How to Optimize Protein Intake for Longevity?

‍Highlights:

• High protein diets should be recommended to clients above the age of 65, clients dealing with obesity, and athletes
• All clients interested in longevity should be encouraged to opt for plant-based sources of protein in place of animal ones to mimic protein restriction

Introduction

Protein intake is an important variable for longevity and healthy aging. Protein restriction is gaining traction as an approach that could improve longevity. But at the same time, we are recommending obese and older adults to increase protein intake to improve their health. So, which is it? Before we try to answer that question, we should clarify what high protein intake and protein restriction actually mean.

Recommended Dietary Allowance (RDA)

A good starting point is the Recommended Dietary Allowance (RDA) for protein which is defined as a daily intake of 0.8 g protein per kg / 0.36 g per pound of body weight. The RDA is designed to prevent muscle wasting for an average sedentary person, a person with average amount of body fat that doesn’t exercise. Unfortunately, we do not have a similar clear definition for a high protein diet. Based on research and what nutritionists prescribe, we can say that such a diet should include at least 1.2 g of protein per kg / 0.55 g per pound of body weight. When it comes to protein restriction, any diet supplying less than the RDA qualifies as protein-restrictive.

Who benefits from a high protein intake?

High protein intake is well-studied in three distinct scenarios. We know that for elderly, obese, and those actively trying to build muscle with no conflicting comorbidities, getting more protein than the RDA is beneficial.

• Overweight and obese – Protein stimulates secretion of insulin which protects against muscle breakdown and glucagon which increases fat burning. It also helps maintain healthy levels of satiety hormones such as cholecystokinin. A high-protein diet is an effective weight management tool that helps maintain muscle mass in a caloric deficit and reduces feelings of hunger (1).

• Athletes – Protein is a crucial component of muscle fibers. That is why people who are trying to build muscle or engage in a lot of physical activity need a higher protein intake to maintain or increase muscle mass and performance. Of course, only increasing protein intake without sufficient training stimulus will not lead to increased muscle mass, at best, it will prevent loss of muscle (2).

• Elderly – After the age of 50 muscle mass typically starts declining at about 10% per decade. This is because the rate of muscle degradation exceeds muscle synthesis. This is a problem as muscle strength is an important determinant of mobility in later life. Older adults need more protein to get to the muscle synthesis rate of younger adults (3). This is why revised guidelines from sarcopenia working groups recommend 1-1.2 g of protein per kg / 0.45-0.55 g per pound of body weight in individuals over the age of 65 (4).

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How does protein restriction benefit longevity?

Signs of potential benefits of protein restriction are showing up in cell studies. Low protein availability slows the growth of cells. The switch from growth which accelerates ageing to a survival mode seems to be what contributes to cell longevity (5). This is confirmed in mice studies. Mice that were fed a low-protein diet with only 9% of calories coming from protein, achieved the best longevity results. It is important to note that there is a trade-off, mice fed more protein achieved significantly better reproduction health (6).

There are a few studies that are also pointing to possible benefits in humans. They are showing that restricting protein intake to less than 10% of calories, or about 0.6 g per kg / 0.27 g per pound of bodyweight, significantly increases Fibroblast Growth Factor 21 (FGF21) levels. This is a liver hormone that regulates energy metabolism and improves sensitivity to glucose and insulin (7).

Who benefits from protein restriction?

Apart from the limited human trials available, we can also look at some observational data to see who might benefit from protein restriction. A retrospective analysis found that a low protein diet with less than 10% of total calories coming from protein was associated with a reduction in insulin-like growth factor 1 (IGF-1), cancer, and mortality in respondents aged 50 to 65 years old. With participants over the age of 65 it was a different story. High protein intake was associated with reduced cancer and overall mortality (8).

There is also the famous Japanese island of Okinawa. This island is considered a Blue Zone, a region where a higher than usual number of people live much longer than average. Diet could very well be one of the factors contributing to the amazing longevity its inhabitants enjoy. Interestingly, people from Okinawa eat a very low protein diet, getting only about 9 % of their calories from protein which is similar to what we see in many mice and human studies looking at protein restriction (9).

Plant-based protein mimics restriction

Protein restriction could also be something to consider for those who eat predominantly animal based protein. Large observational study showed that animal protein intake in the US is related to greater mortality, especially when correlated with other unhealthy behavior such as smoking (10). A different study found that people between 50 and 65 years old that reported high protein intake had a 75% increase in overall mortality and a 4 times increased risk of death from cancer. These associations were greatly reduced if the proteins consumed were plant-based (8).

