Obesity supersizes pain, researchers claim

Chronic pain can make it very difficult to maintain a svelte figure. Almost all the CRPS sufferers I know, myself included, have had significant weight gain since the onset of the illness due to a range of factors. Firstly, pain can make it difficult or impossible to exercise; my thrice-weekly gym visits and three-mile daily walk were rapidly eradicated by the CRPS. Secondly, even though I eat very little, my general immobility means I burn far fewer calories than I did pre-illness. I am forced to spend most of the time sitting with my leg elevated as literally every other position increases my pain and after 6 years, I still haven’t found anything I can do about it.

The other factor is one I’m loath to admit, but admit it I must: pain makes me comfort eat. When I hurt really badly, I want chocolate instead of an apple. If I’m feeling low because pain has yet again stopped me doing what I want, I want ice cream rather than carrot sticks. As much as I try to eat healthily, there are way more times than there should be where I tell myself that suffering so much constant pain means I deserve to enjoy something and that something is never the healthiest choice. And let’s be clear: anyone who claims to gain as much enjoyment from eating salad as they do from pizza is just lying, either to themselves or to us. We know that depression and gaining weight go hand in hand, and it’s not really hard to see why.

Obesity is linked to a lower pain threshold

Now there’s yet more bad news for those of us who like a Cornetto or six; new research has come out suggesting that obese people have a lower pain threshold than those with a ‘healthy’ weight.

The team at Leeds Beckett University tested 74 volunteers, who were split into three groups based on their BMI (body mass index): obese, overweight or healthy. BMI is a commonly used way of assessing whether someone’s at a healthy weight for their height. The ‘healthy’ range is from 18.5 to 24.9, with ‘overweight’ being classed as a BMI of 25 to 29.9 and ‘obese’ including a BMI of 30 and over. A further distinction is sometimes used, where a BMI of 40 or more is described as ‘morbidly obese’. If you’d like to work out your own BMI, then have a look here.

Researchers measured responses to pain, hot and cold

The trial researchers measured the volunteers’ responses to three different types of painful stimuli; pressure, cold and heat. Firstly, they applied each stimulus to the base of the thumb and then to the waist (areas where little and much body fat is stored, respectively) and asked volunteers to report when they started to feel pain. They then got volunteers to stick their hands into icy water, again reporting how soon it started to hurt.

The results were dramatic. Volunteers in the ‘obese’ group reported feeling pain from pressure equivalent to about 4.3kg per square centimetre. Those with a ‘healthy’ BMI registered pain from pressure equivalent to around 8.6kg per square centimetre, considerably more than the ‘obese’ participants. This suggests that those with a lower BMI might have almost twice as high a pain threshold as those who are significantly overweight. Interestingly, all three groups had about the same response to hot and cold, quashing the idea that those with an extra layer of fat might have more protection against pain caused by extremes of temperature.

Do pain and obesity go together?

The results are precisely as might be expected from the large amount of research that says that obese people feel more pain. Previous investigations have shown that pain and obesity seem to go hand in hand, with excess weight being linked to a slew of painful medical conditions like arthritis, fibromyalgia and back pain. There is also evidence, however, that obesity itself can cause pain.

In 2012, American researchers analysed data from more than 1 million adults. They split them into groups, with ‘low-normal’ for those with a BMI less than 25, ‘overweight’ being 25-30, ‘obese 1’ for BMIs of 30-35, ‘obese 2’ for 35-40’ and ‘obese 3’ for BMIs higher than 40. Trial subjects were asked about their experience of physical pain and any painful illnesses. The team found that as weight increased, so did pain, to a staggering extent: the overweight group reported 20% more pain, obese 1 had 68% more, obese 2 stated 136% more and obese 3 reported a huge 254% more pain than the low-normal group.

You can explain some of this by pointing to the well-known correlation between obesity and illness, but these results went beyond that; even when the researchers corrected their results to account for the influence of health problems causing pain, the obese still reported more pain. 14% more pain for those in the obese 1 group, 34% more for obese 2 and 58% more for members of obese 3.

What could be going on here? This paper posits a fascinating potential conclusion: that fat itself causes pain. Researchers suggest that leptin, a hormone produced by fat cells, could play a role in creating painful inflammation. This theory suggests that the more fat you have, the more leptin you produce and thus the greater painful inflammation it causes. So the development of obesity itself could bring about a situation where pain is created in the body. And if you add that inflammation onto the extra strain on joints caused by excess weight, then you could have a very nasty situation.

What does it mean for chronic pain patients?

So do we all need to sign up to Weight Watchers right now? Well of course there are a myriad benefits to maintaining a healthy weight and it’s something we should all aim for, no matter what.

It’s clear that those with higher BMIs feel more pain, but I do wonder about the chicken and egg situation. As I explained at the beginning, severe physical pain will often limit your activity and thus generally your weight will rise. Is it possible therefore that those with pain have higher BMIs, rather than the pain being a product of the higher BMI?

I do think one other finding of the Leeds study is fascinating too; whilst obese volunteers felt pain much more quickly than those with a healthy BMI (at 4.3kg per square centimetre versus 8.6kg), those who fell in the overweight group, with a BMI of 25-30, actually had the highest pain threshold of all, not reporting that they felt pain until the stimulus reached 10kg per square centimetre.

The researchers suggest that this might be because there were many members of the overweight group who took part in physical activity, as this has been shown to have a bearing on pain perception. It’s undoubtedly possible, but I think this impressively high pain tolerance probably warrants further investigation. I don’t know whether it’s likely to get much more attention though, as it doesn’t fit with the medical and social narrative that says thinner is always better.

In general that is widely true, but how great would it be if being slightly overweight became a recommended strategy for dealing with CRPS?! I don’t know exactly what it means for pain patients in general; in this particular pain patient’s case though, I think I’ll take it as reassurance that I can have that one piece of chocolate cake, just maybe not the three that I really want.