Effect of peanut butter supplementation on physical and cognitive functions in community-dwelling older adults: study protocol for a 6-month randomised controlled trial

Abstract

Introduction

Ageing is associated with physical and cognitive declines, which may be further exacerbated by poor nutrition. Nuts are energy and nutrient dense, and their consumption is associated with better physical and cognitive functions in older adults, but data from interventional studies are limited. This 6-month randomised controlled trial is designed to investigate the effects of consuming 43 g/day of peanut butter (equivalent to 1.5 servings of nuts) on physical function, including walking speed (primary outcome), standing and dynamic balance, upper and lower body strength, lower body power and endurance, and associated factors including muscle mass, cognitive function and DNA telomere length in community-dwelling older adults.

Method and analysis

A total of 120 participants aged ≥65 years will be recruited and randomly allocated (1:1 ratio) to either the intervention group (n=60) that will receive individually packaged sealed containers containing 43 g of peanut butter to be consumed once daily for 6 months alongside habitual diet, or the control group (n=60) that will maintain their habitual diet. Primary and secondary outcomes will be assessed at baseline and at 6 months. The primary outcome is walking speed assessed using the 4 m usual gait speed test. Secondary outcomes include other physical function assessments: standing balance, chair stand time, timed-up-and-go test and four-square step test; and hand grip and knee extensor muscle strength; cognitive function assessed using the Montreal Cognitive Assessment and trail making tests; body composition; nutritional status; and DNA telomere length from participants’ buccal cell samples. Linear mixed models will be used to compare changes in outcomes between intervention and control groups.

Ethics and dissemination

The study protocol is approved by the Deakin University Human Research Ethics Committee. The trial is registered with the Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12622001291774. The results will be disseminated through peer-reviewed journals, conference presentations and media.

Trial registration number

ANZCTR12622001291774.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• To our knowledge, this will be the first randomised controlled trial to assess the effects of consuming peanut butter for 6 months on both physical and cognitive functions, and telomere length, in community-dwelling older adults (65 years and older).

• This study will address the current evidence gap on the effects of peanut butter intake on physical function and strengthen the emerging evidence linking higher nut consumption to improved cognitive functions in older adults.

• A set of functional capacity-related, objectively measured, interconnected outcomes will be assessed including body composition by dual-energy X-ray absorptiometry, physical and cognitive functions and nutritional status using standard tests validated for older adults, and DNA telomere length by PCR.

• Using preportioned, individually packaged sealed containers containing the recommended daily dose of study product will facilitate intervention adherence, and modifying the texture of peanuts into butter form makes it easy for older adults to follow the intervention, regardless of dentition issues common with ageing.

• The lack of an energy-matched well-controlled diet in the control group and the nature of the intervention preventing blinding participants to their randomised group are the main limitations of the study.

Introduction

According to the WHO, healthy ageing is a process of maintaining the functional ability to enable well-being in older age.¹ Functional ability in older age is challenged by age-related declines in muscle mass, physical function and cognitive function, and this may be further exacerbated by low-quality diets in older adults.² Nutritional requirements critical for musculoskeletal health include energy, protein and micronutrients. The nutrient requirements increase with ageing but fulfilling them is often challenging as a consequence of poor diet quality, inadequate dietary intake due to poor appetite, impaired dentition, early satiety, impaired digestion and absorption and diseases in older age.^{3 4} Therefore, dietary approaches to improve nutritional intake are crucial to support the health and well-being of older adults.

Nuts are a high-quality source of energy, unsaturated fatty acids, protein, vitamins and minerals and other phytochemicals providing a range of benefits including antioxidant and anti-inflammatory properties.⁵ Tree and ground nuts are generally considered to be energy and nutrient dense and they are often considered as a collective food group in nutrition research.^{6 7} Regular nut consumption (minimum of 7 g/day) has shown to be associated with a higher percentage of the population meeting average requirements for several nutrients and has been shown to improve diet quality.⁸

Observational studies have reported that nut consumption may also be protective against multiple health concerns that are more prevalent in older adults, including cancer,⁹ cardiovascular diseases¹⁰ and diabetes.^{11 12} In a review of the available evidence, we have previously reported that nut intake is associated with better physical and cognitive functions in older adults, likely due to improved diet quality and nutritional status leading to overall better health.¹³ While better mobility was the most frequently reported physical function outcome associated with nut consumption,^{14 15} higher muscle mass and lower risk of falls were also reported.^{16 17} However, this evidence is observational in nature, and most of these studies examined nuts as a component of a diet instead of a stand-alone food. Besides physical function, cognitive function is an important component in older adults’ functional capacity, and together they can impact the quality of life in older adults.¹⁸ Previous reviews^{13 19} supporting the positive associations between nut consumption and cognitive function are further strengthened by findings from a recent 16-week randomised, controlled, cross-over trial which reported improved brain vascular function and memory in response to 60 g/day mixed nut intervention (walnuts, pistachio, cashew and hazelnuts) versus no nut intake among 28 healthy older adults.²⁰

