BOSTON - Two recent reports from researchers at the USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University suggest that there has been little change in fast food portion sizes and product formulation between 1996 and 2013.

The researchers analyzed the calorie, sodium, saturated fat and trans fat content of popular menu items served at three national fast-food chains between 1996 and 2013. They found that average calories, sodium and saturated fat stayed relatively constant, albeit at high levels. The exception was a consistent decline in the trans fat of fries.

“There is a perception that restaurants have significantly expanded their portion sizes over the years, but the fast food we assessed does not appear to be part of that trend,” said Alice H. Lichtenstein, director of the Cardiovascular Nutrition Laboratory at the USDA HNRCA. “Our analysis indicates relative consistency in the quantities of calories, saturated fat and sodium. However, the variability among chains is considerable and the levels are high for most of the individual menu items assessed, particularly for items frequently sold together as a meal, pushing the limits of what we should be eating to maintain a healthy weight and sodium intake.”

The researchers focused on the four most popular menu items: fries, cheeseburgers, grilled chicken sandwiches and regular cola, looking for trends in portion size and nutrient content over an 18-year period. They found only small fluctuations in calorie content and the amount of saturated fat and sodium. The notable exception was fries, which decreased first in saturated fat in 2001 and then in trans fat, likely due to changes to the frying oil.

Despite attempts to limit consumption by some public health campaigns, fast food sales remain strong. Lichtenstein believes that restaurants can help consumers by reducing portion sizes and reformulating foods. “This can be done, gradually, by cutting the amount of sodium using leaner cuts of meat and reduced-fat cheese,” she said, adding,  “From what we hear some fast-food chains are heading in that direction and also introducing new healthier options. If taken advantage of, these changes should help consumers adhere to the current dietary recommendations.”