Intakes of Total and Branched-chain Essential Amino Acids are Positively Associated with Handgrip Strength in African American and White Urban Younger and Older Adults

Abstract

Essential amino acids (EAAs) initiate amino acid–induced stimulation of muscle protein synthesis. Study objectives were to calculate intake of EAAs after creating an EAA database, to explore the association of EAAs and branched-chain amino acids (BCAAs) with handgrip strength (HS) in a younger (<50y) and older (≥50y) sample, and to identify major food groups contributing EAAs. The sample consisted of African American and White adults aged, 33–71 years from the Healthy Aging in Neighborhoods of Diversity across the Life Span study, 2009–2013. Intake of total EAAs and BCAAs/kg body weight were positively associated (p < 0.001) with HS per body mass index (HS/ BMI) ratio. Being male, African American, a nonsmoker, physically active, euglycemic, and normotensive were associated with higher HS/BMI ratio. EAAs were mainly obtained from red meats/poultry and mixed dishes groups. Findings support the role of high-quality proteins and being active in promoting HS.

Introduction

Quality of life, optimal health, and independence are critical for successful aging. It is widely recognized that as individuals age, muscle strength and mass can decline. Reduced handgrip strength is considered a marker for sarcopenia.¹ Approximately 10% of independent living adults aged 60 years and older and between 30 and 50% of those in nursing homes have sarcopenia, the progressive loss of skeletal muscle and strength.² It is prevalent among persons with cardiovascular disease, diabetes mellitus, respiratory disease and dementia.³ The decrease in muscle mass is associated with an increase in body fat, resulting in a decline in basal metabolic rate and possibly weight gain and obesity. Sarcopenia and obesity act synergistically to increase risk for disability and impaired health with age. However, consumption of essential amino acids, particularly leucine and other branched-chain amino acids (BCAAs), along with resistance exercise has been shown to improve muscle synthesis.^4,5 Figure 1 provides an overview of contrasting lifestyles that impact healthy aging.

Figure 1.

Influence of diet and activity on strength during aging.

The contributory role of diet in health promotion and disease prevention is well documented. The moderate consumption of a high-quality diet such as the Mediterranean-style, the Dietary Approaches to Stop Hypertension (DASH) and Healthy United States (US)-style dietary patterns, are associated with decreased risk of many chronic conditions including cardiovascular disease, type 2 diabetes, obesity, and selected cancers.⁶ Older US adults have the highest diet quality compared to younger age groups, measured by the Healthy Eating Index (HEI).⁷ Yet their diets still require improvement to comply with the Dietary Guidelines for Americans as indicated by a score of 63 out of a maximum HEI score of 100.⁶ Scores for minorities and lower income groups tend to be less than the national average of 59.^7–10

Protein has been identified as a key nutrient for older adults for muscle health, energy balance, and cardiovascular function. Branched-chain amino acids (BCAAs: leucine, isoleucine, and valine) are substrates for protein synthesis and can stimulate skeletal muscle synthesis as well as suppress proteolysis.^11,12 These BCAAs have been associated with improved glucose transport and body weight maintenance.¹¹ Current daily recommendations for protein for older adults exceed the Recommended Dietary Allowance (RDA) value of 0.8 gm/kg body weight.¹³ A protein intake between 1.0 and 1.5 g/kg/day with adequate energy intake is recommended to prevent muscle loss in older adults.^14–17 Paddon-Jones and colleagues¹⁸ reported that consuming a variety of high quality dietary protein foods per meal can enhance muscle protein anabolism in both the young and old. Layman and colleagues¹⁵ emphasized the need to consume at least 20–30 g protein per meal to provide anabolic and metabolic benefits. This guideline is consistent with a review by Schoenfeld and colleagues¹⁹ who reported that with a target intake of 0.4 g/kg/meal, with a minimum of four meals, protein intake of 1.6 g/kg/day could be met.

Our previous research with participants of the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study found that protein per kg was associated with handgrip strength (HS), expressed as HS per BMI.²⁰ Research on the association of essential amino acids intake with HS is limited which may be partially explained by the exclusion of amino acids from many nutrient databases. The primary objectives of this study were to calculate intake of the essential amino acids (EAAs) after creating an EAA database, and then to explore the association of EAAs and BCAAs with HS in a younger and older African American and White sample. A secondary objective was to identify the food groups contributing to the intake of EAAs by race.

