Nutritionists from the US' top 2 hospitals reveal their go-to power snacks and lunches

Nutrition experts agree that eating healthy is an exercise in advance preparation.We spoke to two nutritionists from leading US hospitals — the Mayo Clinic and the Cleveland Clinic — and both said they bring their own lunch to work most days.They also include healthy snacks in their daily routines, such as nuts, legumes, and seeds, which science increasingly suggests are some of the best protein sources.Visit Business Insider's homepage for more stories.“There is no such thing as a free lunch,” as the tired saying goes. Well, maybe, but there is such thing as a healthy lunch.The key to good nutrition, most experts agree, is to prepare ahead of time.We asked two registered dietitians and nutritionists from the nation's leading hospitals — Jason Ewoldt from the Mayo Clinic and Julia Zumpano at the Cleveland Clinic in Ohio— what they eat on a typical work day.The similarities were striking: both experts opt for lots of nuts, legumes, plant-based proteins, and fresh veggies. Each of their lunches were also naturally colorful, veggie-filled, and full of good sources of protein (beans, cheese, chicken) as well as fiber.“Eat more of these things that are naturally more filling and more nutritious,” Ewoldt said. “At the end of the day, chances are, you're probably eating less.” Science suggests that foods with fiber, fat, and protein keep us satiated longer and also give our bodies beneficial phyotchemicals, minerals, and essential amino acids and omega fatty acids that the body can't make on its own. Here's what Ewoldt and Zumpano each ate for lunch one recent day at the office. Both dietitians ate chickpeas — a staple of some Mediterranean dietsZumpano said she brought a mixed green salad to work with two hard-boiled eggs and an ounce of goat cheese on top. She sprinkled in some roasted chickpeas, sunflower seeds, oil, and vinegar.Ewlodt, meanwhile, said lunch is often his heartiest meal of the day, so his meal was a bit heavier than Zumpano's. He ate a grilled chicken patty on a “thin bun,” along with a side of prepackaged guacamole.“The star player in today's day and age seems to be avocado,” he said. Replete with healthy, filling, monounsaturated fat, avocados boast a solid dose of fiber and protein. They are also a great source of potassium, a natural antidote to salt that can help maintain healthy blood pressure levels. Alongside his sandwich and avocado, Ewoldt said, he also dipped some vegetables into “a little hummus thing.”You may have noticed one critical shared ingredient in these two lunches: the chickpea (also known as a garbanzo bean). Zumpano put some in her salad, while Ewoldt ate them in his hummus. Chickpeas are high in iron and fiber, and they're a staple of the traditional Mediterranean diet, which studies find time and again to be the best eating plan if you want to up your chances of living a long, healthy life.Mediterranean diets also tend to be heavy on vegetables — as were the two dietitians' lunches. Because of their chemical makeup, veggies and other plants are excellent cancer-fighters, helping keep the body disease-free. Phytochemicals — which give fruits and vegetables their bright colors, odors, and flavors — can help defend us against disease once they get to work inside our bodies. The chemicals can reduce inflammation, which has the potential to make cancer more likely. Phytochemicals act kind of like ingestible body guards, keeping the things we eat, drink, and breathe from becoming cancer-causers in the first place by preventing DNA damage.Planning and habit-forming are crucialEwoldt said he tries to make it as easy as possible to prepare a lunch. He buys some of his sides pre-portioned and in bulk at Costco (like hummus and guacamole), and cuts his veggies ahead of time so that he doesn't have to think about what to pack in the morning before he bolts out the door. “Everything's pre-portioned and ready to go,” he said, adding that the toughest hurdle many of his patients face when it comes to eating healthy is good planning. “Once we can get a plan down, it makes it much more likely that they're going to succeed and a much greater chance that they're going to have a better health outcome,” he said. University of Southern California psychology professor Wendy Wood agrees.“People who have these healthy habits aren't really thinking about the alternatives,” she said. “That's the beauty of forming habits, the response just comes to mind. Usually, we act on it before we have a chance to think.”Wood said she has seen this kind of nutrition choice play out in her own lab experiments. In one, her team trained people to systematically choose carrots as a snack, again and again. Eventually, many research subjects choose carrots over chocolate on their own, without thinking. Veggie-eating had become almost a reflex. The dietitians snack on nuts, cheese, and bananasEating healthy during the day is not just about what you pack for lunch, though. “There's more research that shows if you have a small, healthy, filling snack, you're still hungry for lunch, you're just better able to manage choices and portion how much you're eating,” Ewoldt said. For breakfast, Ewoldt said he'll often opt for Greek yogurt with berries. (That is a go-to morning meal for many other health experts, too.) If he gets a little hungry before lunchtime, Ewoldt said he may snack on a cheese stick or banana.For her snacks, Zumpano said, she also opts for a couple ounces of nuts mid-morning — roughly a handful or two of raw almonds, walnuts, or some other nutty mix. After her cheesy lunch salad, Zumpano said she ate a banana with natural peanut butter in the afternoon. By eating filling, high-protein, low-sugar snacks, Ewoldt added, you're more likely to keep your healthy eating spree going through the rest of the day.“Instead of coming home and you're ravenous, you're coming home and you can wait until dinner,” he said.