A good smoothie should have protein + fiber + healthy fat + fruits/vegetables. Mayo Clinic says a smoothie can be fine daily or as a meal replacement when it has the right balance of carbohydrates, protein, and healthy fats. Harvard also notes that adding protein and healthy fat helps a smoothie work as a meal or meal complement.

Good smoothie formula

Base: water, unsweetened almond milk, low-fat milk, soy milk, or kefir
Protein: Greek yogurt, protein powder, cottage cheese, tofu, or nut butter
Fiber: berries, spinach, chia seeds, flaxseed, oats
Healthy fat: walnuts, chia, flax, avocado, or peanut/almond butter
Flavor: cinnamon, ginger, cocoa powder, vanilla, lemon

Easy anti-inflammatory smoothie

Blend:

• 1 cup berries

• 1 handful spinach

• ¾–1 cup Greek yogurt or soy milk

• 1 tablespoon chia or ground flaxseed

• ½ banana, optional

• Water/ice

• Cinnamon or ginger

That gives you antioxidants, fiber, protein, and healthy fats.

Watch out for “sugar bomb” smoothies

Limit or avoid:

• Fruit juice as the base

• Sweetened yogurt

• Ice cream or frozen yogurt

• Too much honey/agave/maple syrup

• Giant portions

• Smoothies with only fruit and no protein/fat

Johns Hopkins recommends including protein, fruit, greens, and a liquid base, rather than just fruit and juice.

Best serving size

For most adults: 12–16 ounces is plenty.
As a snack: 8–10 ounces.
As a meal: include 20–30 grams of protein and some fiber/fat.

Bottom line: Yes, smoothies are a good option when they are balanced. The best ones are closer to a blended salad/protein meal than a dessert drink.