Methods

Study Participants

The individuals in this study represent adults interviewed and examined in the second HANDLS study visit 2009–2013. The HANDLS study design has been described in detail elsewhere.²¹ Briefly, the HANDLS study was designed to determine the role of race and income in health disparities observed between African American and White men and women residing in Baltimore, Maryland, USA.

Dietary Data

Only those participants who completed two 24-hr dietary recalls with trained interviewers using the US Department of Agriculture (USDA) Automated Multiple Pass Method (AMPM) were included in this study (n=2140).^22,23 The first recall for study visit 2 was obtained in-person and the second by phone. The foods reported consumed were coded using Food and Nutrient Database for Dietary Studies (FNDDS), 2009–2010, which allowed the calculation of energy and protein intakes.²⁴ The HEI-2010, a diet quality measure, was calculated as described in earlier publications with HANDLS study data,²⁰ and the HANDLS study website provides a detailed description of the procedure used.²⁵

Intakes for total and individual EAAs were calculated for each recall day after the creation of a dataset because FNDDS does not include EAAs. The EAA dataset was constructed using amino acid values published in USDA Standard Reference (SR) 28.²⁶ Values for 411 of the 2158 foods reported in the second HANDLS study visit were missing from SR28. For these foods, international data bases such as Canadian Nutrient File²⁷ and FRIDA Food data of Denmark²⁸ and values published in peer-reviewed articles were used to impute EAA values. The HANDLS study EAA database consists of analytical and inputed values and thus represents estimates of intakes. Documentation for all imputed values was archived with HANDLS study dietary protocol.

The EAAs intakes included: histidine, isoleucine, leucine, lysine, methionine+cysteine, phenylalanine, threonine, tryptophan, and valine. Recommendations for the total aromatic amino acid requirement are derived from phenylalanine plus tyrosine. For this study, the sample was considered to be healthy individuals without defects in the hydroxylation pathway, resulting in the synthesis of tyrosine from phenylalanine.^29,30 Thus the aromatic amino acid requirement would be met by phenylalanine alone and is termed the maximal phenylalanine requirement. Branched-chain amino acid intake reflects the sum of isoleucine, leucine, and valine. Intakes of the EAAs were expressed as mg per kg body weight and the proportion of the sample not meeting the US RDA for adults¹³ was calculated for each recall day and then averaged over the 2 days.

Recalled foods were also categorized into 14 major groups with 139 unique subcategories matching the What We Eat in America Food Categories 2017–2018.³¹ For this study, the percentage of EAAs reported consumed for 8 food groups was calculated for each recall day and then averaged. The food groups included: 3 major groups, namely dairy, mixed dishes, and grains, the combination of the meats and poultry subgroups of protein foods, and the remaining 4 subgroups of the protein foods, specifically seafood, cured meats/poultry, plant-based protein, and eggs. Meats included beef, pork, lamb, goat, game, and liver and organ meats. Poultry included chicken, turkey, and duck.

Clinical measures

Handgrip strength represents the mean of two trials using the dominant hand of the participant. The right-hand measure was used for participants who were ambidextrous. The Jamar Hydraulic Hand Dynamometer (Patterson Medical Holdings Inc., Bolingbrook, IL) was used to measure the maximal force in kilograms on both hands. The measurement was performed with participants seated with their elbow resting on a table at approximately 160°. There was a 15–20 second rest between trials. HS was not obtained for those participants who reported pain and/or arthritis in their hand, or having hand surgery within the past 3 months that would impede their ability to successfully complete the handgrip test.

Measured height and weight were used to calculate Body Mass Index (BMI), kg/m². The Novel Products, Inc height meter was used to measure standing height and Med-weigh calibrated digital scale, model 2500, was used to measure weight.

Physical activity measures

Physical activity was assessed by a modified version of the National Aeronautics and Space Administration (NASA)/Johnson Space Center (JCS) scale.^32,33 The NASA/JSC physical activity scale has been shown to have a strong, independent relationship with maximal oxygen uptake in men and women, aged 20 to 79 years.^34,35 The scale ranged from avoided walking or exertion to vigorous activities, running 10 miles or spending 1–3 hours per week doing comparable physical activities.

