From intermittent fasting to juice cleanses, fasting has taken the health world by storm, promising weight loss, mental clarity, and longevity. But is it actually the key to unlocking better health, or just the latest passing craze?
Fasting requires abstaining from food — or, in some cases, both food and drinks — for a set period of time. While different types of fasting exist, the most popular include intermittent fasting (where eating windows are restricted) and prolonged fasting (often lasting 24 hours or more).
But despite its growing popularity, there’s still debate about its true health benefits. While fasting can offer a range of health benefits for many people, it’s not a one-size-fits-all solution and should be approached with caution, especially for those with specific health concerns.
Health Benefits of Fasting
While the results can vary depending on the type and duration of fasting, studies have shown significant improvements in various aspects of health.
Reduce Inflammation
Fasting is like hitting reset on your body’s systems, particularly helping reduce inflammation. A January 2024 study in Cell Reports found that fasting for 24 hours reduced markers of inflammation in both humans and animals, potentially helping to lower the risk of conditions linked to chronic inflammation like arthritis and heart disease.
Balance Blood Sugar
Keeping your blood sugar steady can help prevent those mid-day energy crashes, while also helping prevent or manage type 2 diabetes.
A January 2022 study in Nutrients found it may help reduce risk factors of metabolic syndrome that increase the likelihood of type 2 diabetes, heart disease, and stroke. Additionally, an August 2023 review in Nutrients found that fasting can increase insulin sensitivity, making it an efficient therapy for the medically supervised management of type 2 diabetes.
Support Heart Health
Your heart health is key to everything else — take care of it now, and it’ll take care of you later. Fasting has been linked to improvements in heart health and reduced risk of heart disease, including reductions in blood pressure, LDL “bad” cholesterol, and triglycerides, according to a November 2020 review in Frontiers in Nutrition.
Help Optimize Growth Hormone
When your hormones are in harmony, you’re in the sweet spot for energy and mood. Fasting can help regulate hormones, including those responsible for metabolism and fat storage. An August 2021 review in Endocrinology and Metabolism found that fasting triggers the release of growth hormone, which is involved in metabolism, weight loss, and muscle growth.
Combat Obesity
Effectively managing weight goes beyond calories — it’s about making smarter lifestyle choices. Intermittent fasting has proven to be an effective strategy for weight loss and obesity management.
A December 2021 review in JAMA Open Network concluded that intermittent fasting can help reduce body weight, body mass index, and cardiometabolic risk factors (ex. cholesterol, triglycerides, and blood pressure) in adults with overweight or obesity.
Improve Body Composition
Working on your body composition can help you shed fat and maintain lean muscle. Fasting promotes fat loss while preserving lean muscle mass. A November 2024 study in the Journal of Translational Medicine found that 16-hour fasting can improve body composition in healthy and non-trained individuals.
Protect Your Brain
Forgoing food for a short period of time just might help improve your focus and sharpen your thinking. An August 2024 study in Cell Metabolism found intermittent fasting improved cognition, memory, and executive function in 40 older adults with obesity and insulin resistance.
Additionally, a January 2018 review in Nature Reviews Neuroscience that looked at intermittent metabolic switching — cycling between ketosis (a metabolic state induced by fasting and/or exercise) and recovery (eating, resting, and sleeping) — can improve neuroplasticity (the brain’s ability to change and adapt).
Though research is still emerging on the effect of fasting on the brain of healthy adults, an October 2019 review in Nutrients reports that, in animal studies, fasting has shown the potential to improve cognition, slow cognitive decline associated with aging, and slow neurodegeneration. However, further research is required to determine how fasting affects human brain function.
Potentially Increase Longevity
Slowing the aging process could be as simple as supporting your body’s natural repair systems. Evidence suggests fasting may promote longevity by triggering cellular repair processes like autophagy and reducing inflammation.
