Can you drink a smoothie during intermittent fasting?

Intermittent fasting has become an increasingly popular way to lose weight, improve health, and simplify meal planning. Many people choose to drink smoothies during their fasting periods as a way to get some nutrition while still adhering to the rules of intermittent fasting.

But can you actually drink smoothies while intermittent fasting? And how do smoothies impact your fast? Here is a detailed look at the evidence.

What is Intermittent Fasting?

Intermittent fasting (IF) is an eating pattern that involves cycling between periods of fasting and eating. Rather than restricting what you eat, it controls when you eat.

There are several popular IF protocols, including:

• 16/8 method: Fast for 16 hours per day and restrict eating to an 8-hour window.
• 5:2 diet: Eat normally 5 days a week and restrict calories to 500–600 on 2 days.
• Alternate day fasting: Fast every other day.
• The Warrior diet: Eat small amounts of raw fruits and vegetables during the day and one large meal at night.
• 24-hour fasts: Once or twice a week, don’t eat for 24 hours.

No matter which protocol you choose, the goal of IF is to reduce overall calorie intake to promote weight loss and other health benefits.

Can You Drink Smoothies While Fasting?

Whether or not you can drink smoothies during your fasting window depends on the specific guidelines you are following.

Most intermittent fasting protocols allow for some flexibility during the fast. Black coffee, tea, water, and other zero-calorie beverages are almost always permitted.

However, smoothies made with fruits, vegetables, dairy products, protein powders, or other calorie-containing ingredients would break your fast.

That doesn’t necessarily mean you can’t ever have a smoothie while intermittent fasting. Here are some ways you can make it work:

• Have a smoothie as your first meal to break your fast. Prepare and enjoy it immediately at the end of your fasting period.
• Fit a small smoothie into your eating window. Have it between meals or as a snack.
• Stick to smoothies made with water or unsweetened tea. Avoid adding fruits, vegetables, milks, yogurts, nut butters, protein powders, or other fast-breaking ingredients.

How Smoothies May Impact Your Fast

Drinking a smoothie during your fasting window could influence your results in a few ways:

Calories

The primary concern with smoothies during intermittent fasting is that they provide calories, which breaks your fast. Even smoothies made from healthy ingredients will have calories that could negate some of the benefits of fasting.

For example, here are the approximate calories for some common smoothie additions (1):

• 1 banana: 105 calories
• 1 cup (237 ml) orange juice: 112 calories
• 1 cup (237 ml) 2% milk: 102 calories
• 2 tbsp peanut butter: 188 calories
• 1 scoop whey protein powder: 120 calories

Just one or two ingredients can add 100–200 calories or more to your smoothie, which could technically break your fast.

Blood Sugar and Insulin

Intermittent fasting aims to reduce insulin levels and improve insulin sensitivity. Spiking your blood sugar and insulin works against these goals.

Many ingredients commonly added to smoothies, such as bananas, mangos, and milk, are high glycemic, meaning they cause rapid rises in blood sugar.

A randomized controlled study in 10 people found that consuming a high glycemic index smoothie spiked blood sugar and insulin as much as an equivalent amount of soda (2).

Hunger and Appetite

Another benefit of fasting is allowing hunger and ghrelin, the “hunger hormone,” to decrease. This allows your body to more easily access fat stores for energy.

If you consume calories during your fast by drinking a smoothie, it could stimulate hunger and appetite, making fasting more difficult.

Digestion

One of the proposed benefits of intermittent fasting is giving your digestive system a rest. Smoothies require your body to secrete digestive juices and enzymes to process the food you are consuming.

Although this impact is likely minimal, drinking smoothies may negate some of the potential digestive benefits of fasting.

Tips for Smoothie Fasting

If you want to incorporate smoothies into your intermittent fasting plan, here are some tips to make it more successful:

1. Minimize Ingredients

The more ingredients you add, the more calories, sugar, and nutrients your smoothie will contain. Stick to 1–2 fruits or veggies plus water or unsweetened tea.

