SEAFOOD, GREENS, NUTS AND BEANS HELP US ALL STAY SUPPLE AND LEAN
Researchers at UniSC investigate the Mediterranean diet’s potential to reduce muscle wastage as we age
Corey Linton, Hattie H. Wright, Daniel P. Wadsworth and Mia A. Schaumberg
REVIEWERS
Community Science Club
Pomona & District Community House
ARTICLE INFO
Article type: NEW DISCOVERY
Issue date: 21/08/2024
Issue No.: 4
Authors: Corey Linton, Dr Kathryn Broadhouse
Original peer reviewed article: https://doi.org/10.3390/nu14245319
WHY READ THIS ARTICLE?
This article looks at the complex relationship between diet and muscle health as we age. Rather than looking at individual foods, which can be over simplistic, this study takes one’s diet as a whole, examining the association between inflammatory potential and measures of muscle health. Rather than simply stating that we should eat more fruit and veg to stay healthy (which we all know), this article and the data presented here show us the diets most effective at maintain our health and why.
Muscle health is important at all stages of life, but maintaining strength and mobility as we age can help us to stay healthy and living independently for longer. Frailty in later life is associated with accelerated physical and cognitive decline, disability and death. Understanding the latest research investigating this link between our diet and muscle health gives us the ability to make informed lifestyle decisions that may impact our healthy ageing journey. Furthermore, showing us which diets as a whole, rather than individual foods, help maintain muscle health, is far more useful when making meaningful, long lasting lifestyle changes.
Click to learn more about Corey
Corey's research focus is exploring the influence of diet quality on muscle and bone health in community-dwelling older adults. He is in the last 6-months of his PhD and currently holds a position as an associate lecturer in Nutrition and Dietetics at UniSC where he is expanding his research scope to patients with cancer, falls prevention and overall diet quality for healthy ageing
REVIEWERS' COMMENTS
“This study is a good start into this line of research and it was interesting to see what it takes to run human trials of this nature.This study shows the importance of maintaining muscle strength and mass as we age to avoid frailty. Following a diet as indicated in these findings enables people to have a better quality of life, to stay at home for longer."
SCIENCE COMMUNICATOR'S COMMENTS
"Putting aside the subject of this study, dietary links to muscle health, which is in its self very interesting, I really enjoyed working with the team to write this article because it is a great example of the scientific approach, data analysis and method considerations that go into human research studies.
To create a new article for the Healthy Ageing Community Alliance newsletter I will work from the original peer reviewed scientific article. However, the strict formatting and individual research field each scientific journal targets leads to research findings being written for a very specific academic audience, which is oftentimes challenging to understand for other scientists outside the field and unengaging for the beneficiaries of research themselves, the general public. This can lead to long delays in the translation of findings into everyday practice. Researchers lack a direct link to communicate their work to the general public and the general public are unable to access cutting edge researcher findings. It is this communication gap that inspired the inception of the HACA newsletter.
My background in neuroscience and medical physics is often far removed from most of the studies we write about in the Healthy Ageing Community Alliance newsletter. When I start reading the original peer reviewed scientific papers that form the base of these articles, the numerous acronyms, field specific terminology and assumed background knowledge can be very off putting. However, it is made a lot easier by looking at the data. Numbers, and their relationship to each other are universal. They don’t care what language you speak, what year it is, or if you have 10 or 10million of something. They will still be able to tell you what 50% or 300% of that thing is, and the answer will be the same today or tomorrow. Mathematics is the language of the universe. Understanding data, statistics and what they tell you about the relationship between variables and groups of variable is one of the most valuable skills that I have acquired from my time as a researcher. In this article we take a look at how Corey and the team investigate the relationship between the inflammatory characteristics of a diet and muscle health in a group of healthy community-dwelling older adults. By understanding this relationship, we can all make informed lifestyle decisions to improve our own health and wellbeing as we age."
Dr Kathryn Broadhouse, Science communicator for HACA
INTRODUCTION
Skeletal muscle and the muscle wasting disease, Sarcopenia
Skeletal muscle is the largest organ, by mass, in the body. It is essential for maintaining our other tissue structures and of course moving our physical selves around. Preserving both our tissue structure and our ability to move is essential for maintaining our health and independence at any stage of our lives, but particularly as we age. Healthy skeletal muscle is also important for metabolism and maintaining our bodies temperature by generating heat. It is not surprising then, that a decline in muscle mass and strength in older age has been shown to negatively affect the outcomes of several chronic diseases, which leads to an increase in frailty, hospital admissions and mortality.
