Quick, what is the main food diabetics have to avoid?

If you said sugar, you're under the spell of a common health myth, according to Omaha, Neb., Hy-Vee grocery dietitian Carrie Nielsen.

"I think there’s still a myth that diabetes is all about sugar," Nielsen said. "Really, all foods can (be safe) for diabetics as long as they watch the portion size."

Dr. Christopher D. Saudek writes forJohn Hopkins Hospital, "The fact is that when a person with type 1 or type 2 diabetes ingests concentrated sweets such as candy, pies, cakes and doughnuts, their blood glucose may rise a bit more quickly, but not necessarily any more, than if the person ate an equal number of grams of a complex carbohydrate such as potatoes or rice."

He says that means that people with diabetes can make sugars and sweets part of their diets.

The sugar myth is just one dietitians say they're working to debunk.

Do Carbs Make You Fat?

Speaking of carbs, aren't they all just fattening?

Nationally known dietitian and author of "The Flexitarian Diet"Dawn Jackson Blatner said she cringed when she recently caught a morning news anchor making that claim.

"The only thing that causes weight gain is excess calories, but the problem with carbs is people tend to eat a lot of them. They can be a healthy part of your diet, especially if you choose whole wheat versions and pay attention to portions. Eyeball it to be about baseball size. That’s about a cup," Jackson Blatner said.

In fact, carbohydrates are an important source of energy, so much so that a September 2002 study from the National Academies Institute of Medicine recommended that people focus on getting more good carbs with fiber into their diet, according to WebMD.com. "To meet the body's daily nutritional needs while minimizing risk for chronic disease, adults should get 45 to 65 percent of their calories from carbohydrates."

Across the board, it is the amount of food eaten that accounts for weight loss or gain, Jackson Blatner said, also blasting the myth out of the water that food eaten at night puts on the pounds faster than daytime eating.

8 Glasses A Day?

Then there's that old saw about drinking eight glasses of water a day. Cardiac dietitian for Alegent Health Toni Kuehneman said the widely popular theory was based on a biochemical equation that humans need 1 milliliter of water for every calories expended over the day.

"Health professionals and the public just kept repeating that," Kuehneman said. "Now we go by sense of thirst and color of the urine or how often you urinate. Just a hint of color, you know you’re hydrated. Darker urine means you have more solids than fluid, so you need more water."

Smash Honey's Halo

If you're feeling virtuous that you've swapped out all the sugar in your diet for honey or agave, wait just a minute. Jackson Blatner said she has a lot of clients bragging about just this switch. She said there are some trace minerals in honey and agave that aren't in sugar, but she discourages people from falling for the "halo effect" of those miniscule minerals.

”What we know is that our bodies really don’t know much of a difference between the different types of sweeteners. They all break down so quickly in terms of how your body perceives them," she said. "People start using too much. They’re really still just empty calories like processed white sugar."

Two favorite health myths highlighted by The Hartford Courant include the idea that stretching prevents injured or sore muscles. A growing body of research says it doesn't, the Courant reported, citing research from Consumer Reports. Also, the myth that antioxidant pills prevent disease. "No, popping them seems more and more pointless," the Courant reported.

And that points to another claim Nielsen said she takes a lot of questions about -- the antioxidant power of the acai berry.

"A customer had heard in an Oprah-approved e-mail about it. There are claims being made that aren’t necessarily backed up. This customer was looking for the fountain of youth," Nielsen said.

Read more about what research on acai shows.