Researchers at the US Department of Agriculture (USDA) Human Nutrition Research Centre on Ageing at Tufts University show little change in fast food portion sizes and product formulation between 1996 and 2013.
They analysed the calorie, sodium, saturated fat and trans fat content of popular menu items served at three national fast-food chains between 1996 and 2013.
Researchers 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.
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According to data, calorie content of the cheeseburger meal among the three chains represented 65 per cent to 80 per cent of a 2,000 calorie per day diet and sodium content represented 63 per cent to 91 per cent of the recommendation.
Lichtenstein and colleagues 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 trans fat, likely due to changes to the frying fat.
The research was published in the journal Preventing Chronic Disease.