Osteoarthritis (OA) is the most common type of arthritis in humans, which is increasing in developed and developing countries by changing lifestyles and obesity as well as the rise of the aged population (1). The most common form of OA is in the knees because bearing body weight and is subject to direct pressure. The prevalence of the disease in women is higher than that of men and increases with age (2).
Healthy nutrition is one of the bases for developing a healthy and productive population. Today, the association of nutrition and food choices with community health is fully understood. As growing older, there is a change in the nutritional needs of individuals. Much research has been carried out on the prevalence of nutritional disorders and malnutrition among the elderly with different conditions (free-living, in a nursing home, or in a hospital). Mokhber et al. (3) showed that the prevalence of malnutrition in free-living elderly was 11.5%, and the percentage of elderly with an extraordinary risk of malnutrition was 44%. Cai et al. (4) reported that the diet of the elderly is based on their health status, and individuals with chronic illnesses tend to consume more vegetable-based foods than meat.
Some studies have identified protein as the essential nutrient in the elderly (5). Nowadays, the recommended daily allowance (RDA) has been set at 0⋅83 g per kg of body weight per day of good quality proteins for healthy young adults (6). Animal-based foods are considered the primary source of high-quality protein (7). Today, there is a developing body of evidence that this RDA is insufficient for the elderly. The protein need is increased in the elderly to preserve muscle mass and functionality (8). Protein intake above the recommended levels can reduce the loss of muscle tissue that occurs chronically in the elderly (9). Meanwhile, higher protein intake in the elderly is associated with a reduction in mortality, suggesting that a protein intake of at least 10% of the daily calorie in the elderly is necessary to maintain muscle mass (10). Because of the undesirable environmental effect of intensive animal production and owing to the health benefits of eating fruit, vegetables, and grains, nutritional guidelines in some countries tend to recommend increasing plant protein consumption (11).
The interest and attention to low body mass and sarcopenia increased in the last decades. Recently, the relationship between body mass index (BMI) and OA has been highlighted in studies. Anthropometric measurements such as BMI, hip circumference, and waist-to-hip ratio (WHR) are applied to investigate the correlation between obesity and radiographic OA (12). On the other hand, obesity, commonly defined as BMI ≥ 30 kg/m², does not consider body composition. Other indices are applied to distinguish fat and lean mass to describe overweight conditions compriseing lean body mass (LBM), the mass of body fat (MBF), and soft lean mass (SLM).
The impact of weight loss on pain and bodily function is comprehended in OA patients, but less recognized is the evidence that diet quality may affect pain and function. Knee OA is more common in obese individuals with low LBM than those without low LBM (13). Many studies have shown that skeletal muscle mass prevents the occurrence of OA or established a positive correlation between muscle mass and the width of joint space (14). However, the relation between body composition and symptoms of OA is not clearly defined.
On the other hand, dietary protein improves muscle protein synthesis and prevents muscle protein breakdown, which improves LBM over time (14). Knee OA patients may require even greater protein consumption than RDA since they are mostly older adults, report lower physical activity, have chronic low-grade inflammation, and are predisposed to develop anabolic resistance (15). These considerations propose that the correlation between dietary protein intake, body composition indices, and pain and disability in knee OA patients are not necessarily the same as in older adults.
The correlation between daily dietary protein intake, body composition indices, and clinical symptoms in knee OA is unknown.  Caregivers and patients have queries regarding nutritional necessities and dietary supplements in clinical practice.  Considering the high interest, few studies have focused on dietary intake in patients with knee OA. The objective of this study was to examine the correlation between dietary protein intake and the indicators of body composition, pain, and functional status in patients with knee OA.
 

In this study, 310 patients with knee OA were evaluated to investigate the association between dietary protein and body composition analysis, pain, and functional status. Forty-three patients refuse to participate in the study. Forty-seven patients didn’t meet the eligibility criteria.
We studied 68 males (30.91%) and 152 females (69.09%) with an average age of 56.89 ± 9.45 years. Table 1 shows the demographic findings of the participants.
The total adjusted protein intake in the participant was 55.36±24.14 grams (0.70±0.31 grams per kg weight) per day, of which 14.96±16.45 grams (19.37 ± 27.62%) was plant protein. One hundred and fifty-four participants (70 %) didn’t meet the RDA for protein intake, of which 100 patients (45.4%) didn’t meet the 75 % of RDA for protein intake. Men consumed more protein than women (69.70±27.12 vs. 49.11±19.72 g / day, p<0.001). However, the dietary animal based/plant-based protein ratio was significantly higher in women than in men (p=0.007).

