Long-Term Effects of Intermittent Fasting

Most people have heard about intermittent fasting. It’s become one of the most popular tools people try when they’re looking to lose weight. 

However, skipping breakfast (or dinner) for a couple of months is one thing, but what happens when you do it consistently for several months or even years? 

Here, we’ll take a closer look at the intermittent fasting side effects that can happen with long-term fasting. We’ll also review who should think twice before turning fasting into a permanent lifestyle. 

What Is Intermittent Fasting?

Intermittent fasting isn’t a diet in the traditional sense—it doesn’t tell you what to eat, but when to eat. It involves cycling between periods of eating and periods of little to no calorie intake. 

Here are some of the most common approaches to intermittent fasting: 

• 16:8 fasting: Here, you eat within an 8-hour window and fast for the rest of the 16 hours. This means that if you finish dinner at 8 pm, your next meal isn’t until noon the following day. 

• 5:2: You eat normally for 5 days a week, and then you restrict your intake to roughly 500-600 calories on 2 consecutive days. 

• Alternate-day fasting: You alternate between normal eating days and fasting (or near-fasting) days. 

• Eat-stop-eat: A full 24-hour fast once or twice a week. 

Remember to consult a doctor before trying fasting, particularly if you’re considering longer fasts. And you should never try a long fast if you haven’t done smaller fasts. 

What makes intermittent fasting stand out is how simple it is to follow. Many people find it easier to control what they eat than to obsessively count calories at every meal. 

What Are the Long-Term Effects of Intermittent Fasting? 

Once your body gets used to fasting, you may notice several changes, both positive and negative. 

Looking at the pros and cons of intermittent fasting can help put these changes into perspective.

The Potential Benefits

Here are some of the potential benefits of intermittent fasting (5):

• • Weight management, thanks to a shorter eating window that can reduce calorie intake. 
  • Improved insulin sensitivity, which can help your body manage blood sugar levels more efficiently. 
  • Reduced inflammation, a factor that has been linked to chronic disease and aging. 
  • Better blood sugar control, which may help lower the risk of type 2 diabetes over time. 
  • Cellular repair through autophagy, a process where your body clears out damaged cells and regenerates new ones. 

• Brain health support, including increased levels of BDNF (brain-derived neurotrophic factor), which plays an important role in learning and memory. 

• Better gut health, which can help improve digestion and reduce bloating. 

The Potential Negative Effects

The negative effects of intermittent fasting aren’t widely discussed. However, some people experience the following (4):

• A slower metabolism, similar to what happens with any prolonged calorie restriction. 
• Muscle loss, particularly when the protein intake isn’t prioritized during the eating windows. 
• Electrolyte imbalances, which can lead to fatigue, cramping, or dizziness. 
• Hormonal disruptions, particularly in women. 

However, researchers still don’t have a complete picture of what years of intermittent fasting can do long-term. Most studies have focused on short-term results and in small groups. 

BetterMe: Health Coaching app can help you build a more structured approach to your wellness routine with meal plans, workouts, and habit-tracking tools. Start using the app to explore options that may support your personal fitness and nutrition goals.

Is Intermittent Fasting Safe in the Long Term? 

For most healthy adults, intermittent fasting appears reasonably safe when it’s practiced consistently over months or years. However, safe doesn’t mean risk-free for everyone. 

As mentioned, there is currently little long-term research on the effects of intermittent fasting. This means that we know what it does in the short term (1), but not in the long run. 

Ultimately, safety depends on how you fast. For example, dry fasting, which restricts both food and fluids, carries serious risks such as severe dehydration. Similarly, reducing your calories too much can increase the risk of nutrient deficiencies, regardless of your fasting schedule. 

In addition, it all depends on each body. Some people thrive with intermittent fasting, while others don’t benefit. If you’re generally healthy and listen to your body, long-term fasting can be okay as long as you speak with your healthcare professional first. 

Can You Do Intermittent Fasting for Years? 

Plenty of people practice intermittent fasting for years without having major issues. With that being said, sustainability comes down toseveral factors: 

• Eating enough during your window: Fasting doesn’t mean restricting your calories so much that you’re constantly undereating. 

• Getting enough protein: This helps protect muscle mass long-term. 

• Staying flexible: Life circumstances can change, and your fasting schedule may need to change with them. 

• Listening to your body: Persistent fatigue, mood changes, changes in your menstrual cycle, or disrupted sleep can signal that it’s time to adjust your approach. 

So while you could fast long-term, it depends on how you manage the factors above. It’s about finding a rhythm that fits your lifestyle and adjusting when something isn’t working. 

Read more: Rest Days: How to Eat When You’re Not Working Out

Does Intermittent Fasting Help with Weight Loss in the Long Term? 

Intermittent fasting can help with weight loss, but you need to consider a few things. Studies have shown that intermittent fasting can improve weight loss, similar to a standard calorie restriction diet (3). However, that’s because both focus on a calorie deficit (eating fewer calories than the body needs). 

