Our study is the first to evaluated whether a high-protein diet during the waiting time before admission for primary TKA affects preoperative albumin levels. In our patients, preoperative serum albumin levels were strongly associated with postoperative HAS use in primary TKA and, furthermore, there was a negative dose-response relationship between them. And a high-protein diet during the waiting time before admission for TKA may be a useful tool to improve the albumin levels of these patients and avoid complications after surgery.
Albumin is well known among clinicians for its reliability and sensitivity for assessing nutritional status [16]. Hypoproteinemia can lead to a significantly higher incidence of postoperative complications including delayed wound healing due to reduced collagen synthesis and protein matrix deposition [17, 18] and superficial or deep infection caused by diminished immune response [19], and adverse events such as myocardial infarction, cardiac arrest, stroke and even mortality in TJA [10, 18]. On the other hand, our study showed that preoperative albumin level was significantly associated with HAS use after TKA, showing a negative dose-response relationship: lower preoperative albumin levels correlated with higher risk of postoperative use of HAS. But HAS use has been associated with higher risk of cardiac, pulmonary, and combined complications, acute renal failure, and unplanned intensive care unit admission [12]. Furthermore, hypoproteinemia was directly associated with increased total costs in revision and primary TJA [11]. Clinicians and policy providers should consider this question for optimizing the nutritional status of patients preoperatively and reducing the risk factors that may increase medical costs in the ear of bundled payments for TJA [20].
Serum albumin levels have been associated with long-term mortality in the general population, especially for the elderly [21], and with postoperative course and mortality for patients with geriatric hip fracture [22]. Malnutrition or hypoproteinemia are common in elderly patients, and age and female sex (female) are its independent risk factors, which may be related to associated with their dietary habit of low-quality nutrient intake and/or low economic status [23, 24]. This population accounts for the majority of patients undergoing TKA. Fortunately, compared with emergency operation, the elective nature of TJA allows these patients to have an adequate preoperative nutritional storage for reducing the risk of postoperative HAS use [16, 25]. One study [26] reported that a high-protein diet could improve the overall survival for older adults diagnosed with advanced gastrointestinal cancer. Although serum albumin < 35 g/L is usually considered as malnutrition [27] or hypoproteinemia [28], our study revealed a negative dose-dependent relationship between preoperative serum albumin levels and postoperative HAS use, consistent with a study showing that lower preoperative albumin levels are associated with higher treatment costs [11].
In our patients, about 35 g of dietary protein (about 0.5 g/kg body weight) were added to the daily diet, which resulted in an increase of about 3.2 g in serum albumin from the day of outpatient visit to admission (an average of 39.05±22.78 days). Several studies have evaluated the effects of a high-protein diet. One study [29] reported that a high-protein diet (1.07–1.60 g/kg body weight/day) lasting for 6–12 months was an effective and safe way to reduce weight: the high protein produced satiety and increased energy expenditure. Furthermore, high-protein diets lasting for 12 weeks could significantly improve body composition in women with normal-weight obesity, reducing the waist circumference, fat mass, and body fat percentage and increasing lean body mass [30]. Interestingly, high-protein diets could also improve skeletal muscle mass in patients with gastrointestinal cancer [31], which may be relevant to our patients, since skeletal muscle mass is also important for recovery of function after TKA [32]. Future studies should evaluate the effect of high-protein diets on quadriceps muscle strength, which will provide more evidence for preoperative high-protein diet combined with muscle exercise for the patients planning to undergo TKA.
Our study showed that a high-protein diet had no significant impact on biomarkers of liver, kidney, or lipid metabolism. Tischmann et al. [33] revealed that a high-protein diet lasting for approximately 34 months had no significant effect on the biomarkers of cardiometabolic health and vascular function in overweight participants. In contrast, a previous study [34] reported that high-protein diets can decrease the levels of low-density lipoprotein, total cholesterol, and triglycerides as well as mitigate insulin resistance in patients with type 2 diabetes mellitus. The differences with our study may be associated with the metabolic disorder in diabetic patients and shorter duration of our study.
Our study presents several limitations. First, we excluded patients with renal and hepatic diseases, and therefore the safety of a high-protein diet for these patients must be assessed because of its potential effects on renal function [29, 35]. Second, although we asked patients to fast for 6-8 hours before blood collection, some patients, especially at outpatients visit, may have failed to follow it, which would affect our laboratory test results. Third, although we educated patients in detail, some patients may not have strictly followed our suggestions during the preoperative waiting period. Finally, large randomized controlled studies are needed to compare the effect of a high-protein diet on the rate of HAS use and its consumption. Despite these limitations, we believe that the current study provides new ideas for preoperative nutritional management for patients planning to undergo TKA.