A new study published in the prestigious Journal of Nutrition found that walnuts have 21 per cent fewer calories than what is currently assigned by the United States Department of Agriculture (USDA) to the ‘king of nuts’.
The study led by Dr David J Baer, supervisory research physiologist at the USDA, shows that one serving (1 ounce or 28.35g) of walnuts contains 146 calories. This figure is 39 calories lesser than the currently used value of 185 calories, derived from the Atwater factors. The Atwater factors were developed in the late 19th century and calculate metabolisable energy — or energy available to the body — for many foods. “Yes, these are significant results in the sense that they provide, for the first time, an accurate measure of the number of calories in a serving of walnuts. This research overcomes limitations of research conducted over 100 years ago and whose results are still used today,” Baer said.
“Our results could help explain why consumers of walnuts do not typically gain weight. Given the numerous potential health benefits of consuming walnuts, including reduced risk for cancer, cardiovascular and cognitive diseases, our results could potentially help alleviate any calorie-related concerns consumers might have with incorporating them into their everyday diet,” Baer said.
To reach their conclusion, Baer and his research team studied 18 healthy adults. Each person was assigned randomly to a sequence of two diets: a controlled American diet without walnuts for a 3-week period, and a controlled diet with 1.5 servings of walnuts (42g) for another 3-week period.
Total calorie levels were consistent for individual participants across both treatment periods. Administered diets, walnuts, fecal and urine samples were collected and subject to bomb calorimetry to measure calories. The resulting data was used to calculate the metabolisable energy of the walnuts.
Walnuts contain several antioxidants and polyphenols which provide multiple benefits to health. Commenting on the health benefits of walnuts, Dr H K Chopra, president of Cardiological Society of India said, “Walnuts are one of the richest sources of omega-3 fatty acids, with 2.5g of alpha-linolenic acid (ALA) per serving. Any successful weight management plan must include satiety factor and owing to its high fibre content, walnut is undoubtedly the right food to consider if you are into a weight management programme.” Walnuts are the only nuts that comprise a significant source of alpha-linolenic acid, a plant-based omega-3 fatty acid with heart and brain-health benefits.
He said that there are many aspects of a food item to consider when one decides what and how much to eat. “High fat foods do not necessarily make us fat and low fat foods are not necessarily the healthiest for us to eat,” Baer added. Naini Setalvad, a nutritionist and health consultant, said, “Consuming a diet comprised of walnuts is the key to healthy living. Incorporating walnuts into meals and snacks is a simple, delectable and convenient way to help ensure adequate protein intake, especially among vegetarians. One ounce of walnuts provides 4g of protein, and 2g of fibre. The fibre aspect helps make you feel full, promotes weight management, and can assist in lowering cholesterol and regulating blood glucose levels.”
While the study provides insight into the growing body of research supporting the beneficial role walnuts play in weight management, further research is still needed to better understand the results of the study and how this technique for calculating calories could potentially affect the calorie count of other foods, Baer said.
The study was supported in part by funds from the USDA and the California Walnut Commission.