About half of Americans eat a sandwich on any given day, but the classic lunch item may be contributing to a generally less healthy diet, a new study suggests.

The study found that on the days that people ate sandwiches, they consumed nearly 100 more calories, as well as more sodium, fat and sugar, compared to the days when they didn't eat sandwiches.

The sandwiches that Americans typically consume tend to be high in calories, fat and sodium, and low in produce, study co-author Ruopeng An, an assistant professor of kinesiology and community health at the University of Illinois at Urbana-Champaign, told Live Science.

The finding suggests that people should pay attention to the nutrition content of their sandwiches. "Sandwich consumers are advised to prudently evaluate the calorie and nutrient content of sandwiches in order to make informed and more healthful dietary choices," the researchers wrote in the July 9 issue of the journal Public Health.

In the study, the researchers analyzed information from more than 27,000 U.S. adults who were surveyed about what they ate over the last 24 hours, on two separate days. The data were from a national survey that is given every year by researchers at the Centers for Disease Control and Prevention. For the new study, the researchers used data from 2003 to 2012.

About 53 percent of the participants ate a sandwich on any given day, the study found. The most common types of sandwiches were filled with cold cuts, burgers and poultry. Overall, sandwiches contributed to about one-quarter of people's daily calories, and a third of their fat and sodium for the day.

The researchers then looked at people who reported eating a sandwich on just one of the two survey days. They found that on the days when people ate sandwiches, they consumed an extra 99 calories, 7 grams of fat, 268 grams of sodium and 3 grams of sugar, on average, compared to the days when they didn't eat sandwiches. They also consumed slightly less fruit and vegetables on the days when they ate sandwiches, compared to the days when they didn't eat sandwiches. [6 Ways to Hold the Sodium]

It's possible that people may underestimate how many calories are in their sandwich — in a 2013 study, teens who ate at the fast food chain Subway, which sells sandwiches, underestimated how many calories were in their meal by nearly 500 calories, on average.

For a healthier sandwich, An provided the following tips:

  • Make your own sandwich if possible, so you have more control over what goes in it
  • Add more leafy veggies, but less meat
  • Use whole wheat bread with no salt added
  • Avoid adding processed meat, because it is typically high in fat and sodium
  • Avoid using dressings (like mayo and other sauces)

It's important to note that the new study cannot determine whether sandwiches contribute to weight gain, because the study looked at people's diets at one point in time, and did not follow them over time, An said.

One factor that sets the new study apart from previous work is that the researchers compared the dietary intake for the same person on two different days. This is important, because it means that any differences in nutrition on the two days (extra calories, etc.) are more likely to be due to sandwich consumption, and aren't the result of differences in food preferences, or a person's gender or income (since the comparison is for the same person), the researchers said.

However, the study still couldn't take into account all the factors that could affect a person's diet, like whether that person exercised on one day and not the other, or if he or she was simply hungrier or more emotional on one day.

Since there is such a large variation in the types of sandwiches people eat, more research is needed to study the different nutritional impacts of different types of sandwiches, the researchers said.

Original article on Live Science.

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