Nutrition Diet: What should you not mix in a smoothie?

October 3, 2025 •

4 min read

According to a study published in Food & Function, adding bananas to a berry smoothie can reduce the absorption of heart-healthy flavanols by as much as 84%, highlighting that not all healthy ingredients are compatible when blended together. Understanding what you should not mix in a smoothie is crucial for maximizing its nutritional value and avoiding potential drawbacks.

Quick Summary

This guide covers common smoothie mistakes, such as adding excessive sweeteners, using incompatible food combinations, and including ingredients that can impede digestion or nutrient absorption. It outlines specific ingredients to avoid and better alternatives for creating a truly healthy and balanced blend.

Key Points

Avoid Sugary Additions: Skip fruit juices, flavored yogurts, and unnecessary sweeteners, which add empty calories and sugar.
Be Mindful of Fruit Pairings: High-PPO fruits like bananas can inhibit nutrient absorption from other fruits like berries, so it's best to consume them separately.
Choose the Right Base: Use unsweetened milks or water instead of sugary juices or dairy when blending with acidic fruits to avoid digestive discomfort.
Balance Your Blend: Ensure your smoothie contains a mix of fiber, protein, and healthy fats, not just fruit, to maintain satiety and prevent blood sugar spikes.
Be Cautious with Raw Greens: While healthy, high quantities of raw cruciferous vegetables can be hard on digestion or affect thyroid function; steaming is a good alternative.
Control High-Calorie Ingredients: Use portion control for calorie-dense additions like nut butters and healthy fats to avoid unintended weight gain.
Focus on Whole Foods: Prioritize whole fruits and vegetables over highly processed protein powders or pre-made smoothie mixes.

The Calorie and Sugar Traps: Ingredients to Ditch

Many common smoothie additions can quickly turn a nutritious drink into a high-sugar, high-calorie indulgence. Often mistaken as healthy, these ingredients offer little nutritional benefit and can sabotage your health goals.

Sugary Fruit Juices and Flavored Dairy

Instead of a liquid base of water or unsweetened milk, many people reach for sugary fruit juices, flavored yogurts, or ice cream. These additions are loaded with added sugars, which can cause blood sugar spikes and contribute to weight gain. Fruit juice, in particular, lacks the fiber found in whole fruit, meaning you get all the sugar without the digestion-slowing benefits of fiber.

Avoid:
- Flavored yogurts (especially fat-free, which often contain more sugar)
- Sugar-sweetened fruit juices or concentrates
- Ice cream, sherbet, or sorbet
- Canned fruit in heavy syrup

Excessive "Healthy" Sweeteners

While honey, maple syrup, and agave are often promoted as healthier alternatives to table sugar, they are still added sugars. If your smoothie already contains fruit, additional sweeteners are unnecessary. Excessive sugar intake, regardless of the source, can contribute to health issues. Instead, rely on the natural sweetness of ripe fruits like bananas or mangoes.

Too Much Fruit

Fruit is an essential component of a nutritious diet, but too much can lead to a sugar overload. An all-fruit smoothie, especially a large one, can contain several hundred calories and a high sugar content, causing a rapid energy spike followed by a crash. A balanced approach is key, combining fruit with vegetables, protein, and healthy fats.

Incompatible Combinations: Digestive and Nutritional Roadblocks

Some ingredients, while healthy on their own, can cause digestive issues or reduce nutrient absorption when combined.

The Enzyme Problem: Bananas and Berries

Recent research from UC Davis revealed that blending bananas with berries significantly reduces the bioavailability of flavanols, a heart-healthy compound abundant in berries. This is due to polyphenol oxidase (PPO), an enzyme high in bananas. If you want to maximize your flavanol intake from berries, it's better to avoid combining them with high-PPO fruits like bananas.

