A study published in the International Journal of Obesity shows that a diet heavy in fruits and veggies may not help satiate hunger. In addition, adding fruit juice before meals may actually boost hunger and weight gain for some.
The researchers began by feeding 34 volunteers a regular lunch of all-you-can-eat macaroni and cheese. The participants 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.
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. 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.
However, when the researchers provided the volunteers with 400–550 calories of 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. The participants gained between 3.5 and 5 lbs 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.
The researchers concluded that simply adding fruits and veggies to meet nutritional guidelines may not be enough to help people stay full and lose weight.