by Mary Squillace for SHAPE.com
These foods are surprisingly high in nutrientsAlmost every diet has a blacklist-those foods you must not let pass your lips if you want to melt off pounds fast or cure tummy troubles. Yet many of these "bad" foods are ones we've been told for years contain key nutrients that help us prevent disease and actually lose weight.
All of these mixed messages can leave a woman confused-and hungry. Learn the facts about eight foods shunned by certain diets and why they may do your body a world of good-and never feel guilty about enjoying them again.
1. Whole grains
Forbidden by: gluten-free (with some exceptions) and paleo diets
Whole grains contain compounds called phytates, which can bind to minerals such as zinc, iron, and manganese, preventing our bodies from absorbing these nutrients, according to Cassie Bjork, a Minnesota-based registered dietitian. "Phytates make whole grains less nutrient-dense than a nutrition facts panel would let you believe," she says. "In my opinion whole grains aren't necessary at all. They don't contain any vitamins and minerals you can't get from non-starchy fruits and vegetables."
RELATED: 7 Foods a Nutritionist Would Never Eat
But while phytates and other "antinutrients" can interfere with absorption, they don't completely strip a food of its beneficial parts, says Andrea Giancoli, R.D., a spokesperson for the American Academy of Nutrition and Dietetics. And unless you're really loading up on produce, you're going to miss out on a lot of belly-filling, heart-friendly fiber, adds Bonnie Taub-Dix, R.D., author of Read It Before You Eat It. Plus those without celiac disease or gluten intolerance won't reap any dietary benefits from giving up grains that contain wheat gluten and in fact could become deficient in B vitamins, studies have found.
If you are concerned about phytates, buy sprouted grains or soak yours before cooking, Giancoli says, but most people don't need to worry.
Forbidden by: paleo diet
Like whole grains, beans and legumes contain phytates, as well as proteins called lectins, which have been linked to inflammation. "Additionally legumes are difficult for some to digest due to their high oligosaccharides content, which often results in abdominal pain, bloating, and gas," says Franziska Spritzler, a registered dietitian in southern California. So some people who aren't eating paleo shy away from beans to avoid these side effects.
However, the health benefits outweigh their potentially inflammatory properties, says New York City-based registered dietitian Lyssie Lakatos. Unlike meat, beans serve up a healthy dose of fiber and water along with protein. They're also chockfull of antioxidants, which actually protect the body against inflammation and are thought to ward off cancer and aging, Lakatos says. As with grains, you can soak legumes before cooking to reduce their phytate content.
3. Foods cooked above 114 degrees
Forbidden by: raw food diet
Eating unprocessed, uncooked foods has its merits: When you avoid foods cooked over a certain temperature as part of a raw food diet, by default you're likely going to end up eating more plants, which research shows may decrease the risk of cardiovascular disease and diabetes. But the prevailing theory behind eating raw is that food's nutritional enzymes-which aid digestion and are thought to improve fat burning-begin to break down above a certain temperature (between 114 and 118 degrees).
The truth is, though overcooking certain vegetables causes them to lose some of their water-soluble nutrients (think of that broccoli your grandma boils until it turns brown), this logic is largely flawed, Giancoli says. Heat does kill enzymes, but once those enzymes hit our highly acidic stomachs, they'll be broken down by our digestive system anyway. As for the promise that a raw diet is detoxing, Giancoli says if you eat a healthy diet, your immune system will naturally eliminate any toxins in your body.
"It's better to have a mix of raw foods and cooked foods in your diet," she advises, "as some foods have better absorption of nutrients when they are cooked." In particular heart-boosting lycopene, which gives tomatoes, watermelon, and other produce their red hue, has been found to be more readily absorbed from cooked tomatoes than raw ones or tomato juice. Beta-carotene-an antioxidant in carrots, sweet potatoes, and kale, among other vegetables-is linked to skin and eye health, and is also more bioavailable to the body when cooked.
Forbidden by: Atkins (phase 1 and 2), glycemic-index, paleo, and South Beach diets
Taters are sometimes shirked by diets for their high glycemic index, a measure of the extent to which particular carbohydrates increase your blood sugar. "I call it riding a blood sugar roller coaster," Bjork says. "High blood sugar can lead to mixed emotions, inability to focus, and highs and lows throughout the day." Additionally high blood sugar sets off a chain of linked reactions: Insulin surges, triggering cells to store sugar as fat, and that can lead to weight gain.
