Over the past decade, scientific research has demonstrated remarkable health benefits coming from practices like intermittent fasting, time-restricted eating, and other forms of fasting.
And as the name implies, in order to fast, you must avoid all foods and some beverages for a set amount of time.
However, the traditional definition of fasting leaves plenty of gray areas. For example, what about salt, diet soda, alcohol, or creatine, to name a few?
Keep reading to learn precisely what does and doesn’t break a fast, what to avoid altogether during your fasts, how many calories break a fast, and the wisest ways to end your fast periods.
But first, let’s start with a quick review of what counts as fasting, and all the reasons why it’s a phenomenal health and wellness practice.
Fasting is the practice of intentionally avoiding food and caloric beverages for health, fat loss, spiritual, or religious purposes.
In this article, we’ll be focusing on the best fasting practices for health and fat loss.
However, various styles of fasting cater to different goals. For example, fasting for health and longevity is sometimes different from fasting for fat loss or healthy weight maintenance[*].
Here’s a list of the most common, best-studied forms of fasting:
- Intermittent fasting (IF) is a meal schedule that alternates between schedules of eating and fasting on a regular basis. Typically, when people refer to IF, they mean daily fasting for a set amount of time.
- Time-restricted eating (TRE) includes a limited “eating window” each day, with the rest of the time dedicated to fasting. Generally speaking, it’s more lenient than IF.
- Alternate-day fasting (ADF) involves fasting every other day for 24-36 hours at a time.
- The fast mimicking diet (FMD) isn’t actually fasting, but it offers similar benefits, and we’ll touch on it as we evaluate the effect of foods and drinks on breaking your fast. For FMD, you eat a low-carb, high-fat diet, consuming around a third to half of your usual daily calorie intake for 5 days in a row, then resume your normal eating pattern for several weeks or months.[*].
- Dry fasting is where people avoid food and all liquids during their fast period. It’s not as well-studied as other forms of fasting, although one 5-day medical study found that it may be safe in healthy individuals[*].
However, dry fasting isn’t the focus of this article. If you dry fast, you must avoid all foods and beverages, period — there’s no wiggle room. At Levels, for safety reasons, we don’t recommend you try dry fasting.
And finally, some people engage in various forms of fasting less regularly, for health and longevity purposes. For example, fasting once or more per week or per month. Typically, these types of fasts are for longer durations, such as 24-72+ hours.
11 Benefits of Fasting
- Efficient weight loss without calorie counting[*]
- Resets hunger hormones[*]
- Heightens fat-burning (especially combined with fasted cardio) due to lower insulin levels[*][*][*][*]
- Increases ketone production[*]
- Boosts healthy immune function[*]
- Enhances brain health[*]
- Improves insulin sensitivity and glucose tolerance[*]
- Raises growth hormone (GH) levels[*]
- Extended fasting increases autophagy, allowing healthy cells to “recycle” old, defective cells and their parts[*]
- May prevent chronic diseases[*]
- May increase longevity[*]
Before we dive into specific foods and drinks, here are some helpful guidelines to keep in mind.
Firstly, fasting is mostly about avoiding calories, glucose, and insulin release. Therefore, the majority of calorie-free options are fine during a fast.
Second, your fasting goal determines how much leniency you have.
Here’s a hierarchy of how strictly you need to avoid calories, based on your desired outcome:
- Strictest fasting: Extreme health benefits (immune function, medical purposes, etc.)
- Strict fasting: Longevity
- Less strict: Fat loss
- Least strict: Healthy weight maintenance
The reason you can get away with a few extra calories during a fast for fat loss or weight maintenance is that a small, temporary rise in glucose or insulin won’t end ketosis or significantly inhibit fat-burning for the duration of the fast[*].
On the other hand, benefits like immune function and longevity rely on autophagy, and research shows glucose shuts down autophagy at the cellular level[*].
Therefore, cheating on your fast may “reset” the autophagy you’ve worked hard to achieve — don’t do it.
8 Foods That Are Safe During a Fast
As we just covered, there’s really no such thing as a food that doesn’t break your fast. By definition, food has calories, so you’re breaking your fast when you eat.
