What Is the Smoothie Diet?

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low sugar smoothies
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The 21-Day Smoothie Diet, created by Drew Sgoutas, has spawned dozens of imitations and variations. All promise that replacing some of your meals with smoothies will lead to quick and easy weight loss.

As with so many weight-loss plans, though, the details are important. As part of a balanced diet, smoothies can help you lose weight. But ingredients, portion size, and your overall eating plan will make all the difference.

What Experts Say

"The smoothie diet promises rapid weight loss, but pounds shed may be regained when transitioning back to normal eating habits. While increasing fruit and vegetable intake is smart, some people may struggle to meet protein requirements on this diet without proper planning."
Chrissy Carroll, RD, MPH

Background

Sgoutas is a health coach (not a registered dietitian) who created the 21-Day Smoothie Diet to help clients lose weight. His e-book, "The Smoothie Diet," contains 36 smoothie recipes, shopping lists, and a three-week schedule explaining which smoothies to prepare each day. He also offers a "detox" plan with recipes and instructions for replacing three meals a day with smoothies for three days.

How It Works

On this eating plan, you will prepare and drink two smoothies a day as meal replacements. Your third meal is up to you, but for best results it should be lower in calories. Sgoutas also suggests one "cheat day" per week, but includes a recommended food list for this day. He also says that it is fine to repeat the 21-day cycle anytime you would like to lose weight.

What to Eat

The smoothie ingredients vary, but they focus on fruits and vegetables, with some protein and healthy fats. There is some guidance in e-book for the one solid-food meal you will consume each day (recommendations for what to eat, and some "whole food" recipes). Sgoutas points out that if this meal is too high in calories, the diet won't work for weight loss. The e-book also includes some suggested low-sugar, high-fiber snacks.

Recommended Timing

On the "detox" plan, all three daily meals are replaced with smoothies. On the 21-day plan, you'll consume two meal-replacement smoothies (breakfast and lunch), one solid-food meal, and a few snacks.

Modifications

If necessary, plan a "flex day," in which you consume one smoothie and two regular meals. Also of note: The e-book suggests that this diet is not for people with food allergies.

Pros and Cons

Pros

  • Emphasis on fruits and vegetables

  • Less calorie-counting and food tracking

  • Shopping lists included

Cons

  • Restrictive

  • High in sugar

  • Preparation could be time-consuming

  • Not sustainable

Pros

Fruits and Vegetables

The smoothie diet's recipes contain plenty of fruits and veggies, which are an essential part of a healthy diet. They tend to be low in calories and rich in phytonutrients.

Less Counting

Unlike many other eating plans, the smoothie diet doesn't require carbohydrate counting, a food diary, or full-time calorie counting. It does recommend being aware of the calorie count in the daily solid-food meal. With recipes and weekly meal plans (that is, smoothie plans) provided, there is not a lot of decision-making or tracking involved, which is a boon for some users.

Shopping Lists

The e-book contains shopping lists broken down by smoothie and by week, which simplifies grocery-store visits during the three weeks of the diet.

Even with these benefits, experts have concerns about the smoothie diet's effectiveness and sustainability.

Cons

Restrictive

Most of the diet's smoothies are low in protein, and a few fall short in healthy fats. Sgoutas does emphasize getting enough protein throughout the day, recommending at least 50 grams daily by eating a little with each meal and snack. However, some people may need additional guidance on this issue—and without proper planning, could fall short meeting their protein needs. If you are using a smoothie as a meal replacement, make sure it contains each essential macronutrient: protein, fat, and carbohydrates.

In general, fruit smoothies tend to contain plenty of calories from carbohydrates and perhaps a small amount of fat. But they also need a good source of lean protein. Protein helps build muscle, which you need to maintain a healthy metabolism. Try adding a tablespoon or two of chia seeds to a smoothie. The seeds will thicken your drink and provide a boost of fiber as well.

High in Sugar

The 21-Day Smoothie Diet's smoothies contain a lot of fruit. While fruit contributes healthy nutrients, it also contains a lot of naturally occurring sugar. Some smoothies also call for honey, an added sugar. This could be an issue for people with certain medical conditions (which is why it's not recommended for people with diabetes). This 175-calorie peanut butter smoothie is creamy and sweet without the addition of any extra sugars.

Some smoothie recipes (on the diet and not) are very thick. It can be tempting to thin them out with fruit juice. But juice can add lots of calories and unnecessary sugar. Water will make your smoothie easier to drink and ice will add thickness. Try decreasing the amount of juice and adding water or ice to get the right thickness and flavor for you.

Time-Consuming

Making two or three smoothies a day (and cleaning the blender afterwards) takes time. And while you can easily prep a morning smoothie and take it with you for breakfast on the go, it's much harder to have a smoothie for lunch if you're away from home and don't have access to all your ingredients and a blender.

Not Sustainable

It is likely that users will lose weight quickly when they start this diet, because they are cutting calories (while potentially cutting nutrients like protein and healthy fats). But replacing meals with liquids, and living on so few calories, isn't something that most people can continue doing for a long time. If someone goes back to their regular eating habits and increases their calorie intake, they may find the pounds creeping back. This could be why the e-book suggests repeating the 21-day diet as often as necessary.