Participants reported their activity level over the preceding month through seven questions. For this study the participants’ responses to the seven questions were re-categorized into three groups- Inactive, Somewhat Active (performing less than 150 minutes/week), and Active (performing 150+ minutes/week). The 2018 US physical activity guideline for adults is at least 150 minutes a week of moderate-intensity activity for health benefits.³⁶ Participants who responded yes to avoided walking or exerting myself by using elevators instead of stairs and driving instead of walking were categorized as Inactive. The Somewhat Active consisted of participants who responded yes to any of the following four questions: 1) walked for pleasure, routinely used stairs, and occasionally exercised enough to cause heavy breathing or perspiration; or 2) participated in recreation or work requiring modest physical activity, such as golf, horseback riding, calisthenics, gymnastics, table tennis, bowling, weight lifting, or yard work for 10 – 60 minutes per week; or 3) for more than an hour per week; or 4) ran less than a mile or spent less than 30 minutes each week doing comparable physical activity. The Active group consisted of participants who responded yes to either of the following two questions: 1) ran 5 – 10 miles each week or spent 1–3 hours weekly doing comparable physical activity; or 2) ran 10 miles per week or spent 1–3 hours weekly doing comparable physical activity.

Statistical analysis

The sample was categorized as younger, age < 50 years, or older, aged ≥ 50 or more years. Means and standard errors were calculated for continuous variables and the proportion of participants for relevant categorical variables for descriptive characteristics for the entire sample, and by age groups (younger, older). Analysis of variance (ANOVA) was used to compare demographic and life-style factors, diet quality, and handgrip strength by age groups. Chi squared (χ2) tests were used to test for difference between age groups between categorical sample characteristic data. Adjusting for energy intake, income, and education, the differences for each EAA intake (mg), per kg body weight by age group and race, were explored using regression analyses. The models were performed separately for men and women. The χ2 test was used to determine significant differences in the proportion of the sample not achieving the recommended intake of each EAA per kg body weight between racial groups within age groups for each sex. Statistical significance was established at p <0.05 for all analyses. The Bonferroni test was used to adjust p values for multiple comparisons of continuous variables.

To test if total intake of EAAs per kg body weight or BCAAs intake per kg body weight predicted HS/BMI ratio, separate sequential multiple regression models were used. In the first block the following covariates were included: age, sex, race, income, cigarette smoking status, diabetes, and hypertension. Diabetes and hypertension were included because HS has been shown to be lower in persons with these chronic conditions compared to persons without them.³⁷ Diabetes was categorized into 3 groups- prediabetic, defined as fasting glucose of 100–125 mg/dl; having diabetes, defined as fasting glucose of ≥126 mg/dL³⁸, a history of medication use, or a self-reported diagnosis; or not diabetic. People were categorized as not hypertensive or hypertensive, the latter category being defined as systolic blood pressure (SBP ≥140 mm Hg), diastolic blood pressure (DBP) ≥90 mm Hg, a history of blood pressure medication use, or a self-report of diagnosed hypertension. The second block contained either total EAAs per kg body weight or BCAA intake per kg body weight, mean energy, and diet quality assessed by the Healthy Eating Index-2010. The third block contained physical activity. The last block contained the two-way interaction - sex x race. Blocks in sequential regression were selected since multiple predictors could be entered simultaneously, allowing for testing if the addition of these predictors significantly improved the model. All analyses were performed using IBM SPSS Statistics for Windows, version 28 (IBM Corp., Armonk, N.Y., USA).

Results

Sample characteristics

Table 1 shows characteristic distributions of the selected sample, overall and by age group. The mean age (±SE) was 53.2 years (±0.2) with a range from 33 to 71 years. Approximately 40% of the sample was male and had incomes less than 125% of the 2004 HHS poverty guidelines³⁹, and 64% was African American. Mean overall years of education completed was 12, an educational attainment that did not differ across age groups, sex, race or income. Significant differences between the age groups were found for activity levels, smoking, dietary variables, and HS. The older aged group were less active, but smoked less, while consuming less energy, protein, EAAs and BCAAs, compared to the younger group. However, the quality of their diets was better as evidenced by the higher HEI score (Table 1).

Table 1.

Characteristics of Healthy Aging in Neighborhoods of Diversity across the Life Span Study sample, 2009–2013.

