Results from this study demonstrate that the sham-anti-inflammatory diet effectively blinded all participants while also having no significant effect on inflammation over the 4-week intervention period. This was accomplished by altering the original anti-inflammatory diet to discretely include certain food items that are ostensibly healthy, but which may promote inflammation. This primarily included substituting items high in nutrients with well-established anti-inflammatory benefits (e.g., foods high in omega-3 fatty acids) for similar items with poorer nutrient characteristics (while still eliminating food items that were clearly not part of a healthy diet such as fast food / highly processed food). Additionally, the frequency by which certain potentially proinflammatory foods could be consumed was increased (e.g., red meat allowed 2-3x/week as opposed to 1x/week). Lastly, we included less-established, potentially proinflammatory food items which would generally be viewed as healthy (e.g., nightshade vegetables). Although the proinflammatory nature of these items are supported by only weak/conflicting evidence, or a physiological rationale, they can be effectively incorporated into a sham diet without disrupting blinding as they are not generally viewed as proinflammatory. Together, these changes proved to be sufficient to negate any anti-inflammatory benefit while also being subtle enough to maintain the appearance of the true anti-inflammatory diet.
The original anti-inflammatory diet[4] was designed to eliminate well-established inflammation inducing food items such as processed foods[10], refined sugars[11, 12], refined wheats[13], and trans fatty acids[14] while increasing the consumption of anti-inflammatory foods and nutrients such as healthy fats (omega-3)[5], lean protein[6], and fruits and vegetables[7, 8]. This diet was previously studied by our lab and was shown to significantly reduce inflammation in individuals with SCI compared to a non-dieting control group after 4-weeks with sustained benefit following 12-weeks on the diet[9]. Based on these findings, 4-weeks was deemed an appropriate duration to demonstrate any changes, or lack thereof, in the sham-diet condition. While heavily processed foods (e.g., hot dogs) were still eliminated from the sham diet, (both for blinding purposes, and the general health of participants) other items which could be more discretely altered were substituted with more pro-inflammatory versions.
Nutrients such as omega-3 fatty acids (n3), carotenoids, flavonoids, and tocopherols have well established anti-inflammatory properties[5, 8]. Long chain fatty acids including omega-3 and omega-6 (n6) influence inflammation via numerous intracellular and extracellular mechanisms including changes in the fatty acid composition of cell membranes. While an n6/n3 ratio favoring n6 impacts cell membrane composition and contributes to the production of proinflammatory mediators, increasing n3 consumption can induce anti-inflammatory and inflammation-resolving effects[5]. Carotenoids, flavonoids, tocopherols, and n3 also influence inflammation via antioxidant properties. Free radicals can increase inflammation via mechanisms related to the upregulation of the transcription factor NFkB. As antioxidants protect against free radicals, they may help to reduce cytokine production[15–17]. The increased consumption of fruits and vegetables which are high in these nutrients has been shown to be inversely related to serum inflammatory mediators including CRP, interleukin 1 beta (IL-1β), IL-6, interferon gamma (IFN-y), and tumor necrosis factor alpha (TNF- α) [7, 8]. It was possible to discretely alter dietary advice for the sham diet to encourage a less favorable n6/n3 ratio and antioxidants by altering advice on oils, nuts/seeds, and fish. For example, in the sham group, safflower oil and prepared low fat salad dressings were allowed, while olive, flax, coconut, and avocado oils were no longer promoted. Further nuts with greater n6/n3 ratios such as peanuts, almonds, pistachios, hazelnuts, and cashews as well as seeds such as pumpkin, sunflower, and sesame seeds were allowed. Several beneficial fish options including herring and mackerel were also removed and replaced with tilapia which has a much less favorable n6/n3 ratio[18].