Sarcopenia is an age related, involuntary loss of skeletal muscle mass and strength that affects about 10% of older people worldwide. People affected by sarcopenia experience atrophy – a loss, of type II muscle fibres which leads to the loss of muscle mass and strength.
Frailty is a clinical condition in which the ability of older people to deal with everyday or sudden stressors is hampered by age-related losses in physiological reserve and organ function. It is estimated that 12% of community-dwelling elderly people are afflicted with frailty, and this increases with age. A recent meta analysis of all previous studies, looking at links between the mediterranean diet and frailty has found that "adherence to Mediterranean diet is inversely associated with risk of frailty and pre-frailty in older adults and thus, has a considerable impact" on our healthy ageing journey.
https://doi.org/10.1016/j.arr.2023.101903
Just as a side note on types of muscle fibres, we have slow twitch (type I) and fast twitch (type II) muscle fibres. Fast twitch muscle fibres (type II) are suited for short, fast bursts of activity such as standing up, jumping and short sprints. These are the fibres that are damaged in sarcopenia. Slow twitch fibres (type I) are better suited for long periods of exercise such as long-distance running. The cause of Sarcopenia is poorly understood but it can leave sufferers with increased disability, frailty, increased risk of falls, increased risk of infection, increased need for institutional care, reduced quality of life, increased mortality, and increased healthcare costs. Given the growing global geriatric population Sarcopenia is increasingly being recognised as a major public health concern with a significant personal and societal burden.
Current research into Sarcopenia
To date, there is no cure for sarcopenia. Researchers are therefore turning their attention to understanding steps that can be taken to prevent the disease’s onset and its progression by maintaining muscle mass and strength as we age. We already know that low-grade systemic inflammation, a condition where there is inflammation throughout the body, is a key driver of muscle degeneration and contributes to the development of sarcopenia in older adults. Systemic inflammation happens when our immune system is constantly defending our bodies. Stress, infection, or chronic diseases can put our bodies into a pro-inflammatory state. When this occurs, the immune system becomes primed and ready to create an inflammatory response.
Links between diet and inflammation
It will be no surprise that what we fuel our body with will affect our health. Diets are known to affect systemic inflammation and therefore disease progression. We now understand that the benefits of a good diet aren’t just down to a few nutrients, but rather the combination and blend of many different nutrients as a whole. Certain food combinations, thus diets we follow, can exacerbate or alleviate inflammation. Diets with pro-inflammatory properties are thought to further exacerbate the loss of muscle mass, strength and function. The Mediterranean diet has been touted for some time now as the optimum diet for healthy living and healthy ageing. It is an anti-inflammatory diet made up of seafood, beans, nuts and greens that has been associated with weight loss, improved diabetes management, lower risk of cardiovascular disease and of course reduced chronic inflammation. New research has already shown that a Mediterranean diet is linked to reduced sarcopenia symptomology. In theory any diet that incorporates a lot of anti-inflammatory food such as fruit, vegetables, whole grains, soy-based products, tree nuts, legumes, fatty fish, herbs and spices particularly garlic, ginger, rosemary, black pepper, could have the potential to maintain muscle strength and mass as we age regardless of whether you are a Nonna, Abuelo or Giagia. Conversely, diets that contain a lot of red meat, processed meat, processed food and fried foods are inflammatory and could have negative effects on muscle strength and mass as we age. Consequently, Corey, Hattie and the team wanted to delve deeper and explore the association between the inflammatory potential of ones’ diet and measures of sarcopenia symptomology in community-dwelling older adults here on the Coast.
The dietary inflammatory index (DII)
The DII was developed to quantify the inflammatory potential of a diet. Because anti-inflammatory diets are good, the more negative your score, the better your diet is. Foods such as fruits, vegetables, nuts, seeds, and whole grains are classed as anti-inflammatory foods due to their ability to reduce inflammatory biomarkers. The more of these food you eat the more negative your DII score will be: - = anti-inflammatory. Whereas, processed foods and animal products are associated with increased inflammatory biomarkers and will lead to a more positive DII score; + = pro-inflammatory. The overall score from the DII algorithm combines the effect of dietary components on inflammation and indicates an overall pro- or anti-inflammatory dietary pattern. To date, most research has focused on the association between the inflammatory potential of the diet and chronic disease such as cancer, depression, and cardiovascular disease, but here the team use it to explore links between good eating and muscle health as we age.
A biomarker is a molecule found in blood, body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. We can use biomarkers to see how well the body responds to a treatment for a disease or in this case, see how anti- or pro-inflammatory a diet is.
