Chapter 14
Medical nutrition therapy for chronic pain management

Andrea Glenn¹, Meaghan Kavanagh¹, Laura Bockus-Thorne², Lauren McNeill³, Vesanto Melina⁴, David Jenkins¹, & Shannan Grant^2,5

¹ Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada

² Department of Applied Human Nutrition, Mount Saint Vincent Hospital, Halifax, Nova Scotia, Canada

³ Tasting to Thrive, Toronto, Ontario, Canada

⁴ Nutrispeak, Vancouver, British Columbia, Canada

⁵ Departments of Pediatrics and Obstetrics and Gynaecology, IWK Health Centre, Halifax, Nova Scotia, Canada

Introduction

Nutrition is a cornerstone in the management of a number of chronic diseases, including cardiovascular disease (CVD) and type 2 diabetes [1]. Most commonly, pain management programs have included physical, psychosocial and medical interventions, but not nutritional interventions [2, 3] other than general recommendations to achieve and maintain a “healthy weight” to help manage chronic non‐cancer pain [4]. This lack of focus on nutrition is despite evidence that patients with chronic pain have been shown to have lower diet quality and may consume diets higher in calories, fat and added sugars and lower in fruits and vegetables compared to the recommended Canadian dietary guidelines [5, 6]. Moreover, people with chronic pain have been found to choose animal‐based sources of protein more often, which is also not in agreement with current dietary guidelines that recommend choosing protein that comes from plants more often [5, 6].

Diet has been identified as one of the highest care priorities for people with chronic non‐cancer pain [7]. Moreover, there are physiological and metabolic data indicating patients living with chronic pain can benefit from nutrition intervention [8]. These data are promising, but limited. What is clear, however, is that current evidence supports shared decision‐making [9]. Shared decision making is rooted in patient‐focused care, described as approaching medical care with the feelings, mental health, perceptions and expectations of the patient in mind [10]. Commonly found in nursing literature, person‐centered care takes this concept a step further, keeping the patient at the center of care, but recognizing all people working within organizations and communities, have their own needs, biases, strengths and limitations. This approach to language also aims to actively avoid victimization and hierarchical patient‐provider dynamics [10].

There is emerging evidence that diet may play an important role in chronic pain management, particularly through regulating inflammatory pathways [11]. Many patients with chronic pain have elevated levels of pro‐inflammatory markers, such as C‐reactive protein (CRP), tumor necrosis factor (TNF)‐alpha, and interleukin (IL)‐6, that can be reduced through diet [12, 13]. Undesirable alterations in the microbiome have also been documented in patients with chronic pain and/or depression, through the “microbiota‐gut‐brain” axis and have been associated with several chronic diseases [14]. The microbiome may provide another mechanism in which diet can positively influence outcomes in chronic pain, through promoting the development of a more diverse and stable microbiota [15]. For instance, plant‐based dietary patterns, such as vegan and vegetarian diets, have been found to beneficially modulate the microbiome [15]. Most of the evidence to date in the area of diet and chronic pain management relates to pain measurement scales and inflammation.

Current literature exploring the role of diet and chronic pain

Peer‐reviewed literature exploring the role between diet and chronic pain is heterogeneous and fragmentary, including a diversity of study designs, methods, interventions, outcomes, and patient populations and therefore limiting a health care team’s access to high quality evidence. Systematic reviews and meta‐analyses on diet and pain are lacking due to the inability to combine the different interventions together to determine their overall effect on pain outcomes. Moreover, much of this research has also focused on supplements/natural health products, such as omega‐3 fatty acids (Table 14.1), rather than on whole foods and dietary patterns, which are the key focus of current chronic disease management clinical practice guidelines [1]. Table 14.1 highlights some potential nutrients that may be of concern for people living with chronic pain that should be assessed with the onset of treatment and throughout the care process.

Dietary patterns have, however, shown promise for various chronic pain conditions [8]. Most of the evidence on specific dietary patterns in chronic pain includes plant‐based diets: (1) vegetarian diets that may include dairy and eggs but no meat, poultry or fish, (2) vegan diets which include no animal products or (3) dietary patterns that are mostly‐plant based (i.e. a traditional Mediterranean diet that allows small amounts of meat, poultry, fish, dairy and eggs, but mostly consists of plant foods). The evidence for these dietary patterns is summarized in the following section.