Telomere length is repeatedly shown to decrease with ageing²¹ and thus used as a biomarker to predict the risk of age-related diseases.²² A positive linear association between nuts and seed consumption and telomere length is reported in a large sample of adult males and females.²³ This is likely due to the antioxidative and anti-inflammatory properties of nuts that reduce the oxidative stress and inflammation which are the key mechanisms for telomere shortening.²⁴ However, given evidence on the potential benefits of nut consumption on physical and cognitive functions and telomere length is predominantly derived from observational studies, well-designed, long-term randomised, controlled studies are required to clarify effectiveness.

Peanuts are the most commonly consumed nuts in the world and one of the most affordable and accessible.²⁵ They are botanically classified as legumes but have a nutritional profile similar to nuts with high energy and nutrient density. Peanuts are high in plant proteins (28 g/100 g) with arginine as the predominant amino acid, and are rich in unsaturated fatty acids (41 g/100 g); B group vitamins such as niacin, thiamine, riboflavin, B₆ and folate; vitamin E; and minerals including magnesium, copper and phosphorus. Peanuts are also a good source of bioactive phytochemicals such as flavonoids, resveratrol, plant sterols and dietary fibre. Peanut and peanut product consumption is associated with improved diet quality in free-living men, women and children with a particularly higher intake of vitamin A, vitamin E, folate, calcium, magnesium, zinc, and iron and dietary fibre, and lower intake of saturated fat and cholesterol.²⁶ With the high-nutrient density leading to improved diet quality, peanuts and peanut products may be a simple and cost-effective dietary intervention for older adults. Moreover, the texture of peanuts can be easily modified into peanut butter which may be more appealing and practical to address dentition issues common with ageing in this population.²⁷

The primary aim of the Capacity of Older Individuals after Nut Supplementation (COINS) study is to determine the effects of peanut butter supplementation for 6 months on physical function (walking speed as the primary outcome), cognitive function, body composition, nutritional status and DNA telomere length in community-dwelling older adults at risk for falls. As nut consumption has been reported in previous studies to improve diet quality,²⁶ we will also explore whether the effects of peanut butter supplementation are mediated by changes in diet quality following peanut butter supplementation.

Methods

Study design

The COINS study is a 6-month randomised, controlled, single-blinded clinical trial conducted at the Institute of Physical Activity and Nutrition, Deakin University, Burwood Campus, Melbourne, Australia. The study protocol is reported in accordance with the Standard Protocol Items: Recommendations for Interventional Trials 2013 guidelines for reporting clinical trial protocols.²⁸ The randomised controlled trial (RCT) will include two parallel arms as the intervention and the control. The study is expected to run from June 2023 to December 2024.

Study population

Community-dwelling older males and females aged 65 years or above who are at risk of falls will be included. Participants will be included in the study according to the following inclusion criteria: (1) body mass index (BMI) between 18 and 35 kg/m², (2) reporting no nut allergy, (3) habitually consuming nuts or nut spreads less than two servings per week, (4) generally healthy or with metabolic disease(s) managed through lifestyle or common medications (excluding insulin) and (5) at risk for falls, defined by a score of ≥2 points at simplified falls risk screening questionnaire adapted from our previously used algorithm based on risk factors for falls in this population.²⁹ Table 1 shows the scoring criteria of the falls risk screening questionnaire. Participants will be excluded if they (1) are taking oral nutrition supplements (ONS), (2) undertake structured resistance or exercise programmes more than once a week, (3) report health conditions affecting dietary intake and metabolism (eg, gastrointestinal disease, musculoskeletal conditions or cancer) or (4) report severe osteoarthritis, severe lower back pain, osteoporotic fracture or recent knee/hip replacements that hinder them from performing physical function tests in this study.

Table 1. Scoring criteria of the falls risk screening questionnaire.