How It Compares

Smoothie diets like this one are popular, but you'll also find similarities between the 21-Day Smoothie Diet and other short-term, low-calorie, and meal-replacement diets. Often, these don't meet expert advice on healthy eating plans.

USDA Recommendations

Food Groups

USDA nutrition guidelines suggest filling your plate with a balanced mix of protein, fruit, vegetables, grains, and dairy. That's for each meal, not just one per day. It's difficult to get all those nutrients and food groups into a meal-replacement smoothie and still have it be tasty and low in calories.

Calories

For weight loss, the USDA recommends a daily calorie intake of about 1500 calories. The smoothies in "The Smoothie Diet" clock in at much less than that. The daily solid-food meal is a wild card, but overall, Sgoutas does recommend approximately 1500 calories per day in the e-book.

Creating a calorie deficit is often the best way to lose weight successfully and sustainably. But the right number of calories is different for everyone, because of factors such as age, sex, weight, and activity level. Use this calculator to determine the calorie goal that might work for you.

Similar Diets

These diets all promise quick weight loss. But experts say they're unlikely to lead to lasting change.

The Smoothie Diet

  • General nutrition: For most users, two homemade meal-replacement shakes per day, plus a "regular" meal, may not provide the right balance of calories, protein, carbohydrates, and healthy fats that the body needs.
  • Practicality: A lot of this diet's rules and instructions are spelled out in the e-book, leaving less to figure out on your own. But preparing two smoothies a day could be a challenge for anyone who works outside the home. Plus, there's a lot of clean-up.
  • Effectiveness: In the short term, many followers of this diet will lose weight. But to keep it off, they might have to stay on the diet past the 21-day period.
  • Sustainability: Any meal-replacement diet is tough to stick with for the long haul, since these replacements often aren't as satisfying as real food.

SlimFast

  • General nutrition: On the SlimFast plan, users drink two meal-replacement shakes per day, along with some 100-calorie snacks (SlimFast created or homemade) and one full meal of 500 to 800 calories. The shakes are made with milk products and other added flavors and nutrients, and contain protein, fiber, and fat.
  • Practicality: No blending your own smoothies with this diet; just purchase pre-made SlimFast shakes, or mix your own with nonfat milk and SlimFast power. As with the Smoothie Diet, you will need to track the calories of the daily regular meal.
  • Effectiveness: This diet can certainly be effective in the short term, as it cuts calories and is simple to follow with few choices to make.
  • Sustainability: Transitioning off the meal and snack replacements and consistently eating fewer calories may be challenging for many people.

Special K Diet

  • General nutrition: Instead of replacing meals with smoothies or shakes, cereal and other Special K bars and snacks take center stage on the Special K Diet. Consume them for two out of three meals a day for two weeks. Because these foods are fortified with certain nutrients, and the diet is only two weeks long, it is reasonably safe from a nutrition standpoint.
  • Practicality: Like SlimFast, this diet is pretty simple to follow. There is no guesswork or tracking, and the Special K products are readily available and inexpensive.
  • Effectiveness: Some research shows that cutting calories with this method can lead to weight loss. However, it is unclear how long this loss can be maintained.
  • Sustainability: This diet is meant to be a short-term (two-week) plan. But any weight lost this way may be hard to keep off.

Dr. Oz's 21-Day Diet

  • General nutrition: On this structured meal plan, users choose from a prescribed list of foods: Mostly vegetables and plant-based proteins, with limited servings of fruit, grains, and animal proteins (sugars and all processed foods are off-limits). Even though these foods provide good nutrition, experts say the plan is too restrictive for lifelong use.
  • Practicality: This plan doesn't require any calorie counting or food tracking at all. Everything is laid out in the list of foods, number of servings, and portion sizes. And no special ingredients or supplements are necessary. But preparing all foods (since convenience and processed foods are not allowed) can be time-consuming.
  • Effectiveness: As with the other diets, users may well achieve some short-term success. But just as with the Smoothie Diet, Dr. Oz says that repeating his 21-day plan might be necessary.
  • Sustainability: This diet cuts out a lot of popular foods and restricts calories significantly, so for most people, it's unlikely to be something they can continue for a long time.

A Word From Verywell

While you can get recipe ideas from the Smoothie Diet's e-book, consider making your own healthy smoothies and using them as one part of a sensible, balanced eating plan. For best results, measure each ingredient and tally the complete calorie count for your drink so you know how many you'll consume when you drink it. This could save you from making a common weight loss mistake—underestimating the impact of liquid calories.

Use fresh or frozen fruit, such as blueberries, strawberries, mango, peaches or apples. But also, branch out and use ingredients such as watermelon, spinach or kale to get additional vitamins and minerals.​ Try this ​sweet green smoothie to get vitamin-packed green veggies with your morning meal.

Avoid using high-fat ingredients to get a creamy texture. A smoothie made with ice cream, gelato, frozen yogurt, or a large amount of peanut butter is delicious, but it may be too high in calories, fat, and sugar to help you lose weight. Bananas, either frozen or at room temperature, provide a thick, smooth texture without the added fat and calories. If you love the taste of peanut butter, consider using a peanut butter powder instead of the fatty spread. Experiment to find smoothies that work for you, and other healthy recipes that provide lots of nutrition without a lot of calories.

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