The USDA’s report, called “Healthy Vegetables Undermined by the Company They Keep,” said that processing and preparation methods plays a role in the influence of fruits and vegetables on body weight.
“Earlier ERS research found fruit consumption to be linked to healthier weight status, but for vegetable consumption there was no such link,” said report authors Joanne Guthrie and Biing-Hwan Lin.
The report, issued in early May, said fruits are consumed in their natural states more than vegetables.
“Unlike naturally sweet fruit, American may find vegetables more palatable if prepared with added fats or oils, such as in fried potatoes or creamed spinach, or in a mixed dish like pizza,” according to the study.
Americans often eat vegetables prepared in ways that add calories and sodium and remove dietary fiber, according to the USDA research.
Research in 2002 found that, on average, healthy weight children and adults ate more fruit than their overweight peers.
“Higher fruit consumption was associated with lower BMI for adult men and women and for adolescent girls and boys 10 years of age and above,” according to the study.
However, total vegetable consumption had no association with body weight, the authors said.
The 2002 study found that when vegetables were separated into two groups — white potatoes only, and all other vegetables — white potato intake was associated with higher BMI for both adult men and women. The study found that intake of vegetables other than potatoes was associated with lower BMI among women but not among any other age-sex groups.
USDA researchers found that, on average, Americans ate 1.5 cups of vegetables daily, or about 50% to 60% of the two to three cups recommended for adults and older children. More than half of vegetable intake came from potatoes and tomatoes (51%), whereas only 10% came from dark green and orange vegetables.
Some vegetables were eaten in their raw state — raw carrot sticks or sliced tomatoes— but most were consumed in prepared forms or as part of mixed dishes, according to the study.
Researchers found that potatoes were typically consumed in forms that added fat, with potato chips commonly consumed at home and fried potatoes a popular choice away from home.
While 100 grams of a plain baked potato, eaten with skin contains 97 calories, 100 grams of French fries from a fast food restaurant typically contains 312 calories, according to the USDA.
Tomatoes, the second-most consumed vegetable, showed a heavy processing component to consumption, according to the report. Raw tomatoes accounted for 22% of home tomato consumption, compared with 24% for tomatoes sauces for spaghetti and other pastas. Among foods prepared away from home, pizza provided the largest share of tomatoes consumed, at 32%, followed by raw tomatoes at 17%, and spaghetti and similar pastas with tomato sauce at 15%.
Scrutiny of the issue of fruit and vegetable consumption on weight will increase in advance of the 2015 Dietary Guidelines for Americans.
The 2010 version of the Dietary Guidelines for Americans made only a qualified statement that fruits and vegetables may be a useful part of an overall approach to achieving and/or maintaining a healthy weight.
Looking ahead, the report said consumer messages may assist in preventing obesity and reduce sodium intake.