However, if your goal is fat loss or you’re a beginner to fasting, you can consume small amounts of the following foods or supplements to suppress your appetite, extend your fast, and continue burning fat for longer:
- Bone broth (optional: add sea salt or spices)
- Collagen peptides
- MCT oil or other healthy fats
- Exogenous ketones (like beta-hydroxybutyrate)
- Celery, lettuce, or other watery, fibrous green veggies
- Psyllium husk fiber or other insoluble fiber sources (mixed with water)
- Guar gum or other soluble fiber sources (mixed with water)
But ultimately, to achieve the full health benefits of fasting, you’ll need to avoid all calories to ensure autophagy and other healthful cellular processes occur.
7 Drinks That Won’t Break Your Fast
- Mineral or carbonated water
- Lime or lemon water
- Green tea or other teas (without added honey or sugar)
- Black coffee (no sugar, milk, or cream)
- Apple cider vinegar (dilute it in water if you prefer)
The most critical factor for an effective fast period is avoiding calories and sugar.
But even if you don’t see calories or carbs on the nutrition label, here are some sneaky, calorie-containing ingredients to avoid while fasting:
- Alcohol (beer, wine, or liquor)
- Fruit juice or fruit juice concentrates
- Cane sugar
- High-fructose corn syrup
- Glucose-fructose syrup
- Erythritol, sorbitol, mannitol, xylitol, maltitol, maltitol syrup, lactitol, isomalt, and other sugar alcohols
- Isomaltooligosaccharides (IMOs), sometimes labeled as vegetable fiber, prebiotic fiber, soluble corn fiber, tapioca fiber, or soluble tapioca fiber
Now that we’ve covered the firm dos and don’ts of fasting, here are some “gray area” supplements and ingredients.
For the most part, we recommend steering clear of them during fast periods, especially if you’re fasting for health and longevity reasons.
But we’re also including the reasons so you can make an informed decision on your own.
Avoid Vitamins and Other Antioxidant Supplements During Fasts
Multivitamins, individual vitamins like vitamins C and E, and other antioxidants may interfere with the effects of fasting or a fast-mimicking diet.
And the reason why has nothing to do with calories or carbs.
Basically, when you fast, the cellular stress that occurs can make your cells healthier — in the long run[*].
Scientists call this process hormesis, and it’s similar to the idea that “what doesn’t kill you makes you stronger.”
However, vitamins and other antioxidants reduce cellular stress, which interferes with hormesis, meaning they could negate some of the benefits of fasting[*].
Therefore, take any vitamins or other antioxidant supplements with meals when you aren’t fasting.
Taking probiotics while fasting is probably a waste — without calories or carbs, they’re less likely to survive the digestive process and absorb through your GI tract[*].
Instead, wait until after you break your fast to take probiotic supplements, and take them with food.
Diet Sodas, Chewing Gum, and Most Artificial Sweeteners
If you like diet sodas or sugar-free gum, we’ve got some bad news for you.
Some sweeteners, like sucralose (Splenda), directly increase your insulin levels[*]. And as you already know by now, an increase in insulin negates some of the benefits of fasting.
And other sweeteners, including aspartame, may not spike insulin, but can still increase your appetite[*].
Researchers think that artificial sweeteners might “trick” your brain into seeking rewards in the form of real sugar[*].
And some studies also show that, like sugar, artificial sweeteners light up your brain’s reward centers similarly to hard drugs, resulting in an addiction to sweet treats[*].
Lastly, sucralose and saccharin both appear to disrupt your gut bacteria[*].
However, if you do want the occasional sweet treat while fasting, stick with drinks or chewing gum sweetened with stevia or monk fruit.
Healthy, plant-based natural sweeteners work differently from synthetic ones, and they don’t wreak havoc on your gut microbiome, either.
Protein, Creatine, and BCAAs
Protein, creatine, and BCAAs all have scientifically-proven health and performance benefits.
And some people do use these supplements for various reasons during a fast, especially if they’re lifting weights or training hard while fasting.
