Highlights:
- Vegetables—naturally low in calories and sodium and high
in dietary fiber—are mostly eaten by Americans in prepared forms that
alter their nutrient profile.
- Holding constant the total amount
of food consumed, eating more vegetables in the forms currently favored
by Americans would add calories and sodium.
- Reformulation of
processed foods, improved labeling of packaged foods, and menu labeling
of food prepared away from home may help Americans make more nutritious
vegetable choices.
As the U.S. Government prepares to issue updated
Dietary Guidelines for Americans
in 2015, the question of how best to encourage Americans to eat a
nutritious diet for a healthy weight is once again under discussion.
Vitamin- and mineral-packed vegetables are naturally low-calorie,
low-sodium, high-dietary-fiber foods, so it seems logical that eating
more of them would be a good way to improve diets, reduce overall sodium
intake, and control weight. Yet, research linking fruit and vegetable
consumption to body weight has been inconclusive. Therefore, the 2010
Dietary Guidelines for Americans,
the U.S. Government’s consensus statement of nutrition policy, 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.
An analysis of American diets suggests that the answer is
in the processing and preparation of our favorite vegetable-containing
foods. Earlier USDA Economic Research Service (ERS) research found fruit consumption to be linked to
healthier weight status, but for vegetable consumption there was no such
link. The researchers speculated that the issue might be how the
vegetables are prepared. 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.
More
recently, ERS researchers returned to this question, examining in more
detail the types of vegetables and vegetable-containing foods eaten by
Americans. As hypothesized, they found that instead of eating
vegetables in their simple, unadorned state, Americans often eat
vegetables prepared in ways that add calories and sodium. They also
tend to eat vegetables in forms that remove dietary fiber.
Eating More Fruit Found To Be Associated with Lower Weight—But Not Eating More Vegetables
In
2002, ERS researchers used data from USDA’s Continuing Survey of Food
Intakes by Individuals (CSFII) 1994-96 to investigate the relationship
of fruit and vegetable consumption and weight status among children 5 to
18 years of age and adults. This survey collected data from a
nationally representative sample of Americans on everything they ate and
the amount consumed over 2 nonconsecutive days. Survey respondents
were also asked to report their height and weight, and this information
was used to compute their body mass index (BMI), a measure of overweight
and obesity. Parents or guardians reported dietary and height and
weight information for children less than 13 years of age.
The
number of servings of fruits and vegetables each survey respondent
consumed was calculated using the USDA’s Pyramid Servings Database.
This database identifies the fruit and vegetable component of each food,
whether a simple item like an apple or carrot sticks, or a combination
food like a vegetable soup or a fruit pie, and converts it into the
appropriate number of servings by food group. This allows all the forms
in which fruits and vegetables are consumed—as solid, single items; as
juices; or as part of combination foods—to be aggregated into a measure
of the total number of servings consumed.
The researchers found
that, on average, healthy weight children and adults ate more fruit than
their overweight peers. After conducting a more complex analysis that
controlled for personal characteristics that could affect weight,
including age, gender, and race, they found consistent results.
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.
Total
vegetable consumption had no association with body weight. 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. Intake of vegetables other than potatoes was
associated with lower BMI among women but not among any other age-sex
groups.
Researchers hypothesized that vegetables might not be as
low-calorie as fruit because they are often eaten in ways that add
calories. 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 USDA nutrient
data. Other vegetables might also be frequently prepared in forms that
add calories, explaining the lack of association with healthy weight.
Vegetables Are Frequently Eaten in Forms That Add Fat and Sodium
The
hypothesis that Americans might be eating vegetables most often in
forms that add calories and fat was explored in a second study by ERS
researchers. Researchers used nationally representative dietary data
from the 2003-04 National Health and Nutrition Examination Survey
(NHANES). NHANES interviewers collected dietary information using
methods very similar to the CSFII. As before, participants reported
everything they ate and the amount consumed over a 24-hour period, and
the interview was repeated on a second, nonconsecutive day, providing 2
days of dietary intake data for each participant. USDA nutrient data
were used to estimate the calorie and nutrient content of every food
item consumed. The USDA MyPyramid Equivalents Database (MPED) 2.0 was
constructed for use with the 2003-04 NHANES and used to identify the
vegetable content of each food, such as soups, stews, juices, and
sauces. At the time the study was conducted, a database to identify
vegetable content of foods was not available for NHANES data newer than
2004. However, eating patterns observed in 2003-04 are likely to be
similar to those today since food preferences and eating habits change
slowly.
ERS researchers aggregated individual vegetable
consumption from all sources—plain raw or cooked vegetables; vegetables
from mixed dishes such as soups, stews and pastas; juices; sauces;
etc.—and generated overall estimates of cups of vegetables consumed.
Because Americans often make quite different choices when eating out,
they examined vegetable consumption patterns for food prepared at home
versus those for food prepared away from home. They separated foods by
where prepared, so a sandwich made at home and taken to work for a
brown-bag lunch would be considered a home-prepared food, whereas a
pizza taken home from a restaurant would be considered as prepared away
from home. They examined the effects of the types of vegetables consumed
on intake of calories, sodium, and dietary fiber.