Therefore the RESEARCH HYPOTHESIS this study wanted to test was: participants following an anti-inflammatory diet, a diet similar to a Mediterranean diet, will have higher muscle mass and strength and therefore less sarcopenia symptomology.
METHODS
Participant characteristics: Initially 173 community-dwelling participants aged between 65-85 were recruited and passed the pre-exercise screening to exclude anyone with heart failure, cancer, severe arrhythmia, poorly controlled hypertension, unstable angina, cardiomyopathy, or infectious diseases. Demographic data such as education level, income, physical activity level and living status were recorded along with height, weight, waist circumference to calculate Body Mass Index (BMI).
Diet assessment and DII scores: The team collected 24-hour dietary information on three days over a 2-week period for every participant via phone calls or face-to-face. Diet information was entered into software that calculated the energy and nutritional value of the food and drink intake over the 3, 24-hour periods. The average of the 3 days was then used to calculate the individuals DII score. Now everyone is human and the difficulty with human studies that rely on participants recalling information is that we all make mistakes. We often find in research projects like these that a certain amount of people unintentionally either over or under report their diet intake. To tackle this the team calculated everyone’s Basal metabolic rate (BMR), the number of calories you burn as your body performs basic (basal) life-sustaining functions. This can be done by using the Mifflin St Joer equation, which takes your height, weight, age and sex to work out your BMR. The team then compared this to the reported energy intake (EI) – EI:BMR. If this ratio was over a certain cutoff, then the team excluded the participant for over reporting and likewise, if this ratio was under a certain cutoff then the participant was excluded for under reporting. This was done on the basis that if your true energy intake (EI) was the amount you reported then this would be reflected in your weight which is entered into the BMR calculation. This lead to 33 participants being excluded for under reporting and 1 for over reporting. A further 29 participants had to be excluded as they only completed 1 of the 3 24-hour dietary reports. The team ended up with usable data from 110 participants. You can now see how quickly we lose numbers in human studies to rigorous scientific approach!
Assessment of sarcopenia symptomology and functional frailty: next the team measured the participants’ muscle strength, physical performance and finally muscle quantity.
Muscle strength was measured using the hand grip strength (HGS) test and sit-to-stand (STS) test. In the STS participants were instructed to cross their arms across their chest and rise as fast as possible to a full standing position then return to a full sitting position without using their arms as many times as possible in 30s.
Physical performance was measured using the timed-up-and-go (TUG) test. Starting in a seated position, the time it took for participants to rise, walk three meters forward, turn around, walk back to the chair and sit down was recorded.
Muscle quantity or mass was measured using a whole body x-ray scan which allowed the team to quantify total, upper and lower body skeletal muscle mass. As the x-ray deposits a small amount of radiation into the body 23 participants did not consent to this part of the study, therefore muscle mass data was only available in 87 participants.
The team then used several different statistical analyses to explore the relationship between DII score and the muscle strength - HGS, STS and physical performance TUG scores. If you are interested in learning more about the statistical analysis used in this study flip through the tabs below.
REVIEWERS QUESTIONS: Was there any thought on including bone density data in this of future studies?
RESEARCHER'S RESPONSE: This is a great observation. Bone density data is actually part of the whole, larger project that includes this study and many more. We currently have a paper under scientific review exploring diet quality and bone density and another currently being drafted exploring the change over 2-years. Once we have them published we will be happy to share the results!
REVIEWERS QUESTIONS: Is there possible confirmation bias by dismissing outliers in methods?
RESEARCHER'S RESPONSE: There is, as researchers we do control for contributing factors in our methods and what we can when running our statistics. However, given the study design and the complexities of researching food and muscle this is unfortunately never 100% accurate, but then no experiment is which is why we are also cautious when interpreting and presenting our results.
Statistical analysis
T-tests
T-test are used to test averages, to see whether there is a difference between two groups and whether this difference is significant. 1A shows height data distribution of two groups of adults. You can see that there is a lot of overlap. 1B shows the height distribution of a group of adults and a group of children under 10, here there is less overlap. T-tests measure this overlap and call it the p-value. If this overlap or p-value is less than 5%, less than 5% of the data overlaps, then it is deemed a statistically significant separation and the two groups are determined to be different from one another.