Table 1. General characteristics of participants (n = 220)

Notes: All values are presented as mean ± SD or n (%)
Abbreviations: BMI: body mass index; VAS: visual analogue scale; WOMAC: Western Ontario and McMaster Index
 

The VAS score of participants was 5.52±1.67 in the participants. The WOMAC total score of the participants in the research was 42.96±14.60. Table 2 shows the correlations between adjusted dietary protein intakes with pain severity and functional status. There was a negative and significant association between the total adjusted dietary protein and adjusted animal-based protein intake with pain severity. In the analysis of the findings by the gender of participants, there were negative and significant correlations between the total adjusted dietary protein, adjusted plant-based protein, and adjusted animal-based protein intakes with pain severity only in women but not men. We couldn’t find any significant correlation between dietary protein intakes with WOMAC total, WOMAC pain, WOMAC stiffness, and WOMAC physical function subscale scores (all p>0/05).

Table 2. The association between adjusted dietary protein intake with VAS and WOMAC scores in participants

Notes: * Spearmen correlation test
Abbreviations: VAS: visual analogue scale; WOMAC: Western Ontario and McMaster Index
 

In the subset of participants whose protein intakes were lower than 75 percent of RDA, there were negative and significant correlations between the total adjusted dietary protein and adjusted animal-based protein intakes with pain severity (Table 3). Additionally, there were negative and significant correlations between the adjusted total protein intakes, and adjusted animal-based protein intakes, and WOMAC total score (p=0.006 and p=0.010, respectively), WOMAC pain score (p=0.008, p=0.013, respectively), and WOMAC stiffness score (p=0.003 and p=0.004, respectively). In these patients, there were also negative and significant correlations between total adjusted dietary protein, plant-based protein, and animal-based protein intakes with WOMAC functional scores (p=0.004, p=0.006, and p=0.011, respectively).

Table 3. The association between adjusted dietary protein intake with VAS and WOMAC scores in participants with protein intake of less than 75% RDA

Notes: * Spearmen correlation test
Abbreviations: RDA: recommended dietary allowance; VAS: visual analogue scale; WOMAC: Western Ontario and McMaster Index
 

As shown in Table 4, higher intakes of total and animal-based protein correlated significantly with higher SLM and LBM in women. Furthermore, there was a negative and significant correlation between adjusted plant protein and MBF in women.

Table 4. The association between adjusted dietary protein intakes with body composition indices in participants

Notes: * Spearmen correlation test
Abbreviations: LBM: lean body mass; MBF: mass of body fat; SLM: soft lean mass
 

Pain severity correlated positively with MBF (p=0.001) and negatively with SLM (p=0.032) and LBM (p=0.014). MBF also correlated positively with WOMAC total and WOMAC pain scores (p=0.039 and p=0.004, respectively). Additionally, lower LBM correlated significantly with higher WOMAC stiffness scores in patients (p=0.047). In the analysis of the findings by the gender of participants, there were significant correlations between MBF and pain severity (p<0.001) in men and also between MBF and pain severity (p<0.001), WOMAC total score (p=0.011) and WOMAC pain score (p<0.001) in women. In women, higher SLM and LBM correlated significantly with lower WOMAC total (p=0.013 and p=0.006, respectively) and WOMAC pain scores (p=0.028 and p=0.004, respectively). Furthermore, LBM correlated with WOMAC stiffness (p=0.003) and WOMAC physical function (p=0.024) scores negatively in women but not in men. Data are shown in Table 5.

