Intermittent Fasting: 10 Common Mistakes

Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting. Basically, the daily window for eating is shortened with intermittent fasting so that you only eat between two predetermined times (which can be different for everyone).

While the consensus is still out regarding intermittent fasting and weight loss (some studies show it to be effective, but not necessarily more effective than other types of diets), according to a 2023 review in Nutrients, intermittent fasting has been touted as significantly improving quality of life, decreasing fatigue and lowering IFG-1, an agent that accelerates tumor development and progression.

Think you're ready to give intermittent fasting a try? Reducing your eating time may sound simple enough, but you can easily sabotage your fast if you don't do your research. Here are a few of the most common mistakes made with intermittent fasting.

Not Easing into It

Skip breakfast. Skip lunch. And by 3 p.m. you're willing to eat your arm. "If you normally eat every three to four hours and then suddenly shrink your eating period to an eight-hour window, you'll likely feel hungry all the time and discouraged," says Libby Mills, M.S., RDN, a dietitian at Villanova University's College of Nursing. "Deciding to limit your eating hours may be motivated by weight loss. However, this represents an opportunity to reacquaint yourself with what your body is really feeling. We often are eating every three to four hours and not always because we are hungry."

Plus, you don't have to fast all week. For example, people who follow the 5:2 diet—a type of intermittent fasting—eat regular amounts of healthy food for five days, then flip the switch on the other two days, by reducing caloric intake. A 2021 study in PLoS One suggests that using the 5:2 method might be a feasible way to lose weight.

Consuming Too Many Calories

If you find you consume too many calories while intermittent fasting, you're not alone, says Mills. "It can be easy to overeat when a fast breaks, either because you're feeling ravenous or you justify to yourself that you're making up for lost calories."

Mills advises using a scale of 0 to 10, where 0 is famished and 10 is stuffed. You should feel hungry before eating and you should stop eating when you're full, not just to clean your plate. Mills also recommends slowing down while eating so your brain has time to signal when you're getting full. "It may take 15 to 20 minutes after you start eating," says Mills.

Pictured Recipe: Greek-Inspired Burgers with Herb-Feta Sauce

Sabotaging with Soda

Mills says the carbonation in soda can mask your sense of hunger, which can set you up for being too hungry at your next meal and lead you to overeat. "Artificially sweetened drinks can also raise the satisfaction bar for sweet tastes, so when you do eat a piece of fruit it may not be satisfying."

Mills adds these beverages may also have caffeine, which can affect people differently. "Some caffeine may make you jittery and set you up for craving sweets. While other caffeine may mask your sense of hunger and postpone eating until well past feeling hungry," says Mills.

Not Keeping Track of Water Intake

Pictured Recipe: Watermelon, Cucumber & Feta Salad

In general, you should be drinking 2 liters (that's 1/2 gallon) of water per day. "Water is a part of metabolic reactions in our body and is necessary for it to function properly. Hydration prevents us from mistaking hunger for thirst," says Mills.

During snack breaks, opt for nonstarchy veggies and fruits that contain water (yep, hydrating foods count towards your daily water goal!). Have sliced cucumbers, celery, watermelon and oranges prepped in the fridge or your lunch bag.

Breaking a Fast with the Wrong Foods

Mills says eating adequate lean protein, such as meat, poultry and fish, as well as plant-based proteins like legumes, nuts and seeds with each of your meals will help keep you full longer. "Protein helps us feel full. Plus, if you are losing a few pounds, protein will help maintain your metabolically active lean body mass," says Mills.

Another perk is that fiber from fruits, vegetables, whole grains and legumes will slow the digestion and absorption of the carbs you eat, so you stay full and energized longer between meals. "Plus, choosing foods that provide protein and fiber will provide you with the vitamins, minerals and nutrients you will need as you re-portion your calorie intake," adds Mills.

Going Too Extreme

Sure, you want to grab this diet trend by the lapels and run with it, but there's no need to starve yourself. Taking in less than 800 calories per day might cause greater weight loss—and significantly increased hunger—but also greater bone and muscle loss (which is where some of the lost weight will be coming from). That's not healthy—or sustainable—in the long term.

Not to mention, if you make your window for eating too short, you won't be able to get in all the necessary nutrients you need, nor will you be able to stick with it for long. Make smaller, manageable changes and always listen to your body.

Having Caffeine Withdrawals

Who said to ditch your morning joe, afternoon espresso or warm tea? No one! In fact, coffee isn't bad for you. "A caffeinated beverage, especially if warm, is a comforting bridge between meals," says Mills. Just remember to avoid adding sugar or milk if you drink your cup when you're fasting.

Being Too Rigid

Whether you stick with intermittent fasting for a week or a month, it needs to feel like a natural part of your routine. "Shifting the focus to being more intuitive about when you eat based on your sensation of hunger and fullness is something that makes sense for a lifetime," says Mills. "Choosing foods that nourish your body with the nutrients it needs to stay energized changes a calorie-counting mindset to a quality of life focus." It's less diet mode and more a new way of thinking about—and consuming—food.

Engaging in an Intense Workout

You can exercise, just not like the Hulk. It's hard to go all out in a workout if your tank is empty. Moderate exercise is important for health benefits, but if you want to go a little more hardcore, make sure you're not hours away from your next meal. Basically, don't hit the gym at 5 a.m. and then not break your fast until 2 p.m. Your body needs fuel to get you through a tough workout and to replenish your stores after one.

Giving Up

Avoid throwing in the towel or beating yourself up if you end up eating at the "wrong time." You won't undo all your work with one meal, but you might with a bad attitude. Take the time to reassess and make sure the schedule you've set up continues to work with your lifestyle. Maybe it doesn't anymore and you want to shift your eating window or relax it a bit. That's OK. Also, remember to focus on your food choices and eat as many high-quality, nutritious foods as possible. If you have the right balance of protein, fiber, nonstarchy veggies and H2O, you won't be as hungry throughout the day.

Bottom Line

The research is mixed regarding the benefits of intermittent fasting. If you choose to give intermittent fasting a try, start slow and ease into it. Choose a variety of nourishing foods to eat during your window of eating opportunity. Stay well-hydrated, pay attention to how you're feeling, be flexible with it and don't beat yourself up if you eat outside your fasting period. There is no one perfect way to eat. Listen to your body and do what works best for you and your lifestyle.