Criteria	Score
1. Age in years
<70	0
70–75	1
>75	2
2. Experience of two or more slips or trips (but not fallen) in the past 12 months	1
3. Feeling unsteady on feet sometimes when standing or walking or doing other daily activities	1
4. Feeling at risk of falls	1
5. Having difficulty when rising from a chair or toilet without using arms	1
6. Taking ≥4 types of medication	1

Sample size and recruitment

This RCT was powered based on the hypothesised improvement in 4 m walking speed following peanut supplementation. With no previous studies that specifically investigated the effect of nut supplementation on the physical function of older adults, the sample size calculation was based on an intervention trial that used an ONS supplementation that has comparable energy and protein content as peanut butter in older adults.³⁰ This study reported an average improvement in walking speed by 0.15 m/s, and we hypothesised that a similar effect size will be observed in our study. This expected improvement aligns with the minimum clinically important difference for change in walking speed in older adults.³¹ Therefore, based on an expected between-group difference of 0.15 m/s, at an SD of 0.2 m/s³² and an attrition rate of 15%, 60 participants per group (120 in total) will be recruited to detect a significant difference between the study groups at 80% statistical power.

The participants will be recruited from Melbourne, Victoria, between May 2023 and July 2024 via advertisements through social media, local area news bulletins, and flyers and pamphlets distributed in the community such as retirement villages. Volunteers who express interest will be screened via an online survey or by telephone to determine eligibility. Eligible volunteers will commence the study on obtaining their written informed consent by a researcher at the baseline study visit. At the time of written consent, participants are informed of their right to withdraw if they do not wish to continue participation.

Randomisation and blinding

The recruited participants will be randomised in 1:1 ratio to the intervention or the control group on completion of the baseline visit following the assessment of primary and secondary outcomes. A stratified randomisation allocation will be developed using the Research Electronic Data Capture secure web application by a biostatistician not involved in the study. Randomisation will be stratified by age (≤80 or >80 years old), sex (male or female) and BMI (≤25 or >25 kg/m²). The randomisation group allocation will be known to the researcher overseeing the RCT and will be disclosed to the participant. The other researchers collecting study outcomes and conducting statistical analysis will remain blinded to the group allocation to avoid potential measurement bias.

Intervention and control groups

Participants in the intervention group will be instructed to supplement their habitual diet daily for 6 months with 43 g of peanut butter per day. The peanut butter will be delivered in convenient, preportioned and individually packaged airtight sealed plastic containers. This amount represents 1.5 servings of nuts and provides 250 kcal, 20 g fat (>90% as unsaturated fats important for optimal health) and 10 g protein. The participants in the intervention group will be given 96 containers of peanut butter at the baseline visit and another 96 containers at an additional visit at the 3 months of the study. Since the peanut butter products are shelf stable at room temperature, participants will be given instructions to store them in their pantry at room temperature and fully consume the content in one container per day at any time during the day either alone or incorporated into main meals or snacks. Instructions will be given to maintain their habitual diet with the addition of peanut butter. Participants will also receive a colourful reminder note with a fridge magnet to put up on the refrigerator door as a daily reminder to have peanut butter and they will receive text message reminders fortnightly for the duration of the intervention. The participants in the intervention group will be asked not to share the peanut butter with family and to return the unconsumed containers during the visits at 3 and 6 months to assess compliance. The participants in the control group will be asked to maintain their habitual diet. According to our study design, participants in the intervention group may have additional energy intake from peanut butter that may impact the weight and body composition changes. However, previous reviews have shown that energy from nuts is compensated from subsequent meals and does not lead to weight gain.^{33 34} Participants in both groups will be instructed to maintain their usual levels of physical activity and exercise throughout the study period.

Adherence to intervention

The number of unconsumed peanut butter containers returned by each participant during the visits at 3 and 6 months will be recorded. The total number of peanut butter containers consumed will be calculated as the difference between the total provided and the total returned. Adherence to the intervention will be calculated as the ratio between the total number of peanut butter containers consumed divided by the total number of days in the follow-up period.

Outcomes

All participants recruited will attend baseline and 6-month study assessment visits to the clinical facility at Deakin University Burwood Campus (Melbourne) (table 2). It will be requested that participants fast and abstain from heavy exercise for at least 2 hours before each visit.

Table 2. Summary of the outcomes and participant assessments.

