"The noodles themselves are pretty harmless," said Ron Konzak, author of The Book of Ramen. (Yes, someone actually wrote a book about ramen. There are web sites devoted to the topic, too.) "Usually it's the MSG in the flavor packets that can harm people on low sodium [diets] or [who are] allergic to the stuff."

MSG, or monosodium glutamate, is a "flavor enhancer" used to improve the taste of sweet, salty, bitter, or sour foods. Supposedly, it has a pleasant flavor of its own. Instant noodle makers use it to make their shrimp flavors "shrimpier" and beef flavors "beefier."

According to Stephanie Brooks, a San Francisco Bay Area dietitian, MSG triggers an allergic reaction in 1 to 2% of the population. "People allergic to MSG can get burning sensations, chest and facial flushing, or pain and headaches from it," Brooks said.

Even those who don't suffer from those symptoms should be careful not to overdo it when it comes to the noodles, or at least the flavor packs, which Brooks says are also high in sodium. A sampling of the three main brands of instant noodles revealed sodium amounts of 687 to 830 milligrams per serving. (That's 28 to 34% of the recommended daily value for a person consuming a 2,000-calorie-a-day diet.) On top of that, each serving contains between 7 and 11 grams of total fat (11 to 17% of the recommended daily value).
Source(s):
http://www.medicinenet.com