This Is Why You Can't Drink Diet Drinks If You're Doing Intermittent Fasting
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You’ve likely heard celebs and influencers tout the benefits of various trendy diets, but one buzzy eating plan continues to stay in the spotlight: intermittent fasting. People swear by the benefits of structuring *when* they eat and snack, but the fasting schedule begs a lot of questions. Are there side effects? Will I lose weight? Do I have to give up my morning coffee? What can I drink without breaking my fast?
The latter are the questions that bring us here today. Keep reading for everything you need to know about what you can—and can 't—drink while fasting.
Why What You Drink During Intermittent Fasting Is So Important
“Many beverages have calories that can break your fast, trigger an insulin response, and prevent your body from going into autophagy, which is one of the benefits of fasting,” says Ana Reisdorf, RD, founder of The Food Trends.
That being said, it’s especially easy to become dehydrated while fasting (no matter what type of fast you’re on), says Reisdorf. “You may not realize, but a lot of your daily fluid needs come from food, and when you avoid eating for a period of time, this means you will need to drink more water or other calorie-free liquids to compensate," she explains.
Be intentional about your sipping and aim to drink at least 2.7 liters of water per day. The only time as much plain water as you want is not allowed is if you’re on a dry fast, which Reisdorf does not recommend and says can lead to severe dehydration.
What *Not* To Drink While Fasting
A good rule of thumb is to avoid any drinks that have any calories while you're fasting, says Erin Palinski-Wade, RD, author of 2 Day Diabetes Diet who is based in New Jersey.
This includes sweetened beverages, such as juice or soda, milk or other dairy-based beverages, and alcohol, says Reisdorf. Some schools of thought also recommend avoiding diet sodas, even though they are calorie-free, since artificial sweeteners can trigger an insulin response, she adds.
What You *Can* Drink While Fasting
Okay, but what you can actually drink when fasting may be a little hazy. And there are some surprising hacks that allow you to have some flavor without breaking your fast. (Think: adding spices to your coffee or a splash of fruit juice to your H20.)
Below, what you should know about some of the most popular drinks you might want to consume while doing intermittent fasting, and whether or not they'll sabotage your fasted state.
Meet the Experts: Ana Reisdorf, RD, is the founder of The Food Trends. Erin Palinski-Wade, RD, is the author of 2 Day Diabetes Diet. Regan Jones, RDN, ACSM-CPT, is the host of This Unmillennial Life.
Drink: Coffee
Black coffee is calorie-free, so it's fine to enjoy during the fasting phase. But adding in sugar, cream, or milk is best avoided, as it can add calories to the drink that can take you out of a fasted state.
“If you do want to flavor your coffee during a fast, experiment with calorie-free flavoring from a spice like cinnamon,” says Palinski-Wade. “Save the coffee add-ons for your non-fast windows of time."
Wondering about a keto-approved creamer or MCT oil? “This tends to be a little bit more controversial or at least open for interpretation depending on who you talk to,” says Regan Jones, RDN, ACSM-CPT, host of This Unmillennial Life.
"From a strict fasting standpoint, adding fats to your coffee does break the fast," Jones says. "But I actually do recommend high-quality MCT for people who are consistently doing day-to-day IF programs, especially if their goals are less about cutting calories and more about keeping blood glucose low and giving the body time to rest and digest.”
Fats do not have the same sort of blood glucose raising ability of carbohydrates or protein, so they do not really impact your fast if what you're trying to achieve is improving your overall insulin sensitivity, according to Jones. Plus, “Many people report better focus in the morning sipping coffee with MCT oil since the medium-chain fats in MCT oil get immediately converted to ketones, which are an alternative fuel source for the brain versus glucose.”
Additionally, avoid having more than one cup, or switch to decaf, when you're fasting. Excessive caffeine, especially on an empty stomach, may increase those jittery feelings which can often increase appetite and the desire to snack. Jones adds that caffeine raises cortisol which can “cause a cascade of hormonal responses that ultimately leads to an increase in blood glucose, [which is] something we are trying to avoid when fasting,” states Jones.
Drink: Tea
Just like coffee, tea is naturally calorie-free and fine to have during a fast, so long as it’s simply brewed tea that comes from tea bags, leaves, or flakes. Bottled ice tea is often heavily sweetened, so if you go that route, make sure you’re opting for one that is unsweetened and not loaded with added sugar and calories, says Palinski-Wade. Caloric add-ons such as honey, milk or cream should be reserved for non-fasting times, just like with coffee.
“Since tea is naturally lower in caffeine than coffee, you can have a bit more during fasts, however I would still recommend opting for decaf when possible,” she says.
Drink: Water and seltzer
Water is naturally calorie-free so there's no need to restrict it, says Palinski-Wade. Water in general is a good idea to sip on during fasting times to ensure hydration but also as a way to fill your stomach and prevent hunger.
If you enjoy flavored water, you can add in fruit wedges or a splash of lemon or lime juice (or a splash of another juice) as long as it is a true "splash" (around one tablespoon per 12 ounces) and doesn’t add more than a trivial amount of calories, says Palinski-Wade. Carbonated water/seltzer can be treated in the same way as water, as long as it is naturally flavored and calorie-free.
Skip: Apple cider vinegar
When it comes to fasting, many people think apple cider vinegar (ACV) or an apple cider vinegar tonic is okay to consume. According toJones, both ACV and bone broth have calories. "While minimal, the calories would ultimately lead to a metabolic breaking of the fast," says Jones.
