Obesity commonly correlates with increased pain. One of the mechanisms for this is relatively straightforward; having central adiposity (fat around the stomach region) or being obese is associated with low-grade chronic inflammation, and this, in turn, is associated with a greater incidence and severity of chronic pain conditions. In the recent study authors (Song. et al, 2018) wanted to study the effects of diet and obesity on postoperative pain. There were 2.7 million surgeries performed in 2016 according to the Australian Institute of Health and Welfare. Each surgery is associated with some degree of acute pain, and the severity and duration of acute pain experienced is a risk factor for the development of chronic pain. So any modifiable factor that increases pain intensity or duration post surgery is worthy of note, as it may help to reduce progression to chronic pain.
The study had some interesting findings, one of which was that negative outcomes occurred with greater frequency in males than females. To summarise the findings, a high-fat diet:
- Resulted in prolonged pain particularly in males.
- Delayed skin wound healing and rates of nerve regeneration.
- Caused increased macrophage (immune) activity and sensitivity, leading to increased inflammation.
Alarmingly the study implied that even 1 week of high-fat eating in the lead up to surgery can contribute to the above effects. However, on the flip side, a moderate fat diet in the two weeks leading up to surgery can help mitigate the effects even if no weight loss is achieved.
The authors noted that changes to the composition of the gut microbiome are proposed to play a role in the low-grade inflammation in obesity or during high-fat diets. The changes in composition lead to increased endotoxin production, which is seen as a danger by the immune system leads to increased immune activation and as such inflammation in both the peripheral and central nervous systems. The authors also note there are likely other factors that account for the effects of dietary fat on post-operative pain but the above mechanism has a potentially significant role.
So what are the potential take-home points from this study?
- For both men and women, but men, in particular, prepare for surgery by consuming a lower fat diet (30% of total kilojoule intake or less).
- Of the 30% or less fat intake, choose a predominance of healthy fats including monounsaturates (olive oil, avocado, nuts & seeds) and polyunsaturates (SMASH fish – salmon, mackerel, anchovies, sardines and herrings, chia seeds, flax seeds).
- Increase vegetable intake to at least 5 serves (cups) per day, legumes and whole grain intake, which will provide fibre to bind fats and help eliminate before they are absorbed. These foods will also support a healthy microbiome, with less endotoxin production e.g all vegetables, rolled oats, brown bread, wholemeal pasta, quinoa, lentils, and beans.
Reference: Song, Z., Xie, W., Strong, J. A., Berta, T., Ulrich-Lai, Y. M., Guo, Q., & Zhang, J. M. (2018). High-fat diet exacerbates postoperative pain and inflammation in a sex-dependent manner. Pain, 159(9), 1731-1741.