Smoothies have become an increasingly popular meal replacement strategy for those looking to lose weight and improve their health. Proponents of the smoothie diet claim that replacing meals with blended fruits and vegetables can lead to quick weight loss and better overall nutrition. But does drinking your meals actually lead to sustainable results?
What is the smoothie diet?
The smoothie diet involves replacing one or more meals per day with a blended smoothie. Common smoothie ingredients include fruits, vegetables, leafy greens, nuts, seeds, nut butter, protein powder, yogurt, milk or plant-based milk.
The idea behind the smoothie diet is that blending all of your meal ingredients into drinkable form makes nutrients easier to digest while keeping calories low. Some plans, like the 10-day green smoothie cleanse, involve drinking only smoothies for multiple days in a row. Other versions take a more moderate approach, replacing just one or two meals per day with smoothies.
Proponents claim that smoothies provide the following benefits:
- Increased fruit and vegetable intake compared to an average diet
- Higher fiber, vitamin and mineral consumption
- Reduced calorie intake compared to solid meals
- Decreased hunger and cravings due to liquid form
- Potential improvements in skin, digestion, energy levels, immunity and cholesterol
Does the research support smoothie diet claims?
While replacing some meals with smoothies can be a healthy strategy for many people, the claims made by hardcore smoothie diet advocates aren’t all supported by research. Here’s what the science has to say:
Increased nutrition
It’s true that smoothies are an easy way to pack more fruits, veggies, fiber and vitamins into your diet. Blended smoothies eliminate the chewing required by whole fruits and vegetables, making it simpler to consume more produce each day.
For example, one study in the International Journal of Obesity found that replacing one meal per day with a smoothie containing fruits and vegetables led to increased produce intake and overall improved diet quality in obese patients following a weight loss diet. Participants drank one smoothie per day containing fruits and veggies equivalent to approximately five servings.
However, nutrition will depend heavily on your specific ingredients. Loading up on sugary fruits, fruit juices and added sweeteners can spike blood sugar, while smoothies with more greens, protein and healthy fats will provide balanced nutrition.
Weight loss
Several studies have associated replacing meals with smoothies containing protein-rich ingredients like yogurt and whey protein with successful weight loss. However, results are mixed when it comes to only consuming smoothies.
One study in Nutrition & Metabolism had obese women follow a 10-day smoothie-only diet using a commercial weight loss smoothie product. Women lost an average of 11.1 pounds after 10 days.
However, this rapid initial weight loss was likely mostly due to water weight rather than fat loss. Study authors noted that a non-smoothie diet following similar calorie restrictions would likely cause similar rates of weight change. So results cannot be attributed to smoothies alone.
Longer-term research on liquid meal replacement diets similarly shows they can be effective for weight loss, but that results are comparable to a standard calorie-restricted diet.
Ultimately, smoothies can help with weight loss when used to replace higher calorie meals with lower calorie options. But they do not cause uniquely accelerated or enhanced fat loss. Any type of caloric deficit will cause weight loss.
Reduced hunger and cravings
Some smoothie diet programs claim that smoothies are more satisfying than solid meals, helping dieters eat fewer calories without feeling hungry. However, reviews are mixed.
A study in the Journal of the American Dietetic Association tested hunger and fullness after drinking a blended soup compared to a solid meal. Blended soup did lead to reduced hunger and increased fullness compared to solid foods. But effects diminished after 150 minutes.
Yet other studies have found that liquid and solid meals have comparable effects on satiety. Puréed or blended foods may help you consume fewer calories during a meal. But benefits do not seem to continue between meals when hunger returns.
More research is needed to determine if smoothies truly suppress appetite and cravings compared to other calorie-controlled diets. Claims of uniquely satisfied hunger are not completely substantiated.
Improved health
Replacing processed foods or ready-to-eat meals with antioxidant-rich smoothies containing veggies and fruits can support overall health.
Fiber from smoothies may improve digestion and blood cholesterol levels. One study in the Annals of Internal Medicine found that a diet high in dietary fiber helped reduce “bad” LDL cholesterol.
However, these benefits are not exclusive to smoothies. Any antioxidant and fiber-rich diet that includes plenty of whole fruits and vegetables can provide the same perks.
Some ingredients like chia seeds, flax seeds and walnuts can give your smoothie an extra health boost due to their anti-inflammatory omega-3 fatty acids. But smoothies are not a required part of an anti-inflammatory diet.
Potential downsides of a smoothie diet
While smoothies can certainly be healthy if made smartly, exclusively drinking your meals can backfire. Here are some potential downsides to watch out for:
Nutrient deficiencies
Smoothies cannot completely replace a balanced meal plan. Vitamins and minerals found only in fortified foods or animal products like B12, iron, zinc, vitamin D and calcium may be lacking.
Pairing smoothies with a side of nuts, seeds or a dairy product can help prevent deficiencies. Variety of produce is also key – don’t stick to just a handful of ingredients.
Blood sugar spikes
Blending concentrates fruits and separates them from fiber found in whole pieces. This allows sugar to enter your bloodstream very rapidly after drinking.
Focus your smoothies on vegetables over fruits. Include protein, fat or high-fiber carbs to help blunt blood sugar spikes. Avoid juice and sweeteners when possible.
Lower protein
Smoothies often lack adequate protein, especially if made only from produce. Protein helps maintain muscle mass when losing weight.
Add Greek yogurt, nut butter, protein powder or milk to boost the protein your smoothie provides to help avoid muscle loss.
Reduced chewing
Chewing is an important appetite-regulating mechanism. Liquifying meals allows you to consume more food in less time. This can lead to reduced feelings of fullness.
Try to avoid “drinking your calories” whenever possible at meals. Chew thoroughly and pace your smoothie intake.
