Muscle Damage
Now that we have reviewed some key adaptive processes and concepts related to oxidative stress and inflammation and the benefits of these factors, it is important to discuss some downsides in more depth. Exercise-induced oxidation and inflammation can also lead to muscle damage that creates the recovery time between workouts (12,13,14). This is especially true for isolated bouts or frequencies that are beyond the recovery capacity of the individual as there is a U-shaped curve with regards to the positive effects. The research is currently pointing towards muscle damage likely not being a causative factor for adaptations (this can be debated further and is outside of the scope of this series). If too much is present, then all of one’s resources can be spent trying to repair the damage, and little is left to stimulate the adaptations that lead to progress. It just so happens that what tends to be most effective for stimulating the signals for adaptations also increases muscle damage to a large extent. This trend in the research has caused debate on if antioxidants and anti-inflammatory compounds are useful to combine with exercise to reduce muscle damage, enhance recovery, and allow for better adaptations as a result.
While some view antioxidants and anti-inflammatory compounds as useful recovery tools, as some research has supported this notion, others argue that one is merely trading improved recovery for diminished adaptations (14). This is due to the data suggesting that various antioxidants and anti-inflammatory compounds can blunt the upregulation of Nrf2 produced from exercise, blunt the increase in mitochondrial ROS, blunt the release and production of IL-6, and blunt other transcription factors related to adaptations such as protein synthesis (2,3,15,16,19,20). When discussing recovery, we will be referring to the general idea of decreased muscle damage, improved return to performance, and reduced delayed onset
Antioxidant and Anti-Inflammatory Compounds in the Diet
After reviewing the potential pros and cons of antioxidants and anti-inflammatory compounds, that begs the question of how these compounds naturally occurring in our diet may impact our results. I personally do not think we should avoid these compounds as naturally occurring elements in our diet; in fact, I believe there is a strong basis that they provide many benefits to our exercise adaptations, body composition, and health. Animal research has shown that eating a diet full of these healthy components, such as omega-3 fatty acids, can benefit muscle growth and function (21). While animal data is not a one to one match for human data, it is an excellent research model to understand physiology in a very controlled setting. In this trial, the researchers generated a chronic inflammatory state and simulated resistance exercise in a placebo and anti-inflammatory diet group. The resistance exercise helped prevent muscle loss induced by the chronic inflammatory state, but the anti-inflammatory diet further prevented muscle loss. Similar effects have been seen in humans regarding a chronic inflammatory status and the use of compounds such as omega-3 fatty acids (23, 24).
When it comes to diet quality, it has been associated with the level of physical performance in humans (25). In marathon runners, the antioxidant vitamin A and a high naturally occurring intake in the diet was associated with lower pre-race IL-6 levels but was not associated with lower post-race IL-6 levels, which is what we want (22). Most of us think of antioxidant vitamins such as vitamin C when we talk about antioxidants, but a class of antioxidants we can acquire from a healthy diet in a large amount are polyphenols. Polyphenols are a class of non-essential compounds from plant foods; such are fruits and vegetables, which have antioxidant and anti-inflammatory properties. A high total dietary polyphenol intake is associated with a lower risk of substantial decline in physical performance in the elderly and may play a role in maintaining physical function throughout one’s lifespan (26). Dietary intake of polyphenols can be as high as one gram per day in various populations, and these amounts can match the quantities provided by supplements, but the intake from the diet does not seem to produce blood levels of those seen from supplemental preparations (27, 28). This may be due to how polyphenols in the diet typically have a lower bioavailability than supplemental preparations (22). As a result of this difference, dietary polyphenols can undergo biotransformation by the bacteria in our gut microbiome, and the metabolites can then be absorbed (30). These altered compounds can provide their antioxidant and anti-inflammatory effects by upregulating Nrf2 instead of fighting ROS production directly (29). Another potential mechanism of benefit is that the gut microbiome shift that can result as of polyphenol exposure may impact our oxidant and inflammatory status (30). Some very early research even suggests that the status of our gut microbiome may directly impact exercise performance and muscle growth (31, 32).
Polyphenols such as anthocyanins, flavan-3-ols, and proanthocyanidins (that can be found in oranges, grapes, and berries as examples) are associated with lower fat mass independent of shared genetics or other dietary components in female twins ages 18-83 (33). When humans are given 200 grams of frozen blueberries in a smoothie around eccentric exercise, it does not impact post-workout inflammatory markers such as IL-6 up to 60 hours after (34). Oxidative stress at the 36-hour mark does start to be attenuated but by naturally occurring antioxidant production, which is characteristic of upregulated Nrf2 (34). They also noted faster recovery of some return to performance markers during the 60-hour post-workout window compared to the placebo (34). The polyphenols naturally occurring in coffee are associated with additional endurance and resistance training performance on top of what caffeine alone provides (35). In young men who resistance train and whose diet lacks an abundance of overall antioxidant compounds, when three cups of green tea are added to get their antioxidant intake to a level typically seen with a healthy diet, they have less muscle damage after resistance training, an increase in internal antioxidant activity, and no meaningful effect on oxidative stress markers 15 minutes post-workout (36). Two weeks of 40 grams of dark chocolate consumption reduced the oxygen cost of moderate-intensity exercise and improved performance (37). Lastly, since we should be focused on exercise adaptations and health together, a high dietary polyphenol intake is linked with overall longevity (40).
Other dietary components worth mentioning are choline and betaine. Choline is an essential nutrient found in high amounts in foods such as eggs and meat. It has antioxidant and anti-inflammatory proprieties (38, 39). Betaine is an active metabolite of choline and can be found in grains, fruits, vegetables, meat, and dairy. It also has both antioxidant and anti-inflammatory proprieties (45, 46). In a study investigating if there is an association with better body composition in an adult population, they found that those with the highest intakes of dietary choline and betaine had the least amount of body fat and the most muscle mass (47).
Given the data presented in both animal and human models, I feel a healthy diet providing antioxidant vitamins, a wide variety of polyphenols, omega-3 fatty acids, choline, and betaine is supportive of exercise performance, exercise adaptations, body composition, and overall health. I do not see a reason to avoid these health-promoting compounds in the diet or around exercise as a result.