Plant‐based dietary patterns and pain

Using a systematic review approach, two trained and experienced reviewers (AG and MK) identified 14 intervention studies on plant‐based dietary patterns and chronic pain [16–29]. The most common chronic pain condition that was investigated was rheumatoid arthritis [16, 22, 23,25–28]. Other chronic pain conditions that were examined included: fibromyalgia [17, 21, 24], migraines [18], general chronic pain [29], osteoarthritis [20], and diabetic neuropathy [19]. The plant‐based dietary pattern interventions varied considerably between the studies identified, however, all the diets shared common characteristics of being high in fiber, plant‐based proteins, fruit, vegetables, nuts, and whole grains. Two studies assessed vegetarian diets [16, 29] and three studies assessed a whole foods low‐fat plant‐based diet (i.e. vegan) [19, 20, 26]. The remaining studies included a vegetarian dietary pattern with additional interventions such as a fasting period, raw foods only, or a gluten‐free diet. Most studies were conducted over 15 years ago, with nine of the 14 being published before 2005 [16, 17, 21,23–28]. The average length of the studies was 4.7 months, and the most common way to assess pain was through quantification of patient report using standardized tools. Thirteen of the studies assessed pain using a visual analogue pain scale (VAS), which is frequently used in standard care [30], while Towery et al. used a numeric pain rating scale [29]. Other questionnaires were used to measure additional health outcomes, such as the Health Assessment Questionnaire (HAQ) and the Short Form Health Survey (SF‐36), both of which also include a VAS pain scale. Overall, 11 of the 14 studies found the plant‐based diet interventions improved pain and related health outcomes. Two of the higher‐quality studies, Hafström et al [23] and Clinton et al [20], included a randomized controlled trial (RCT) design, and are described in more detail below.

Hafström et al. investigated a gluten‐free vegan diet over nine months in 66 patients with rheumatoid arthritis compared to the non‐vegan control diet [23]. The gluten‐free aspect of the diet counselled patients to replace gluten‐containing foods with whole grains such as buckwheat and millet. The primary outcome of the study was change in patients’ signs and symptoms of rheumatoid arthritis, measured by the American College of Rheumatology response criteria (ACR20) [23, 31] . After nine months, significant improvements in pain and the number of tender and swollen joints were found in patients randomized to the vegan group compared to the control group [23]. It is important to note that the gluten‐free diet aspect of this study is not essential to improve chronic pain or inflammatory outcomes [16,18–20, 26], unless the patient has diagnosed gluten sensitivity or celiac disease. Gluten‐free diets can be more expensive, may be lacking in certain micronutrients (such as iron), and some gluten‐free grains are of higher glycemic index [32–34], therefore, these diets should only be recommended when medically necessary and in consultation with a Registered Dietitian. Clinton et al [20] investigated a whole‐foods plant‐based diet (i.e. vegan) over six weeks in 40 patients with osteoarthritis compared to a control group who maintained their usual diet [20]. The primary outcome of the study was change in both pain and physical function. Significant improvements in both pain and physical function were found in the vegan group compared to the control group.