	Total Sample n=2140	<50y n=766	≥50y n=1374	p
Sex, % men	41.2	40.5	41.6	0.624
Race, % African American	64.4	62.4	60.9	0.499
Income, % <125% povertya	39.8	41.0	39.1	0.387
Education, y	12.2±0.1 n=2094	12.2±0.1 n=751	12.2±0.1 n=1343	0.879
Activity, % achieved recommended levelb	37	42	34	0.012
Cigarette smoker, %	40.3 n=1971	53.8 n=706	37.1 n=1265	<0.001
Energy, kcal	2025±18	2187±32	1933±22	<0.001
Protein, g	76.5±0.8	81.3±1.4	73.84±0.90	<0.001
Protein per kg, g	0.93±0.01	0.98±0.02	0.90±0.01	<0.001
Total Essential Amino Acids, g	29.8±0.3	31.5±0.5	28.8±0.4	<0.001
Total Essential Amino Acids per kg, mg	360.1±4.2	377.2±7.3	350.7±5.2	0.003
Branched-chain Essential Amino Acids, g	12.9±0.1	13.7±0.2	12.5±0.2	<0.001
Healthy Eating Index-2010 Scorec,25	46.3±0.3	44.6±0.4	47.2±0.3	<0.001
Handgrip Strength, kg	35.3±0.3 n=1956	38.19±0.46 n=726	33.66±0.32 n=1230	<0.001

^aDefined as < 125% of the 2004 United States Health and Human Services poverty guidelines³⁹

^bDetermined by responses to National Aeronautics and Space Administration (NASA)/Johnson Space Center (JCS) scale and 2018 US physical activity guideline for adults.^32,33,36

^cMaximum score of 100

Essential amino acid intakes of HANDLS study participants

Intakes of EAAs by age group and race (i.e. Age×Race), among men and women separately, are provided in Table 2. Within the group of younger men, African American men had significantly higher intakes of isoleucine, lysine and threonine compared to White men (Table 2). With the exception of leucine and phenylalanine, African American men aged 50+ years had higher intakes of EAAs than older White men. There were no significant differences between African American and White women for either age group (Table 2).

Table 2.

Mean (±Standard Error) intakes of essential amino acids of HANDLS study participants, 2009–2010 and percent of sample consuming less than recommended levels.

EAA	RDA	Men (n=860)
		<50 y (n=303)				≥ 50 y (n=557)
		AA(n=280)	W(n=111)	AA(n=280)	W(n=111)	AA (n=343)	W (n=214)	AA (n=343)	W (n=214)
	mg/kg	X±SE, mg/kg	X±SE, mg/kg	% < RDA	% < RDA	X±SE, mg/kg	X±SE, mg/kg	% < RDA	% < RDA
Histidine	14	25.27±0.76	22.86±1.00	12.4	9.6	26.06±0.56	24.18±0.71*	12.2	11.9
Isoleucine	19	40.44±1.21	36.55±1.59*	6.2	6.1	41.80±0.89	38.28±1.14*	7.3	7.9
Leucine	42	69.27±2.03	64.91±2.68	13.0	10.4	71.46±1.50	67.19±1.91	14.5	13.7
Lysine	38	62.55±2.02	54.88±2.67*	14.0	14.8	64.82±1.50	58.20±1.90**	16.0	20.3
Methionine	19	33.21±0.99	30.10±1.30	12.4	9.6	34.46±0.73	31.59±0.93*	11.6	12.3
Phenylalanine	33	38.74±1.10	36.57±1.45	27.5	25.2	38.13±1.03	40.19±0.81	33.7	36.6
Threonine	20	34.35±1.03	30.87±1.36*	12.4	9.6	35.86±0.76	32.59±0.97**	12.5	15.4
Tryptophan	5	10.00±0.30	9.22±0.40	6.7	5.2	10.58±0.23	9.65±0.29**	6.7	9.3
Valine	24	45.60±1.33	42.24±1.75	8.3	7.0	47.28±0.98	44.17±1.25*	9.0	11.0
		Women (n=1229)
		<50 y (n= 446)				≥ 50 y (n=783)
		AA(n=280)	W(n=166)	AA(n=280)	W(n=166)	AA (n=490)	W (n=293)	AA (n=490)	W (n=293)
Histidine	14	24.22±0.62	24.98±0.81	20.8	23.7	25.37±0.48	24.83±0.61	25.9	22.9
Isoleucine	19	39.41±0.99	40.67±1.28	13.1	12.1	41.42±0.76	40.34±0.97	16.7	12.9
Leucine	42	67.69±1.66	70.84±2.16	26.9	27.2	70.85±1.28	71.04±1.63	29.9	24.2
Lysine	38	60.82±1.65	60.31±2.15	27.2	32.4	63.81±1.28	59.98±1.62	33.0	31.3
Methionine	19	32.39±0.81	33.07±1.05	21.2	23.7	34.11±0.62	33.13±0.79	26.1	22.6
Phenylalanine	33	38.14±0.90	40.40±1.17	49.8	45.7	39.94±0.69	40.42±0.88	59.1	49.0**
Threonine	20	33.54±0.84	34.10±1.09	22.6	24.3	35.32±0.65	33.88±0.83	26.9	26.5
Tryptophan	5	10.13±0.25	10.40±0.32	14.8	16.2	10.57±0.19	10.34±0.24	16.5	15.9
Valine	24	44.81±1.08	46.74±1.41	17.7	15.6	47.03±0.84	46.81±1.06	20.4	16.8