Notes:* Spearmen correlation test
Abbreviations: LBM: lean body mass; MBF: mass of body fat; SLM: soft lean mass; VAS: visual analogue scale; WOMAC: Western Ontario and McMaster Index

Discussion

In this study, we investigated 220 patients with knee OA to evaluate the possible relationship between dietary protein intake and body composition analysis, pain, and functional status. Total protein intake was 55.36±24.14 grams (0.70±0.31 grams per kg weight) per day. According to the results of this study, 70 percent of participants did not meet the protein RDA of whom more than forty percent consumed lower than three-fourths of RDA.
The recommended dietary intake for adults based on the diet and nutrition board is 0.8 g per kilogram of body weight per day. Receiving protein equivalent to 17-21% of the daily calorie in adults of all ages is required (20). In the elderly, to maintain muscle function, more amounts of 1-1.2 g protein per kilogram of body weight per day and even 1-2.5 g protein per kilogram of body weight per day are suggested, partly because of anabolic resistance that is disturbed by repercussions in the synthesis of protein in muscles on dietary protein intake (15). It is particularly vital in the elderly with malnutrition or at risk of malnutrition due to acute or chronic illness or injury.
According to the previous studies focused on much younger participants, the popular features of Iranian dietary intake comprise a high consumption of refined grains and hydrogenated fats and also a high energy intake from carbohydrates which are comparable to those of the dietary patterns in the Middle East, Europe, and the United States (21). A small number of investigations have been performed for energy and macronutrient intake evaluation among middle-aged and elderliesy, in Iran and worldwide. Along with the results of the present study, Zwart et al. (15) found that the current RDA for protein intake is met by only 34.9% of the patients with knee osteoarthritis. According to the National Health and Nutrition Examination Survey, 7–41 percent of older adults were described to have a daily protein intake lower than the RDA. Additionally, this survey has shown that protein intake is reduced with age. So, at the age of 19-30, it is 91 ± 22 g /day and decreases in the elderly by about 66 ± 17 g / day (20). In the study by Heidari et al., the mean for daily protein consumption in men (86 and 70 g) was lesser than those reported in a study in United States (approximately 102 g) (22). Animal-based protein Per capita consumption among Iranian people is significantly lower than among American or European populations (9.2 kg per capita compared with 65.3 and 58.3 kg per capita, respectively) (23). In the study by Farvid et al., the mean consumption of total red meat was only 0.19 servings per day in the Golestan Cohort Study in Iran (24). These suggest that daily dietary protein intake requires to be improved and that dietary protein consumption could be a practical intervention objective, especially in elderly patients with a chronic disease (knee OA).
According to our findings, the dietary protein intake was higher in men than in women. However, the dietary animal based/plant-based protein ratio was significantly higher in women than in men. Consistent with our findings, other surveys described higher macronutrient intakes in men than in women (25).
According to findings, patients who consumed higher total and animal-based proteins had lower pain severity. The reverse correlation between plant-based protein intake and pain severity was found only in women.
In patients with protein intakes lower than 75 percent of RDA, higher physical dysfunction, according to WOMAC total, WOMAC pain, and WOMAC stiffness scores, correlated with lower intakes of total and animal-based protein. There was also a reverse correlation between all types of protein intakes with physical dysfunction, according to WOMAC functional score, in these patients.
Dietary protein intake has a vital role in relieving pain through muscle recuperation. The protein supplements decrease muscle injury and benefit muscle recovery by renovating skeletal muscle. Published articles are scarce on the correlation between dietary protein intake and pain severity in OA. Noh et al. (26) showed that inadequate protein intake (<0.8 g/kg/day) correlated with high odds of pain in women with low back pain (LBP) (OR 1.83; 95% CI 1.12–2.99). Shell et al. (27) studied the effects of The raminem, an amino acid blend 68405-1, on joint pain. Park (28) showed that adults over 40 with high polygenic risk scores (PRS) should have a higher protein intake to alleviate OA risk.
According to the findings, women with higher total and animal protein intakes had higher SLM and LBM. Furthermore, women with higher plant-based protein intake had lower MBF.
The influence of protein consumption on muscle mass is of specific concern in knee OA due to the medical importance of muscle strength in this disorder (14). Generally, most animal-based protein sources are considered high quality for supporting essential amino acid necessities for human growth and development (11). Plant-based proteins may have inadequate amounts of one or more essential amino acids. Legumes are low in the sulfur-containing amino acids methionine and cysteine, and lysine is limiting in grains. However, plant-based proteins correlated with benefits concerning health and physical function (29). In previous studies, a protein diet was associated with muscle mass. In a community-level investigation of adults, participants in the highest quartile protein intake lost 40% less lean mass comparing the lowest quartiles over the three years. Receiving 1.1 g protein per kilogram of body weight per day or 18% of dietary calories was found to be associated with the lowest loss of LBM in the elderly (70-79 years old) (30).