Potential binging
Strict smoothie detoxes can lead to cravings and binges when you finish. Banning certain food groups completely increases desire for those foods when able to eat normally again.
Avoid prolonged smoothie-only cleanses. Include smoothies as part of a balanced, sustainable diet you can maintain long-term.
Creating a healthy smoothie diet
While exclusively drinking smoothies has risks, incorporating one or two smoothies into your daily routine can be a nutritious choice. Here are some tips for healthy smoothie meal planning:
Include protein and fat
Aim for at least 15-20 grams of protein per smoothie to help fill you up and preserve muscle. Good options include Greek yogurt, nut butter, protein powder, milk, chia seeds, hemp seeds or eggs.
Adding some healthy fat can also increase satiety. Options include avocado, nut butter, chia seeds, flaxseed or coconut milk.
Vary produce
Rotate different fruits and vegetables to maximize nutrient diversity.
Focus on leafy greens like spinach, kale and swiss chard which pack nutrients and fiber.
Control carbs
Stick to 1-2 servings of fruits and avoid adding sugars, honey or syrups. Use whole fruits instead of juices to benefit from fiber.
You can add carb sources like oats, quinoa or starchy veggies, but control portions to avoid blood sugar spikes.
Skip unhealthy ingredients
Resist packing smoothies with ice cream, candy, chocolate, baked goods or other high-calorie, low-nutrient foods. These turn a potential health drink into a sugar bomb.
Stick to whole food ingredients over processed additions like Energy drinks, neon food dyes, sugary syrups or low-quality protein powders.
Make it complete
Don’t rely solely on smoothies for full nutrition. Have one smoothie meal paired with balanced solid meals containing protein, fat, complex carbs and plenty of vegetables.
You can also include smoothie “boosters” on the side like nuts, nut butter, yogurt, oats or chia pudding.
Watch portions
Smoothies can be easy to over-consume since liquids empty from your stomach faster than solids. Measure ingredients and stick to standard meal portion sizes of about 400-600 calories.
Listen to hunger and fullness cues. If still hungry after finishing your smoothie, have a small side like veggies or nuts instead of a second smoothie.
Smoothie diet meal plan
Here is a sample one week smoothie diet plan including two smoothies per day as meal replacements:
Day 1
Breakfast: Green protein power smoothie
– 1 cup spinach
– 1/2 cup milk of choice
– 1/2 cup Greek yogurt
– 1 tbsp nut butter
– 1 scoop protein powder
– 1/2 banana
– 1 tbsp ground flaxseed
– Ice cubes
Lunch: Chicken salad wrap with vegetables and greens
Dinner: Berry beet smoothie
– 1/2 cup beets
– 1 cup mixed berries
– 1/2 cup Greek yogurt
– 1/2 cup milk of choice
– 1 tbsp chia seeds
– Ice cubes
Snack: Hardboiled egg and raw veggie sticks
Day 2
Breakfast: Veggie tofu scramble
Lunch: Green goddess smoothie
– 2 cups spinach
– 1/2 cup pineapple
– 1/4 avocado
– 1/4 cup cucumber
– 2 tbsp hemp seeds
– 1 cup coconut water
– Ice cubes
Dinner: Turkey burger with oven baked sweet potato fries and salad
Snack: Cottage cheese and mixed nuts
Day 3
Breakfast: Overnight oats with nuts and berries
Lunch: Chicken caesar salad
Dinner: Chocolate peanut butter smoothie
– 1 banana
– 2 tbsp peanut butter
– 1 tbsp cacao powder
– 1 cup milk of choice
– 1 scoop protein powder
– Ice cubes
Snack: Carrots and hummus
Day 4
Breakfast: Frittata with veggies and cheese
Lunch: Strawberries and cream smoothie
– 1 cup strawberries
– 1 banana
– 1/2 cup Greek yogurt
– 1/2 cup milk of choice
– 1 tbsp chia seeds
– Ice cubes
Dinner: Shrimp fajitas with peppers and onions on tortillas
Snack: Cottage cheese and mixed nuts
Day 5
Breakfast: Breakfast sandwich with egg, vegetables and cheese on whole grain toast
Lunch: Peanut butter banana smoothie
– 1 banana
– 2 tbsp peanut butter
– 1 cup milk of choice
– 1 scoop protein powder
– 1/2 cup spinach
– Ice cubes
Dinner: Chicken stir fry with broccoli and brown rice
Snack: Greek yogurt with blueberries and honey
Day 6
Breakfast: Avocado toast with poached egg
Lunch: Almond butter apple smoothie
– 1 apple, cored and chopped
– 2 tbsp almond butter
– 1 cup almond milk
– 1 tsp cinnamon
– Ice cubes
Dinner: Veggie and bean chili with quinoa
Snack: Celery sticks with nut butter
Day 7
Breakfast: Veggie omelet with cheese, tomatoes, spinach
Lunch: Mean green smoothie
– 2 cups kale
– 1 banana
– 1 cup pineapple
– 1/2 cup Greek yogurt
– 1 tbsp spirulina or wheat grass powder
– Ice cubes
Dinner: Grilled salmon with roasted potatoes and Brussels sprouts
Snack: Dark chocolate and raspberries
The bottom line
Smoothies can be a healthy part of your diet when focused on whole foods and balanced nutrition. But living off smoothies alone risks nutrient deficiencies, muscle loss, food binges, and inadequate protein and fiber.
For best results, include smoothies as one or two meals per day alongside a variety of healthy solid meals and snacks. Avoid prolonged liquid fasts or cleanses.
With smart smoothie meal planning and reasonable portion sizes, smoothies can help increase your intake of fruits, veggies and other valuable nutrients. But they should complement, not completely replace, balanced solid meals.
