Does Animal Protein Reduce Risk of Mortality in the Elderly?

Written by Zachary Wenger

December 17, 2021

Meroño, Tomás et al. “Animal protein intake is inversely associated with mortality in older adults: the InCHIANTI study.” The journals of gerontology. Series A, Biological sciences and medical sciences, glab334. 27 Nov. 2021, doi:10.1093/gerona/glab334

Introduction:

Protein is a macronutrient that is foundational in human nutrition. Protein plays many crucial roles within the body and requirements will vary based on factors including body weight, age, and physiological states.

In the elderly, the importance of protein is directly related to quality of life and health. Loss of muscle mass, strength, and mobility that progressively occurs with aging is known as sarcopenia. As a result, it is often recommended that protein intake in the elderly is greater than the RDA set at 0.8 g protein/kg of body weight (1). For example, The European Society for Clinical Nutrition and Metabolism recommends that healthy older adults consume 1-1.2 g protein/kg of body weight (6).

The relevance of plant and animal protein in relation to cardiovascular disease (CVD), cancer, and/or all-cause mortality (ACM) has been investigated previously (2,3), however, there is a paucity of data in the elderly population. The goal of this current study was aimed to evaluate the association of animal and plant protein intake with all-cause, cardiovascular, and cancer mortality after 20-years of follow-up in an Italian cohort study (4). 

The Study:

The study was a prospective cohort study including 1,139 older adults in Tuscany, Italy and participants aged ≥ 65 years were evaluated. Dietary intake was assessed by utilizing a food frequency questionnaire (FFQ) developed and validated in the EPIC study (5). Dietary intake by FFQs and clinical information were assessed five times during the 20-years of follow-up (mean follow-up ~12 years).

The study population’s mean age was 75 years at baseline. In addition, the mean value of protein consumed in this cohort was 74 grams/day and animal protein consisted of 63% of that. Regarding the protein breakdown, “sources of animal protein were: 26% for dairy products, 26% for processed meat products, 20% for red meat, 7.7% for fish and seafood, 6.3% for chicken, 2.7% for eggs, and the rest from other meats. Sources of plant protein were: 73% for cereals, 11.4% for vegetables, 9.0% for fruits and nuts, and 5.3% for legumes.”

Results:

  1. In the fully adjusted model, there was a statistically significant 40% reduction in CVD mortality, between the highest quintile of total protein intake (~18.7% of energy), relative to the lowest quintile of total protein intake (~13.3% of energy) (HR 0.60, 95% CI 0.40-0.90).
  2. In the fully adjusted model, there was a statistically significant 51% reduction in CVD mortality, between the highest quintile of animal protein intake (13.3% of energy), relative to the lowest quintile of animal protein intake (7.2% of energy) (HR 0.49, 95% CI 0.31-0.76).
  3. In the fully adjusted model, there weren’t any statistically significant associations between the highest quintile of plant protein intake (7.1% of energy), relative to the lowest quintile of plant protein intake (4.4% of energy), with any of the outcomes investigated, which were all-cause, CVD, and cancer mortality.

Analyzing:

Strengths: 

  • The mean age at baseline of 75 years old, which is older than most cohorts investigating this particular research question. 
  • The follow-up time of the publication was sufficient, given the baseline characteristics of the study participants.
  • The repeated dietary measures to minimize measurement errors.

Limitations: 

  • The overall small sample size (n=1,139), as well as the low incidence of CVD and cancer mortality. 
  • The dietary makeup of plant protein was rather homogenous, primarily characterized as “cereals.”
  • The over-adjustment for saturated fat, as that is often a key differentiator between many plant and animal sources of protein, and would expect that adjustment to impact risk for ACM and CVD mortality. This particular adjustment could have been included and excluded in a sensitivity analysis. 
  • The overall contrast and absolute amount of plant protein consumed was minuscule, relative to total and animal protein. Hence, why the researchers only investigated the HRs of 1% of energy from protein increase. 

Interpretation:

In the elderly, protein intake is often a correlate for overall health, as declines in muscle mass and strength are major contributors to increased mortality. Thus, in a study population where the mean age is ~75 years at baseline, given a long follow-up, we would expect that in the presence of wide contrasts in protein intake and high absolute amounts of protein intake, we would see significant reductions in mortality compared to lower amounts of protein. This indeed was observed for total protein and animal protein, which had differences in energy from protein of 13.3% to 18.7% (difference of 5.4%) and 7.2% to 13.3% (difference of 6.1%), respectively, within the low and high quintiles. Notably, we have a wide contrast in protein intake, as well as higher absolute amounts within the upper quintiles. 

However, the same reduction in mortality was not observed for plant protein. Interestingly, this can likely be explained by the absence of characteristics noted for total and animal protein. Specifically, the lack of contrast in plant protein intake, as well as the lower absolute amounts of overall plant protein consumed. The difference in energy from plant protein was 4.4% to 7.1%, within the low and high quintiles, which is a difference of 2.7% of energy coming from protein. To put this into perspective in regards to total protein intake, the individuals with the highest quintile of plant protein, at 7.1% of total energy, would be roughly equivalent to the individuals with the lowest quintile of animal protein, at 7.2% of total energy. This difference is striking and the authors state: “Because animal protein intake doubled the one of plant protein, our results must be interpreted considering this different contribution to the amount of total protein.” 

