An Outdated Method
The calorie content of foods is mainly calculated by a system called "the Atwater general factor system," which was first developed back in the late 1800s. According to the Atwater factors, the macronutrients (and alcohol, which isn't classified as a nutrient, but rather as a toxin) are assigned a certain number of calories per gram, despite the food in which they're found. Carbohydrates and protein both yield four calories per gram, fat yields nine calories per gram, and alcohol yields seven calories per gram.
However, scientists say the results from the recent study on almonds demonstrate that the Atwater factor system of calculating the calorie content of certain foods groups, namely nuts, may not be entirely accurate. Although this recent study looked specifically at almonds, researchers believe the system may be a poor predictor of the energy content of all nuts and may possibly be a poor predictor of the calorie content of whole grains and peanuts as well. Scientists speculate that the rigid structure of the almond's cell membranes (and possibly the cell membranes of other plants) could lock in a portion of the fat, preventing it from being fully digested and absorbed. This may be due to the fact that the membrane that contains fiber encases the cell wall, and fiber isn't digested and therefore passes through the gastrointestinal tract unabsorbed.
Not Just Almonds, But Pistachios Too
The study itself involved 18 participants who were fed randomized mixed diets containing three different doses of almonds. Macronutrient and calorie amounts excreted in feces and urine were analyzed and compared to what would be expected from calculations using the Atwater factors. The same team of researchers also found in an earlier study that pistachios could have six percent fewer calories than previously considered.
Researchers point out that these results apply to whole almonds and that if the cell walls were to be broken down, possibly through grinding, slicing, or roasting the almonds, this may affect the amount of macronutrients that are absorbed. Therefore, processing nuts may impact the total calories that we absorb from them.
It may be a while before results of studies like these prompt government agencies to make any changes to Nutrition Facts panels. But for now, let's all enjoy a handful of nuts every day to reap the rewards we are already aware of. Nuts, regardless of the exact number of calories they contribute, provide us with heart-healthy fats, fiber, protein, minerals and powerful antioxidants. And most of all--they're delicious!
Kari Hartel, RD, LD is a Registered, Licensed Dietitian and freelance writer based out of St. Louis, MO. Kari is passionate about nutrition education and the prevention of chronic disease through a healthy diet and active lifestyle. Kari holds a Bachelor of Science in Dietetics from Southeast Missouri State University and is committed to helping people lead healthy lives. She completed a yearlong dietetic internship at OSF St. Francis Medical Center in Peoria, IL, where she worked with a multitude of clients and patients with complicated diagnoses. She planned, marketed, and implemented nutrition education programs and cooking demonstrations for the general public as well as for special populations, including patients with cancer, heart disease, diabetes, Alzheimer's disease, obesity, and school-aged children. If you would be interested in working with Kari one-on-one, sign-up for FitDay Dietitian.