Pearson’s correlation
The Pearson’s correlation coefficient is a measure of how well data fits a straight line and in what direction that line goes. Pearson’s correlation ranges between -1 and 1 and measures the strength of the linear relationship between two variables. It tells us how one variable changes linearly with the other. If there is a strong negative relationship as in A, Pearson’s coefficient (r) is negative, then skeletal muscle mass (mm) decreases with increasing DII score. If there is no relationship as in B, Pearson’s coefficient is 0, there is no relationship between DII and muscle mass. Finally, if there is a strong positive relationship as in C, skeletal muscle mass increases with increasing DII score. Given all we know about muscle mass and inflammatory diets we would expect a relationship like A to be present in the team’s data.
Multiple linear regression
Simple Pearson’s correlations that just look at the relationship between two things often oversimplify data. For example, if you were to plot ice cream sales and shark attacks over the year and you knew nothing about human behaviour when the sun comes out, you may be able to convince yourself that ice cream consumption is causing shark attacks. The data move together, as ice cream sales go up so do shark attacks. This is a silly example but you can see how we could mistake correlation for causation if we don’t know enough about the system we are observing. In MLR, the dependent variable (i.e. muscle strength) is the outcome we're trying to predict. The independent variables (DII, age, sex etc.) are the things that explain our muscle strength. We can use them to build a model that accurately predicts muscle strength.
RESULTS
COMPARING GROUP CHARACTERISTICS
Firstly, participants were grouped into either pro-inflammatory (a positive DII - more "unhealthy diet") or anti-inflammatory (a negative DII, - a "healthier diet"). T-tests were used to compare the demographic characteristics (height, marital status, physical activity levels etc.) and muscle data between the two groups to make sure they were not different in any way apart from diet.
Table 1 below shows the results. As you can see there are no significant differences in any of the characteristic data; the p-values in the right column are all above 0.05, or 5%. The two groups are the same in terms of age, number of males to females, income, marital status, education levels, BMI and physical activity levels etc. The only thing that is different is their diets. This is good because we want to explore the effect of diet so it is important that all other variables are the same. With this sample of participants, we can now investigate the impact of an inflammatory diet on muscle mass, strength and overall frailty and therefore, sarcopenia symptomology rather than the effect of other factors which we haven’t accounted for.
If the exercise levels were different (they aren’t, p-value is far greater than 0.05, it is = 0.5) then we might be measuring the impact of exercise on the frailty measures of muscle mass strength rather than diet.
COMPARING FRAILTY MEASURES BETWEEN GROUPS
Table 2 shows the T-test results comparing sarcopenia symptomology between the two groups. As you can see hand grip strength was significantly reduced (p-value = 0.009 or 0.9%) and physical performance was somewhat reduced in the pro-inflammatory group (p-value = 0.058, or 5.8%). This is what we would expect from everything we have learnt in the introduction section. Our hypothesis was that a pro-inflammatory diet (a positive DII score - more unhealthy diets) would negatively impact muscle strength and mass and increase sarcopenia symptomology and frailty. So far our experimental results confirm this hypothesis.
THE RELATIONSHIP BETWEEN DIET AND FRAILTY
When the team looked at the relationship between hand grip strength and muscle mass and DII score they found that as DII score increased (the unhealthier your diet became) the weaker hand grip strength and less muscle mass you had (accounting for age, gender, number of co-morbidities, waist circumference and physical activity levels). If we look at the two models the team have produced from analysing the data we have DII plotted on the horizontal axis and predicted muscle measures plotted on the vertical axis. We can see that the two graphs have a negative correlation (the slope down from left to right). This means that the more pro-inflammatory your diet (more unhealthy) the more reduction in muscle strength and mass you are likely to experience. In other words, a lower inflammatory diet (a healthier mediterranean style diet) is associated with lower sarcopenia symptomology and lower frailty.
PREDICTING FRAILTY MEASURES FROM OUR DIET
With all this data the team also modelled how a change in DII would affect muscle mass and strength measures generally. With this data you or I could then work out our diet’s DII score and then potentially predict our muscle health from this model and more importantly how our muscle health would change with a change in diet. The Multiple Linear Regression model (see stats flip book above for info) that showed that for every 1 point decrease in DII score (one point step towards a healthier diet, a more mediterranean diet), will lead to an increase in hand grip strength and muscle mass by 0.16kg and 0.15kg/m2!
