Upside: Most of these foods (such as white bread, white sugar and white-flour pasta) are white because they are heavily refined, with fiber and other natural nutrients stripped away. “The difference is, white potatoes come out of the ground that color,” explains Orlando, Florida, nutritionist Tara Gidus, RD, author of The Flat Belly Cookbook for Dummies. Unprocessed potatoes are rich in an ingredient called resistant starch, a kind of carbohydrate that makes you feel full and keeps you that way longer. Resistant starch is not completely broken down by digestive enzymes, leaving it to be consumed by certain bacteria in the GI tract. “These bacteria produce by-products that in turn stimulate the production of leptin, a hormone that shuts off your appetite,” Sandon explains. A 2012 Australian study found that obesity-prone rats gained much less weight when they consumed high levels of resistant starch.
Research from Louisiana State University suggests that the hormonal changes sparked by resistant starch may be especially beneficial as we get older. The starch balances “the populations of bacteria in the intestine,” explains -Maria Marco, PhD, professor of food science and technology at the University of California Davis. “Those changes might result in improved glucose tolerance, reduced levels of systemic inflammation and better appetite control.”
Caveat: To avoid excess fat, eat white potatoes boiled or baked (not fried) and don’t slather them with butter, cheese, sour cream or bacon bits. Healthier toppings include plain Greek yogurt or a tablespoon of grated Parmesan.
Downside: Egg yolks are one of the most concentrated sources of dietary cholesterol—they contain about 184 milligrams—and people concerned about their blood levels of cholesterol have long avoided eggs or egg yolks.
Upside: The current thinking is that “the real culprits for high blood cholesterol are saturated fats, trans fats and overconsumption of processed carbohydrates,” says Bonci. In fact, eggs may even be good for the heart. A study in Atherosclerosis reported that adults referred for coronary angiography who consumed more than one egg per week had less plaque clogging their coronary arteries than their peers who ate eggs less frequently. This may be partly because eggs supply a precursor of nitric oxide, which keeps blood vessels functioning.
Recently, the benefits of eggs have earned them new respect: Eggs are rich in protein, vitamins A and D, iron and lutein (a carotenoid beneficial for the brain and eyes), and the yolk is a great source of choline, a nutrient in which many women are deficient.
Caveat: While it’s safe for many people to consume up to an egg a day, those with multiple risk factors for cardiovascular disease should check with their doctor. Some studies suggest that regular egg consumption may lead to an increased risk of heart disease among diabetics.
Downside: Its high fat content and big calorie count (two tablespoons contain 16 grams of fat and 190 calories) long ago landed it on the dietary taboo list.
Upside: In recent years, nutrition experts have recognized that peanut butter contains mainly heart-healthy monounsaturated and polyunsaturated fats rather than the artery-clogging kind. Peanut butter may also improve blood sugar regulation, which reduces the risk for type 2 diabetes. A recent study in the British Journal of Nutrition found that overweight women who ate peanut butter as part of a healthy breakfast experienced a smaller rise in blood sugar after the meal than a control group not given peanut butter. The reason: Peanut butter “reduces blood sugar jumps by slowing the body’s absorption of carbohydrates,” explains study coauthor Richard Mattes, PhD, professor of nutrition science at Purdue University. In the study, the peanut butter eaters also had less desire to eat, 120 and 370 minutes later, than the control subjects.