Researchers
found that on average, Americans ate 1.5 cups of vegetables daily, about
50-60 percent of the 2-3 cups recommended for adults and older
children. More than half of vegetable intake came from potatoes and
tomatoes (51 percent), whereas only 10 percent came from dark green and
orange vegetables. Some vegetables were eaten in their unadorned
state—raw carrot sticks or sliced tomatoes—but most were consumed in
prepared forms or as part of mixed dishes.
Potatoes,
as had been hypothesized, were typically consumed in forms that added
fat. At home, potato chips were the most commonly eaten form, whereas
away from home, fried potatoes predominated. Other potato dishes, such
as mashed and scalloped potatoes, are often prepared with added fats and
sodium. Baked potatoes were popular, but most commonly—especially when
eating out—the skin was not eaten, reducing dietary fiber content.
The
predominance of fried potatoes was expected, but the results for
tomatoes, the second-most consumed vegetable by Americans, may be more
surprising. Although popular raw, most tomato is consumed as an
ingredient in popular mixed foods, such as pastas and pizzas. To
illustrate, when the researchers examined the leading sources of tomato
consumed, they found that at home, raw tomato accounted for 22 percent
of tomato consumption, while 24 percent came from tomato sauces for
spaghetti and similar pastas. Among foods prepared away from home,
pizza provided the largest share of tomato consumed, at 32 percent,
followed by raw tomato at 17 percent, and spaghetti and similar pastas
with tomato sauce at 15 percent.
The
Dietary Guidelines
recommend that Americans should lower their sodium intakes from the
current average of approximately 3,400 mg daily to no more than 2,300
mg/day. Although tomatoes are naturally low in sodium, many of the
tomato sauces featured in mixed dishes are high in sodium. While a cup
of raw tomato has only 9 mg of sodium, according to the most recent USDA
nutrient data canned tomato sauce typically contains more than 1,000 mg
of sodium per cup.
Adding More American-Style Vegetables Can Increase Calories and Sodium
Having
found that so much of Americans’ vegetable consumption is obtained in
forms that add fat or sodium and reduce dietary fiber, ERS researchers
analyzed the effect of adding more vegetables—in forms currently
consumed by Americans—to the diet on calorie intake, sodium density
(mg/1,000 kcal), and dietary fiber density (g/1,000 kcal). Researchers
held the total amount of food consumed as measured in weight (grams)
constant; as more vegetables were eaten, the amount of other foods
consumed was lowered. For the analysis, they examined four categories
of vegetables: potatoes, tomatoes, dark green and orange vegetables, and
all other vegetables. Researchers estimated the effects of adding more
vegetables and vegetable-containing foods to the diet using a method
that controls for individual differences that may affect food intake
such as age, gender, and personal tastes and preferences.
Contradicting
what might have been expected from a shift to a higher vegetable diet,
researchers found that calorie intake increased, with effects varying by
type of vegetable and where the food was prepared. Eating an
additional cup of potatoes in the forms prepared at home resulted in an
increase of 88 calories, whereas eating an additional cup of potatoes
prepared away from home increased calorie intake almost twice as much.
This reflects the predominance of fried potatoes when eating out.
For
tomatoes, the difference in the calorie increase from foods prepared at
home versus away from home was even larger. An additional cup of
tomatoes from home foods increased calories by 59 versus a 364-calorie
increase from away-from-home foods. This may be attributable to the
popularity of calorie-laden combination foods like pizza as a tomato
source. According to USDA’s MyPlate guidance, a piece of pepperoni
pizza provides ¼ cup of vegetable, but also contains approximately 400
calories, making it a high-calorie source of vegetables.
Whether
at home or away, increasing tomato consumption resulted in a more
sodium-dense diet, likely reflecting the sodium content of tomato-sauce
dishes that make up the bulk of tomato consumption. Eating more
potatoes, whether at home or away, decreased sodium. Increasing dark
green and orange vegetable intake of foods prepared at home by 1 cup
reduced sodium density by 56 milligrams. But away-from-home foods
containing dark green and orange vegetables had the opposite effect,
increasing sodium by 186 milligrams per cup consumed. Both at home and
away, raw carrots and greens are popular choices, but among the leading
away-from-home choices are also dishes that include dark green and
orange vegetables cooked with soy sauce, spinach dips, and other higher
sodium items.