Interestingly, previous research has suggested that when the protein content is indeed equated between plant and animal sources, we observe significant reductions in ACM and CVD mortality, when substituting 3% of energy from animal protein for plant protein sources (8). Additionally, this is in the presence of a much larger sample size (n=​​416,104), concomitant greater incidence rate (77,614 deaths), as well as another long follow-up time (median, 15.5 years), and still studying the older population (median, 62.2 yr old men and 62.0 yr old women.) 

Having said that, the researchers did examine 1% of total energy from protein increases from the different protein sources and still found statistically significant reductions in ACM and CVD mortality with animal protein and not from plant protein. While a 1% increase isn’t incredibly informative, it’s still important to touch on why plant protein may still have not found significant reductions in any of the outcomes. Ultimately, this boils down to the overall diversity of plant protein intake. Recall that 73% of the plant protein intake was composed of “cereals.” Cereals can be broken up into whole grains or refined grains and we know from previous research that the type of grain impacts mortality differently (7). As a result, I emailed one of the authors of this study, asking if there was any data or insight on the cereal breakdown. This is what I received: “In our study, we do not have the information on whole grain vs refined cereals. However, in our old Italian population, most of the consumed cereal is typically refined.” Perhaps increasing 1% of energy from refined grains isn’t the brightest idea for combatting declining muscle mass and strength in the elderly, and ultimately reducing risk for mortality? Personally, that finding doesn’t surprise me. Additionally, within the publication, the authors were aware of this: “In this study, plant protein was mostly coming from cereals, and this fact could be related to the null association between plant protein and mortality. Indeed, in Asian studies where an inverse association between plant protein and all-cause mortality was observed, legumes and pulses contributed to approximately 25% of total plant protein.”

Take Home Message: 

Ultimately, the finding is concordant with previous research and current understandings. As stated previously, specifically in the elderly, the significance of protein is directly related to quality of life and health, and declines in muscle mass and strength are major contributors to increased mortality. In this study, when the contrast in protein intake was sizable and the overall protein content was high, substantial reductions in mortality were observed, in the case of total and animal protein. However, when those characteristics weren’t applied, in the case of plant protein, and the majority of that plant protein came in the form of refined grains, the same significant reductions in mortality were undetected. This echoes the importance of consuming enough protein in the elderly, which is emphasized by large bodies and expert groups, including The European Society for Clinical Nutrition and Metabolism. Specifically, they recommend that healthy older adults consume 1-1.2 g protein/kg of body weight from their diet and for those that are malnourished or at risk due to an acute or chronic illness, that protein should be further increased to 1.2-1.5 g protein/kg of body weight, with even higher intake for individuals with severe illness or injury (6). 

References:

  1. Baum, Jamie I et al. “Protein Consumption and the Elderly: What Is the Optimal Level of Intake?.” Nutrients vol. 8,6 359. 8 Jun. 2016, doi:10.3390/nu8060359
  2. Zhong, Victor W et al. “Protein foods from animal sources, incident cardiovascular disease and all-cause mortality: a substitution analysis.” International journal of epidemiology vol. 50,1 (2021): 223-233. doi:10.1093/ije/dyaa205
  3. Budhathoki, Sanjeev et al. “Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality in a Japanese Cohort.” JAMA internal medicine vol. 179,11 (2019): 1509-1518. doi:10.1001/jamainternmed.2019.2806
  4. Meroño, Tomás et al. “Animal protein intake is inversely associated with mortality in older adults: the InCHIANTI study.” The journals of gerontology. Series A, Biological sciences and medical sciences, glab334. 27 Nov. 2021, doi:10.1093/gerona/glab334
  5. Pisani, P et al. “Relative validity and reproducibility of a food frequency dietary questionnaire for use in the Italian EPIC centres.” International journal of epidemiology vol. 26 Suppl 1 (1997): S152-60. doi:10.1093/ije/26.suppl_1.s152
  6. Deutz, Nicolaas E P et al. “Protein intake and exercise for optimal muscle function with aging: recommendations from the ESPEN Expert Group.” Clinical nutrition (Edinburgh, Scotland) vol. 33,6 (2014): 929-36. doi:10.1016/j.clnu.2014.04.007
  7. Aune, Dagfinn et al. “Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies.” BMJ (Clinical research ed.) vol. 353 i2716. 14 Jun. 2016, doi:10.1136/bmj.i2716
  8. Huang, Jiaqi et al. “Association Between Plant and Animal Protein Intake and Overall and Cause-Specific Mortality.” JAMA internal medicine vol. 180,9 (2020): 1173-1184. doi:10.1001/jamainternmed.2020.2790