How accurate is calorie counting?

Rougher than the numbers in your app suggest. Checked against a lab measure, careful food recalls came in 12 to 20% low, and labels can be off too. Counting still works, because you don’t need it exact. You need it consistent. Log the same way every day and let your scale correct the total.

An app shows 1,847 calories, and that looks precise. Every part of it is an estimate: the portion you picked, the label it came from and what you remembered to log.

The simple version

Counting calories is like tracking your spending from memory. You land in the right neighborhood, usually a little low. Your scale is the bank statement.

Where the error comes from

• Memory. In a 2003 study of 484 US adults, measured against what they really burned, a careful 24-hour recall missed 12 to 14% of men’s calories and 16 to 20% of women’s. A food questionnaire missed about a third.
• Labels. US rules let a food hold up to 20% more calories than its label states before it’s treated as mislabeled.
• Restaurants. In a 2010 study, 29 restaurant dishes sold as lower-calorie had 18% more calories than stated on average, and some had twice as many. Free side dishes brought the meals to about 2.5 times the entree’s stated calories.
• The extreme. In a 1992 study of people who said they couldn’t lose on under 1,200 calories, intake was under-reported by 47%.

What to do

• Log as you eat, not from memory at bedtime. In Gyroscope, Food XRAY estimates calories, macros and micronutrients from a photo of your meal.
• Weigh your food for a few days to calibrate your eye.
• After four weeks, compare your log with your weight trend on the real TDEE calculator. If the scale says you burn less than the math, your log is probably running low.