AUSTIN, Texas — A diet high in refined sugars, carbohydrates, and transfats likely has an effect on how a patient will experience pain, according to data presented this week.
Stacie Totsch, a predoctoral fellow in Dr Robert Sorge’s IMPACT (Immune Modulation of Pain and Addiction for Comprehensive Therapeutics) laboratory at the University of Alabama at Birmingham presented a poster at the American Pain Society’s 35th Annual Meeting, investigating the effects of a typical American diet on pain and pain recovery.
Previous data from the IMPACT lab showed that poor diet prolongs recovery from injury, prompting researchers to study a “standard American diet” (SAD) in rats that was high in refined sugars, carbohydrates, and transfats. The diet under testing had an omega 6 to omega 3 ratio of 15:1 to mimic the American diet, which strays from a regular diet where the standard omega 6 to 3 ratio is 5-6:1.
The researchers initially baseline-tested the animals’ mechanical and thermal sensitivity as well as their locomotor activity, and randomized them to either regular chow or to the SAD. Every week after they started the diet, animals were weighed and tested for their mechanical and thermal sensitivity; every month, blood glucose and locomotor activity were measured. After 20 weeks of diet exposure, a chronic pain injury was induced by injecting complete Freund’s adjuvant (CFA) into the hind paw.
Upon recovery, both male and female groups had gained weight. However, females on SAD gained more weight over time than those on the regular diet. This was not observed in males. With the mechanical and thermal sensitivity, investigators did not record any changes in the baseline or the acute pain.
Locomotor activity, which was measured as the distance traveled over a 30-minute period, did not show sex differences, but the researchers noticed that the animals consuming the poor diet tended to be more active in general. Males on the poor diet had significantly higher blood glucose levels, which were measured every 4 weeks, starting at week 12, whereas females showed differences at weeks 8 and 20. In general, animals on the SAD diet had higher blood glucose.
Both males and females had increased fat levels on the poor diet, but the interesting finding was that males, not females displayed a decrease in lean fat. Females on SAD diet had higher levels of triglycerides – males only displayed increased levels of leptin, compared with their counterparts on a regular diet.
When researchers looked at cytokines which are specific to pain, they noted increases in interleukin (Il) 6 and TNF-α in both males and females subjected to the poor diet. Males on SAD also showed increases in Il-1β, whereas females displayed higher levels of TNF-α and IFN-γ. Those results indicate possible physiological differences, as cytokines upregulated in females (Il-4 and Il-13) are T cell-specific, whereas those whose levels were increased by poor diet in males are microglia-related.
Animals on the poor diet had a decrease in bone mineral density. Upon induction of chronic injury, animals on SAD diet had prolonged recovery: rats on a regular diet returned to pre-CFA baseline levels by day 12 and 19 for males and females respectively, whereas animals on SAD did not recover until day 40. The researchers also noted a 3-fold increase in microglia activation in the spinal cord, as assessed by Iba-1 immunostaining.
The SAD diet had physiological effects, there were sex differences, and the poor diet prolonged recovery from pain injury for both male and female animals. Because microglia were increased in the absence of pain, the researchers explained that there are likely prolonged behavioral and physiological changes caused by diet and not necessarily by pain.
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1. Totsch S, Waite M, Quinn T, et al. Sex differences in the impact of the suboptimal American diet in rats: effects on behavior, physiology and recovery. Presented at: 35th Annual Scientific Meeting of the American Pain Society; May 11-14, 2016; Austin, Texas.