NEW YORK (NYTIMES) - Fast food chains have tried for years to woo health-conscious diners by mixing lighter fare like salads and yogurt with the usual burgers, fried chicken and shakes.

But as menus swelled over the past three decades with grilled chicken wraps (McDonald's) and "fresco" burritos (Taco Bell), many options grew in size and the calories and sodium in them surged, according to new study from researchers at Boston University and Tufts.

The researchers studied 1,787 entrees, sides and desserts at 10 chains - Arby's, Burger King, Carl's Jr, Dairy Queen, Hardee's, Jack in the Box, KFC, Long John Silver's, McDonald's and Wendy's - from 1986 to 2016. In that time, the number of items in those three categories rose 226 per cent.

According to the study - published last week in The Journal of the Academy of Nutrition and Dietetics - even with lighter items in the mix, fast food menus are less healthy than they were 30 years ago.

BULGING PORTIONS

The fat and salt content and the sheer size of fast food meals have long been a public health concern. They are often blamed for pushing up the obesity rate among adults in the United States, which rose to 40 per cent in 2016 from 13 per cent in the early 1960s.

The new study suggests the problem is getting worse.

Across the 10 chains, the researchers found, the average entree weighed 39g more in 2016 than in 1986 and had 90 more calories. It also had 41.6 per cent of the recommended daily allotment of sodium, up from 27.8 per cent.

Customers could be forgiven for not knowing. Local governments have adopted menu-labelling initiatives that require fast food restaurants to list calorie counts for the items they sell, but such measures have faced substantial opposition, including from the Food and Drug Administration.

"The restaurants really haven't done enough," Dr Megan A. McCrory, the lead researcher, said.

"The big picture is that there have been some positive changes, but they're small, and overall, the changes have gotten worse."

SUPERSIZE SWEETS

In 2016, the average fast food dessert weighed an extra 71g and had 186 more caloriesthan the average dessert 30 years earlier, the researchers found.

One possible reason is that restaurants are counting on bigger sundaes and cookies as a way of increasing the amount spent on each order and attracting more customers, said Mr Darren Seifer, a food and beverage industry analyst at NPD.

"The majority of fast food traffic is around lunchtime, when people aren't typically getting dessert," he said. "But offering larger portion sizes is one way restaurants can promise more value."

Just last month, McDonald's introduced "doughnut sticks" dusted with cinnamon sugar. Six sticks have 280 calories. But you can also order a serving twice the size for less than the cost of two single orders.

ADDING THOSE EXTRAS ADDS UP

The researchers found that there were 42 more calories on average in items like chips, soups and french fries in 2016 than there were in 1986. Sodium content rose to 23.2 per cent of the recommended daily allotment from 11.6 per cent, even though portion size did not grow substantially.

Consumed together as a single meal, the study found, the average entree and side account for nearly 40 per cent of a 2,000-calorie daily diet.

The study mentions several proposals meant to help consumers scale back their fast food intake, including a system that would let them order smaller portions at lower prices.

Whether the industry will embrace such ideas is unclear. In the meantime, menus continue to grow, sometimes blurring the line between entree and side. Jack in the Box is testing Burger Dippers, which the company describes as "the burger you eat like a fry".

As with those that preceded them, some of the new offerings appear to be geared towards people who want to eat healthy foods. Carl's Jr recently added a plant-based burger, the Beyond Famous Star, to its lineup.

Ordered with cheese, it has more than 700 calories.