Smoothies can be a great choice to help you lose weight. Prepared the right way, they are packed with fiber, low in calorie density, filling, and high in nutritional content.

Characteristics of an ideal weight loss smoothie:

No added sugar
No added fruit juice (or just a very small amount)
Instead of sugar or juice, blend in whole fruit for sweetness
Leafy greens or vegetables - the more the better
Blended well (makes it more filling from air content)

Tips

Spinach and cucumber are almost tasteless when added to a fruit-based smoothie. It is a wonderful way to sneak in fiber and nutrition into every smoothie. Add a handful of spinach, or roughly 1/4 of a cucumber, depending on preference -- ideally add as much as you can and over time, increase the amount of vegetables you add. You can cut cucumbers ahead of time and freeze the chunks for ease and convenience.

Add some protein such as yogurt, protein powder or cottage cheese to make the smoothie more filling. For the lowest calories the protein source should be fat-free or low-fat and sugar-free.

Frozen fruit (typically in chunks) is a convenient source of fruit for a smoothie because you don't have to worry about keeping fresh fruit on hand, and it helps make smoothies thick (use in place of ice cubes if desired).

Cautions

Studies have shown that it's easier to consume calories we drink so it is possible to consume too many calories with smoothies. Making a THICKER smoothie can solve the problem -- especially if it requires you to eat it with a spoon. Also, blending it on high for longer adds air which makes it more filling.

Be careful of commercial smoothies made in restaurants, bakeries, etc. Particularly fruit smoothies. Ask if it has added sugar. They typically do, which turns it into a high-calorie treat instead of being helpful for weight loss. They also may have a lot of fruit juice, which also adds sugary content. If possible, get a 100% whole fruit smoothie. (On the positive side: any fruit smoothie will have at least some fruit and fiber and that's better than many other alternatives if you are craving something sweet).

Smoothies aren't magical. They only help you lose weight if they help you control calorie intake. A high-fat smoothie may work well on a ketogenic diet, but probably not for other diets (and even on keto, fat calories have to be limited in order to lose weight). As always, be sure you know the total calories of the smoothie and make sure it fits within your calorie budget or diet.