Nutrition during injury
Sustaining an injury is difficult and frustrating for any athlete, and for many the motivation to eat well may be diminished in the early stages of recovery. However, a focus on good food and a well-balanced diet, providing all the nutrients required to support recovery during the rehabilitation period, is one of the positive things athletes can do to enable them to get back to training as soon as possible.
This article will discuss some of the key nutrients that play essential roles in the healing process.
The healing processes
The length of time taken for an injury to heal will depend on the severity and type of injury. The repair pathway is similar regardless of the cause of the injury, and involves the immune system orchestrating a complex network of immune cells that peak at different time during the process. This helps to distinguish the four different stages, which are haemostasis, inflammation, proliferation and remodelling.
Haemostasis and inflammation are the body’s initial response to the acute injury, and during this phase the aim is to control blood loss and cellular damage, remove debris and control or eliminate invading bacteria. This phase starts from the time of injury, can last for 3-4 days and is marked by vasoconstriction to stop bleeding, platelet accumulation to form a clot, and leukocyte migration to engulf bacteria and debris to clean the wound site. The injury may appear warm, red and swollen during this phase. The inflammatory response is an important part of the healing process and strategies to reduce it would likely not be beneficial at this stage.1
During the proliferation phase, granulation occurs: new blood vessels are formed and fibroblasts produce collagen, the wound edges pull together (contracture) and the surface of the wound is covered with epithelial tissue. This phase can start around day 3 and can last for 2-3 weeks.
Finally, the remodelling phase can start 2-3 weeks after injury and last up to 2 years, during which time collagen and other proteins become more organised in structure and type III collagen is replaced with the stronger type I. The scar tissue which develops is 70-80% as strong as the original tissue.2
How can nutrition help?
There are many nutrients involved in the healing process, and a deficiency can compromise the speed of recovery. Some of the key nutrients involved include protein, vitamin C, A, B complex, E, K, D, selenium, zinc, iron and copper. Calcium and vitamin D also play a significant role in maintaining the health and integrity of bone tissue.3
Sufficient energy is also required from carbohydrate and fat during injury to support the healing metabolic processes.
The amount of energy needed following injury depends on the extent of the injury and how much it affects normal activity levels. Acute injury, including post-surgical procedures and inflammation, will increase metabolic stress and so energy requirements are likely to be higher in the early phase of recovery. Energy requirements also remain high if the use of crutches is required for athletes to remain mobile.
In general, most athletes are likely to require a reduced energy intake compared to when they are in full training. This will depend on the extent of their daily activity and the demands of the rehabilitation program they are following. Ideally energy balance should be the aim, avoiding either excess energy intake leading to unwanted gains in body fat, or overly restricting energy intake, which may interfere with wound healing and increase muscle loss.1, 4
Protein deficiency can contribute towards poor wound healing by prolonging the inflammatory process, impairing collagen synthesis and inhibiting wound remodelling.5, 6 Immobility following injury can also lead to a degree of muscle atrophy. Athletes need to ensure they consume sufficient energy and increased protein post injury to help optimise healing and to limit excessive losses in muscle mass.4
Recommendations for protein intake during injury are in the region of 2-2.5g/kg body weight.1 Protein with a high leucine content (2.5-3g) such as lean meat, fish, poultry, eggs, dairy foods and whey protein may help enhance muscle protein synthesis,7 and consuming 0.25-0.3g protein/kg per meal every 3-4 hours may maximise the response.8, 9 A greater intake (0.4g protein/kg) may be required if whole body training is undertaken.10 Including a bedtime slow-release protein such as milk or casein may also be beneficial.11 Supplements such as HMB and creatine may also need to be considered to minimise muscle protein loss.7
Joint and connective tissue injuries are common, and there is growing evidence that as well as a good diet, combining specific loading exercise with an appropriately timed supplement of hydrolysed collagen or gelatin, both of which contain specific amino acids required for collagen synthesis, alongside vitamin C, may provide the stimulus to the cells of tendons or ligaments to increase collagen synthesis and promote healing.12, 13, 14
There have been several studies looking at the impact of collagen supplementation on connective tissue. McAlindon et al. (2011)15 observed thickened knee cartilage in osteoarthritic patients supplementing with 10g collagen hydrolysate over a 6-month period. Clark et al. (2008)16 reported a decrease in knee pain in athletes taking 10g collagen hydrolysate daily over 24 weeks.