Effects of eating more vegetable-rich foods can vary, depending on type of vegetable and where prepared
| | Effects of increasing intake of each type of vegetable by 1 cup, holding total amount of food consumed constant |
|---|
| | Potatoes | Tomatoes | Dark green
and orange vegetables | Other vegetables |
|---|
| Where prepared |
At home |
Away |
At home |
Away |
At home |
Away |
At home |
Away |
| Calories |
88 |
159 |
59 |
364 |
80 |
NS |
NS |
NS |
| Sodium (mg) |
-52 |
-76 |
179 |
113 |
-56 |
186 |
75 |
91 |
| Dietary fiber (g) |
0.30 |
NS |
0.86 |
NS |
1.38 |
1.07 |
1.14 |
0.49 |
Note: Effects on nutrient intake are
attributable to consumption of vegetable-containing foods, including
other non-vegetable ingredients. For example, potatoes may be fried with
oil and have added salt; tomatoes may be consumed as a sauce on pasta
or pizza.
NS= not significant.
Source: USDA, Economic Research Service analysis using data from the 2003-04 National Health and Nutrition Examination Survey. |
Increasing Dark Green and Orange Vegetables Boosted Dietary Fiber
Dietary
fiber is provided by nondigestable carbohydrates and related compounds
in the foods we eat. Its bulk promotes a feeling of fullness, which may
help control calorie intake, and it promotes healthy digestion.
Vegetables, along with fruits and whole grains, are naturally rich
sources of dietary fiber. However, fiber is often removed from
vegetables by peeling, removing seeds, or extracting juice.
The
Dietary Guidelines for Americans
recommend 14 grams of dietary fiber per 1,000 calories consumed, which
would be equivalent to about 28 grams per day for a 2,000 calorie diet.
On average, Americans consume about 15 grams of dietary fiber daily,
far less than recommended. The
Dietary Guidelines state that
these low intakes constitute a public health concern. Adding more
potatoes and tomatoes from food prepared away from home would not
significantly increase dietary fiber, probably because of losses during
preparation or because individuals choose not to eat the skins on
potatoes.
Eating more tomatoes and potatoes as prepared at home
would boost dietary fiber, but not as much as increasing dark green and
orange vegetables would. Consumption of an additional cup of dark green
and orange vegetables as prepared at home would increase fiber by 1.38
grams, whereas an additional cup as prepared away from home would result
in a 1.07-gram increase. Increased consumption of other vegetables was
also associated with increased fiber intake, particularly the
home-prepared versions, which added 1.14 grams of dietary fiber per cup.
Public-Private Efforts May Promote Healthier Vegetable Choices
When
considering how increased vegetable consumption can support efforts to
prevent obesity and reduce sodium intake, thinking about the typical
forms in which Americans eat vegetables is important. Rather than
simply eating more of their current favorite forms of
vegetable-containing foods, Americans will need to add vegetables in
forms that come with fewer added calories and sodium.
Combination
foods such as pizzas and pastas may seem like a tasty and convenient way
to add vegetables to the diet, and the vegetables in those foods do
make nutritional contributions. For example, tomato sauce contains
vitamins A and C and potassium. However, consumers need to be aware
that along with the vegetable content of combination foods may come
calories and sodium from the other parts of the dish. The presence of
vegetables in a mixed food like heavily sauced pasta may lend a “health
halo” to the dish in the minds of many consumers—that is, consumers may
have an overly positive impression of the healthfulness of the dish
based on considering only its healthy attributes. This may be most
likely when eating out, since consumers may not know all the ingredients
in an item. Calorie labeling will soon be required in American
restaurant chains of 20 or more establishments. Such labeling may help
consumers make healthier choices when eating out and create incentives
for restaurants to offer more nutritious items.
Most sodium
consumed by Americans is not added at the table from the salt shaker,
but rather comes from processed items such as tomato sauce and canned
soups. For this reason, the 2010
Dietary Guidelines for Americans
emphasized the importance of reducing the sodium content of packaged
foods. Many food companies have made efforts to reduce the sodium
content of their foods, encouraged by public-private efforts such as the
National Salt Reduction Initiative. This initiative set voluntary goals
for sodium reduction in packaged and restaurant foods. In 2013, the
Initiative reported that 21 companies had made changes that met one or
more of its goals. Nevertheless, changes are uneven.
A recent report
from the Center for Science in the Public Interest assessed changes in
sodium content of 480 food products between 2005 and 2011. Of that
group, sodium content had declined in 205 products, but it increased in
158. Sodium content of similar products varied considerably—for
example one brand of tomato paste contained five times the amount of
sodium as another brand. Unless consumers check the nutrition label and
choose the lower sodium options, they may not consistently benefit from
the improved products available.
Although the U.S. Food
and Drug Administration permits front-of-label claims for low sodium
products that could assist consumers to identify these products, some
food companies may not choose to make these claims. They assert that
consumers associate “low salt” claims with poor-tasting foods, making it
difficult to successfully market lower sodium products. Instead, these
food companies practice what has been called “stealth health,” reducing
the sodium content of the item but not publicizing the change with
front-of-label claims.
A report from the Institute of Medicine stated
that successfully marketing lower sodium products has been difficult for
food companies. Consumers who are used to larger amounts of added salt
may find it hard to accept lower salt versions of their favorite foods.
New USDA school meal standards call for a gradual reduction in the
sodium content of meals. This may help the younger generation grow up
with more acceptance of a lower sodium diet.