However, most protein supplements, as well as creatine and BCAAs, are not conducive to reaping the core benefits of fasting.
- BCAAs and most protein supplements can cause a temporary insulin spike — which is excellent for building muscle, but could shut down autophagy[*][*][*]
- Most protein powders, BCAAs, and especially leucine also increase levels of mTOR, a growth pathway, which shuts down autophagy[*][*][*][*]
- Creatine doesn’t contain calories or raise insulin levels, but it does appear to boost mTOR[*]
Fortunately, since you won’t be fasting 24/7, the simple solution is to use these supplements at the end of fasts, or during your eating periods.
Likewise, at Levels, we recommend weight training in the fed state — not during your fast.
For more info on the best times to take BCAAs, whey protein, and creatine, check out:
- When to Take BCAAs: What Science Says (Plus 5 Fitness and Health Benefits)
- Protein Shake Before or After a Workout? What the Science Says
- How & When to Take Creatine: The Best Time (Plus 4 Benefits)
When the time comes, what’s the best food to break your fast, intentionally?
In the area of food selection, you’ve got plenty of room for experimentation and preference.
And in case you’re wondering how many calories to break a fast, that depends on your goal. There’s no specific calorie amount that’s best for ending a fast.
Generally speaking, if your goal is fat loss, you should start slowly with foods that fill your stomach easily, so you don’t go overboard on calories. Conversely, if your goals include hypertrophy or athletic performance, you can eat a full-sized regular meal to break your fast.
Here are our favorite suggestions as a starting point, organized according to your goal (fat loss, muscle-building, athletic performance, or health and longevity).
For Fat Loss
If you want to burn fat and lose weight, the key to breaking your fast wisely is not to undermine your fasting results by overeating.
Here are the best foods to keep your appetite in check as you end the fast:
- Healthy fats (try eggs or avocados)
- Rich, filling soups
- Fruit and veggie smoothies
- Grass-fed whey protein powder
- Collagen peptides
For Muscle Building
If your goal is to build muscle, you need to activate the growth pathways that were suppressed during your fast.
Here are some of the most effective options:
- Nutrient-dense, whole food protein sources like steak
- Grass-fed whey protein powder
Carbs can also boost muscle growth by raising insulin levels, but unless you have a workout scheduled, you don’t have to eat them right when you break your fast.
For a comprehensive list of foods that can help you grow, don’t miss Clean Bulking: 13 Diet and Training Tips to Gain Muscle, Not Fat.
For Athletic Performance
Athletic performance depends on providing your muscles with energy, so the number one priority is replacing the glycogen (glucose stored as fuel) that you lost while fasting.
Try these clean carbohydrate sources to boost your athletic performance after a fast:
- Rice (white, brown, or other)
- Breakfast cereal
- Sprouted-grain bread
- Sweet potatoes
- Muffins, bagels, or other bread-based foods
- Natural jelly or jam
- Dextrose (pre-workout blended 4-to-1 with whey protein powder)
How to End Longer Fasts
If you’re fasting primarily for health reasons, you may not care as much about fat loss, muscle building, or performance.
Additionally, your stomach is more likely to be sensitive after a long, health-oriented fast.
Try these gentle food choices for your first 1-2 meals to ease back into eating without upsetting your gut:
- Frozen fruit smoothies
- Fresh berries
- Bone broth
- Light soups (low in protein and fats)
- Fermented foods, especially unsweetened yogurt or kefir
- Soft, cooked veggies
And the longer you just fasted, the longer you should take to go back to normal eating. Don’t rush the process, especially if you’re inexperienced with prolonged fasting.
Fasting is a wonderful health and wellness practice.
No matter whether your goal is lean mass, fat loss, preventing chronic disease, or living into the triple digits, you can enhance your results by fasting from time to time.
However, keep in mind that your goal determines how strict you must be with food and drink during the fast. Otherwise, you’re unlikely to get the full benefits of fasting.
And it’s wise to speak to your doctor before you try fasting, especially if you have a medical condition, take medication, or are pregnant, nursing, or a senior citizen.