Should we recommend more protein for older adults?

Dietary proteins are essential for building and maintaining healthy body structures such as muscle and bone.

Protein also plays pivotal roles in all sorts of processes including vision, healing, acid-base balance, fluid balance, and as important components of enzymes, hormones, and antibodies. As we age one of the threats to independent living is the loss or decline in many of these functions.
 
As such, investigations of protein intakes on health outcomes in older adults has become an active area of research, which has kicked off ongoing scientific debate about optimal intake levels.

Do protein requirements increase in older age?
 
Several international groups of scientific experts have advocated for higher recommended protein intakes for older adults – and a number of countries have taken the initiative to increase their reference values for this life stage.
 
Other countries have not landed on higher protein intake values despite a review of available evidence or have simply not taken the steps to update the literature – and the underlying data remain outdated.
 
Today population protein intakes for healthy older adults range from 0.8 g to 1.3 g per kg body weight (BW) per day. And some expert groups recommend up to 2 g protein/kg BW or higher.

The Study

The systematic review we present this week was adapted from a background document aimed to advise the Dutch government on its dietary reference values (DRVs) for protein focused specifically on older adults (> 60 years).
 
This is an excellent paper with many teachable moments. Make sure to tune into our MOYO Nutrition podcast Episode 4 for a more in-depth discussion.
 
In summary, the authors started their review with the latest European Food Safety Authority (EFSA) scientific report on protein published in 2012 to evaluate whether they agreed with their scientific basis and methodology.

• Bottomline – they were happy with EFSA’s approach and the derived protein requirement of 0.83 g/kg BW based on the evidence available at that time.

Next, in an effort to update the literature, they searched for recent systematic reviews and transparent reports on protein intake in relation to health outcomes in older adults. 

• Bottomline – they were not happy with any of the available systematic reviews with respect to their own goal of deriving a dietary recommendation for protein.

So, they set off to conduct their own systematic review aimed specifically at determining whether protein intakes higher than 0.83 g/kg BW elicit health benefits or harm in older adults.
 
Nine health outcomes were selected for evaluation: lean body mass, muscle strength, physical performance, bone health, blood pressure, serum glucose and insulin, serum lipids, kidney function, and cognition.
 
They only selected randomised controlled trials conducted among older adults in the general population. Participants had to have an average habitual daily protein intake of greater than or equal to 0.8 g/kg BW.
 
This consideration for habitual protein intake report is an important factor as they needed to understand if additional protein intake beyond the current recommendation (0.8 g/kg BW/d) would be beneficial. Previous reviews have failed to account for this – making interpretation difficult, especially when trying to derive dietary reference values.
 
All RCTs had to be a minimum duration of 4 weeks, performed among older adults with a minimal age of 50 y and who were living at home independently.
 
Physical exercise was also considered given the potential additive or synergistic effect on muscle mass and muscle strength in older adults compared to protein intake alone.

As with all systematic reviews, the 'risk of bias' of included studies were reported. This addresses bias arising from the randomisation process, deviations from intended study protocols, missing outcome data, and so on. The risk of bias is then scored as ‘low risk’, ‘some concerns’ or ‘high risk’.
 
Lastly sensitivity analyses were conducted to examine heterogeneity in results across studies by type of protein intervention, risk of bias, and if the study was statistically powered for the given outcome measure.
 
Of particular note – we want to highlight the six predefined categories of conclusions – or what the authors’ called ‘decision rules’ were used to judge the ‘totality of the evidence’ for each health outcome.

Rules ranged from convincing (beneficial/unfavourable) effect, a likely (beneficial/unfavourable) effect, a possible (beneficial/unfavourable) effect, an ambiguous effect, likely no effect or too few studies.
 
All of the rules with the exception of ‘too few studies’, had to include at least 3 or more studies. A convincing effect meant that > 75% of the studies showed a beneficial, whereas a likely beneficial effect meant that 50-74% of studies showed a beneficial effect – and so on.  
 
All-in-all, this systematic review was very well designed.
 
The Results
 
Of the 266 RCTs selected for assessment, only 18 studies were included in the review. Publication years ranged from 1995 to 2019 - however, the majority of studies were published since 2015.
 
In most studies the habitual daily protein intake was between 0.8 and 1.1 g/kg BW; and 9 of the 18 included studies had a physical exercise intervention.
 
None of the studies had a low risk of bias, 50% had some concerns of risk bias and the remaining had high risk of bias.
 
Increased protein intake showed to beneficially affect:

• Lean body mass in 7 of 18 RCTs
• Muscle strength in 3 of 8 RCTs in the context of physical exercise and 1 of 7 RCTS without physical exercise

For the other outcomes, less than 30% of the RCTs showed a statistically significant effect.

So, in applying the decision rules, the authors concluded that increased protein intake has a possible beneficial effect on:

• lean body mass
• muscle strength but only when combined with physical exercise

Increased protein intakes had likely no effect on:

• muscle strength when not combined with physical exercise
• bone health

An ambigous effect (meaning conflicting results) on:

• Serum lipids

And too few RCTS were available to allow for conclusions on physical performance, blood pressure, serum glucose and insulin, cognition and kidney function.

The Outcome

Well.. hold fire. It was concluded that the systematic review did not provide convincing evidence that a daily protein intake beyond 0.8 g/kg BW elicits health benefits in older adults.



A Few Worthy Points

In the sensitivity analysis there was no evidence that results differed according to the type of protein. However, all but one of the trials used dairy-based proteins so conclusions on whether outcomes differ with plant-based proteins could not be made.

It is also worth noting the RCTS that observed a beneficial effect on lean body mass when higher levels of protein were combined with physical exercise were all in females, and the dose of protein was taken immediately following a training session, instead of spread over the day. Participants had also started training 8 weeks before the start of the trial. In this case, it is possible that the increased training load increased protein requirement - a phenomenon we also see in younger novices embarking on a new training program.