Produce-packed juices and smoothies have a place in any healthy diet: They can help you get an extra serving of veggies, give you a protein boost, and score you vitamins that might be otherwise missing from your diet.
But subsisting solely on liquids? Not so much. Sucking through a straw for a couple days, weeks, or months in a row does not detox your body, improve your nutrition, or lead to long-term weight loss, says Jaime Mass, RD, president of Jaime Mass Nutritionals in Florida. Following a juice or smoothie diet plan, however, does come with this startling list of side effects:
1. Nutritional Deficiencies
"Liquid diets are usually not going to provide you everything your body requires," Mass says. The result: Poor energy levels, thinning hair, difficulty concentrating, dizziness, nausea, headaches, and a foul mood. "Even if a liquid diet claims to provide balanced nutrition, be very wary," she says.
2. Muscle Loss
The average juice or smoothie diet plan hinges on severe calorie restriction. And while that can lead to weight loss in the short term, most of that weight will be from muscle, not fat, she says. Losing muscle can compromise your physique, cardiovascular health, and sports performance, and raise your risk of injuries, Mass says. What's more, many plans are lacking in the protein department, only exacerbating muscle deterioration.
3. Rebound Weight Gain
"Liquid diets for weight loss usually leave the dieter feeling like a failure, when they were in fact not set up for success," Mass says. "Consuming very low calorie diets can damage your metabolism and cause aggressive rebound weight gain."
4. Sugar Spikes
Juices and smoothies can be incredibly low in calories and sugars. But other times, they're like sucking down a candy bar—only without the taste-bud tingles. Some juices on the market contain up to 72 grams of carbohydrates and 60 grams per serving. That's comparable to about five slices of white bread—or a 20-ounce sugar-filled soda. Meanwhile, yogurt- or sherbet-heavy smoothies are little more than 600-plus-calorie messes with more carbs and sugar than you will find in not one but two candy bars. "Now imagine drinking that four to six times a day," Mass says.
5. Crazy Cravings
Even if smoothies fill you up, they probably won't leave you satisfied, as the latter hinges on not only the nutrients, but also on the temperature, texture, consistency, and flavor of your foods, she says. Enter, cravings and eventual binge eating.
When you get all of your meals in liquid form, your digestive track doesn't operate as designed, Mass says. For that reason, while on liquid diets some people can stop secreting bile, which is needed for proper digestion. This can lead to gallstones.
7. Digestive Issues
"When you consume sugar in large quantities, the body will bring fluid into the gut to balance it out," she says. "This can lead to stomach upset, bloating, pain, and diarrhea."
8. An Unhealthy Relationship with Food
"These diets don't teach us anything about healthy eating, portion control, meal timing, food shopping, how to eat healthfully at restaurants, or what healthy weight control is," Mass says. "They foster disordered eating behaviors and lead us to believe that fast weight loss is good—and that could not be further from the truth."