"Everyone wants to lose weight. They want to feel healthy and they think this might be an option," Raj told TODAY's Willie Geist. "If you find yourself even thinking about a cleanse, it's probably a sign that in general you're not happy with the way you're eating and you might want to talk to someone about a balanced approach that's a more long-term solution."
Raj, a gastroenterologist at NYU Langone Medical Center in New York, warned that cleanses are potentially dangerous, especially for people with medical conditions or those taking medication, along with pregnant women and the elderly.
"Some of the cleanses are very extreme and they incorporate only very few ingredients in them, so you're really limiting yourself in terms of not getting enough protein, potentially not enough fiber and even healthy fats that you need," Raj said.
People who cleanse are unlikely to maintain any weight loss, she said.
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"It's very temporary water weight that you're losing so it's not going to persist," Raj said. "You're going to eat more later because you're hungrier. It's just not a balanced approach to weight loss, and this notion that you can sort of eat whatever you want and then cleanse for a week and get rid of all the bad effects from the prior poor eating just doesn't make sense."
"You want to, of course, eat a lot of fruits and vegetables," she added, "but have a balanced diet and you need a long-term plan, not just a three-day or a six-day cleanse."
Raj offered warnings on three types of cleanses.
The juice cleanse, she said, purports to help with the immune system and to detoxify the body.
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"The truth is, you're just getting a lot of fruits and vegetables, which is a good thing, but to the exclusion of everything else, not so great," Raj said, adding that many of the juice products have a lot of sugar. "I don't mind having a juice drink instead of one meal, but when it's three meals for several days, it's not a good idea."
She said the drawback of adding herbal supplements to a cleanse is that you do not know how they will react in your body or with medication are taking. A cleanse made only of raw fruits and vegetables is too limiting for the body, she said.
—By Lisa Flam, Today Show