TAMPA, Fla. — The most famous player in Yankees history had the most infamous diet. Babe Ruth was said to subsist, at least in part, on hot dogs and beer, the fuel that added to his legendary persona as a charismatic, fun-loving superstar.  But if the Babe played for the Yankees today and ambled into their cafeteria looking for sausages and suds, he would instead find sweet potatoes, avocados, quinoa and dark chocolate.  As teams in every sport try to upgrade players’ nutrition for a competitive advantage, the Yankees have joined the fray. This winter they hired Cynthia Sass, a nutritionist, and gave her a mission to recommend the finest and healthiest food spread in baseball and persuade the players to eat it.  “We’re trying to build a more perfect beast,” Yankees General Manager Brian Cashman said.  There is no evidence that ingesting brown rice, kale and grilled skinless chicken breast will contribute to even one win. After all, Ruth did pretty well without them. But he was not competing against opponents who were consuming kale smoothies and doing yoga, as more athletes are today.  Most teams are providing healthier foods to their players than in years past. The Baltimore Orioles took their chef on the road during the playoffs last year to maintain their standards. Many other teams, like the Boston Red Sox and the Los Angeles Angels, are also seeking competitive advantage through nutrition.  The belief is that certain foods can reduce players’ inflammation, encourage healing and boost their immune systems, while unhealthy foods do the opposite. If the right foods can keep one player in the lineup for one extra day, and that player helps win a game, then why not?  “People really accept now the adage ‘You are what you eat,’ ” Sass said in a telephone interview. “So every time you eat or drink, it’s an opportunity to make your body stronger and healthier.”  In recent years, Cashman grew increasingly unhappy with the food that the Yankees were serving to the players, believing it was not in line with the latest research. So at the recommendation of the trainer Steve Donohue, Cashman hired Sass (and another nutritionist to oversee minor league players) to upgrade the Yankees’ health and performance through a better diet.  He also hired the former Yankees minor league pitcher John Kremer as a high performance science director to coordinate the departments that have an impact on player performance: food preparation, medical staff, coaches, scouts and the players themselves. Kremer’s task is to streamline communication and create language common for all the departments.  Sass is a big part of that process. She said she had 20 years of experience working in nutrition, including three with the Philadelphia Phillies and the last eight with the Tampa Bay Rays. She has also been working with the Rangers of the N.H.L.  After the Yankees hired her away from the Rays this winter, Sass met with the chefs at Yankee Stadium and at the team’s spring training complex here to learn what they served to the players and how it was prepared. She made general recommendations, but did not turn the Yankees’ cafeteria into an East Village vegan cafe, at least not yet.  The idea is to add healthy alternatives, educate the players about them, see what they like and then make adjustments. As a general rule, teams provide players with two meals per day: breakfast and lunch for day games and lunch and dinner for night games. On the road, opposing teams provide the food, and Sass said she might make general requests to those teams. For example: Always provide produce.  She said that at Yankee Stadium, there would always be a lean meat protein like grilled fish or chicken breast; lots of fruits and vegetables, which she said were paramount for athletes; and an easy-to-digest, nutrient-rich carbohydrate like brown rice.  Nothing would be prohibited, but the unhealthy foods would not be on display. If someone desperately wanted a bacon cheeseburger and a strawberry milkshake, they could ask for it. Perhaps they would grow self-conscious, like a teenager trying to buy beer, and give in to the grilled salmon, quinoa and nuts.  “I’m not there to shove it down their throat,” Sass said. “It’s not going to happen overnight. The goal is to make the best foods for athletes always available. If they want more of it, we’ll provide it.”  The Yankees have had nutritional experts in the past, including one that the former owner George Steinbrenner borrowed from the United States Olympic Committee. But this time they seem to be making a more concerted push, and players who are more interested in prolonging their careers applaud the effort.  “Baseball in general is way behind the times when it comes to nutrition,” first baseman Mark Teixeira said. “But most teams over the last couple of years have put some effort into it, which is nice to see.”  Early in spring training, Sass spoke to the players and provided a video of best practices. They also heard an expert discuss the merits of sleep.  Sass got their attention by pointing out how certain foods could enhance their performance. For example, carrots really do improve night vision. And research from the University of Georgia shows that green vegetables can improve contrast vision, or the ability to see a white ball with red laces against a night sky. What hitter would not want that edge?  She also explained how sweet potatoes helped support the immune system, something vital for players facing extensive travel and a grueling schedule. Some players knew that, and most said the changes to the menu in Tampa this spring had been minimal.  “Grilled chicken breast and a sweet potato is fine for me,” said Teixeira, who came to spring training with a new gluten-free diet of his own and eats avocado almost every day.  Sass said she helped players find a personal chef, if they wanted one, or with anything else to do with food. For a typical game day, she recommends eggs (the so-called perfect protein) with lots of vegetables in them, oatmeal and fruit for breakfast. Lunch should include a lean meat protein, a quinoa grain bowl or a salad with olive oil vinaigrette and avocados. For dinner, grilled salmon, baked sweet potato, lots of grilled vegetables and fruit on the side.  She also promotes the virtues of avocado and organic dark chocolate, which she says has natural substances that relax blood vessels and open up circulation. The small amount of caffeine is nice, too.  “I noticed they don’t have bagels or fried chicken out anymore, and that makes sense,” pitcher Adam Warren said. “I try to eat better, and I feel it. I had a pizza the other night, and I felt really sluggish the next day.”  Oh, goodness, not pizza. An athlete might as well guzzle a bucket of lard. According to Sass, the worst foods are ones that combine several unhealthy elements. A pepperoni pizza, for example, is made of three no-nos: refined flour stripped of most of its nutritional value and fiber, fatty meat and gooey cheese. Don’t even mention soda.  But players are human. Many spent years in the minor leagues devouring fast food and peanut butter and jelly by the barrel. Outfielder Carlos Beltran described his minor league road routine: He would buy eight tacos from Taco Bell, eating four before the game and four after it. Brett Gardner said that during long bus rides the team would stop at a gas station and players would grab a bag of chips and a soda.  “That would hold you over,” he said, “until you got to the stadium for the peanut butter and jelly.”  Those are old habits, and even young players are increasingly aware of their diet. Now the hope for the Yankees is to go the next step, with seven helpings of produce per day and perhaps a treat of avocado ice cream and dark chocolate.  “We’re not the food police,” Cashman said. “We can’t force them to eat it. We will provide healthy alternatives and help them understand why those options are good. The rest is up to them.”  (Full disclosure: This article was written during the consumption of peanut butter and Marshmallow Fluff on white bread with iced coffee, not exactly the new Yankee diet.)  A version of this article appears in print on March 20, 2015, on page B9 of the New York edition with the headline: Pinstripes May Be Slimming, but a Nutritionist Helps. Order Reprints| Today's Paper|Subscribe
The Yankees, forever looking for a competitive edge, hired a new nutritionist over the winter and charged her with recommending healthy foods and persuading players to eat them.