The Acidic Clash: Fruits and Dairy

According to Ayurvedic principles, mixing fruit with dairy (milk or yogurt) can be problematic. The combination may slow down digestion, leading to bloating and discomfort. The acidity of certain fruits, like citrus, can cause milk to curdle in the stomach, further hindering digestion. Alternatives like unsweetened nut milks or dairy-free yogurt can offer creaminess without the potential digestive distress.

The Goitrogen Concern: Raw Cruciferous Vegetables

Raw vegetables like kale, broccoli, and cauliflower are packed with nutrients, but they contain goitrogens, compounds that can interfere with thyroid function. While this is not an issue for most people in moderate amounts, consistently consuming high quantities of raw cruciferous veggies, especially if you have thyroid issues, could be problematic. Lightly steaming these vegetables can reduce their goitrogenic effects.

Making the Best Choices: Comparison Table


Bad Smoothie Additions	Why to Avoid	Healthier Alternatives
Sugary fruit juices	High in sugar, lacks fiber, can spike blood sugar.	Water, unsweetened almond/oat milk, green tea.
Flavored yogurt	Often contains high amounts of added sugars and artificial ingredients.	Plain Greek yogurt, unsweetened kefir, or dairy-free yogurt.
Extra added sweeteners (honey, syrup)	Adds unnecessary calories and sugar, even if natural.	Natural fruit sweetness from berries or dates, or a few drops of stevia.
Bananas with berries	Enzyme (PPO) in bananas destroys flavanols in berries, reducing health benefits.	Use berries alone or with lower-PPO fruits; eat banana separately.
Dairy milk with acidic fruit	Can cause curdling, leading to slow digestion and bloating.	Plant-based milks like almond, oat, or coconut milk.
Fibrous, stringy vegetables (celery)	Don't blend well, leading to unpleasant texture.	Opt for smoother greens like spinach or blend pre-steamed fibrous veggies.
Excessive nut butter	High-calorie density can contribute to unwanted weight gain if not portioned correctly.	Use in moderation (1 tbsp) or add whole seeds like chia or flax.

Conclusion: Making Smarter Choices for Your Smoothie

Creating a healthy and beneficial smoothie is about more than just tossing fruits and greens into a blender. It requires mindfulness about ingredient combinations and the potential impacts on nutrient absorption and digestion. By avoiding excessive added sugars, opting for balanced liquid bases, and being aware of specific food pairing incompatibilities, you can craft a delicious and truly nutritious drink. Remember that your smoothie is meant to supplement a balanced diet, not to be a replacement for all your daily nutrients. Making these smart ingredient swaps will help you reap the maximum health rewards from every blend. For more tips on diet and nutrition, you can consult authoritative health resources, such as those provided by Northwestern Medicine.

Frequently Asked Questions

Using fruit juice adds significant amounts of sugar without the beneficial fiber found in whole fruit. This can lead to rapid blood sugar spikes. It's better to use water, unsweetened nut milk, or whole fruits.

Recent studies show that combining bananas with berries can significantly reduce the absorption of heart-healthy flavanols from the berries due to the high polyphenol oxidase enzyme content in bananas. Eating them separately is recommended for maximum nutrient intake.

Flavored yogurts, especially low-fat versions, are often loaded with added sugars and artificial flavors to compensate for the lack of fat. Plain Greek yogurt or unsweetened kefir are much healthier alternatives.

Yes, incompatible food pairings can cause digestive issues. For example, mixing acidic fruits with dairy can cause curdling and slow digestion. Some raw, fibrous vegetables can also be hard to digest for sensitive stomachs.

You can use naturally sweet, ripe fruits like mangoes, dates, or ripe bananas. If you need a zero-calorie option, a few drops of stevia can also work.

Adding ice can dilute the flavor and water down your smoothie. A better option is to use frozen fruits to thicken the consistency and chill the drink without compromising taste.

For natural protein, you can add plain Greek yogurt, cottage cheese, nut butter (in moderation), or seeds like chia and flax. These options provide protein along with other beneficial nutrients.