In more recent studies Lis and Baar (2019)17 looked at the effect of different preparations of collagen supplements on collagen synthesis rate in bone. Subjects took 15g vitamin C (48mg) enriched collagen either as a drink containing gelatin or hydrolysed collagen or as a gummy containing equal parts of both. To load the musculoskeletal system and stimulate bone collagen synthesis subjects did 6 minutes of continuous jump rope 1 hour after consuming the supplement.
Procollagen 1 N-terminal Propeptide (PINP), measured to represent bone collagen synthesis, increased approximately 20% (although not statistically significant) from baseline in the gelatin and hydrolysed collagen groups, but not in the gummy group - authors suggested this may be due to a lack of vitamin C, which could have been deactivated due to heat exposure - or placebo group 4 hours after completing the 6-minute jump rope.
Previous work done by Shaw et al. (2017)12 looked at collagen synthesis in bone but also in engineered ligaments. The randomised cross-over study was designed to compare the impact on collagen synthesis of a supplement containing either 0g, 5g or 15g gelatin with 48mg vitamin C taken 1 hour before 6 minutes of rope skipping to load the musculoskeletal system.
Those subjects consuming 15g gelatin showed twice the collagen synthesis, measured through serum propeptide (PINP) levels, as either placebo or the 5g group. When serum from the subjects with increasing doses of gelatin was added to engineered ligaments for 6 days, there was a corresponding increase in collagen content.
Although there is still much more work yet to be done in this area, current evidence suggests that during injury, starting an exercise/rehabilitation bout 60 minutes after consuming ~10g collagen hydrolysate or 15g gelatin with 50mg vitamin C results in greater collagen synthesis in the recovery period after exercise, and may be beneficial to the healing process.
There may be several benefits to increasing intake of omega-3 fats during injury, due to the impact of these fats on the immune and inflammatory response18 and also on the muscle protein synthesis pathway.19 Good food sources for athletes to include in their diet are oily fish, linseeds, walnuts and chia seeds. However, an omega-3 supplement may be required, particularly if once the initial healing response is well underway inflammation becomes excessive or prolonged, as it can be difficult to obtain the desired amount of omega-3 from food alone.
Vitamin C is essential for wound healing, as it is a co-factor in the hydroxylation of proline and lysine during the formation of collagen. It also enhances leukocyte function and acts as an antioxidant.12 Deficiency of vitamin C may impair wound healing due to the capillaries and connective tissue at the wound site being too fragile and so new scar tissue cannot adequately be formed. Deficiency may also increase susceptibility to wound infection.21
At intakes of approximately 200mg per day, tissue saturation is reached, and to achieve this vitamin C-rich foods should be consumed each day. Vitamin C is found in virtually all fruit and vegetables, but especially good sources are sweet peppers, brussels sprouts, broccoli, watercress, tomatoes, guava, blackcurrants, kiwi, citrus fruits, strawberries, lychees and mango. Fresh fruit and vegetables need to be eaten within a few days of buying, as the vitamin C content gradually diminishes. A supplement of vitamin C may be beneficial if dietary intake is not optimal.
Zinc plays a role in all stages of wound healing and deficiency is associated with reduced epithelialisation, decreased scar strength and collagen production. If zinc status is good, supplementing with additional zinc does not accelerate wound healing. However, in those that are deficient, supplementing with zinc may enhance the wound healing process.22, 23 Athletes recovering from injury should include rich sources of zinc in their diet, including lean meat, fish, shellfish, pulses, seeds, nuts and wholegrains.
Vitamin D is well established for its role in bone health, and is also found to impact numerous other physiological systems such as immune function, neuromuscular function, cellular differentiation and proliferation in muscle tissues, and mitochondrial function.24, 25, 26, 27 It is also suggested to play a role in the wound healing process.28
Vitamin D's potential to be important to the recovery of damaged muscle tissue was demonstrated by Owens et al. (2015b),29 who found significant improvement in recovery of muscle strength following a muscle-damaging protocol in active male adults with suboptimal serum vitamin D levels, when supplemented with vitamin D3 for 6 weeks, compared with pre-supplementation.
Elevated concentration of systemic inflammatory markers and delayed recovery from orthopaedic surgery have also been linked to poor vitamin D status.30 An increase in systemic inflammatory biomarkers could be significant in the development and progression of over-training syndrome and/or chronic injury.30, 31
Vitamin D deficiency can delay functional rehabilitation in hospitalised patients, which is an important consideration for athletes undergoing injury rehabilitation.32
It is clear that nutrition has a key role to play in the recovery from acute and chronic injury. It is important that athletes receive nutrition support during this stressful and difficult time to help them back to training as soon as possible.