Abbreviations: AA- African American, RDA- Recommended Dietary Allowance¹³,W-White. Means adjusted for energy, income, education.

^*p<.05

^**p< 0.01.

Cysteine intake is included in methionine estimate.

As shown in Table 2, the percent of the sample not meeting the RDA varied considerably among race and sex. The only significant racial difference in the percentage not achieving the RDA was for older women for phenylalanine intake (Table 2). Comparisons of the percent with less than the RDA for each EAA within sex by race groups were performed to determine significant differences by age group. Two significant differences were found. Larger proportions of older African American women and older White men did not consume the RDA for phenylalanine compared to younger African American women (p=0.013) and younger White men (p=0.035), respectively. Within the race and age groups, the percent of African American women not consuming the RDA for all the EAAs was significantly greater than that of African American men (p<0.05). Comparisons by sex within age were also done for the White participants. The percentage of White women not consuming the RDA was significantly higher for all EAAs (p<0.05) except isoleucine for both age groups (younger: p=0.09; older: p=0.065) and valine for the older group (p=0.058).

Food groups contributing majority of essential amino acids

The contribution of each EAA from 8 food groups for the overall sample (presenting in descending order), as well as by African American and White participants, is provided in Table 3. Of these eight groups, four groups would be considered high-quality protein sources, namely meats/poultry, dairy, eggs, and fish. The top two food groups which contributed EAAs to the HANDLS study participants were meats/poultry and mixed dishes. Meats/poultry were to top contributing food group for histidine, isoleucine, lysine, methionine/cysteine, threonine, and valine. Mixed dishes, consisting of 8 subgroups: combinations of meats, bean/vegetable, and grain-based items, Asian, Mexican, soups, pizza or singled-coded sandwiches, ranked first for leucine, phenylalanine, and tryptophan. These two groups contributed roughly half of the daily intake of the EAAs. The high-quality protein groups that contributed the smallest quantities of EAAs daily were eggs and fish. For the HANDLS study total sample, the plant-based protein group contributed approximately 2% of each of the EAAs, ranking last (Table 3).

Table 3.

Percent contribution of essential amino acid by food group for total sample and by race.

