The idea that filling up on fruits and vegetables will cut one's appetite for higher-calorie fare did not pan out in a new study; in fact, adding fruit juice before meals boosted hunger and weight gain for some participants.
Eating apples and grapes before lunch helped people feel fuller and eat slightly less than when they drank an equivalent amount of fruit juice as an appetizer in the experiment. However, putting volunteers on a fruit- and vegetable-heavy diet for months made no long-term difference in their assessments of their own hunger and fullness, researchers found.
Some doctors have hoped that encouraging people to eat greater volumes of fruits and veggies, which are less "energy-dense" than burgers and pizza, might help them feel full for longer and prevent overeating and weight gain.
But the new study suggests loading up on more carrots, broccoli and oranges every day won't ward off hunger over the long run. And having fruit in beverage form simply added calories to the day's tally without displacing any.
The findings follow results from the same trial showing 34 participants - some overweight or obese, some a healthy weight - gained between 3.5 and 5 pounds when they were given eight weeks of fruit juice to incorporate into their diet. Heavier participants, in particular, also gained weight when they received extra fresh fruit and vegetables.
"If you tell people to add anything to their diet, you're going to potentially have no weight loss, or weight gain, even with fruits and vegetables," said Barbara Rolls, chair of nutritional sciences at The Pennsylvania State University in University Park.
"You need to be careful to make sure that you emphasize substitution, not just, 'Eat more of this or that,'" Rolls, who was not involved in the new research, told Reuters Health.
That's especially true for beverages, she said, since the body regulates hunger and thirst differently - and people often don't think to eat less to make up for juice or other calorie-filled beverages.
Richard Mattes from Purdue University in West Lafayette, Indiana, and his colleagues found that when they fed volunteers a regular lunch of all-you-can-eat macaroni and cheese, they ate an average of 785 or 821 calories of it, depending on the day.
When the same participants started a meal with fresh and dried fruit, then went on to the main course, they ended up eating 678 calories of lunch, the fruit course included. When they started with fruit juice instead, the volunteers took in a total of 891 calories.
People ate about 400 more calories, on average, during the test day when they started lunch with juice, compared to when they started with solid fruit, according to the findings published in the International Journal of Obesity.
But those results in favor of fresh and dried fruit did not hold up over the longer-term, Mattes and his team found. When the researchers provided the volunteers with 400 to 550 calories of either fruits and vegetables or fruit juice each day for eight weeks, there was no change in how they rated their hunger or fullness at regular intervals during each test period.
That means simply adding fruits and veggies to meet nutritional guidelines may not be enough to help people stay full and lose weight - and may actually make it harder for them to shed extra pounds, researchers said.