Nuts may provide up to 26 per cent less kilojoules than previously thought, with new Australian research highlighting a flaw in the kilojoule count of tree nuts and peanuts (1).

The University of Wollongong research found the actual kilojoules absorbed from nuts were significantly less than kilojoules stated on food labels (1).

The Atwater system has been used globally to calculate kilojoules for more than 100 years and it is the mandated measuring system for Australian food labels. It determines kilojoules based on grams of fat, protein, carbohydrates and alcohol in a particular food, but lead researcher Cassandra Nikodijevic says it doesn’t take into account how our bodies metabolise food.

“When it comes to nuts, our bodies can’t absorb all the fat they contain and traditional kilojoule counts do not factor this in,” said Ms Nikodijevic, dietitian and PhD Candidate, School of Medical, Indigenous and Health Sciences, Faculty of Science, Medicine and Health, University of Wollongong.

“Due to the crunchy texture of nuts, a portion of the fat remains locked within their fibrous cell walls and cannot be absorbed by our bodies. It is excreted out.

“In comparing the data on the kilojoules from nuts our bodies actually digest, versus standard Atwater measures, we consistently found the kilojoules in nuts and peanuts had been significantly over estimated, in some cases by up to 26 per cent.” 

The University of Wollongong’s systematic literature review (SLR) examined 21 published papers on the metabolised energy (digestible kilojoules) of nuts.

The SLR included 13 carefully controlled, feeding trials that followed participants on either a control diet or a diet containing nuts. These studies involved the collection and analysis of urine and faeces samples from study participants to work out how much of the fat from nuts was digested and converted into energy in the body, and how much was excreted.

Using the metabolised energy method for determining digestible kilojoules, the SLR found:

• Almonds had 18.5 kilojoules per gram – 26% less than measured by the Atwater system
• Walnuts had 21.8 kilojoules per gram – 22% less than measured by the Atwater system
• Cashews had 20.5 kilojoules per gram – 14% less than measured by the Atwater system
• Pistachios had 22.6 kilojoules per gram – 5% less than measured by the Atwater system

Human studies on the digestible kilojoules of other nut varieties, such as peanuts, hazelnuts, macadamias, pecans, Brazil nuts and pine nuts, were not available, but Ms Nikodijevic believed a similar pattern of overestimation would apply to all nuts.

Ms Nikodijevic said the results of the research may help to explain why regularly eating nuts, an energy-dense food, was not associated with weight gain.

“Concerns regarding weight gain remain a key barrier to eating nuts with consumption of nuts in Australia well below recommended intakes,” said Ms Nikodijevic.

“It’s important health professionals and the Australian public have accurate information about the kilojoules in nuts, to provide greater confidence in recommending and regularly eating nuts as part of a healthy diet. Increasing nut consumption is a simple dietary change that could help reduce the risk and prevalence of some of our most common and chronic diseases including cardiovascular disease, coronary heart disease, various cancers and diabetes.”

In the United States, in 2020, a series of similar research papers prompted nut bar company KIND to change the nutrition labels across its range, resulting in a 10-30 calorie reduction per bar (2-5).

Nuts for Life, Australia’s leading authority on the nutrition and health benefits of nuts, hopes this paper is the first step towards seeking similar labelling changes in Australia.

Nuts for Life program manager and dietitian Belinda Neville said this was crucial research to address kilojoule concerns and misconceptions that were a genuine barrier to Australians eating more nuts.

“Only two per cent of Australians eat the recommended 30 g of nuts a day missing out on the protective heart health benefits of this core food,” said Ms Neville (6).

“We’ll continue to support further research on the digestible kilojoules in nuts and explore how changes to labelling could impact consumption. Our aim is to ultimately change food labelling in Australia to better reflect the actual kilojoules absorbed from nuts.”

The University of Wollongong SLR also identified potential factors for variance in digestible kilojoules between nut varieties.

“This may be due to the difference in nutrient make up and texture of each nut variety,” said Ms Nikodijevic.

“Studies have shown people tend to chew firmer, brittle nuts for longer, breaking them down into smaller particles, which ruptures cell walls and makes it easier for the body to absorb more fat.

“Similarly, the form of nuts impacts the amount of fat available for absorption. Changes to the cell wall from crushing nuts or roasting increases the amount of fat that can be absorbed, and as a result, nut butters, crushed nuts and roasted nuts provided more kilojoules.”

Learn more on this topic:

Video of presentation: Nut consumption in Australia & the relationship between nuts and body weight

Published paper: The metabolizable energy and lipid bioaccessibility of tree nuts and peanuts: A systematic review with narrative synthesis of human and in vitro studies

Published paper: The effects of tree nut and peanut consumption on energy compensation and energy expenditure: A systematic review and meta-analysis