Essential Amino Acid	Total, %	African American, %	White, %
Histidine
Meats & Poultry	26.8	19.7	7.1
Mixed Dishes	23.2	12.7	10.5
Cured Meats/Poultry	10.2	6.8	3.4
Grains	9.9	5.7	4.1
Dairy	9.8	4.0	5.8
Fish	3.1	2.3	0.8
Eggs	2.6	1.8	0.8
Plant-based Protein	1.7	0.8	1.0
Isoleucine
Meats & Poultry	25.2	18.7	6.5
Mixed Dishes	22.9	12.7	10.2
Dairy	11.5	4.6	6.9
Grains	10.6	6.2	4.4
Cured Meats/Poultry	8.5	5.7	2.8
Fish	3.4	2.5	0.9
Eggs	3.3	2.2	1.1
Plant-based Protein	1.6	0.7	0.9
Leucine
Mixed Dishes	23.4	12.9	10.5
Meats & Poultry	23.2	17.1	6.1
Dairy	12.2	4.9	7.3
Grains	11.6	6.8	4.8
Cured Meats/Poultry	8.4	5.6	2.8
Fish	3.4	2.5	0.9
Eggs	3.2	2.3	1.0
Plant-based Protein	1.6	0.7	0.9
Lysine
Meats & Poultry	28.5	21.0	7.5
Mixed Dishes	22.7	12.5	10.2
Dairy	10.9	4.4	6.5
Cured Meats/Poultry	10.4	6.9	3.5
Grains	5.6	3.3	2.3
Fish	4.1	3.1	1.1
Eggs	3.0	2.1	1.0
Plant-based Protein	1.4	0.6	0.8
Methionine + Cysteine
Meats & Poultry	24.7	18.3	6.4
Mixed Dishes	22.7	12.5	10.2
Grains	13.0	7.6	5.4
Dairy	10.7	4.2	6.5
Cured Meats/Poultry	8.5	5.6	2.9
Eggs	3.8	2.6	1.2
Fish	3.5	2.6	0.9
Plant-based Protein	1.3	0.6	0.7
Phenylalanine
Mixed Dishes	23.6	13.0	10.6
Meats & Poultry	21.3	15.8	5.5
Grains	13.7	7.9	5.8
Dairy	11.3	4.6	6.7
Cured Meats/Poultry	7.7	5.1	2.6
Eggs	3.4	2.4	1.1
Fish	3.0	2.2	0.8
Plant-based Protein	2.2	1.0	1.2
Threonine
Meats & Poultry	25.5	18.9	6.6
Mixed Dishes	23.1	12.8	10.3
Grains	10.0	5.8	4.2
Dairy	9.5	3.9	5.6
Cured Meats/Poultry	9.3	6.2	3.2
Fish	3.7	2.7	0.9
Eggs	3.2	2.2	1.0
Plant-based Protein	1.6	0.7	0.9
Tryptophan
Mixed Dishes	22.0	12.2	9.8
Meats & Poultry	21.1	15.9	5.2
Grains	13.4	7.7	5.6
Dairy	12.2	5.1	7.1
Cured Meats/Poultry	7.4	4.9	2.6
Fish	3.4	2.5	0.9
Eggs	3.3	2.2	1.0
Plant-based Protein	1.8	0.8	1.0
Valine
Meats & Poultry	22.8	16.9	5.9
Mixed Dishes	22.8	12.6	10.2
Dairy	12.9	5.3	7.7
Grains	11.2	6.5	4.7
Cured Meats/Poultry	8.0	5.4	2.6
Eggs	3.7	2.5	1.2
Fish	3.2	2.4	0.8
Plant-based Protein	1.7	0.8	1.0

The meats/poultry group provided the highest proportion of each EAA presented in Table 3 for African Americans, while mixed dishes group contributed the higher percentage for Whites. The percentage of each amino acid contributed by the dairy group was greater for Whites compared to African Americans. In contrast, the percentage of each amino acid contributed from cured meats/poultry and fish groups was greater for African Americans compared to Whites (Table 3).

Association of intake of essential amino acids and handgrip strength

As presented in Table 4, after adjusting for age, sex, race, income, smoking, diabetes, and hypertension, intake of BCAAs per kg body weight was positively associated (p < 0.001) with HS/ BMI ratio. Using a separate model, intake of total EAAs per kg body weight was also positively associated (p < 0.001) with HS/ BMI ratio (Table 5). Diet quality was not a significant predictor in either model. Energy intake was inversely associated with HS/BMI. Although the change in R² was low with the addition of physical activity in both models, it was significant. Being active had a positive association with HS/BMI. Amongst the covariates, being male, African American, a nonsmoker, euglycemic, and normotensive were associated with a higher HS/BMI ratio. Income was not associated with HS/BMI. The interaction of sex x race was tested and found significant for the model using total EAAs (p=0.048) but only trending towards significance in the BCAA model (p = 0.052). The overall R² of the models were 0.564 (Table 4) and 0.563 (Table 5).

Table 4.

Association of handgrip strength per Body Mass Index with branched-chain Essential Amino Acid (EAA) Intake per kg and selected sociodemographic and health-related characteristics (n=1271).

		β	SE	p
Block 1	Age (Younger vs. Older)	−0.081	0.023	<0.001
	Sex (Female vs. Male)	0.665	0.021	<0.001
	Race (White vs. African American)	0.066	0.021	0.002
	Income (≥125% vs. <125% poverty guidelines39)	−0.023	0.022	0.297
	Cigarette Smoker (No vs. Yes)	−0.096	0.022	<0.001
	Diabetes (No, Pre, vs. Yes)	−0.119	0.014	<0.001
	Hypertension (No vs Yes)	−0.167	0.023	<0.001
Block 2	Branched-chain EAAs/kg	1.791	0.167	<0.001
	Healthy Eating Index-2010	0.000	0.001	0.608
	Energy	7.563×10−5	0.000	<0.001
Block 3	Physical Activity (Active, Somewhat Active vs. Inactive)a	−0.091	0.015	<0.001
Block 4	Sex x Race	0.077	0.040	0.052
Model Fit		R2
	Block 1	0.509		<0.001
	Δ R2 with Block 2	0.047		<0.001
	Δ R2 with Block 3	0.013		<0.001
	Δ R2 with Block 3	0.001		0.052
	Final Model	0.566