One way to explain this would be through the different amino acid composition of animal and plant proteins. Plant protein is lower in several amino acids such as tryptophan and methionine. Reduced intake of these amino acids can inhibit the mammalian target of rapamycin (mTOR) pathway and the growth hormone and insulin-like growth factor 1 (IGF-1) axis, similar effects that happen with overall protein restriction. This has been shown to reduce cancer incidence or increase longevity in model organisms independently of calorie intake (8).

What should you recommend to healthy, weight-stable clients?

There are convincing arguments for both high protein and protein restricted diet recommendations. The problem is that most of the research in this area does not really tell us much about what to tell clients that are generally healthy, normal-weight, and middle aged. High-protein research is mostly focused on overweight people, elderly, and athletes. Protein restricted diets are missing long-term human studies to be completely convincing. There are still several key takeaways, despite these gaps in research.

• High protein diets should be recommended to clients who are obese or overweight to assist with weight loss. Protein intake can be increased up to 30% of total calories.
• High protein diets should be recommended to clients above the age of 65 to boost muscle synthesis. A range of 1–1.2 g of protein per kg / 0.45-0.55 g per pound of body weight should be the goal.
• High protein intake brings no additional benefits to healthy, weight-stable, middle-aged clients.
• All clients interested in longevity should be encouraged to increase plant-based sources of protein and limit animal ones to mimic protein restriction.
• It is not possible to recommend going below the RDA for protein based on current available evidence.

When you’re trying to help your clients optimize their protein intake, it’s important to approach them on an individual basis. Those dealing with excess weight will benefit from increased protein just like your elderly clients. On the other hand, middle-aged clients that are at their optimal weight won’t benefit from further increases in protein intake. You can advise these clients to instead look at the source of their protein and encourage them to lean more in the direction of plant protein. There is not currently sufficient evidence to warrant recommending long-term protein restriction below the RDA.

References:

1) Caroline Giezenaar, Amy T Hutchison, Natalie D Luscombe-Marsh, Ian Chapman, Michael Horowitz, Stijn Soenen. Effect of Age on Blood Glucose and Plasma Insulin, Glucagon, Ghrelin, CCK, GIP, and GLP-1 Responses to Whey Protein Ingestion. Nutrients. 2017 Dec 21;10(1):2. doi: 10.3390/nu10010002.

2) Joshua L Hudson, Yu Wang, Robert E Bergia III, Wayne W Campbell. Protein Intake Greater than the RDA Differentially Influences Whole-Body Lean Mass Responses to Purposeful Catabolic and Anabolic Stressors: A Systematic Review and Meta-analysis. Advances in Nutrition, Volume 11, Issue 3, May 2020, Pages 548–558, https://doi.org/10.1093/advances/nmz106

3) Jamie I. Baum, Il-Young Kim, Robert R. Wolfe. Protein Consumption and the Elderly: What Is the Optimal Level of Intake? Nutrients. 2016 Jun; 8(6): 359. Published online 2016 Jun 8. doi: 10.3390/nu8060359

4) Jürgen Bauer et al., Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013 Aug;14(8):542-59. doi: 10.1016/j.jamda.2013.05.021. Epub 2013 Jul 16.

5) Cara L Green, Dudley W Lamming. Regulation of metabolic health by essential dietary amino acids. Mech Ageing Dev. 2019 Jan;177:186-200. doi: 10.1016/j.mad.2018.07.004. Epub 2018 Jul 22.

6) Samantha M. Solon-Biet, Kirsty A. Walters, Ulla K. Simanainen et al. Macronutrient balance, reproductive function, and lifespan in aging mice. PNAS, March 2, 2015 | 112 (11) 3481-3486 | https://doi.org/10.1073/pnas.1422041112

7) Cara L. Green, Dudley W. Lamming. Regulation of metabolic health by essential dietary amino acids. Mech Ageing Dev. Author manuscript; available in PMC 2020 Jan 1. doi: 10.1016/j.mad.2018.07.004

8) Morgan E Levine et al. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metab. 2014 Mar 4;19(3):407-17. doi: 10.1016/j.cmet.2014.02.006.

9) Donald Craig Willcox, Giovanni Scapagnini, Bradley J Willcox. Healthy aging diets other than the Mediterranean: a focus on the Okinawan diet. Mech Ageing Dev. Mar-Apr 2014;136-137:148-62. doi: 10.1016/j.mad.2014.01.002. Epub 2014 Jan 21.

10) Mingyang Song et al. Animal and plant protein intake and all-cause and cause-specific mortality: results from two prospective US cohort studies. JAMA Intern Med. Author manuscript; available in PMC 2017 Oct 1. doi: 10.1001/jamainternmed.2016.4182

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