Take Home Points…
- Long-term dietary behaviors play a pivotal role in maintaining healthy tendons
- People with diabetes are prone to poor tendon health due to accumulation of advanced glycation end products, collagen cross links, inflammation and oxidative damage
- Higher average blood glucose levels, still considered in the normal range, are associated with other chronic diseases and increased risk for rotator cuff tendon tears
- High body fat percentage, particularly abdominal fat, is associated with developing degenerative tendinopathies
- The non-diabetic population can likely improve tendon-health by improving their glycemic control
- Other foods added to a lower-carbohydrate diet may improve tendon health including turmeric, green tea, and glycine-rich foods
Tendinopathy (a chronic tendon injury characterized by degenerative tissue, pain and impaired performance) is one of the most common problems managed in sports medicine. It causes mobility deficits, pain, and decreased performance. Degenerative tendonopathy presents in a wide variety of individuals from highly active athletes to the more sedentary population. It is accumulative and can eventually progress to complete tendon ruptures. I feel strongly about considering preventative lifestyle strategies due to a paucity of highly effective treatment options. Mechanical loads and genetics are clearly important contributors in the pathophysiology of degenerative connective tissues. There appears to be an equally important systemic input that is often neglected in the context of tendon health.
Tendon tissue consists of tendon cells (tenocytes) and extracellular matrix (ECM). Tendon ECM consists of Type 1 collagen, proteoglycans, and glycosaminoglycans and contributes greatly to tendon biomechanical properties . The ECM is continuously remodeled and an equilibrium between synthesis and degradation is achieved when in homeostasis (i.e. healthy) . Much like bone, mechanical forces are necessary to maintain homeostasis [3, 4] and tendons that experience higher mechanical loads experience accelerated ECM turnover [3, 5]. Aberrant ECM turnover likely contributes to the progression of chronic tendinopathies . Though stem cells have been demonstrated , tendons lack the same degree of regenerative capacity that is present in many other tissues. Highly active individuals experience accelerated ECM turn over in a tissue that has a lower regenerative capacity and is continuously exposed to the body’s extracellular fluids. This vulnerability to accumulative damage highlights the importance of maintaining long-term homeostasis in tendon tissue.
The mechanisms contributing to the development of tendinopathies are poorly understood. In degenerative tendon the ECM becomes disorganized with less parallel structure to collagen, and has changes in the proteoglycan content with increased blood vessel growth (neovascularization) [8, 9]. It is a common assumption that inflammation’s role in tendinopathy is minimal, though this is now being re-evaluated as it likely does contribute to the degenerative process .
Now we will discuss some dietary interventions that likely improve tendon health by helping to slow degenerative change.
1.) Low carbohydrate diet
Diabetes is an independent risk factor for degenerative tendon pathology. Tendons of diabetics are thicker, have more disorganized ECM, and more aberrant calcification which increases the risk of tearing [11-14]. The tendons are mechanically different with increased stiffness and decreased elasticity [13, 15, 16]. These differences appear to stem from chronic hyperglycemia which leads to an accelerated accumulation of advanced glycation endproducts (AGE’s), collagen cross links and elevated systemic inflammation with oxidative stress [17, 18]. The heightened inflammatory state further accelerates collagen cross linking in a feed forward cycle of damage .
Tendon ECM remodeling is also significantly altered by a hyperglycemic environment . Consistently elevated glucose concentration appears to up-regulate certain proteins involved in ECM turnover (matrix metalloproteinases)  which may push the equilibrium more towards degradation further contributing to damage.
AGE-mediated collagen cross links negatively impact tendon biomechanics  and tendon stiffness is increased proportional to the amount of accumulated cross links [22-24]. Tendons of diabetics also have reduced proteoglycan levels which likely alters biomechanical properties even further . This process appears to be independent of AGE accumulation, supporting the idea that there are multiple pathways that consistent hyperglycemia impacts tendon.
You don’t have to have to meet the diagnostic criteria for diabetes to have elevated serum AGE levels [26, 27] and AGE accumulation is important in the development of many other chronic diseases. A recent study demonstrated that higher average blood glucose levels, still below the diabetic range, were associated with increased risk for dementia . Elevated serum levels of AGE’s are predictive of all cause mortality, cardiovascular mortality and the severity of coronary artery disease in people without diabetes [29, 30].
A study in the British Journal of Sports Medicine examined fasting glucose levels in a non-diabetic population and its association with rotator cuff tears. They found that patients with statistically higher fasting glucose levels, still within the normal range (defined as <100mg/dL), was significant risk factor for rotator cuff tears .
Reducing simple processed sugar and acellular carbohydrate intake will likely reduce the accumulation of AGE’s and therefore reduce the associated collagen cross linking, inflammation and oxidative damage. Optimizing your fasting blood sugar levels and improving insulin sensitivity, through reduced consumption of highly process carbohydrate, is likely one of the most potent anti-inflammatory ‘medications’ one can take, not to mention with improvements to your gut microbiome adding greater improvements in systemic inflammation levels .
