potential side effects to consider.

Most of us are accustomed to having three meals a day, plus snacks, starting soon after we wake up and often continuing until just before bed. Late-night eating (especially while watching TV) can add up in calories and might lead to digestive issues or disrupted sleep. Over time, if this eating pattern is combined with low physical activity, it can contribute to weight gain and other health problems.

Intermittent fasting changes that common pattern — potentially returning us to an eating schedule more like that of our ancestors, before electric lights and 24/7 TV changed our habits.

One popular version of intermittent fasting concentrates on limiting eating to an eight-hour window each day. For example, you might choose to eat only between 11 a.m. and 7 p.m. or between 9 a.m. and 5 p.m. During the remaining 16 hours (including your sleep time), you stick to water, tea or coffee without calories. Some variations allow for a longer eating window of 10 or 11 hours, while another approach involves eating normally for five days a week and consuming minimal calories (around 500-600) on the other two days.

This straightforward method can be a useful way to adjust your eating habits while exploring the potential health benefits.

How it may work

By focusing your meals during specific hours — especially by avoiding late-night eating — you may naturally reduce your overall calorie intake. When you consistently burn more calories than you consume it can lead to weight loss.

Intermittent fasting works in more ways than just calorie reduction. Your body primarily relies on glucose (sugar from food) for energy. When you go 12 hours or more without eating, your body begins converting stored fat into energy. This change can alter hormone levels — resulting in lower insulin and reduced inflammation, which are key factors in conditions like high cholesterol, high blood pressure, diabetes and heart disease. Some research even suggests that this approach might help slow the aging process and boost your immune system.

Of course, it's important to keep in mind that there can be downsides as well.

Side effects of intermittent fasting

Hunger is the most common side effect of intermittent fasting. If you're used to eating frequently, going without food for a while can sometimes lead to headaches, fatigue and even lightheadedness. You might also feel a bit cranky — what many call "hangry" — or find it harder to concentrate. Because food contributes about one-fifth of our daily water intake, skipping meals might even lead to dehydration. And after fasting for around 16 hours, it's natural to feel tempted to overeat, which can sometimes cause weight gain, indigestion or other issues.

Most of these side effects are mild and tend to lessen as your body adjusts to the new routine. They can often be managed by making sure you get proper nutrition during your eating window and by keeping an eye on your activity levels.

That said, there are a few more serious considerations. One study found that restricting your eating to less than an eight-hour window might increase the risk of heart disease compared to having a longer eating window of 12 to 16 hours.

If you have a history of diabetes, heart disease, low blood sugar, low blood pressure, kidney issues, eating disorders or irregular menstrual cycles, it's important to talk to your doctor before starting intermittent fasting. Similarly, if you take medications that need to be taken with food, you should consult your healthcare team before making any changes to your eating schedule.

Intermittent fasting isn't recommended for everyone. It's generally not advised for children or teens under 18, or for women who are pregnant, trying to conceive or breastfeeding. It may also not be suitable for people with serious health conditions or those who are underweight or frail.

If your healthcare team gives you the green light, here are some tips to help you ease into intermittent fasting without unwanted side effects:

• Eat a balanced diet: Focus on plenty of protein, fiber, vegetables and other nutrient-dense foods during your eating window.
• Choose a flexible eating window: Aim for at least a 10-hour window that fits comfortably with your lifestyle.
• Plan your workouts: Try to schedule exercise so you can eat before or soon after, preventing extreme hunger or fatigue.
• Strengthen your body: Include weight-bearing exercises to build strong bones and lean muscle.
• Manage hunger mindfully: Consider trying meditation or other relaxation techniques to handle hunger pangs during fasting hours.
• Stay hydrated: Drink water throughout the day — even during fasting hours. A slice of lemon or cucumber can add a refreshing twist without extra calories.

Remember, the goal of adjusting your eating habits is to help you feel better and boost your overall health. If intermittent fasting — or any other eating plan — doesn't work for you, it's perfectly OK to explore other options that better suit your needs.