^aDetermined by responses to National Aeronautics and Space Administration (NASA)/Johnson Space

Center (JCS) scale and 2018 US physical activity guideline for adults.^32,33,36

Table 5.

Association of handgrip strength per Body Mass Index with total Essential Amino Acid (EAA) Intake per kg and selected sociodemographic and health-related characteristics (n=1271).

		β	SE	p
Block 1	Age (Younger vs. Older)	−0.081	0.023	<0.001
	Sex (Female vs. Male)	0.665	0.021	<0.001
	Race (White vs. African American)	0.066	0.021	0.002
	Income (≥125% vs. <125% poverty guidelines39)	−0.023	0.022	0.297
	Cigarette Smoker (No vs. Yes)	−0.096	0.022	<0.001
	Diabetes (No, Pre, vs. Yes)	−0.119	0.014	<0.001
	Hypertension (No vs Yes)	−0.167	0.023	<0.001
Block 2	Total EAAs/kg	0.741	0.071	<0.001
	Healthy Eating Index-2010	0.000	0.001	0.567
	Energy	−6.957×10−5	0.000	<0.001
Block 3	Physical Activity (Active, Somewhat Active vs. Inactive)	−0.090	0.015	<0.001
Block 4	Sex x Race	0.079	0.040	0.048
Model Fit		R2
	Block 1	0.509		<0.001
	Δ R2 with Block 2	0.044		<0.001
	Δ R2 with Block 3	0.013		<0.001
	Δ R2 with Block 3	0.001		0.048
	Final Model	0.568

^aDetermined by responses to National Aeronautics and Space Administration (NASA)/Johnson Space

Center (JCS) scale and 2018 US physical activity guideline for adults.^32,33,36

Discussion

To our knowledge this study is the first to report the EAAs per kg intake (in mg) of an African American and White urban adult sample in the US. The mean total EAA intake expressed as mg per kg body weight of both the younger and older aged groups did exceed the recommended requirements for healthy adults 18 years and older with both minimal and moderate physical activity.⁴⁰ The total EAA intake expressed as g and mg/kg, of individuals over 50 years of age was lower than that of the younger aged group, despite the higher overall quality of diets. The recommended intakes of individual EAAs was not achieved by many. More women, regardless of race, consumed less than recommended amounts of the EAAs compared to men. When diets are limited or absent of EAAs, protein turnover is not balanced. Protein synthesis in the body will decline while breakdown continues, resulting in muscle loss.¹³

Recommended intakes of leucine were not achieved by 24–30% of women, compared to 10–15% of men. This finding is worrisome since the leucine trigger hypothesis for regulation of muscle protein synthesis following a meal has been supported by a systematic review.⁴¹ Furthermore, Volpi and colleagues⁴² have shown that essential amino acids are primarily responsible for the amino acid–induced stimulation of muscle protein synthesis in older adults.

The study findings provide evidence that EAA intake – both total and BCAA – were positively associated with handgrip strength. The findings of this study expand our knowledge by showing the impact of change on HS/BMI of BCAA/kg intake was greater than that of total EAA/kg, as evidenced by the β coefficients. Our findings are consistent with those of Park and colleagues⁴³ who reported an association between BCAA intake and HS in a Korean adult sample. Although Park and colleagues⁴³ included physical activity in their analyses, a direct comparison of results could not be made. Stokes and colleagues⁴⁴ found that increasing activity by walking could increase daily muscle protein synthesis in older women, independent of protein intake. Our study found that meeting recommended levels of physical activity was directly associated with HS/BMI. Fewer adults in the older group achieved recommended activity levels compared to the younger group. These findings suggest the need for better communication by health professionals of the importance of consuming high-quality proteins in combination with activity to maintain strength with age.