What’s the right dose? The healthiest amount of human carbohydrate intake is a source of great contention on the interwebs. For some reason this topic gets people very fired up! Carb intake should be determined on a case-by-case basis, considering many variables such as your carbohydrate sources, activity levels, genetics, stress levels, sleep habits, insulin sensitivity, etc., and more discussion regarding this is beyond the scope of this blog post. The main point here is that the quantity of highly processed carbohydrate and sugar in a standard Western Diet is not just harmful to your cardiovascular and endocrine systems, but likely to your connective tissues as well. This is accelerated by two main systemic inputs as we currently understand it; hyperglycemia and oxidative stress (inflammation) though they are both interrelated. If your glucose levels are in the high-normal range (fasting or postprandial or both), you likely have some room for improvement. For your cardiovascular health and your connective tissues which translates to better mobility later in life…and therefore indirectly…cardiovascular health.
2.) Body composition (especially central adiposity)
There is evidence that higher body fat percentage is an independent risk factor for developing tendinopathies. Waist-to-hip ratios and increased waist circumference [33-35] are associated with tendinopathies independent of diabetes. It is believed that this is due to both increased mechanical loading and a heightened inflammatory state. This is particularly true for abdominal fat deposition  and may involve some of the same cytokines that are involved in the associated cardiovascular disease risk . More often than not, central obesity and insulin resistance coincide and likely provide a double hit to connective tissues. Optimizing insulin sensitivity and improving body composition also go hand-in-hand and may go a long way for tendon health.
Curcumin, the principle curcuminoid of the plant turmeric, has significant antioxidant and anti-inflammatory properties  and appears to down regulate genes that are associated with ECM degradation, and apoptosis in human tendon cells . In a hyperglycemic environment, Curcumin can significantly reduce the accumulation of AGE’s and cross links in tendon cells . This likely occurs through reduced oxidative damage as it appears to not improve hyperglycemia. Important to note, Curcumin may be much more effective at preventing AGE accumulation rather than treating AGE’s that already exist .
Turmeric is a member of the ginger family and is a commonly used spice in Indian cuisine. Increasing Turmeric in your diet, or curcumin through supplementation, may slow the accumulation of AGE’s and collagen cross linking over time. More research is needed to better characterize this relationship, but It tastes great and has minimal downsides. It is important to remember that it is a supplement and not a substitute for a high quality whole food diet with appropriate carbohydrate consumption.
4.) Green Tea
Green tea (Camellia sinesis) has many anti-inflammatory properties [40, 41] and appears to improve insulin sensitivity [42, 43]. Green tea is also shown to reduce AGE accumulation and cross linking in rat tendon exposed to a hyperglycemic environment [44, 45]. When combined with Glycine (see below), it accelerated ECM remodeling following tendon damage . Green tea is delicious and soothing, so go ahead and use it to wash down that nutrient dense diet. Just avoid the high-sugar versions as consuming these would be missing the point!
Glycine makes up 35% of a collagen molecule and is a non-essential amino acid, meaning that your body can synthesize it. The body’s ability to make glycine, however, may not be efficient enough to maintain healthy collagen, so sufficient dietary intake remains important . This may be more important in highly active athletes with larger amounts of ECM turnover. Glycine is also an important modulator of systemic inflammation [48-50]. A higher-glycine diet has been shown to increase tendon glycosaminoglycan content, improve collagen organization, accelerate ECM remodeling, and improved Achilles tendon mechanical properties .
One of my favorite glycine-rich foods, which is gaining in popularity, is bone broth, oxtail and tendon soups. Bone broth also contains a lot of proline, proteoglycans, glycosaminoglycans, chondroitin and glycoproteins, all compounds that can support healthy connective tissues (52). Even Kobe Bryant consumes bone broth for improved recovery.
I personally like Dr. Colin Champ’s recipe for breakfast found here, and Michele Tam’s slow cooker recipe found here.
Taking it home…
Chronic degenerative tendon injuries are incredibly common and there are many variables contributing to the pathological processes. Bio-mechanics, mobility, muscle strength and endurance, mechanical loading patterns, training regimen, and genetics all contribute. There also appears to be a large systemic component to the pathological process. This input that can be modulated with long term dietary habits, giving practitioners yet another important reason to discuss healthy diet with patients.
Much like many other components of human health, diet is a feed-forward system of dominoes that can fall in the direction of better health if managed well, or in the opposite direction toward chronic disease if managed poorly. For tendon health, like many other chronic diseases, diet should be considered one of the lead dominoes.
More studies are still needed to better characterize the relationship between blood sugar levels, AGEs, collagen cross links, ECM turnover and tendon health.
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