Low Carb Diets: Pitfalls of Low Carb Weight Loss (cont.)

"All of the B vitamins work together in a very complicated metabolic pathway and they need each other -- so if you are not going to get your source in foods, then a vitamin supplement is a must," says Heller.

Sondike agrees and says that, "Any time you are on a weight-loss diet you need a good multivitamin, regardless of whether you are limiting your carbohydrate intake or not," he says.

Although there has been some evidence that a low-carb diet can also take its toll on calcium levels, Sondike says that fortunately, this is usually only on a short-term basis.

"Your body will often shift metabolism when you do something different to it -- but it equalizes -- you see a rapid shift and a return to normal -- and the longer-term studies show normal results in this area," says Sondike. Still, he tells WebMD it's a "smart idea" to take a calcium supplement beginning at the start of your low-carb diet to safeguard against a possible deficiency. Tofu can also be a good source of calcium.

Another mineral you may want to supplement is potassium. While there is no concrete evidence that a dramatic potassium loss occurs on a low-carb regimen, Sondike says to ensure against problems he recommends patients use Morton's Light Salt -- a potassium chloride product that he says can add back any of this important mineral that's lost. Eating a few almonds is also a good way to supplement this mineral without adding carbs to your diet.

Finally, if you stick to your low-carb diet via the use of prepackaged foods, experts say read the label carefully to avoid ingredients that are notoriously responsible for gastrointestinal upsets, and especially excess gas. Among the worst offenders: sugar alcohol, found in sweeteners such as sorbitol.

"Anything above 10 grams or more of sorbitol at a time has been shown to cause gastrointestinal upset -- and some of these low-carb diet foods have as much as 30 grams a serving," says Heller. While it won't make you violently ill, she says, it can make you -- and those in the same room -- pretty uncomfortable.

Sondike agrees and also cautions us to "read the labels."

"If a product is advertised as having 3 net carbs but the label says 35 grams of carbs, then it's likely that 32 grams are sugar alcohol -- and it's probably going to upset your stomach," says Sondike.

SOURCES: Stephen Sondike, MD, director, Nutrition, Exercise and Weight Management Program (NEW), Children's Hospital of Wisconsin, Milwaukee. Doris Pasteur, MD, director, Nutrition Wellness Program at Mt. Sinai Medical Center, New York City. Samantha Heller, MS, RD, nutritionist, NYU Medical Center, New York City.

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