We know that people with chronic pain are more likely to be obese; but does this happen because people with chronic pain struggle to exercise and suffer from a high load of stress hormones which promote stress eating, or does it happen because obesity causes more wear and tear on joints, which can lead to back problems, pinched nerves, and challenges to exercise? Or could it be that both scenarios are sometimes true?
This question affects our decision-making as doctors in a big way. When we see a patient who is overweight and in pain, what do we tackle first? Do we assume that the extra weight is responsible for the pain? Or do we assume that the pain must be resolved before more exercise and nutrient-dense dietary choices become feasible?
In recent years, physicians are thankfully more aware of the dangers of “fatphobia”—a prejudice against fat people which can lead some doctors to incorrectly assume that the patient’s weight is the cause of any health problems they may report.
Tragically, fatphobia is believed to contribute to higher morbidity and mortality rates for fat patients since some doctors may fail to order potentially lifesaving diagnostic tests for fat patients due to an assumption that a person’s body weight must be the cause of their symptoms.
A wide variety of illnesses, including heart attacks and cancer, have been missed in their earliest and most treatable stages as a result of doctors assuming that symptoms like pain, shortness of breath, and overall feelings of illness and discomfort were related to patients’ high body mass index. As doctors, we must treat all patients equally and avoid unwarranted assumptions about our patient’s health.
However, there is also evidence that patients with high BMIs have worse outcomes from many health problems, including COVID-19 and several other important causes of morbidity and mortality.
So, let us look at the evidence for which comes first: obesity or chronic pain.
Early evidence may suggest that obesity aggravates chronic pain. One well-known 1992 study showed that women with osteoarthritis experienced less pain after losing weight; another study in 2004 showed that weight loss in obese women reduced pain levels and allowed the women in the study to undertake a broader range of daily activities. A 2015 study found that obesity increases chronic pain, and chronic pain also tends to increase weight through reduced levels of physical activity and increased stress eating.
According to Stone and Broderick’s 2012 paper, there appears to be a linear relationship between chronic pain and body mass index (BMI). McVinnie’s 2013 paper goes on to elaborate that obesity’s impact on pain may be explained by the increased levels of inflammatory markers interleukin 6 (IL-6), tumor necrosis factor ɑ (TNF- ɑ), and C-reactive protein (CRP). All of these are chemical messengers that change the body’s metabolic function, and all are found at higher levels, on average, in obese patients.
More investigation is needed into why this occurs and whether this relation is caused directly by a person’s BMI or by matters like dietary choices, which may be correlated to (but not caused by) both obesity and higher levels of these chemical messengers. Since some chemical messengers are known to increase in response to different types of foods, illnesses, and stresses, there is more work about correlation vs. causation.
However, the fact remains that a robust correlation was found between a person’s BMI and their levels of chronic pain. It is reasonable to assume, then, that lifestyle changes which lead to weight loss should also lead to reductions in chronic pain.
Another possible mechanism by which obesity may aggravate or even cause chronic pain is the simple mechanical stress placed on joints when carrying extra weight. We know that proteins called “mechanoreceptors,” which detect mechanical loads on the cartilage that cushions our bones at the joints, are activated when our joints are asked to carry heavy loads.
This activation of mechanoreceptors in our cartilage leads to the activation of intracellular pathways that produce metalloproteases and interleukin 1 (IL-1). These enzymes and chemical messengers degrade the cartilage extracellular matrix and activate inflammatory processes, which can lead to sensations of pain and illness.
This all makes intuitive sense. In obese patients, the joints and circulatory system are asked to handle a significantly heavier workload than the body systems of other people.
In highly fit people, this may be less of a problem; a person with strong supporting muscles and a highly trained cardiovascular system may be prepared to handle this workload without health problems. This is illustrated by several overweight athletes and performers, who achieve astonishing athleticism, which is all the more astonishing for being performed while carrying considerably more weight on their bones, muscles, and joints than most people.
However, a person with poor nutrition and an inactive lifestyle has not developed their body’s capabilities to be able to handle this load, and the combination of poor fitness and nutrition with a high workload placed on the body by a high body mass is likely to result in illness and injury over time.
However, it is essential to know that body weight is not the whole story of chronic pain. Many people who are not overweight struggle with chronic pain. While studies suggest that a decrease usually follows weight loss in chronic pain, it may not eliminate it. Nor is obesity necessarily the first cause of chronic pain; sometimes, it is a consequence of reduced mobility from chronic pain, albeit a consequence that usually worsens the chronic pain.
We cannot neglect chronic pain issues regarding weight loss programs and exercise. Pain is painful. That sounds obvious, but when we are in pain, the initial reaction is to remove the pain-causing stimulus. If walking causes pain, we stop walking. It is a natural survival mechanism. Moreover, when pain is caused by tissue damage from mechanical overloading of weight on our joints, sometimes that is a wise course of action.
According to McVinnie (2013), a study investigating activity levels in patients with knee osteoarthritis found that 12.9 percent of males and 7.7 percent of females were reaching only the minimum recommended amount of physical activity. Activity levels are unlikely to rise significantly as long as they are hampered by chronic pain.
Additionally, we cannot ignore nutrition’s impact on both pain and obesity. Pleasure eating is a real issue, especially in those with pain. We know that stress hormones encourage people to eat more fatty and high-carb foods while discouraging the consumption of nutrient-dense low-calorie foods. Eating is used both as a mechanism to help cope with pain and as an analgesic to reduce pain temporarily.
Both pain and obesity can have a multitude of causes. Therefore, reducing pain and body weight should be approached in a multifactorial way; nutritionally, physically, mentally, and emotionally. Failure to do so may result in short-term success but long-term failure.
Francisco M. Torres is an interventional physiatrist specializing in diagnosing and treating patients with spine-related pain syndromes. He is certified by the American Board of Physical Medicine and Rehabilitation and the American Board of Pain Medicine and can be reached at Florida Spine Institute and Wellness.
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