Do you know how much salt is in your fast food?

How good are you at estimating the amount of sodium in your food?

Most of our readers are pretty aware of what they eat, so I'd guess that you're better than most. You're probably also aware that a lot of restaurant foods, whether it's a sit down restaurant or a fast food chain, are higher in sodium than they really need to be. On the whole, however, you'd be surprised at how many people don't know the recommended daily maximum of sodium (about 2,400 milligrams for most, in case you don't know), let alone the number of calories they should be consuming.

Researchers with Harvard decided to find out if those who ate fast food were aware of how much salt was in their food, so they went to the source to ask, surveying consumers at local fast food restaurants (Appetite 2017;113:155-161).

They targeted 6 of the fast food restaurants with the highest national sales and at least two locations in the four cities selected for the survey (Boston, Massachusetts; Springfield, Massachusetts; Providence, Rhode Island; and Hartford, CT). None of the restaurants printed sodium information on their menus, but the information was always available to consumers on the chains' websites, while some restaurants also made the information available in the restaurant through wall posters or food wrappers/containers.

The research assistants who performed the surveying spoke to restaurant customers on their way in to each restaurant and invited them to save their receipts in order to participate in a survey as they left the restaurant.

Upon exiting the restaurant, the assistants collected the receipts and determined which items on the receipt the person surveyed had personally consumed, then administered a questionnaire about the foods.

The questionnaire asked the respondent to estimate the number of calories and amount of sodium they had just consumed and further asked if they were aware if calorie information was available in the restaurant. They were also asked to estimate the average daily calorie and sodium recommendations.

The authors collected responses from people aged 11-20 around lunchtime (termed "adolescents" for the purposes of this study) and from people aged 18 and up at dinner time. The nearly 800 adults surveyed consumed meals with an average of about 1,300 milligrams of sodium - and 10% of them purchased meals with more 2,300 milligrams of sodium. Yet 85% of them underestimated the amount of sodium in their meals, and more than 60% underestimated by more than 500 milligrams. The adolescents did no better: they purchased meals containing about 1,100 milligrams of sodium (on average) and 88% also underestimated the actual amount, with 63% underestimating by more than 500 milligrams.

There were two other outcomes I found interesting: first, the more sodium a meal actually contained, the more likely it was that the consumer underestimated the amount - and the greater the difference between the estimate and the reality. Second, adolescents were worse at estimating the amount of sodium in foods they purchased from Dunkin' Donuts than they were at estimating the amount in places like McDonald's. This may be due to people thinking that a doughnut or muffin will be better for you than a fast food burger.

What this means for you

Those who were aware of the availability of nutrition information in the restaurant did better at estimating the amount of sodium they had just consumed. Follow their lead by researching where you're going to eat before you get there and making healthier choices accordingly. A good rule of thumb is less than about 600 milligrams of sodium per item.

First posted: March 15, 2017