A February 2021 study in the International Journal of Molecular Science found that periodic fasting increased the diversity of helpful gut bacteria, including a type related to longevity. Furthermore, a March 2022 review in Nature Aging states intermittent fasting has “positive effects on risk factors for aging, diabetes, autoimmunity, cardiovascular disease, neurodegeneration and cancer.”
Types of Fasting
Fasting comes in many forms, each with its own approach and potential benefits. Here’s a breakdown of the most common types of fasting:
- Water Fasting: consuming only water for a set period, typically 24 to 72 hours, often used for detoxification or spiritual reasons
- Dry Fasting: avoiding both food and water, usually for shorter periods (12 to 24 hours) but risks dehydration
- Juice Fasting: only fresh fruit and vegetable juices for a period of time, eliminating solid foods but providing more nutrients than water/dry fasting
- Intermittent Fasting (IF): eating windows are restricted, like Alternate-Day Fasting (switching between days of fasting and eating), 16:8 Method (fasting 16 hours, eating during an 8-hour period), and 5:2 Method (eating 5 days a week, fasting for 2 days)
- Eat-Stop-Eat: fasting for a full 24 hours once or twice a week, typically from dinner one day to dinner the next day
- One Meal a Day (OMAD): consuming all your calories in one meal each day, fasting for the remaining 23 hours
- Partial Fasting: limits specific foods or food groups (such as meat, dairy, or processed foods) while allowing others, usually for several days or weeks
- Fasting Mimicking Diet (FMD): a low-calorie, plant-based diet designed to mimic the effects of fasting while still providing some nutrients
Is Intermittent Fasting Healthy?
Whether Intermittent Fasting is a good fit for you depends on your health status and goals. It may be an effective strategy for weight loss and improving metabolic health for some, but others may find the approach too restrictive.
Hunger, low energy, and irritability are common during fasting periods, especially in the beginning. Also, fasting may disrupt hormones, particularly in women, potentially leading to menstrual irregularities, according to the Cleveland Clinic.
If you’re considering Intermittent Fasting, it’s essential to listen to your body, start slowly, and consult a healthcare provider to ensure it’s safe and sustainable for your lifestyle.
Side Effects of Fasting
If you’re new to fasting or pushing your limits, these are some side effects you might experience, according to Harvard Health Publishing:
- Hunger and overeating (in recovery periods)
- Fatigue and lethargy
- Constipation
- Metabolic issues
- Nausea (especially if you’re on medication taken with food)
- Electrolyte imbalance
- Headaches
- Irritability and crankiness
- Unhealthy weight loss that affects your bones, immune system, and energy level
If these symptoms become severe or persist for an extended period, it’s important to stop fasting and consult with your doctor to ensure your health isn’t at risk.
Who Should Not Fast?
While fasting can benefit many people, it’s not suitable for everyone. Certain individuals should avoid fasting or consult a healthcare provider before trying it:
- Children and teens under 18
- People who are pregnant or breastfeeding
- Individuals with type 1 diabetes who take insulin
- Those with a history of eating disorders
- People with certain chronic health conditions like heart or kidney disease
- Individuals with weakened immune system
Frequently Asked Questions
What can I eat while fasting?
During fasting periods, you should avoid consuming any food. However, some types of fasting, such as intermittent fasting, may allow non-caloric beverages like water, tea, or black coffee. Be sure to check the specific fasting method you’re following for guidelines.
How long is it safe to fast?
The length of a fast should depend on the method you’re following and your health. Generally, intermittent fasting methods like 16:8 are considered safe for most people. Extended fasting (more than 48 hours) should be done under medical supervision.
How long do I need to fast for it to be effective?
For intermittent fasting to be effective, you typically need to follow a consistent fasting schedule, with methods like 16:8 showing results after several weeks. Longer fasts (24 hours or more) may offer additional benefits but should be approached with caution.
What is dirty fasting?
Dirty fasting refers to a more relaxed version of fasting where you may consume small amounts of calories (like a splash of milk in your coffee or a sugar-free drink) during fasting hours, while traditional fasting requires no caloric intake at all during fasting periods.