The tricky part is what happens during the eating windows. For some people, fasting periods can trigger a strong biological urge to eat more afterward—overeating once they’re in their eating windows. As a result, this can affect the calorie deficit you want to create from a shorter eating window. 

So, long-term weight loss success depends more on your fasting schedule and what you eat during your eating window. To make it work, focus on nutrient-dense, balanced meals to stay on track during your eating window.

Workouts, weight management tools, and recipe ideas come together in the BetterMe: Health Coaching app, giving you practical support for building a more consistent wellness routine.

How Does Intermittent Fasting Affect Metabolism Over Time? 

Metabolism is one of the most misunderstood aspects of long-term fasting. Some people assume that fasting can “boost” the metabolism, while others worry it’s going to mess it up. Both sides have some truth in them. 

During fasting periods, your body eventually shifts from burning glucose to burning stored fat for energy, a process called ketosis. This shift can support fat loss and may improve certain metabolic markers over time (2). 

However, as with any form of calorie restriction, intermittent fasting can slow your metabolism if you practice it too aggressively for too long. And, as mentioned, it will depend on what you eat during your eating window. 

This is why moderation matters. A sustainable, moderate fasting window tends to help preserve metabolic health better than extreme fasts or overly restrictive calories during the eating window. 

What Happens When You Stop Intermittent Fasting? 

If you decide to stop intermittent fasting after months or years, your body will gradually readjust to a regular eating pattern. Here’s what can happen: 

• Appetite regulation shifts back: Ghrelin (your hunger hormone) resets to your new eating schedule. 

• Weight may return: This happens if you’re not careful with your eating habits. 

• Digestion adjusts: Some people thrive on more meals, while others may have more digestive issues. 

Read more: 72-Hour Water Fast: What No One Tells You About It

Who Should Avoid Long-Term Intermittent Fasting?

Long-term fasting isn’t ideal for everyone. There are certain groups of people who have higher risks when practicing intermittent fasting and they should talk to a healthcare provider before doing this eating pattern short- or long-term. 

• Pregnant or breastfeeding women: Due to increased nutritional needs. 

• People with a history of eating disorders: Restrictive eating patterns can trigger disordered behavior. 

• Children and adolescents: They need consistent nutrition for growth and development. 

• People who are taking diabetes medication: Particularly those taking insulin or sulfonylureas, which can produce dangerous low blood sugar levels while fasting. 

• Older adults: Intermittent fasting can increase the risk of muscle loss and affect bone density and immune function. 

• Anyone with adrenal insufficiency: Intermittent fasting can increase the risk of unstable blood sugar levels. 

The side effects of intermittent fasting for women deserve a bit more attention. Some women report changes in their menstrual cycle or hormonal disruptions when fasting windows are too aggressive or the calorie intake drops too low. 

This doesn’t mean that women can’t fast safely, but it does mean that you need to pay closer attention to how your body responds and adjust your approach if something feels off. 

On the other hand, the side effects of fasting for males tend to be less tied to hormonal function. If it’s not done properly, it can increase the risk of poor immune function, fatigue, or electrolyte imbalance. 

FAQs

• Is it okay to fast every day?

Yes, for most healthy adults, it’s okay to do daily fasting, particularly if you’re doing the 16:8 fast. However, be careful if you’re considering or doing longer fasts, and make sure you get enough nutrients during your eating window. 

• Can you do intermittent fasting forever?

Some people can practice intermittent fasting indefinitely without issues. However, it depends on what happens during your eating windows and how your body responds to fasting. 

• Can you gain weight after stopping intermittent fasting?

Yes, it’s possible to gain weight even while doing intermittent fasting—it all depends on what you eat during your eating window. Weight loss happens when you eat fewer calories than your body needs (a calorie deficit). So, if you’re eating a large number of calories during your eating windows, you can still gain weight, even when fasting. 

• Is intermittent fasting hard to maintain in the long term?

It depends on the person and the fasting method. Some people find the schedule easy to stick to once their body adjusts, while others struggle with hunger or social situations that don’t align with their eating window. 

• Can you take breaks from intermittent fasting?

Of course! Taking breaks is a normal part of keeping a sustainable routine. So, if you’re feeling run down, dealing with stress, or your schedule changes, you can change or pause your fasting schedule. 

The Bottom Line

Intermittent fasting can be part of a sustainable healthy lifestyle if it’s approached the right way. While most studies focus on short-term results, there are some long-term studies that have shown promising results. 

The important thing is that you listen to your body. Pay attention to your energy levels, mood, and how you feel during and after your eating windows. If something feels off, don’t be afraid to adjust and to speak with your healthcare provider for guidance. 

And if you’re starting fasting, ease into it gradually rather than jumping straight into an aggressive schedule. If you have an underlying condition or are taking medication, remember to speak with a healthcare provider before you make intermittent fasting a long-term habit.