Fasting and Pain

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This morning, while scrolling through my facebook feed (yes, yes I know, don’t crucify me), I encountered an article about how food-deprived mice feel less inflammatory pain. That caught my attention.

Inflammatory pain is the pain that happens when something in your body is inflamed (as the name suggests), which is usually connected to immune cells doing their job. Another kind of pain is acute pain, which is, for example, you, stepping on a Lego. It’s not something you experience over a prolonged amount of time. At least in most cases. I don’t know how long your walks on Lego usually last.

Anyway, in the study, they tested the response of mice to inflammatory pain and acute pain, either food deprived or fed. What they found was, that hungry mice didn’t react to inflammatory pain as much as on-hungry ones. In contrast, acute pain caused them to take longer to start eating when offered food again¹.

These findings are an interesting example for how mice, and humans most likely too, prioritize without even realizing it. A sudden pain might indicate immediate danger, from which an animal has to get away as fast as possible, no thoughts should be wasted on food. But inflammatory pain? That can last for days, in bad cases even weeks. It shouldn’t keep you from eating or you’ll surely starve. _@suesa

One reason for the decreased inflammatory pain response appears to be neuropeptide Y¹, which generally serves as a signal to eat. If you’re interested in how exactly your appetite is controlled by hormones, check out my post on Hunger Hormones from about three months ago.

But how does this knowledge help us in any way? I mean, great, if you’re hungry, it’s not so bad that the gunshot wound on your leg got infected, but what else?

That’s not a common problem? Oh.

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Well, “inflammatory pain” can be more than just “I got an infection”. Rheumatoid arthritis is an inflammatory pain too!

And there have been studies which show, that short-term fasting can improve rheumatoid arthritis, as well as for the treatment of chronic pain and stress ². Especially when followed by a vegetarian or lacto-vegetarian diet, the effects can be lasting. Of course, just fasting once in a while doesn’t heal you, medical treatment is still needed. But it can help improve the general condition – as long as one sticks to a certain diet after fasting. ³

But that’s the usual problem, isn’t it? People fast or diet, reach the desired result, and then fall back into old eating patterns, just to wonder why they gain weight or why their old symptoms come back.

If you don’t suffer from something like rheumatoid arthritis, you might still consider fasting once in a while (only after properly informing yourself on how to do it, of course. Don’t just stop eating.), because it appears to increase the availability of serotonin, endogenous opioids and endocannabinoids ^{4, 5}.

Especially the endocannabinoid system serves to mediate pain, specifically inflammatory pain⁶, in our bodies. Based on this, it’s not surprising that chronic pain seems to lessen when we’re hungry. (For more info on the endocannabinoid system, check out my post Sex, Drugs, and Neurotransmitters).

But.

But.

There’s always a but. From an evolutionary view, it wouldn’t make any sense to associate the lack of food only with reduced pain and a state of euphoria. We humans, and all other animals would just stop eating. After all, it’d decrease our tolerance to chronic and inflammatory pain, right?

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That’s the point where the hormone leptin comes in (also referenced in the “Hunger Hormones” post).

Leptin is supposed to suppress our desire for food, which means dropping levels of it cause us to be hungry. Humans and mice that are insensitive to leptin tend to be obese, while the leptin levels in patients with anorexia nervosa are incredibly low. The decrease of leptin is triggered by the loss of fat mass, but also short-term fasting, which generally doesn’t lead to weight loss. ⁷

Interestingly, low leptin levels seem to also lead to an almost hyperactive need for movement, which can be observed in cases of anorexia nervosa. Now, many of the patients exercise more to lose weight, but the same effects can be observed in mice too, which suggests at least some influence by the hormone. ⁸

But how does that all fit together? How does it make any sense?

Leptin positively influences the immune system, which means a lack of it leads to a weaker immune system. But! Inflammatory pain is usually caused by immune cells. Downregulating leptin can thus downregulate the activity of the cells in question and reduce inflammatory responses and, as a result, inflammatory pain. ⁹

As always, it’s not easy to draw conclusions applicable to our normal life from this. Should you fast from time to time? Should you avoid it? What food should you eat?

I can’t give you definite answers, it all depends on you, your body and your goals. If you’re generally healthy, you can just test what feels best. If you suffer from a disease, consult your doctor before trying out any extreme things to “cure” yourself. That can lead to more damage than you might expect.

Stay curious, stay informed. Don’t make dumb, uninformed decisions.

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Sources:

¹ A Neural Circuit for the Suppression of Pain by a Competing Need State

² Short-Term Therapeutic Fasting in the Treatment for Chronic Pain and Stress Syndromes. Effects of Mineral Supplements on Side Effects and Well-Being

³ Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis

⁴ Prolonged Fasting as a Method of Mood Enhancement in Chronic Pain Syndromes: A Review of Clinical Evidence and Mechanisms

⁵ The Short-term Effects of Fasting on the Neuroendocrine System in Patients with Chronic Pain Syndromes

⁶ Endocannabinoids and pain: spinal and peripheral analgesia in inflammation and neuropathy

⁷ The role of falling leptin levels in the neuroendocrine and metabolic adaptation to short-term starvation in healthy men

⁸ Elevated Physical Activity and Low Leptin Levels Co-occur in Patients with Anorexia Nervosa

⁹ Serum leptin in rheumatoid arthritis

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