The Dietary Guidelines for Americans and its cheat sheet, MyPlate.gov, stresses the importance of eating more fruits and vegetables. Half of everything we eat should be a fruit or vegetable, minimally processed.

Not fruit juice, not smoothies, not apple sauce, not frozen fruit sorbet. When consumed, the fruit or vegetable’s harvest-ready shape should still be recognizable. If American adults consumed the recommended amount of fruits and vegetables, minimally processed, their risk of obesity, heart disease, stroke, diabetes and cancer in middle age would be a small fraction of what their risk is today.

American adults currently consume less than half of the fruits and vegetables that they should be consuming daily. Intervention studies are showing that Americans can double their intake of fruits and vegetables, minimally processed, with some help from dietitians, and that doing so helps them be more successful at losing excess weight and keeping the excess weight off than traditional approaches to weight loss.

Fruits and vegetables, by weight, are made up mostly of water. When water is bound up with dietary fiber, fruits and vegetables fill people up with fewer calories, so they feel fuller after eating fewer calories than happens with other dietary patterns. Processed fruits and vegetables, such as smoothies, are less satiating and can even contribute to weight gain when consumed in lieu of fruits and vegetables, minimally processed.

What prevents American adults from eating more fruits and vegetables, minimally processed? There are many reasons, which include availability, convenience and cost. But an under-appreciated influence on liking for fruits and vegetables is previous exposure to the full range of fruit and vegetable choices.

Most humans are born with an active dislike of vegetables, which the physiologists call “vegetable neophobia,” fear of the new vegetable. It takes 10 to 12 exposures to a botanically distinct new plant food to overcome one’s initial, instinctive dislike for the food.

This was nicely demonstrated in a study of 40 British preschoolers, whose mothers agreed to follow the study’s dietary instructions if their child were randomized to the special intervention. All of these 3 and 4 year olds tasted a range of vegetables, indicating which ones they actively disliked. The mothers of half of these 3 and 4 year olds were then told to ask their child to have at least a taste of the vegetable they had already said that they actively disliked and to do this for 14 consecutive days.

The mothers of the remaining 3 and 4 year olds were given a pamphlet recommending that children eat more fruits and vegetables but the mothers were not told to ask their child to eat a disliked vegetable every day. At the end of the 14-day experiment all of the 3 and 4 year olds were once again asked to rate how much they liked a range of vegetable choices. This time, most of the 3 and 4 year olds in the vegetable exposure group now said that they actively LIKED the previously disliked vegetable whereas the vegetable preferences for the remaining 3 and 4 year olds largely stayed the same.

Vegetable neophobia is a phenomenon not limited to children. American adults, when they travel and encounter new foods not commonly found in the U.S., usually find they don’t like the taste of the new food. Vegetable neophobia is thought to be an evolutionary vestige of days when humans ate a much broader range of vegetables than they do today and where some of the possible vegetables (think: poisonous mushrooms) were toxic.

Our Paleolithic forebears survived their encounters with new (and unbeknownst to them, poisonous) mushrooms by limiting themselves to just a small taste, even if they were very hungry. The dose makes the poison. A little bit of poisonous mushroom would make you sick but a feast of poisonous mushooms would result in painful death. Humans learned to avoid foods that made them vomit.

If a new plant food did not make them sick after 10 to 12 exposures, our Paleolithic forebears learned to like the new plant food and to eat greater quantities. This neophobic response to new plant foods represents a challenge to parents and school food service directors trying to get them to eat new vegetables. For both parents and school food service directors, the advice is to keep exposing the children to new plant foods, even though it will result in increased food waste.

The food waste is part of the learning process. Of course, there will always be select foods that individuals will never like but for most children, regular exposure to new plant foods will eventually lead to their liking the new food. But parents, teachers, cafeteria managers, and pediatricians need to regularly encourage the children to at least taste new vegetables.

Parents need to model good food choices and nonetheless respect the child when the child says that she/he does not like the new vegetable. “Just a taste, honey!” should be sufficient. School boards should not insist that food service directors reduce student food waste to a minimum. The schools with the least fruit and vegetable plate waste are probably not trying hard enough.

Pediatricians should link their assessments of the child’s growth, weight, blood glucose and blood pressure to what the child is eating and how much the child is physically active. When talking about ways of staying in good health, teachers need to highlight the many ways in which filling half of one’s plate with fruits and vegetables every day is a recipe for a longer, slimmer, happier, more disease-free life.

If schools are truly committed to optimizing the health and learning potential of their students, they need to be more proactive in promoting fruit and vegetable intake by students and in promoting physical activity throughout the school day. A “Harvest of the Month” talk about a new fruit or vegetable embedded in health lectures would help. Involving students in growing edible plants in school gardens would help. Having food taste-test booths during the school lunch period such as the food taste booths that one finds at Costco will help. Engaging students in aerobic physical activity before lunch, to help them engender increased hunger for water-bearing foods such as fruits and vegetables will help.

If school boards and parents are truly committed to optimizing our children’s health and growth, they will find effective ways to get students to eat more fruits and vegetables during school lunch. It just takes determination, resourcefulness and patience.