Variables	Data collection methods	Data collection time points
		Baseline	3 months	6 months
Physical function	4 m gait speed test (primary outcome)	x		x
	Standing balance tests	x		x
	Chair stand tests	x		x
	Five times sit-to-stand test	x		x
	30 s sit-to-stand test	x		x
	Four-square step test	x		x
	Timed-up-and-go test	x		x
Muscle strength	Hand grip strength	x		x
	Isometric knee extensor strength	x		x
Cognitive function	Montreal Cognitive Assessment	x		x
	Trail making tests A and B	x		x
Body composition	Dual energy X-ray absorptiometry, total body and segmental lean mass	x		x
	Bioimpedance spectroscopy, fat mass and fat-free mass	x		x
Anthropometry	Height, weight, waist, mid-upper arm and calf circumference, and body mass index	x		x
DNA telomere length	Quantitative PCR	x		x
Nutritional and health status	Mini Nutrition Assessment	x		x
	Blood pressure	x		x
Dietary intake	3-day food records	x		x
General appetite	Simplified nutritional appetite questionnaire	x		x
Physical activity	Physical Activity Scale for the Elderly	x		x
Functional capacity	Late-Life Function and Disability Instrument	x		x
Sarcopenia risk	SARC-F screening tool	x		x
Intervention characteristics (intervention group only)
Adherence	Number of peanut butter containers returned		x	x
Liking	Perception on the intervention		x	x

SARC-FStrength (S), Assistance walking (A), Rising from a chair (R), Climbing stairs (C), and Falls (F)

Physical function and muscle strength

Physical function will be assessed using gait speed, standing balance tests, chair stand tests, timed-up-and-go (TUG) test and four-square step test (FSST). Participants’ walking speed will be measured using the 4 m gait speed test. The participants will be asked to walk a 4 m distance on a flat surface at their usual pace and the test will be repeated twice. The time taken to complete the test will be recorded using timing gates (Swift Speedlink Performance Equipment systems). Participants will be given one practice trial following two test trials. The fastest time measured to the nearest 0.01 s will be used to calculate the walking speed (metre per second).³⁵

The ability to maintain balance will be tested in three standing positions, including feet together side by side, semi-tandem and full tandem. Participants will be asked to maintain balance in each position for 10 s. A score of 1 point each will be given if the participant can maintain balance for 10 s in the position side-by-side and semi-tandem stands. For the tandem stand, the participant’s ability to hold the position for a maximum of 10, 3–9.99, or <3 s will receive a score of 2, 1 or 0, respectively. If the participant cannot maintain balance for the tested duration or is not attempted, a score of 0 will be assigned.³⁶ The chair stand test will be performed if participants are able to stand from a chair to a fully upright position without using their arms. They will be encouraged to perform the task as fast as possible, and the time taken to perform five full sit-to-stands (in seconds) and the number of full sit-to-stands performed in 30 s will be recorded.

In the TUG test, participants will be asked to rise from a chair, walk at their maximum speed to a cone placed on the floor at a 3.0 m distance, turn around, and walk back and return to sitting in the chair. In the FSST, participants will be asked to step forward, sideways and backwards over two rods placed flat on the floor in a cross formation making four squares. They will be asked to step as fast as they can, first in a clockwise direction immediately followed by anticlockwise direction, and return to the starting position. In both tests, participants will be given a practice trial, and the test will be repeated twice. The shortest time (to the nearest 0.1 s) will be used in the analysis.

Upper and lower body muscle strength will be assessed using the hand grip strength (HGS) and knee extension strength (KES) tests, respectively. The HGS (in kilograms) will be assessed using a calibrated handheld dynamometer (Jamar Plus, Digital Hand Dynamometer), and the participants will be instructed to squeeze the dynamometer with their maximum strength in a seated position with the elbow bent at 90 degrees and without the arm touching the trunk. Participants will be given three attempts for each hand alternating; the maximum strength by any given attempt (independent of right or left hand) will be used as the participant’s maximum HGS.³⁷ The KES (in kilograms) will be assessed by using a strain gauge and a scale attached to a metal bar at the rear of a chair via a metal hook. Participants will be instructed to sit on the chair with their hips and knees bent at 90 degrees and a non-stretching strap firmly attached around their dominant leg connected to the strain gauge. They will be asked to kick forward against the strap with the maximum effort and hold for 2–3 s. Two attempts will be given, and the force exerted will be detected by the scale. The maximum force exerted at any given attempt will be considered as the participants’ KES.³⁸

