A 21 day smoothie challenge can help you lose some weight, but only because it cuts calories, not because smoothies "detox" your body. The best-known version, The Smoothie Diet by health coach Drew Sgoutas, replaces two meals a day with smoothies and has no published research behind it. A safer approach is one protein-rich smoothie a day, with balanced meals around it.
21 day smoothie challenge, the key facts:
- The product: The Smoothie Diet, a 21-day e-book plan that swaps two meals a day for smoothies.
- The evidence: Healthline's dietitian review found "no research to back it up".
- Detox claims: the NIH's NCCIH says a 2015 review found "no compelling research" for detox diets for weight management.
- What does work: structured meal replacements beat comparison diets by 1.44 kg (about 3 pounds) at one year in a 23-trial review.
- Who should skip it: people with diabetes, kidney stones, pregnancy or an eating disorder history, unless their doctor agrees.
What Is the 21-Day Smoothie Diet?
It is The Smoothie Diet, a digital recipe plan by Drew Sgoutas, who is described as a health coach. According to a Healthline review by a registered dietitian, the plan works like this:
- Two meals a day are replaced with smoothies from 36 recipes.
- You eat one solid meal and two snacks of about 150 to 200 calories each.
- One "cheat day" a week has no smoothies.
- An optional 3-day "detox" replaces all three meals with smoothies.
The creator estimates about 1,500 calories a day. Healthline reported a $47 price in 2022.
What Does the Smoothie Diet Claim?
It claims faster weight loss, better immunity, more energy, better skin and gut health, and detoxification. Website testimonials described losing up to 9 pounds in 3 days, Healthline noted. These are anecdotes, not trial results.
The Federal Trade Commission warns: "Any promise of miraculous weight loss is simply untrue." It also lists "You can lose 30 pounds in 30 days" as a claim to distrust.
Do Smoothie Detoxes Remove Toxins?
No. Your body already removes waste through the liver, kidneys, digestive tract and skin, as Cleveland Clinic dietitians explain. No smoothie speeds that up.
The NIH's National Center for Complementary and Integrative Health says a 2015 review found "no compelling research" supporting detox diets for weight management. A 2017 review found juicing and detox diets cause initial weight loss "because of low intake of calories", which tends to be regained. NCCIH also says people prone to kidney stones should limit high-oxalate foods. Spinach, a common smoothie green, is high in oxalate.
Do Meal Replacement Shakes Work for Weight Loss?
Structured meal replacements can help, but they are not the same as fruit smoothies. A 2019 systematic review in Obesity Reviews pooled 23 trials with 7,884 adults. Diets including meal replacements produced 1.44 kg more weight loss at one year than other diets.
Those trials used formulated products with set calories, protein and nutrients. A homemade fruit smoothie can be very different. Healthline found many Smoothie Diet recipes low in protein and calories, which can leave you hungry and tired.
How Much Sugar Is in a Fruit Smoothie?
It depends on the fruit, and it adds up fast. A medium banana has about 14 grams of natural sugar, based on USDA FoodData Central values. Recipes that stack banana, mango and juice climb quickly.
Juice is the bigger issue. The CDC lists fruit juice concentrates and nectars as forms of added sugar. It advises no more than 10 grams of added sugar in a single meal. Skip juice, honey and sweetened yogurt, and use one serving of whole fruit.
How Much Protein Should a Smoothie Meal Have?
Aim for about 20 to 30 grams. The Dietary Guidelines for Americans, 2025-2030 suggest 1.2 to 1.6 grams of protein per kilogram of body weight a day. For a 150-pound (68 kg) adult, that is about 82 to 109 grams. Plain low-fat Greek yogurt has about 10 grams of protein per 100 grams in USDA data.
How Can You Do a 21-Day Smoothie Challenge Safely?
Replace one meal a day, not two, and build each smoothie like a real meal. Follow these seven steps:
- Replace one meal only, usually breakfast or lunch. Eat two balanced solid meals.
- Use the formula below for protein, fiber, vegetables and some fat.
- Keep fruit to one serving and skip juice, honey and sweetened yogurt.
- Rotate greens, such as spinach, kale and frozen cauliflower, to limit oxalate load.
- Walk most days. Adults need 150 minutes of moderate activity a week.
- Weigh in weekly and aim for 1 to 2 pounds a week, the CDC's suggested pace.
- Plan your exit. On day 22, keep the habits that worked.
What Is a Balanced Smoothie Formula?
| Part | Amount | Options |
|---|---|---|
| Protein | 20 to 30 g | 3/4 cup plain Greek yogurt, cottage cheese, soy milk, or unsweetened protein powder |
| Vegetables | 1 to 2 handfuls | Spinach, kale, frozen cauliflower, cucumber |
| Fruit | 1 serving | 1/2 banana or 3/4 cup frozen berries |
| Fiber | 1 to 2 tbsp | Rolled oats, chia seeds or ground flaxseed |
| Fat | 1 tbsp | Peanut butter, almond butter or a quarter avocado |
| Liquid | 1 cup | Water, unsweetened milk or soy milk |
For cheap ingredients, see our guide to weight loss on a budget for USDA price data. If you are considering prescription weight-loss drugs instead, read about the FDA's new GLP-1 eye warning.
Talk to a doctor first if you have diabetes, kidney disease or kidney stones, are pregnant or breastfeeding, or have a history of eating disorders. NIDDK also notes that losing weight very quickly may raise the risk of gallstones.
FAQs
How much weight can you lose on a 21 day smoothie diet?
There is no research on this specific plan. At the CDC's suggested pace of 1 to 2 pounds a week, about 3 to 6 pounds over 21 days is a realistic range.
Is the 21 day smoothie diet safe?
It is not suitable for everyone. Healthline's dietitian review flagged low protein, hunger, fatigue and possible weight regain as the main concerns.
Do detox smoothies really work?
Not as detoxes. Your liver and kidneys handle that. Any weight lost comes from eating fewer calories.
Can I replace two meals a day with smoothies?
You can, but one replacement is easier to sustain and protects protein intake. Check with your doctor first if you take diabetes medicine.
This article is for general information and is not medical advice. Checked on November 12, 2026, against NIH NCCIH, the FTC, the CDC, Healthline, a 2019 Obesity Reviews meta-analysis and USDA FoodData Central.