CONCLUSION
The teams key findings here show that a low DII diet, a diet similar to the Mediterranean diet is associated with higher muscle mass and higher upper extremity muscle strength in functionally able community dwelling older adults. The team found that following a pro-inflammatory diet, a diet with more processed food for example, was associated with poorer sarcopenia symptomology, which indicates that dietary inflammatory potential may be an important modifiable risk factor for combating the progression of sarcopenia. This is an important finding as it demonstrates the potential impact of the whole-of-diet composition on the prevention of sarcopenia and shows that we have the potential to modify our own healthy ageing journey when it comes to muscular mass, strength and fitness by modifying our diets. However, this study is a snapshot in time. It only shows one time point in a healthy older population. What we now need is a larger, longitudinal study that follows participants over months and years to see how diet, DII score and sarcopenia symptomology evolve over time. We also need to study participants who have already been diagnosed with sarcopenia to see how improving one’s diet has the potential to slow or reduce disease progression. However, this is not easy. We have seen how many participants were excluded or did not complete all examinations, and this drop-out rate is dramatically increased when we ask people to come back multiple times. People have busy lives and signing up for a longitudinal research study is a very big commitment. Imagine now, how many participants the team would need to recruit at the beginning to have enough at the end to carryout meaningful statistical analyses. But these follow-up longitudinal studies are necessary for us to understand the larger picture. To be able to pick apart the complex relationship between diet, disease prevention and healthy ageing would be a huge advancement and benefit for all, but requires a team of dedicated researchers and participants working together. In the meantime, while we wait for Corey, Hattie, Dan and Mia’s next findings or call for participants we can do our bit and start to add more nuts, beans, herbs, spices, seafood and greens to our diets.
This study seems like a very good springboard to set up a community kitchen to help provide healthy meals for our community with far reaching benefits. There is also huge potential to run longitudinal studies in aged care homes to assess the impact of providing "anti-inflammatory", mediterranean style meals to residents and assessing frailty measures over time.
Corey's take home message
"I don’t want there to be a misconception that diet is the most important factor to maintain muscle nor is it the sole reason. But, if we can optimize diet to maintain muscle and achieve healthy ageing it may take the pressure of an individual to achieve this through other means such as exercise which they may not like or be able to do. Maintain muscle strength itself is important to achieve healthy ageing as we know as muscle diminishes, as to does one’s ability to perform tasks such as standing up and sitting down, opening doors or jars and holding onto things without dropping them. We all wish to remain living independently for as long as possible. Maintaining our muscle health and preventing frailty is important to achieve this "
REVIEWERS' QUESTIONS: Is there any existing data out there indicating how long does it takes to change DII and muscle mass after you change your diet?
RESEARCHERS RESPONSE: There is not to my knowledge however, this is a similar project I am wanting to build on in the future, specifically exploring the acute inflammation effect from a meal (within a couple of hours) to then progress to exploring muscle response from the inflammation change of the meal.
REVIEWERS' QUESTIONS: Are you planning to do a longitudinal study and if so could you give a few details on study design and how many people you would need to recruit at the beginning considering drop off rate etc?
RESEARCHERS RESPONSE: The study written up in this newsletter did progress into a 2-year longitudinal study which we are still analysing and writing up. We collected data at 0-months, 3-months, 6-months, 1-year and 2-year. Originally, we recruited approximately 200 participants for the baseline assessment and have approximately 100 participants retained for the entirety of the study. We are looking forward to sharing the results with you when we have analysed everything.
REVIEWERS' QUESTIONS: Would there be an opportunity to get aged care facilities on board as in the recently televised trial in aged care facilities on ABC?
RESEARCHERS RESPONSE: There most certainly would be an opportunity to have aged care facilities involved. The exact inclusion criteria (criteria that the researchers define at the beginning of the study when applying for ethics approval that determine who can participate) for this study and our planned future longitudinal study would have to be fleshed out further however. Our current research proposal looks at community-dwelling older adults rather than adults in care homes. Any research activities within this project would have to adhered to these criteria. We would need to expand on the eligibility criteria in our next study.
REVIEWERS' QUESTIONS: Would it be feasible to carry out an intergenerational study? – community living project where aged care dwellers and infants cared for in one facility?
RESEARCHERS RESPONSE: This would be fascinating to explore further. As a social project it seems a no-brainer, as a research project though, my first thought is that it would be tricky to integrate as there would be a number of study design considerations we would need to sort out to make sure the research is rigorous. As a diet study we would want to keep all external factors very similar to what is normal to ensure we are seeing the change based off the diet change rather than anything else. Previous studies have shown that placing care home residents and infants together has far reaching benefits for both groups, improving social, physical and emotional wellbeing. From a purely dietary research point of view, it would be difficult for us to tease out the impact of the diet from all of the other benefits. This highlights the difference between community and research projects. In research we need to be able to measure improvements as well as observe them, which can often make research seem clunky and slow.
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