Table 14.1 Potential nutrients of concern for people living with chronic pain

Nutrient	Rationale for Concern	Mechanisms	Sources (Foods and Supplements)
Magnesium	Magnesium has been suggested as an important nutrient for chronic pain conditions [62] This mineral is “probably effective” for migraine prevention [63] While evidence in other types of chronic pain (i.e. complex regional pain syndrome and refractory chronic low back pain) exists, more research is needed [64]	Anti‐inflammatory and analgesic effects Main mechanism is through blocking the N‐methyl‐D‐aspartate (NMDA) receptor	Nuts, seeds, whole grains, and legumes (beans, peas, lentils and soy foods) Magnesium is a central mineral in the chlorophyll molecule, therefore, leafy greens are a good source Supplementation may be considered as many patients do not consume enough magnesium‐rich foods in their regular diet
Omega‐3 Fatty Acids	The Western diet provides relatively high intakes of omega‐6 fatty acids along with low levels of omega‐3 fatty acids By increasing intakes of omega‐3 fatty acids or omega‐3 to omega‐6 ratio, it is possible to decrease the production of omega‐6 metabolites which may contribute to inflammation and immune dysregulation Evidence suggests that omega‐3 polyunsaturated fatty acid supplementation can reduce arthritic pain, especially in those with rheumatoid arthritis [65] Fish oil was found to improve osteoarthritis‐related pain in overweight adults [66]	The essential omega‐3 fatty acid alpha‐linolenic acid (ALA) is an essential omega‐3 fatty acid and can be converted into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) within the body, although the conversion is low All compete for the same enzyme for elongation, thus relatively high intakes of omega‐6 fatty acids reduce the already low conversion rate of ALA to long chain EPA and DHA	ALA is found in walnuts, hempseeds, chia seeds and ground flaxseeds EPA and DHA are mostly found in fish, however, the actual sources are other marine sources, such as algae Algae‐based supplements may be used for some patients Fish oil has been a major commercial source of EPA and DHA, however, their original sources (algae), are available and may have additional health benefits
Vitamin D	Deficiency is common in patients with chronic pain Association between low levels of serum vitamin D (25‐hydroxyvitamin D3) and higher pain intensity have been found [67]	The role of vitamin D in chronic pain is not fully understood, however, this vitamin has immunoregulation and anti‐inflammatory effects High serum vitamin D associated with lower levels of inflammatory markers such as CRP	Vitamin D is found in: Fortified foods such as non‐dairy and dairy milks and margarines Oily fish (sardines, salmon, herring etc.) Some egg yolks Sun‐dried or UV‐exposed mushrooms Supplements are recommended for those residing in latitudes far from the equator, in urban areas with smog, those who get little sun exposure and in countries where fortification is less common (such as Europe)
Vitamin B12 (cyanocobalamin)	Deficiency can lead to sensory symptoms or unexplained chronic pain Deficiency is common in chronic pain populations (found to be present in 10% of people living with chronic pain) Supplements have been shown to improve various pain conditions, such as diabetic neuropathy and lower back pain	Major role in nervous system functioning Co‐factor in myelin formation, required for methylation of the myelin basic protein which makes up the myelin sheath around nerves	Supplementation is recommended for those with gastrointestinal diseases, those who follow a vegetarian or vegan diet, and for those over the age of 50 years Patients on PPIs, histamine H2‐receptor antagonists or metformin are at higher risk of deficiency
Fiber	Low fiber intake is common in the general Canadian population and in those with chronic pain [5] Opioid‐induced‐constipation has been reported in 41–81% of patients receiving opioids [52, 68]	Fiber improves bowel movements and weight management, and helps contribute to a healthy microbiome Short‐chain fatty acids are produced from soluble fiber fermentation with key roles in regulating host metabolism	Fiber sources include fruits, vegetables, legumes and whole grains Increase in water intake along with high fiber foods and supplements is important Increase in fiber through plant foods and specific foods such as bran and prunes can help avoid opioid‐induced constipation Patients should be counseled to start eating a high fiber diet prior to starting opioids Fiber supplementation should be started at the same time as opioid prescription

In addition to this evidence, other mostly plant‐based dietary patterns, such as the Mediterranean (Med) Diet, have also been explored as medical nutrition therapy for patients with rheumatoid arthritis [35]. For example, a randomized controlled trial investigated the effects of a Med diet over 12 weeks in 51 patients with rheumatoid arthritis [36]. The Med Diet significantly improved pain and related outcomes such as disease activity (i.e. joint tenderness and swelling), physical function and quality of life when compared to a standard Western control diet. These plant‐based diet interventions have been described in a recent systematic review and meta‐analysis [8]. However, more research is needed to make stronger conclusions on the role of nutrition in chronic pain. As discussed, the diets investigated in chronic pain management are diverse and heterogeneous, however, the overall collection of evidence for plant‐based dietary patterns is promising, especially given the breadth of evidence in support of plant‐based diets in other chronic diseases, for many of which pain is often a symptom.

Specific foods for chronic pain management and inflammation

Many specific foods have been studied for their role in chronic pain and inflammation. Table 14.2 highlights some of these specific foods that have been linked to outcomes in people living with chronic pain or have been found to have anti‐inflammatory or pro‐inflammatory effects.

Dietary patterns for common pain comorbidities

Medical diagnoses for chronic diseases, including obesity, type 2 diabetes (T2DM) and CVD have been linked with chronic pain [37]. For example, rates of overweight and obesity have been found to be higher in those with chronic pain compared to the general population [7], although several factors are likely impacting this finding. For instance, undesired weight gain can be the result of chronic pain’s impact on one’s ability to shop, cook and exercise. That said, evidence implies chronic pain may be caused or exacerbated by overweight and obesity. Counseling patients on maintaining a healthy weight is often part of standard pain management, with particular evidence for those with osteoarthritis or joint pain [4]. This approach is not in agreement with recent clinical practice guidelines for the prevention and management of obesity (as a chronic disease), which is now focused on behavior‐based interventions rather than on weight management or weight loss as a goal of treatment [38]. It is now well‐accepted that some people can carry “extra weight” without health issues [39]

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