Proteins are macronutrients and have crucial role in many physiological procedures involved in body homeostasis, comprising the structure and function. While carbohydrates and fat are stored in the body for use in conditions of necessity, protein cannot be stored in an inactive compound, so an acceptable source of dietary proteins is vital to preserving body homeostasis and function (7). Low protein intake through diet (less than 0.45 g per kilogram body weight per day) in the elderly is associated with decreased plasma levels of IGF-I and fibroblastic atrophy of skeletal muscle (8).  
According to our findings, patients with higher MBF and lower SLM and LBM had higher pain severity based on VAS. Additionally, higher MBF and lower LBM correlated with higher physical disabilities according to WOMAC total and pain scores and WOMAC stiffness scores, respectively. In women, lower SLM was associated with higher WOMAC total and pain scores. LBM was also reversely correlated with WOMAC stiffness and physical function scores in women but not men.
Jeanmaire C et al. (31) examined an association between low LBM with OA symptoms (pain, dysfunction, and quality of life) in 358 patients with a cross-sectional pattern. Low LBM significantly correlated to the quality of life and WOMAC score disorder. In patients with normal BMI, WOMAC scores in patients with lower lean body mass were higher than those with the normal body composition analysis findings, and the components of quality of life score were lower.
Along with our study, Zoico et al. (32) reported that a high total body fat mass independent of lean mass is associated with limiting climbing stairs in women. Based on the evidence, gender is an important determinant, and women are more affected than men (33). In a cohort study (34) that evaluated foot pain in an overweight population, an increase in fat mass, rather than a weight loss, was predictive of foot pain.
Leptin is a pro-inflammatory adipokine. Leptin is dominantly secreted by subcutaneous fat tissue and is a mediator of weight loss and knee OA. The association between leptin with malignant skeletal muscle pain has been shown in women (35).  The articular chondrocytes have a receptor for leptin, so a mechanical pathway provides a direct route to the adipose tissue to interfere with articular cartilage, which justifies the relationship between obesity and knee pain with topical function.
According to the findings, daily dietary protein intake needs to improve in patients with knee OA. The dietary protein intake might be an intermediation objective in patients with knee OA. However, enhancing muscle protein synthesis through dietary protein intake is more complicated than improving the daily protein intake. Focusing on daily dietary protein intake does not equal higher dietary calorie consumption, because the prevalence of overweight/obesity is considerable in patients with knee OA and weight control is highly recommended.
The study has some limitations. Firstly, it is impossible to make any causal conclusion about the relationship between dietary protein intake and body composition analysis in the cross-sectional data. Secondly, the dietary protein intake was evaluated using the semi-quantitative FFQ. Retrospective food frequency questionnaires are less precise in measuring food intake than the nutrition diary. Thirdly, although the association between dietary protein intake and body composition is biologically acceptable, the probability that total energy intake can be (partly) accountable for this correlation cannot be excluded.

 

Conclusion

The results of this study propose that most participants with knee OA had a dietary protein intake lower than the current RDA. Patients with higher dietary total and animal-based protein intakes had lower pain severity. In patients with protein intakes lower than 75 percent of RDA, higher dietary total and animal-based protein correlated with lower physical disabilities. In women with knee OA, higher total and animal-based protein intakes were associated with a higher SLM and LBM and higher plant-based protein intake were associated with a lower MBF. MBF correlated positively, and SLM and LBM correlated negatively with pain severity in the patients. The patients with higher MBF and lower LBM had higher physical dysfunction according to the various subscales of the WOMAC index. This study opens new horizons in the nutritional care of subjects with knee OA. More studies with the longitudinal and interventional design are required to prove whether dietary protein intake has a causal impact on body composition, pain, and functional disorder in subjects with knee OA.

 

Acknowledgements

This study was derived from the research project no. 58004 approved by the authorities of Tabriz University of Medical Sciences. We are thankful to all personnel of Physical Medicine and Rehabilitation Research Center of Tabriz University of Medical Sciences and all participants who assisted with conducting this study. The results presented in this article were a part of a MD thesis by S. Emamizad.

 

Conflicts of Interest

All authors declare they have no conflict of interest.