Christie Aschwanden in FiveThirtyEight:
As the new year begins, millions of people are vowing to shape up their eating habits. This usually involves dividing foods into moralistic categories: good/bad, healthy/unhealthy, nutritious/indulgent, slimming/fattening — but which foods belong where depends on whom you ask.
The U.S. Dietary Guidelines Advisory Committee recently released its latest guidelines, which define a healthy diet as one that emphasizes vegetables, fruits, whole grains, low- or nonfat dairy products, seafood, legumes and nuts while reducing red and processed meat, refined grains, and sugary foods and beverages.1 Some cardiologists recommend a Mediterranean diet rich in olive oil, the American Diabetes Association gives the nod to bothlow-carbohydrate and low-fat diets, and the Physicians Committee for Responsible Medicine promotes a vegetarian diet. Ask a hard-bodied CrossFit aficionado, and she may champion a “Paleo” diet based on foods our Paleolithic ancestors (supposedly) ate. My colleague Walt Hickey swears by the keto diet.
Who’s right? It’s hard to say. When it comes to nutrition, everyone has an opinion. What no one has is an airtight case. The problem begins with a lack of consensus on what makes a diet healthy. Is the aim to make you slender? To build muscles? To keep your bones strong? Or to prevent heart attacks or cancer or keep dementia at bay? Whatever you’re worried about, there’s no shortage of diets or foods purported to help you. Linking dietary habits and individual foods to health factors is easy — ridiculously so — as you’ll soon see from the little experiment we conducted.