Physical activity and functional capacity

Habitual physical activity levels will be determined using the validated Physical Activity Scale for the Elderly (PASE) questionnaire,³⁹ which will be self-administered. The PASE assesses the frequency, duration and intensity of leisure, household and occupational activities performed over the past week. A score is assigned ranging from 0 to 793, with higher scores indicating greater physical activity. Participants’ overall function will be determined through a self-administered 16-item Late-Life Function and Disability Instrument, which has been validated to assess the function (eight items) and disability (eight items) of community-dwelling older adults.⁴⁰ The risk of sarcopenia will be identified using the SARC-F screening tool that encompasses five self-reported questions on strength (S), assistance with walking (A), rising from a chair (R), climbing stairs (C) and history of falls (F), and which is recommended for use in older adults by the international sarcopenia guidelines.⁴¹

Cognitive function

Participants’ cognitive function will be assessed by trained researchers using Montreal Cognitive Assessment (MoCA), a tool validated to identify mild cognitive impairment in older adults.⁴² MoCA is a 30-point tool with series of questions and tasks assessing multiple cognitive domains, including short-term memory, visuospatial abilities, executive functioning, attention, concentration, working memory, language and orientation to time and place. A higher score indicates better cognitive function and a score below 26 is the suggested clinical cut-off for mild cognitive impairment. Participants’ working memory and executive functioning will be further assessed using the trail making tests A and B.⁴³ In test A, participants will be asked to connect randomly positioned numbers in numerical order (eg, 1→2→3), while in test B, to connect randomly positioned numbers and letters in numerical and alphabetical order in an alternating progressive sequence (eg, A→1→B→2→C→3) as fast as they can. The time (in seconds) taken to complete each task will be recorded. A shorter time indicates better performance.

Anthropometry and body composition

Participant’s weight will be measured to the nearest 0.1 kg in minimal clothing using a digital weighing scale (UC-321; A&D, Australia). Standing height will be measured to the nearest 0.1 cm without footwear using a wall-mounted stadiometer. BMI will be calculated as the body weight (kg)/height (m) squared (kg/m²). Waist circumference, mid-upper arm circumference and the calf circumference will be measured to the nearest 0.1 cm using a non-stretchable measuring tape. All measurements will be performed following the protocols outlined in the anthropometry procedure manual by the International Society for the Advancement of Kinanthropometry.⁴⁴ All measurements will be taken in duplicate and the mean value will be recorded. If the two measurements are different by 10%, a third measurement will be taken, and the two measurements with <10% difference will be used to calculate the mean value. Participants’ total and segmental lean and fat mass will be assessed using dual-energy X-ray absorptiometry (DXA) (Lunar iDXA; GE HealthCare, Australia and New Zealand). DXA quality assurance will be performed daily to ensure scanner reliability, and similar scan protocols will be performed for all participants. Bioimpedance spectroscopy (ImpediMed, SOZO, Australia) will be used to measure participants’ fluid status and other tissue mass.

DNA telomere length

Buccal cell samples from participants’ inner cheeks will be collected using the Isohelix RapiDri Buccal Swab Kit, following the procedure outlined in the kit. Instructions to refrain from eating or drinking for 2 hours and to rinse their mouth with water before sample collection will be given. Participants will be asked to gently scrape the cell layers of their inner cheek for 60 s using the swab head. The cell samples will be sealed in collection pouches and stored at −80°C freezer until processed and analysed for DNA telomere length using the quantitative PCR method.

Nutrition, health and demographic data

The nutritional status of the participants will be assessed using the Mini Nutrition Assessment, a validated nutrition assessment tool in older adults, by a trained researcher.⁴⁵ Participants’ blood pressure on the left arm will be measured in a relaxed, seated position using a digital sphygmomanometer (UA-651BLE, A&D Medical, Tokyo, Japan) following the standard guidelines by the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.⁴⁶

The participants will also be instructed to record their dietary intake for 3 days (two weekdays and one weekend day) using the food record method during the first week after the baseline visit and the week before the end of study visit. Participants will be instructed to choose regular days to record their food intake, not to deviate from their usual intake and to provide specific details about the food items (type of food, additions, brand names, preparation methods) and the portion consumed in household measurements (eg, cup, teaspoon). Participants in the intervention group will be instructed to follow their habitual diet during the first week while they record food intake and commence the intervention from the second week. Accordingly, the end of study visits of the participants in the intervention group will be scheduled 6 months from the date the intervention commenced for each participant. The returned food records will be cross-checked to ensure completeness by a qualified nutritionist/dietitian. Dietary intake will be analysed using the FoodWorks 10 Professional software that uses nutrition composition data predominantly from AusFoods (AUSNUT 2011–2013 and the new Australian Food Composition Database) and AusBrands databases. Diet quality will be assessed using two validated methods including the Dietary Guideline Index (Australian context)⁴⁷ and the 14-item Mediterranean Diet Adherence Score (range 0–14, international context).¹⁶

Participants’ appetite will be determined using the self-administered simplified nutritional appetite questionnaire validated for use in community-dwelling older adults.⁴⁸ Standard self-reported questionnaires will be used to document information on participants’ health conditions and medication use both at the baseline and at the end of the study and demographic characteristics including age, sex, education and socioeconomic status at the baseline only.

