Researchers from the University of Toronto sampled hundreds of meals at 19 chain sit-down restaurants and found that average breakfast, lunch and dinner meals contained 1,128 calories, or 56 percent of the daily 2,000 calorie recommendation.
They also contained loads of salt -- 2,269 milligrams or 151 percent of the recommended amount for most adults, which is 1,500 milligrams per day -- and 89 percent of the daily value for fat.
The meals contained on average 83 percent of the daily value for saturated fat, and more than 60 percent of the daily value for cholesterol.
"Overall, the results of this study demonstrate that calorie, fat, saturated fat and sodium levels are alarmingly high," said the research letter in the Journal of the American Medical Association.
"Therefore, addressing the profile of restaurant meals should be a major public health priority."
A second study in JAMA focused on dishes available at 33 small independent and small chain restaurants in the Boston area, and found that the average meal contained two-thirds of daily calorie requirements.
Samples were taken from Mexican, American, Chinese, Italian, Japanese, Thai, Indian, Greek and Vietnamese restaurants.
"On average, the meals studied contained 1,327 calories, which significantly exceeds the estimated energy needs of an individual adult at a single meal," said senior author Susan Roberts.
"Meals from all restaurant types provided substantially more energy than is needed for weight maintenance," said Roberts, director of the Energy Metabolism Laboratory at the Human Nutrition Research Center on Aging at Tufts University.
Italian meals had the highest average calories per meal (1,755), followed by American (1,494 calories) and Chinese (1,474 calories).
Vietnamese meals had the fewest calories on average (922), and Japanese meals had the second lowest (1,027).