But the glycemic index isn't a very accurate measure, says Joy Dubost, R.D., spokesperson for the American Academy of Nutrition and Dietetics. It only assesses the potential blood sugar spike for foods when they are consumed in isolation, so a potato's GI drops when eaten with protein and fats, which help stabilize blood sugar. By these standards, a baked potato with sour cream is actually better for you than a plain one. Beyond that, potatoes contain nutrients that Americans typically fall short of, such as potassium (which helps lower blood pressure) and fiber. As long as French fries and chips aren't your main potato intake, spuds have a place in your diet.
Forbidden by: macrobiotic, paleo, raw food, and vegan diets
Aside from animal rights issues, dieters' main beef with dairy has to do with digestive issues. Macrobiotics say dairy contains "toxins," while some paleo enthusiasts say it's inflammatory. See, milk contains a sugar called lactose. As babies we have an enzyme, lactase, that helps us digest human milk and also allows our bodies to process cow's milk. As we grow older, some people keep processing the enzyme while others don't, leading to lactose intolerance.
But for those without lactose sensitivity, eschewing milk products won't do much good, as it's beneficial for bones and potentially for weight loss. "We typically don't get enough calcium or vitamin D, and milk's a great delivery source of both," Dubost says. "Unless you have an allergy or intolerance, I wouldn't recommend you eliminate it."
6. Nightshade vegetables
Forbidden by: macrobiotic diet
The macrobiotic diet strives to prevent chronic degenerative diseases and has roots in eastern medicine. While this eating plan is mostly plant-based, nightshades-a family of veggies that includes tomatoes, potatoes, eggplants, and peppers-are banned because followers say the alkaloids in these cause joint pain and arthritis.
However, although some people are sensitive to nightshade vegetables, there is no research to support this theory. "It's a very individual thing," Taub-Dix says. "Some people with aches and pains from arthritis find eliminating these vegetables helpful, but plenty of people who eliminate these foods don't notice a difference." And while you won't become deficient in any one nutrient by bypassing nightshades, you miss out on several potential health benefits. For example, tomatoes are our greatest dietary source of lycopene and have been linked to decreased risk of cancer and cardiovascular disease; a study in the Journal of Nutrition reported that yellow and purple potatoes may decrease inflammation; eggplant may have heart benefits; and different colored peppers provide varying levels of free-radical-fighting vitamin C. So if you aren't experiencing joint problems, keep noshing nightshades.
7. White rice, pasta, or bread
Forbidden by: Atkins, gluten-free (with the exception of gluten-free items), glycemic index, paleo, raw food, and South Beach diets
Similar to potatoes, foods made with processed grains such as white pasta, white rice, and white bread are carb-heavy and have high glycemic indexes. However, unlike spuds, these eats have few redeeming qualities. "Research indicates that a diet rich in whole grains can ward off risk of cardiovascular disease and cancer," Dubost says. But refined grains have been stripped of their bran (the grain's outer shell) and germ (the part of the seed that sprouts)-the places where you'll find fiber, B vitamins, vitamin E, magnesium, iron, and disease-fighting antioxidants-so you're not getting any health benefit.
"Processed grains are digested very quickly, resulting in a spike in blood sugar often followed by a drop, which may lead to hunger and irritability," Spritzler says. Experts agree that whenever possible, substitute refined grains with more nutrient-dense carbohydrates such as fruits, vegetables, and whole grains.
Forbidden by: macrobiotic (with the exception of fish), raw food, vegan, and vegetarian diets
Those following a macrobiotic diet try to balance "yin" (cold, sweet, passive) and "yang" (hot, salty, aggressive) foods, and they believe meat makes the body too yang. Many others reject meat out of consideration for animal welfare, but you can make a strong case against meat based on human health too. "Research shows that people who eat more red meat may have higher incidences of heart disease and cancer," says Tammy Lakatos Shames, a dietitian in New York City. Certain cuts of red meat also carry a lot of saturated fat and cholesterol, and meats cooked at a high temperature have been shown to create carcinogens. Plus you can still get protein and almost all of the nutrients that meat provides from plant sources.
RELATED: 7 Surprising Ways Junk Food Makes You Miserable
On the flip side, meat can definitely be a part of a healthy diet. Iron from red meat, dark poultry meat, and seafood is essential to keep blood stocked with oxygen, warding off fatigue. Vitamin B12, which makes DNA and maintains healthy nerves and blood cells, is only naturally found in animal sources. And of course there is protein, praised for building and repairing muscle and keeping you full. The key with meat is keeping your portion sizes between 3 and 3 1/2 ounces and choosing lean varieties, Dubost says. For red meat, she recommends 93-percent lean ground beef and cuts with 'round' or 'eye' in the name.
More on SHAPE:
11 Ways to Rev Up Your Metabolism
The Ultimate 20-Minute Weight-Loss Circuit
20 Sweet and Salty Snacks Under 200 Calories
by Mary Squillace for SHAPE.com