Meals consumed in restaurants were judged to contain higher levels of sodium and cholesterol than those consumed in fast-food outlets and at home.
The study, published in the European Journal of Clinical Nutrition, found that Americans eating out at either fast-food outlets or full-service restaurants would typically consume 200 calories more per day than when staying at home for meals.
"These findings reveal that eating at a full-service restaurant is not necessarily healthier than eating at a fast-food outlet," states study author Ruopeng An. "In fact, you may be at higher risk of overeating in a full-service restaurant than when eating fast food."
Prof. An, a kinesiology and community health professor at the University of Illinois, analyzed data from the National Health and Nutrition Examination Survey (NHANES) for 2003-10, looking at the eating habits of 18,098 adults living in the US.
In particular, Prof. An measured daily intake of total calories and 24 nutrients considered to be of public health concern, including sodium and cholesterol.
He discovered that eating in full-service restaurants was just as unhealthy as eating at fast-food outlets. The main problem with eating in restaurants was found to be that diners would typically consume more sodium and cholesterol in their meals than elsewhere.
"People who ate at full-service restaurants consumed significantly more cholesterol per day than people who ate at home," Prof. An explains. "This extra intake of cholesterol, about 58 mg per day, accounts for 20% of the recommended upper bound of total cholesterol intake of 300 mg per day."
In comparison, people eating at fast-food outlets consume 10 mg more cholesterol than people eating at home.
Even though people eating in restaurants would take in more healthy nutrients such as potassium and omega-3 fatty acids than people eating at home or in fast-food outlets, they would be consuming significantly large amounts of two nutrients - cholesterol and sodium - that Americans tend to eat too much of already, even at home.
High sodium intake increases risk of hypertension and heart disease
Prof. An found that an individual's daily sodium intake would be increased on average by 300 mg by eating at a fast-food outlet and by 412 mg by eating in a restaurant.
"The additional sodium is even more worrisome because the average daily sodium intake among Americans is already so far above the recommended upper limit, posing a significant public health concern, such as hypertension and heart disease," the researcher says.
Adults are recommended to consume between 1,500 and 2,300 mg of sodium per day. Currently, however, Americans are estimated to consume around 3,100 mg per day when eating at home.
Another area of nutrition where both fast-food outlets and restaurants were found to perform badly was the fat content of their meals. Prof. An found that those who ate at either fast-food outlets or restaurants would consume 3.49 g and 2.46 g more saturated fat respectively than people eating a meal prepared at home.
Total fat consumption at these food venues was around 10 g higher than at home.
Prof. An also observed that eating out at these venues affected different demographic groups in different ways. African-American diners eating out were found to consume higher levels of total fat, saturated fat, sodium and sugar than white and Hispanic counterparts doing the same, he states.
Daily total energy intake was influenced by eating at fast-food outlets the most among people with lower educational attainment while people defined as being in the middle-income range were found to have the highest daily intake of total energy, total fat, saturated fat and sodium of people eating at restaurants.
"My advice to those hoping to consume a healthy diet and not overeat is that it is healthier to prepare your own foods, and to avoid eating outside the home whenever possible," Prof. An concludes.