Did you know that the calorie labels on foods are only required to be accurate within 20%? That’s a pretty wide margin, but it exists for a reason: Calories are complicated.

Sources:

• Energy in pistachios
  Baer D J, Gebauer SK, Novotny JA. Measured energy value of pistachios in the human diet. Br J Nutr 2012; 107 (1):120-5.
• Energy in almonds
  Novotny JA, Gebauer SK, Baer DJ. Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human diets. Am J Clin Nutr 2012; 96 (2):296-301.
• Energy in walnuts
  Baer DJ, Gebauer SK, Novotny JA. Walnuts Consumed by Healthy Adults Provide Less Available Energy than Predicted by the Atwater Factors. J Nutr 2016; 146 (1):9-13.
• Energy in different forms of almonds
  Gebauer SK, Novotny JA, Bornhorst GM, Baer DJ. Food processing and structure impact the metabolizable energy of almonds. Food & Function 2016; 7(10):4231-4238.
• Energy in cashews
  Baer DJ, Novotny JA. Metabolizable Energy from Cashew Nuts is Less than that Predicted by Atwater Factors. Nutrients 2019; 24;11(1).
• Weighing in on calories
• Calorie restriction
• H.R.3562 - Nutrition Labeling and Education Act of 1990
• What are calories?
• Understanding calories
• Food label accuracy
• Bomb calorimeter
• How are calories calculated?
• How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods?
• General chemistry: calorimeter