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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 appetiser 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 vegetables, which are less "energy-dense" than burgers and pizza, might help them feel full for longer and prevent overeating and weight gain.
Fruit adds kilojoules
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 kilojoules 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 incorporated fruit juice into their diet for eight weeks. 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 Dr Barbara Rolls, chair of nutritional sciences at The Pennsylvania State University in University Park.
"You need to be careful to make sure that you emphasise substitution, not just, 'Eat more of this or that,'" said Dr Rolls, who was not involved in the new research.
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.
'Careful implementation of recommendations'
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 3297 or 3448.2 kilojoules 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 2847.6 kilojoules of lunch, the fruit course included. When they started with fruit juice instead, the volunteers took in a total of 3742.2 kilojoules.
People ate about 1680 more kilojoules, on average, during the test day when they started lunch with juice, compared to when they started with solid fruit, according to a report online in the International Journal of Obesity.
But those results in favour of fresh and dried fruit did not hold up over the longer-term. When the researchers provided the volunteers with 1680 to 2310 kilojoules 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.
Mattes and his colleagues advised "careful implementation of recommendations" through counselling or other nutrition programmes to make sure people taking steps to improve their diet don't end up accidentally putting on more weight.
(Reuters Health, November 2012)
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