4. Snubbing Carbs
On the flip side of the so-called superfoods are foods that get demonized. If you purge your diet of them, you could pay a price, nutritionally.
Carbohydrates are a prime example. You do want to cut down on white bread and white rice, because these and other refined grains are low in nutrients. The U.S. government's guidelines recommend that at least half of your grains are whole grains.
Fix it: Don't cut carbohydrates entirely from your diet. "Carbs are the primary foods for energy," Nolan says. Whole-grain bread, oatmeal, and brown rice are high in fiber and rich in B vitamins like folic acid, which are nutritional essentials.
5. Fat-Free Fallacy
There was a time when "low-fat" and "fat-free" were dieters' mantras. Food manufacturers catered to this trend by introducing trimmed-down versions of their products, such as fat-free cookies and low-fat salad dressings -- and many people promptly went overboard.
But fat is no longer the dietary bad guy. Doctors and dietitians stress that fats are good for us. We need them.
"Fat is a component of every cell in our body. In order to be as effective as possible metabolically for our cells to do their jobs, we need to have fat in our diet," Nolan says.
Fat is especially important at every meal when you're dieting, she says. "Fat helps you stay full. It satiates you. If you cut all of the fat out of your diet or have very little fat, your blood sugar doesn't stay stable for as long a period of time and you notice that you're hungry sooner," Nolan says.
Fix it: Choose healthier fats -- unsaturated fats from plant sources -- and not too much.
Nuts, seeds, and vegetable oils like canola or olive oil are the healthiest kinds. Fatty fish are a great source of heart- and brain-healthy omega-3 fatty acids. The FDA and EPA recommend that women of childbearing age not eat shark, swordfish, king mackerel, or tilefish because those fish contain high levels of mercury; to eat up to 12 ounces per week (about two average servings) of a variety of lower-mercury fish and shellfish, and to limit albacore ("white") tuna to 6 ounces per week.