A simple nutritional tweak could soon transform the way we recover from hip and knee replacements. New evidence, published in the Journal of Orthopaedic Surgery and Research, suggests that a targeted “protein boost” before and after surgery may help patients hold on to precious muscle, potentially speeding up their return to mobility and independence.

This is not just another dietary fad. It is a finding that could reshape peri-operative care for millions facing joint replacement, a procedure that is becoming ever more common as populations age.

The research, a systematic review and meta-analysis conducted by a team of scientists from several leading medical universities in Iran, set out to answer a straightforward but critical question: can giving patients extra protein or essential amino acids (EAAs) around the time of surgery reduce the muscle wasting that so often follows hip or knee replacement?

The answer, based on a careful analysis of 19 clinical studies involving nearly 1,000 patients, is a cautious but encouraging yes. Yet, as with all things in medicine, the story is more nuanced than a simple headline.

Why does muscle matter so much in joint replacement? Osteoarthritis, the main reason for these operations, is a degenerative joint disease that causes pain, stiffness and loss of function, especially in the hips and knees. It is a condition that creeps up with age, weight gain and years of wear and tear.

For many, the pain becomes so severe that only a new joint offers hope of relief. But while a new hip or knee can banish pain, it does not reverse the slow, steady loss of muscle that comes with ageing or the sudden muscle loss that follows surgery and enforced rest.

After a joint replacement, patients often face a double whammy. First, there is age-related sarcopenia, the gradual loss of muscle mass and strength that affects all older adults. Then comes the period of immobility after surgery, when muscles are deprived of their usual activity. This combination can lead to rapid muscle shrinkage, making it harder to get back on your feet, increasing the risk of falls and even threatening the long-term stability of the new joint.

As one expert involved in the review put it, muscle acts like the rubber band that keeps a joint properly aligned. If that band goes slack, the joint can wobble, and recovery can stall.

Protein is the building block of muscle. Within every protein are amino acids, some of which the body cannot make and must get from food. These are the essential amino acids. In sports medicine and research on frailty in older adults, protein and amino acid supplements have shown promise in preserving lean mass and aiding muscle repair after exercise or injury. But until now, it was unclear whether a similar approach could help patients undergoing joint replacement.

To find out, the researchers combed through the world’s medical literature, searching databases such as PubMed, Embase, Web of Science and Scopus up to February 2025. They looked for studies that specifically tested dietary protein or amino acid supplementation in adults having a total knee or hip replacement. Each study was assessed for quality using established tools, and where possible, the results were pooled in a meta-analysis to give a clearer picture of the overall effect.

The findings are intriguing. Supplementing with essential amino acids, either by mouth or through an intravenous drip, was linked to a modest but statistically significant reduction in muscle loss. The effect was most pronounced in the quadriceps and hamstring muscles, the key muscle groups that support the knee and hip.

For the quadriceps, the standardised mean difference was 0.69, with a confidence interval from 0.44 to 0.95. For the hamstrings, the effect was even larger, with a standardised mean difference of 1.04. These numbers may not mean much to the lay reader, but in the world of clinical research, they represent a real and meaningful difference.

However, the story does not end there. While muscle mass was preserved, the impact on muscle strength and function was less clear. Across the studies, there was no significant pooled improvement in measures such as quadriceps strength or handgrip. In other words, patients kept more muscle, but this did not always translate into greater strength or better function. This is a crucial point. Muscle mass is only one part of the recovery puzzle. The ability to rise from a chair, climb stairs or walk unaided depends on many factors, including pain control, physiotherapy and the gradual reintroduction of weight-bearing exercise.

The method of supplementation also mattered. Intravenous amino acid infusions, given during the peri-operative period, showed additional benefits, such as improved muscle protein synthesis and reduced blood loss during surgery. Oral supplements, typically in the form of EAA drinks, were also effective, especially when given in the week before and after surgery. The optimal dose appeared to be in the range of 10 to 15 grams of EAAs per day, similar to what is used in sports nutrition.

Timing was another key variable. Short-term supplementation, lasting less than six weeks, was beneficial for muscle mass. There is little data on the effects of longer-term supplementation, and the studies varied widely in terms of dosage, timing and the specific formula used. This makes it difficult to issue a one-size-fits-all recommendation. What works for a frail, undernourished patient may not be necessary for a fit, well-nourished one.

So, what does this mean for patient care? According to experts in nutrition and orthopaedics, the findings suggest that hospitals should consider screening patients for protein malnutrition before surgery, especially those over 65 or with a low body mass index. For those at risk, offering oral EAA drinks in the days leading up to and following surgery could be a simple, low-cost intervention. In the hospital, short-term intravenous amino acid infusions might be considered for frail patients or those at high risk of bleeding. Crucially, any nutritional intervention should be closely coordinated with physiotherapists and dietitians to ensure that diet and exercise plans are aligned.

Yet, the authors of the review urge caution. The studies included in the analysis varied widely in design, size and quality. Some were small, some were not randomised, and outcomes were measured at different times using different tools. There is a clear need for larger, high-quality trials that compare standard care with combined oral and intravenous amino acid strategies. There is also uncertainty about the optimal protein dose, the best supplement composition (whey, casein, branched-chain amino acids or full EAA mixes) and the ideal timing relative to surgery. Long-term outcomes, such as muscle strength, physical performance, patient satisfaction and healthcare costs at six months or a year, remain largely unknown.

Despite these limitations, the practical message is clear. Protein supplementation is unlikely to do harm and may do good, especially in patients at risk of malnutrition or excessive muscle loss. Experts are not suggesting that every joint replacement patient needs a cocktail of amino acids. But for those who are frail or have low muscle reserves, this simple intervention could be a valuable addition to enhanced recovery protocols.

This research shines a spotlight on nutrition as a key, and often overlooked, component of surgical recovery. In recent years, enhanced recovery after surgery (ERAS) pathways have revolutionised care in fields such as colorectal and gynaecological surgery by standardising pain control, early mobilisation and fluid management. Now, orthopaedic teams are beginning to consider how targeted protein or amino acid supplementation could be integrated into similar protocols for joint replacement.

Imagine the orthopaedic ward as a bustling kitchen. Fluid balance is the stock pot, pain relief adds the herbs and spices, and protein supplementation is the protein of the dish. Each ingredient is essential. Leave one out, and the final result may be flat. Get them all working together, and recovery becomes a feast.

Beyond the hospital, this line of research has wider implications for public health. Maintaining muscle mass is not just important for patients after surgery. It is vital for preventing falls, fractures and frailty in the general population. These insights are already influencing programmes aimed at promoting active ageing and injury prevention.

Looking to the future, the rise of precision medicine may one day allow us to personalise peri-operative nutrition based on genetic, metabolic or microbiome profiles. For now, the key message from this systematic review is that peri-operative protein or amino acid supplementation is a promising, low-cost strategy to reduce muscle atrophy in patients undergoing total hip or knee replacement. While we await further large-scale trials to iron out the details, orthopaedic teams and dietitians can begin to consider how best to incorporate these nutritional tools into their practice.

In the end, joint replacement is about more than just metal and plastic. Surgeons may debate the best implant design, and physiotherapists may argue over the optimal exercise regime. But this study reminds us that what happens in the gastrointestinal tract – the simple act of digesting essential amino acids – plays a starring role in the theatre of recovery.

By viewing nutrition as a fundamental part of peri-operative care, we can give patients the best chance not just to walk again, but to stride confidently into the next chapter of their lives.