However, if you really enjoy sipping ACV or an ACV tonic at other (non fasted) times, you're in luck. “If the goal is to simply reduce caloric intake overall throughout the day and give the body an extended period of digestive rest and lower insulin levels, I would say the ACV is less likely to raise insulin levels than bone broth,” Jones says.
Skip: Bone broth
Unfortunately, if you enjoy sipping on a warm mug of bone broth, you may want to wait until after you have finished your fast. “Bone broth, while very popular in paleo and some fasting circles, can be a nutritious and satisfying beverage, but it can also be a source of protein. Protein raises blood glucose, which raises insulin levels," says Jones. While protein won't impact blood sugar and insulin levels as much as carbohydrate, it will still break your fast.
Skip: Soda
If you're wondering if you can drink soda (or diet soda) while you're doing intermittent fasting, Palinski-Wade recommends staying away from soda in general, even if you’re not following a diet like intermittent fasting.
Regular sodas are usually loaded with sugar and calories and offer no nutritional value, she says. There also isn’t enough data and research to say whether diet soda is okay to drink during IF, but research suggests that consuming too many artificial sweeteners (as diet sodas tend to have) can increase cravings and appetite, as well as promote weight gain and the storage of fat.
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.“Your best bet is to limit all sodas as much as possible and satisfy carbonation cravings with seltzer or carbonated water,” she says.
Skip: Alcohol
Alcohol should never be consumed when in a fasting period, as its effects can be intensified when consumed on an empty stomach, says Palinski-Wade. Alcohol is also a source of calories, so drinking it would break your fast while also likely stimulating your appetite and leading to increased hunger and cravings.
Frequently Asked Questions
Who should try intermittent fasting?
Intermittent fasting is typically safe for most healthy people, but you should always consult with your doctor or a registered dietitian to see if it’s right for you, says Reisdorf. It is more important that certain groups avoid intermittent fasting, she adds.
People who should not do intermittent fasting include:
Those with medical conditions, particularly metabolic disorders like diabetes
Pregnant or breastfeeding women
Children and teens
Those who are underweight
Those with a history of disordered eating
Older adults who may have different nutritional needs
What are the pros of intermittent fasting?
Everyone is different and has unique needs, but intermittent fasting may lead to faster weight loss, improved body composition, and improved insulin sensitivity, says Reisdorf. On top of that, it’s a relatively easy plan to follow which involves less meal prep, she adds.
What are the cons of intermittent fasting?
Intermittent fasting may be too restrictive and difficult to sustain for some, says Reisdorf. In the same vein, it can trigger disordered eating and unhealthy eating patterns, she adds. It’s also not recommended for those with underlying health conditions or nutritional deficiencies.
What is the best thing to drink when intermittent fasting?
Plain water, black coffee, and unsweetened tea are the best beverages to sip while fasting, says Reisdorf. At the end of the day, you want to consume close to zero calories during fasting periods. By avoiding sweetened drinks like soda and bottled iced tea, as well as caloric add-ons in your hot beverages, you can ensure you follow your IF plan correctly and successfully.
What should you eat while intermittent fasting?
It’s clear that what you drink while fasting contributes to your success, but what you eat (when you're not actually fasting!) is also key. A main perk of intermittent fasting is that you technically don’t have to alter what you eat, you just have to eat within a certain window of time.
That said, you want to be sure your meals are well-balanced, says Reisdorf. Prioritize fruits, vegetables, and protein during your feeding window, and focus on foods that are high in fiber and healthy fats, she adds. Think quinoa, spinach, apples, avocado, salmon, almonds, sweet potato, and chicken.
You also want to avoid or minimize processed foods, simple carbs, refined sugars, and sugary drinks.
What about taking supplements during a fasting period?
This depends on the fasting schedule you're following, and you should discuss any supplements with your doctor before beginning to take them, says Palinski-Wade. If you fast for a set amount of hours each day, take your supplements during the eating hours (unless otherwise instructed by your doctor or dietitian), since most supplements like a multivitamin are better absorbed when taken with food.
If you practice intermittent fasting that involves fasting on specific days, like the 5:2 diet, taking supplements is still recommended to ensure you are meeting your nutrient needs each day. Palinski-Wade recommends taking a high-quality multivitamin daily when following any IF plan.
“Generally, the small amount of calories found in a chewable/gummy/liquid vitamin would not offset a fast day,” she says. "But do discuss this with your doctor or dietitian first to make sure you can take your supplement on an empty stomach.”
Types Of Intermittent Fasting
Consider these different types of fasting that focus on *when* you can eat. Remember: Always talk to your doctor before overhauling your eating regimen and know that we’re not necessarily endorsing these strategies, just shedding some light on what they involve.
16/8 Method: This is the most popular method that involves fasting for 16 hours each day and limiting your eating window to eight hours, says Reisdorf. This is relatively easy to follow since it usually involves skipping breakfast and having your first meal around noon, she adds.
5:2 Diet: With this plan, you eat “normally” for five days a week and restrict calorie intake to 500 to 600 calories for two non-consecutive days, says Reisdorf.
Eat-Stop-Eat: This method involves fasting for 24 hours once or twice a week, says Reisdorf. So, you would eat dinner one day and fast all the way until dinner the next day.
Alternate-Day Fasting: This method involves fasting every other day, Reisdorf explains. On fasting days, calorie intake is either restricted to 500 to 600 calories or completely avoided, she adds.
OMAD (One Meal a Day): OMAD involves fasting for approximately 23 hours and consuming all your daily calories within a one-hour eating window, explains Reisdorf. This is the most extreme form of fasting.
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