30th June 2025, A/Prof Chee L Khoo
There are many reasons why some of our patients go vegetarian. A primarily plant-based diet with less meat is supposed to lower the morbidity of chronic diseases, including cardiovascular diseases, type 2 diabetes, and certain cancers [1]. Some patients may choose to reduce their food-related ecological footprint. A transition to a diet that contains more plant-based products and less meat could increase food availability while releasing the burden on the environment [2]. We have previously explored the importance of consuming adequate protein in older adults, especially those already frail and sarcopenic, to prevent deterioration of muscle function leading to sarcopenia.
Naturally, when we look at frailty and sarcopenia, we think of our older patients who are most at-risk. When we look at the adequacy of protein intake, we need to look at both the quantity of protein as well as the quality of protein consumed. As most older patients have early satiation, smaller stomachs and poor appetite, consuming lower protein quantity and quality makes reaching adequate protein intake very challenging.
In the general Dutch adult population (age 18–79), shifting from a 40% to a 60% plant-based protein scenario showed that sufficient protein intake was achieved [3]. A simulation study performed on data from the Dutch National Food Consumption Survey (DNFCS) (2007–2010) in a younger adult population (18–65 years) showed a decrease in protein intake of about 20% in a “no meat, no dairy” dietary pattern but no one fell before the recommended Estimated Average Requirements (EAR) in that study. Note that the population was no older than 65 years old and the quality and digestibility of the protein was not examined.
A recent Dutch study by Borkent et al looked at the issue of adequacy of protein intake in older (>65yo) adults by exploring various types of diets specifically on older adults and calculating the quantity and quality of protein intake based on amino acid score and digestibility (4). They used the data from the Dutch National Food Consumption Survey (2019–2021).
They narrowed their analysis to 607 adults between 65-79 years old. Food consumption data was collected via two non-consecutive 24-h dietary recalls per participant using the GloboDiet program [5]. Both recalls were performed within 2–6 weeks of each other. Participants aged between 65 and 70 were interviewed twice via telephone, while individuals aged 70 or older were interviewed once at home and once via telephone.
The quality of a protein source is determined by the digestibility and proportion of indispensable amino acids (IAA) combined, known as the Protein Digestibility–Corrected Amino Acid Score (PDCAAS) [8]. The total protein intake (quantity), available protein intake after digestibility and utilizable protein intake in this study was based on the PDCAAS (quality).
They went through the laborious process of calculating and analysing the amino acid content, nitrogen content and utilisable protein content of each food item based on dataset from Danish, English, American and Japanese food composition tables.
The authors explored many different dietary scenarios: two flexitarian (40%/80% of the meat replaced), one pescetarian (no meat, but fish and other animal-based products are included), one vegetarian (no meat and fish, but other animal-based products are included) and one vegan dietary scenario (no fish, meat, and animal-based products are included).
What did they find?
In the reference scenario, the plant-based proportion of total protein intake was 39.0% in men and 37.7% in women. In the vegetarian scenario, the plant proportion of total protein intake was 59.1% in men and 54.2% in women, while in the vegan scenario, plant-based protein was nearly 100%. Total energy intake remained relatively stable (~ <100 kcal) for all scenarios in both genders. The median habitual daily protein intake in the original diet was 82.5 g (0.96 g/kg bw/day) for men and 67.9 g (0.94 g/kg bw/day) for women.
- Compared to the original diet, the difference in daily protein intake was relatively low in most scenarios (2–6%) except in the vegan scenario where loss amounted up to 25% (62.9 g for men and 51.5 g for women).
- In the flexitarian-40/80, pescetarian and vegetarian scenarios, utilisable protein intake was comparable with intake based on digestible protein. However, in the vegan scenario, utilisable protein intake was approximately 13% lower than intake based on digestible protein.
- In the reference scenario, the prevalence of intake below EAR (utilisable protein intake below 0.58 g/kg bw/day) was 7.5% in men and 11.1% in women. This was to 12.5% and 16.4% in the vegetarian scenario while in the vegan scenario, over half of older adults had an intake below EAR (56.7% in males and 60.2% in females).
- The highest median protein intake was observed at dinner. The lowest intake was seen in the vegan scenario with 26 g for men and 21 g for women. At dinner, the proportion of protein that cannot be utilised due to digestibility or amino acid composition was 10−13% in most scenarios and 20% in the vegan scenario.
- The loss in protein intake quantity in all scenarios was mainly observed at dinner. This was expected as most protein during that meal moment comes from meat, which we replaced with alternatives that sometimes had lower protein quantities. The loss in protein quality was greatest at breakfast and lunch.
The authors concluded that replacing animal-based with plant-based protein sources in the diet of older adults led to reductions in protein quantity and quality only when all animal-based foods were eliminated. Changing protein intake to 60% plant-based protein seems to be safe for older adults in terms of protein intake. In contrast, a vegan pattern was associated with a substantial decline in protein availability, leading to more than half of older adults not reaching the recommended protein levels.
The study assumed that the average intake of 0.85g protein per kg of body weight was adequate. However, in many of our patients who are already frail and sarcopenic, the recommended protein intake is substantially more than 0.85g/kg bw. Further, while most of our older patients have not deliberately gone vegan, practically, they are eating very low amounts of non-plant protein for various reasons including financial. In primary care, we need to take a dietary history to ascertain the adequacy of their protein intake to prevent continuation of their muscle function decline.
References:
- J.P. Rocha, J. Laster, B. Parag, N.U. Shah. Multiple health benefits and minimal risks associated with vegetarian diets. Curr Nutr Rep., 8 (4) (2019), pp. 374-381
- C. Chen, A. Chaudhary, A. Mathys. Dietary change scenarios and implications for environmental, nutrition, human health and economic dimensions of food sustainability. Nutrients., 11 (4) (2019), p. 856
- S.N. Heerschop, P. van’t veer, S. Biesbroek, A. Kanellopoulos. The effect of a modelled shift from a 40% to 60% plant-based protein intake on dietary health. Wageningen University & Research (2023)
- Jos W. Borkent, Pol Grootswagers, Joost Linschooten, Annet J.C. Roodenburg, Marga Ocké, Marian A.E. de van der Schueren. A vegan dietary pattern is associated with high prevalence of inadequate protein intake in older adults; a simulation study. The Journal of nutrition, health and aging, Volume 29, Issue 5, 2025, 100536.
- S. Leser. The 2013 FAO report on dietary protein quality evaluation in human nutrition: recommendations and implications. Nutr Bull., 38 (4) (2013)