The quality of the diet, assessed by the Healthy Eating Index-2010, was not associated with HS/BMI. Perhaps this could be partially explained by the limited variance in scores among the HANDLS study participants. Andrich and colleagues⁴⁵ are of the opinion that the difference in muscle mass between individuals is attributed to physical activity and weight rather than diet. This explanation is plausible. Yet improvement in the quality of foods consumed by the HANDLS study sample is warranted given the mean HEI-2010 scores of the HANDLS sample were lower than the national US average by about 16 points. The HANDLS study design incorporated a 4-way stratification with income as one of the four factors. Self-reported household income was categorized as less than or above 125% of the 2004 Health and Human Services poverty guidelines³⁹ with reported household incomes maximized ~$75,000 at the initial study visit. Among the participants of the second HANDLS study visit, 6% of those 50+ years and 8.5% of those younger than 50 years reported that they often ate less than they felt they should because there was not enough money to buy food in the past 12 months. Barriers to diet quality among African American adults, other racial minorities, and individuals of low-income include cost, lack of time to prepare healthful food, and the convenience of fast-food restaurants.^9,46

For the overall sample, the main dietary contributors were foods categorized as meats/poultry and mixed dishes. This finding was not unexpected since the prevalent dietary patterns among the HANDLS study sample were identified by sandwiches and pizza.^47,48 Park and colleagues⁴³ found that grains and grain-products were the main dietary contributors of BCAAs to older Korean adults. They also found that older Koreans whose BCAA intake came from a variety of food sources had better HS, compared to those whose BCAAs were derived primarily from grains. McLean and colleagues⁴⁹ found that higher total and animal protein intakes, but not plant protein intake, were protective against muscle strength loss in persons 60+ years of age in the Framingham Offspring cohort, a community-dwelling sample.⁴⁹ Their finding could be explained by the fact that plant proteins tend to contain less leucine, a BCAA, than animal proteins.⁵⁰

Approximately 7–10% of each of the EAAs intake was from cured/processed meats/poultry. Even though the origin of cured meats is red meats and poultry, the added salt and nitrates with processing makes them a less healthful diet choice. Additionally, these food items should be consumed less since they are considered a food-born illness safety risk for older adults by Food and Drug Administration.⁵¹ Recommendations published in the Dietary Guidelines for Americans 2020–2025 state that fresh, frozen or canned and lean forms of meats and poultry be consumed in place of such processed meats as luncheon meats, sausage, and hot dogs.⁶ Innovative approaches to education which identify strategies that increase purchasing power for healthful foods and encourage less purchasing of deli meat, sandwiches and pizza might help to modify food shopping and restaurant habits, thereby improving the quality of the diets of HANDLS study sample. It is anticipated that food insecurity among the HANDLS study sample may increase in times of a pandemic, such as COVID-19, and with inflation, emphasizing the need to provide older consumers with ideas to protect their spending power for healthful foods.

Strengths of this study include the contribution of new information on EAA intake of a sample with diversity underrepresented in research, the inclusion of both dietary and activity data in exploring the association with HS, the use of 2 days of 24-hour recalls, and the use of the AMPM. The AMPM which has been shown to reduce bias in the collection of energy intakes and is the same methodology used in NHANES studies.²³ The limitations include the potential of bias associated with the use of 24-hour recalls, such as the underreporting of food and beverage intake ^52,53 and social desirability bias ⁵⁴, and bias related to the types of activities in NASA/JCS scale such as golf, horseback riding, calisthenics, gymnastics, table tennis, bowling, weight lifting, or yard work that may not be categories of exertion that are widely participated in by African Americans and low-income individuals. The imputation of EAA data for 19% of the foods reported consumed which could result in estimation errors. In addition, the intake of EAAs does not include nutritional supplements. Although this study is cross-sectional, data from the HANDLS study will be used in the future to assess longitudinal change in HS with change in intake of EAAs over 3 visits.

Take-away points

• Intake of essential amino acids, especially branched-chain amino acids, impact handgrip strength.

• Unfavorable nutrition environments and economic barriers can make it challenging for some older adults to obtain high-quality proteins.

• Health professionals should emphasize the importance of consuming high-quality proteins and being active to maintain/gain strength when counseling older adults.

Data Availability Statement:

Data are available upon request to researchers with valid proposals who agree to the confidentiality agreement as required by our Institutional Review Board. We publicize our policies on our website https://handls.nih.gov. Requests for data access may be sent to Alan Zonderman (co-author) or the study manager, Jennifer Norbeck, at norbeckje@mail.nih.gov.