High-protein/low-carb fad diets have come under some heavy criticism from the experts.
Zied speaks specifically about the Atkins diet, although many high-protein diets are what she calls "imbalanced diets." "By cutting out carbohydrates, it eliminates the food that is supposed to be the main source of fuel for your body," says Zied.
Many of the high-protein diets ignore the nutritional differences between different kinds of carbohydrates, experts say. But there's a world of difference -- nutritionally speaking -- between carbohydrates like refined sugar and a kiwi, says Elaine Magee, MPH, RD, the "Recipe Doctor" for WebMD's Weight Loss Clinic and the author of Fry Light, Fry Right.
So what specifically might someone on a high-protein diet be missing?
- Fiber, which is in many of the carbohydrates that are eliminated in high-protein diets, helps with digestion. It may also help prevent some serious diseases, such as heart disease.
- Water. "Carbohydrates have a lot of water in them," says Zied. "So when you cut them out, it's easy to get dehydrated without realizing it."
- Vitamins, such as A, B, C, and E, are plentiful in many high-carb vegetables, fruits, and grains.
- Folic acid is in dark leafy greens and fruits and vegetables. It's also in many fortified foods, like cereals, that Atkins prohibits. Folic acid may reduce the risk of cancers, heart disease, and other problems.
- Phytochemicals and antioxidants are in whole grains, fruits, and vegetables. "We know that these things can help prevent a lot of different diseases, including heart disease and cancer," says Tara Geise, RD, a spokeswoman for the American Dietetic Association.
Many experts also believe that high-protein diets allow far too much fat. And even protein can be a problem in large amounts. "Overloading on protein can harm your kidneys and affect your fluid balance," says Zied. For some people, especially people who already have kidney problems, these diets may be dangerous.
The South Beach Diet
The South Beach diet emphasizes an initial phase of low carbs but later changes to add more "good carbs." With this diet, you may be in danger of not getting enough fiber, vitamins A, B, C, and E, and important phytochemicals and antioxidants from carbohydrates.