For more information about the health effects, please refer to the background paper by Ólöf Guðný Geirsdóttir and Anne-Maria Pajari (Geirsdóttir & Pajari, 2023).
Dietary sources and intake. The main sources of animal protein are meat, fish, milk, and eggs, and the main sources of plant protein are cereals, legumes, nuts, and seeds. Fungi (in the form of mycoprotein) are also a source of non-animal protein. In the Nordic countries and Estonia, the average intake of protein varies between 15 and 19 E%. In Latvia and Lithuania, the intake is also between the range, despite of different calculation procedures (Lemming & Pitsi, 2022).
Main functions. Protein is an essential nutrient needed in the human body for growth and maintenance. Proteins provide essential amino acids, nitrogen, and energy. Severe protein deficiency results in oedema, muscle weakness, and changes to the hair and skin. Protein deficiency is often concomitant to deficiency of energy and other nutrients; however, protein-energy malnutrition is uncommon in the Nordic and Baltic countries.
The health effects of protein intake are difficult to separate from effects of other nutrients or ingredients in protein-rich foods. The results are inconclusive or seem neutral for the association between total protein intake and obesity, cardiovascular disease, glycaemic control, bone health, kidney function, oesophageal cancer and prostate cancer in adults (Geirsdóttir & Pajari, 2023). A de novo SR for NNR2023 concluded that a high-protein diet in infancy was suggested as a risk factor for childhood overweight and obesity (Arnesen et al., 2022). There was probable evidence for a causal relationship between total and animal protein intake and higher BMI in children up to 18 years of age. Evidence for substituting animal protein with plant protein to reduce the risk of cardiovascular disease mortality and type 2 diabetes incidence is limited but suggestive, as evaluated in another de novo SR (Lamberg-Allardt et al., 2023b). Results from studies on protein sources and mortality are mixed.
Interaction with other nutrients and food components. Unprocessed plant protein sources often contain phytates, tannins, and protease inhibitors which interfere with the digestion of plant proteins, making them less well-digestible than animal-source proteins (Sarwar Gilani et al., 2012). In practice, the differences in quality between proteins might be less critical in diets containing a variety of protein sources (Lemming & Pitsi, 2022).
Indicator for recommended intake. While some biomarkers are used in the clinical setting, there is no specific biological marker to evaluate optimal protein status. On a long-term basis, intake and losses of nitrogen should be equal in weight-stable, healthy adults. Nitrogen-balance studies have been used to establish DRVs.
Main data gaps. The underlying assumptions to the nitrogen-to-protein conversion factor of 6.25 traditionally applied for measuring protein content in foods may lead to errors in the estimation. Evidence for associations between protein intakes and health outcomes are limited or suggestive. Studies are needed on both subjects.
Deficiency and risk groups. Proteins are required during active growth in late pregnancy, lactation and childhood. Older adults are at higher risk of inadequate protein intakes (Geirsdóttir & Pajari, 2023). Individuals with chronic kidney disease are sensitive to high protein intakes (IOM, 2005; WHO/FAO/UNU, 2007).
Dietary reference values. Based on the available evidence of nitrogen balance and isotope tracer studies, AR and RI were set to 0.66 g/kg and 0.83 g/kg body weight per day for adults, respectively (EFSA, 2012a). This protein intake should also adequately meet the requirements for essential amino acids. The recommended intake range is 10–20 E%. For planning purposes, 15 E% can be recommended. With energy intake below approximately 8 MJ (e.g., at low body weight, low physical activity levels or during intentional weight loss), the protein E% should increase accordingly to ensure that the AR and RI is met. The AR and RI based on nitrogen balance is the same for older adults. However, recent studies have found that intakes above the RI may be optimal to prevent decline of physical functioning (Geirsdóttir & Pajari, 2023). Therefore, the recommended range for older adults is 1.2–1.5 g/kg body weight, approximately 15–20 E%. For older adults, 18 E% is recommended for planning and assessment (Geirsdóttir & Pajari, 2023). For young children below 2 years of age, it is advisable not to exceed a range of 10–15 E% protein.
Dietary proteins of animal origin or a combination of plant proteins from, for example, legumes and cereal grains, give a good distribution of essential amino acids. Replacing a part of animal proteins in the current Nordic diet with plant proteins would provide enough protein and essential amino acids at recommended protein intake levels (Geirsdóttir & Pajari, 2023).