2. Misguided Vegetarianism
More than 7 million people in the U.S follow a vegetarian diet. Most of them do it with the best of intentions. Either they love animals too much to eat them, or they're opting for what they see as a healthier lifestyle. A healthy vegetarian diet has been linked to lower rates of obesity, diabetes, and heart disease.
What many people don't realize is that vegetarian doesn't necessarily mean low-fat or low-calorie.
"If you're eating carbohydrate- or starch-rich foods, calorically, you might be eating more," Nolan says.
In other words, if cheese, pasta, and smoothies are the foundations of your vegetarian diet, you can still gain weight and be unhealthy.
Fix it: Make vegetables the centerpiece of each meal. Add whole grains, fruit, and other healthy non-meat foods. Make sure you get enough protein from vegetable sources like beans, nuts, and tofu and essential amino acids from foods like brown rice.
3. Too Much of a Good Thing
A steady stream of research touts the benefits of one food or another. Chocolate, red wine, olive oil, avocados, and nuts have all had their day in the dietary sun.
True, these foods have health benefits. But that doesn't mean more is better.
For instance, chocolate, olive oil, avocados, and nuts are all high in calories. "One of my clients said...he'd heard avocados are good because he had heart disease. He was eating three avocados a day," Nolan recalls. "While they're nutrient-rich and good for you, he was eating at least 500 to 600 calories in avocados each day."
One tablespoon of olive oil has 120 calories. Red wine is alcohol, which in large quantities can raise your risk for heart problems and cancer.
Fix It: It's OK to add a healthy ingredient into your diet. But do it in moderation and as part of an overall healthy eating plan. That means a little olive oil, not a couple of glugs. Or a handful of nuts, not the whole bag. You get the idea.
What about so-called superfoods, like the açai berry -- an antioxidant-rich fruit from Central and South America -- which supposedly have amazing health benefits? Take the hype with a grain of salt, Greaves says.
"There is no such thing as a superfood," she says. "The benefit of the food is only going to be as good as your entire diet. Different foods work synergistically for your entire health." The big picture is what counts.