2. Choose Low Glycemic Fruits/Veggies

Some smart smoothie additions include:

• Berries
• Citrus fruits
• Apple
• Pears
• Leafy greens
• Cucumber

These foods provide fewer calories and less of a blood sugar spike.

3. Use Water or Unsweetened Tea

Avoid liquid calories by mixing your smoothie with water, sparkling water, unsweetened tea, or a low-calorie protein shake.

4. Add Protein and Fiber

Adding a scoop of protein powder or teaspoon of chia seeds can help keep you full.

5. Make It Slimming

Blend in ice, flaxseed, avocado, spinach, and/or kale to ramp up nutrients and keep calories down.

6. Portion Control

Limit smoothies to 1–2 cups (237–473 ml) to avoid excess calories that could break your fast.

7. Save for Later

Make your smoothie, but don’t drink it until your eating window opens. Store in the fridge or freezer.

Sample Smoothie Recipes for Fasting

Here are a few smoothie recipes to try that are lower in calories and carbs to keep your fast intact:

Berry Green Smoothie

• 1 cup (148 grams) frozen mixed berries
• 1 cup (30 grams) spinach
• 1⁄4 cucumber
• 1 tbsp ground flaxseed
• 1 cup (237 ml) water

Blend all ingredients together in a high-powered blender until smooth. Enjoy!

Orange Creamsicle Smoothie

• 1 orange, peeled
• 1 cup (237 ml) unsweetened almond milk
• 1⁄2 banana
• 1⁄4 tsp vanilla extract
• 3–5 ice cubes

Blend all ingredients until smooth and creamy.

Green Apple Smoothie

• 1 green apple, cored
• 1 cup (30 grams) spinach
• 1 tbsp peanut butter
• 1⁄2 cup (118 ml) water
• 1 tsp cinnamon
• 1 cup (237 ml) unsweetened tea

Combine all ingredients in a blender and mix thoroughly.

The Bottom Line

Technically, drinking a smoothie during your fasting window will break your fast and disrupt some of the benefits. However, you can strategically incorporate smoothies into your eating plan.

To minimize the impact, opt for smoothies with minimal ingredients, low sugar fruits and veggies, protein, fiber, and healthy fats. Limit portions to 1–2 cups.

Time your smoothies right before or after your fast, rather than during. This allows you to get all the nutritional benefits of smoothies without reducing the effects of fasting.

With some planning and careful smoothie construction, you can modify intermittent fasting to suit your preferences and still accomplish your health goals.

Frequently Asked Questions

Can I add protein powder to my smoothie while fasting?

Most protein powders contain calories and nutrients that need to be processed by the body, so they would technically break your fast. Save them for your eating window or look for a zero-calorie protein powder option.

What about milk or yogurt in smoothies when fasting?

Dairy products like milk and yogurt have calories and carbs that will break your fast. If you want a creamy smoothie, opt for unsweetened almond or coconut milk.

Can I use frozen fruit in fasting smoothies?

Yes, frozen fruit works well and provides a thicker, cold smoothie without adding ice. Berries and pineapple are good low sugar frozen fruits to try.

Are smoothies good for weight loss with intermittent fasting?

Smoothies can be an excellent way to increase veggie intake and provide nutrition on restricted calorie days of intermittent fasting. Just be mindful of portions and ingredients.

Should I avoid bananas in smoothies when fasting?

Bananas are high glycemic, meaning they raise blood sugar rapidly. If you do use banana, limit to 1/4 or 1/2 a banana and pair with low glycemic fruits and veggies.

The Takeaway

Intermittent fasting calls for avoiding calories during fasting periods. For most people, smoothies made with fruits, vegetables, dairy, or other ingredients would constitute breaking your fast.

However, you have options. Time smoothies for before or after fasting, limit ingredients, and carefully control portions. This allows you to reap the many nutrition benefits of smoothies without diminishing the positive effects of intermittent fasting.