Perception towards intervention (intervention group only)

Participants’ perception towards the peanut butter intervention will be assessed using a self-administered questionnaire during the visits at 3 and 6 months. This will include ratings of participants’ perception of the taste, texture, appearance, flavour and the ease of following peanut butter intervention using a 9-point Likert scale.

Data management

Data will be directly entered into a secure university-supported online database. A unique identification code will be assigned for all the participants at the recruitment, and participants’ data will be saved under this code. For the purpose of study management and participant follow-up, the code can be matched to a participant’s identification details until data collection is completed. All data will be deidentified and the researchers will ensure participants’ anonymity will be maintained.

Statistical analysis

Descriptive statistics will be reported as the mean and SD (if normally distributed) or median and IQR (if non-normally distributed). Linear mixed model analyses will be used to determine the differences in the change in outcomes between the groups in response to the peanut butter intervention. The model will include group, time and group×time interaction as fixed factors and a random intercept term for each participant to account for the correlation between repeated measures. The model will be adjusted for baseline energy intake and physical activity level. An intention-to-treat approach will be employed, including data from all participants. Additionally, a sensitivity analysis adhering to the per-protocol principle will be conducted, only including participants with ≥80% intervention adherence. Mediation analyses will be performed to determine if the effects of peanut butter supplementation on physical and cognitive functions in older adults are mediated by the overall diet quality.⁴⁹ All statistical analyses will be performed using the Stata statistical software (V.18.0, StataCorp, College Station, Texas). Statistical significance will be set at p<0.05.

Ethics and dissemination

The study protocol is approved by the Deakin University Human Research Ethics Committee (2022-279). Written informed consent will be obtained from all participants at the first visit prior to any assessment. The study is registered in the Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12622001291774. The trial will be conducted in accordance with the principles of the Declaration of Helsinki and Good Clinical Practice guidelines. Findings will be published in peer-reviewed journals, conference presentations, social media, broadcast and print media.

Patient and public involvement

Potential participants were not involved in the design or conduct of this study. However, the individual results will be communicated to the study participants and the study findings will be disseminated to the participants who wish to be notified.

Discussion

Peanut butter is a familiar food with a unique taste, texture and nutrient profile. We hypothesise that the positive effects of peanut butter on the expected outcomes in older adults are attributable to its unique overall energy and nutrient profile rather than a single nutrient/few nutrients. Therefore, it was challenging to find or formulate an energy and nutrient-matched placebo for peanut butter. Some previous nut studies have chosen energy-matched (but not other nutrients) foods such as high-refined carbohydrate pretzels,⁵⁰ but such placebo food may have unintended negative consequences on the study outcomes potentially resulting in the observation of an erroneous net benefit for the peanut butter intervention in this study. Therefore, to avoid potential bias from a placebo with limited suitability, we decided to compare the intervention to no intervention which prevented us from performing double blinding in the study. Comparing intervention to no intervention also helps easy translation of the study findings into clinical practice by showing the effects of adding peanut butter to the diet not in exchange of another food item. Unlike other nutrition supplementation studies using liquid/powder formula or pills, this approach is considered appropriate for studies using whole food as the intervention.^{20 51}

According to the Australian Dietary Guidelines, the recommended daily nut intake is one serving which is equivalent to 30 g. In this study, a higher dose of peanut butter (43 g) is chosen, which is equivalent to 1.5 servings of nuts per day, to maximise the potential therapeutic benefits of peanut butter in older adults in this study who are at risk of falls. Similar doses have been used in previous interventional studies and have shown to be feasible and effective in improving related outcomes such as diet quality⁵² and delaying cognitive decline.⁵³ Moreover, in 2017, the US Food and Drug Administration has approved a qualified health claim linking 1.5 oz (42.5 g/day) of macadamia nuts to a reduced risk of coronary heart diseases.⁵⁴

The Peanut Institute reviewed the study design and provided individually packaged sealed containers of peanut butter as the study product. They have no involvement in the implementation of the study, data collection, data analysis and preparation of manuscripts for publication.