The sham diet also allowed increased consumption of proinflammatory foods. The consumption of refined grains such as white breads, pastas and rice have been shown to be positively correlated with serum inflammatory markers[13]. This has been proposed to be due to a corresponding rapid spike in blood sugar which results in the production of advanced glycation end products (AGEs) associated with inflammation[19]. White breads, pastas, and rice are generally understood to be less healthy alternatives to whole grain products (which have lower glycemic indices and have a more favorable effect on blood sugar) or fermented breads like sourdough (which contain beneficial prebiotics). However, whole wheat and multigrain products which are also often believed to be healthier alternatives, often contain refined flour and are stripped of many nutrients. As such, whole wheat products may have a similar pro-inflammatory effect to that of refined wheat options despite appearing to be a healthy option. Similarly refined sugar has well-established proinflammatory properties. Acutely, it has been proposed to result in inflammation by promoting the synthesis of free fatty acids (FFA) in the liver which produce FFA metabolites that trigger inflammatory processes and the formation of reactive oxygen species (ROS)[11]. Chronic consumption of refined sugar also contributes to the development of inflammatory conditions such as obesity, diabetes, and cardiovascular disease. While refined white sugar is generally well-known to be unhealthy and pro-inflammatory, there is a general misconception that brown sugar is a healthier alternative. Allowing brown sugar while prohibiting white sugar on the sham-diet promoted the appearance of a healthier alternative despite having the same impact on inflammation.
Advice for the consumption of red meat and alcohol was altered to allow increased consumption. While the original anti-inflammatory diet limited red meat consumption to once per week, individuals on the sham diet were allowed to consume red meat up to 3 times per week. Increased consumption of red meat is associated with higher concentrations of serum inflammatory mediators[6] and the substitution of red meat for other proteins including poultry, fish and legumes has been shown to be associated with a healthier biomarker profile of inflammatory mediators and glucose metabolism[6]. Alcohol consumption was limited to 2 bottles of beer (341ml) per week in the original anti-inflammatory diet while the sham diet allowed consumption of alcohol in ‘moderation’, while only excluding spirits, thereby allowing for increased consumption. Alcohol consumption has been shown to increase translocation of lipopolysaccharides (LPS) from the gut[20]. Regular consumption may therefore contribute to impaired gut and liver function and contribute to persistent inflammation.
The original anti-inflammatory diet also restricted certain food items that ‘may’ contribute to inflammation. These include food items with only weak and/or conflicting evidence in the literature such as nightshade vegetables, non-pressure-cooked beans, coffee, and cow’s milk. As there is a scarcity of high-quality trials assessing the impact of these items on inflammation, they are not established proinflammatory foods and it has been suggested that individual differences (sensitivities, intolerances) may dictate whether they result in inflammation. However, as these items were viewed as potentially proinflammatory they were eliminated from the original anti-inflammatory diet. As these items are typically viewed as healthy in the general population, their inclusion in the sham diet provided an effective means of maintaining participant blinding while potentially helping to negate the inflammatory benefit of the anti-inflammatory diet.
A limitation of the current study is the lack of an anti-inflammatory diet group for direct comparison with the sham-diet group. Due to recruitment challenges associated with the COVID-19 pandemic (which particularly impacted at-risk groups such as those with SCI), the study could not be sufficiently powered with 3 groups. However, this did not impact our ability to assess blinding as participants randomized to the sham-diet condition were still told they would be randomized to either an anti-inflammatory diet or sham-diet condition. Further, our lab previously demonstrated that the anti-inflammatory diet induced a significant reduction in inflammation by 4-weeks compared to a non-dieting control group[9]. As such, if the sham-diet was insufficiently altered from the original, changes in inflammation would have been expected following the 4-week intervention period. As this study, and previous work by our lab was performed in individuals with SCI, future trials are warranted to assess the applicability in other populations.
This pilot study represents the first whole-diet intervention to assess the utility of a sham anti-inflammatory diet and include an assessment of blinding. Our findings that 4-weeks on the sham diet produced no changes in inflammation relative to the control group, paired with the effective blinding of participants, therefore provide valuable insights regarding the utility of the sham-anti-inflammatory diet.