'Gut Feelings': Medicine, Gender and Health

 

BBC News reported today that gut flora - the trillions of bacteria that live in our digestive system - may ‘boost’ cancer therapy. Scientists in France and the USA tested the microbiome in cancer patients, finding evidence that a diverse biome, composed of a wide range of 'good' bacteria, contributed to the effectiveness of immunotherapy drugs.

This report is part of a more widespread recognition that the biome affects our physical and mental health. Other, recent stories reveal that gut bacteria can stop asthma  and provide a weapon against obesity.  Gut bacteria might, further, influence mental health conditions like anxiety, as well as the trajectory of debilitating diseases like Alzheimer’s. 

This is not the first time the gut has been seen as crucial to the conservation of health.  In 1907 The Abdominal and Pelvic Brain, written by the American physician Byron Robinson, identified the Enteric Nervous System in the gut as equivalent to the Central Nervous System associated with the brain.  Robinson anticipated more the American physiologist Michael F. Gershon's discussion of the gut as a ‘second brain’ in the 1990s.

The reason? The gut contains between 200 and 600 million neurons, the same number as the spinal cord. Moreover, more than two thirds of the body’s immune system can be located in the gut.

In this context, the most recent revelations about gut bacteria influencing immunology drugs makes sense: it is the manifestation of  'cross-talk' between brain and body: and a scientific explanation for ‘gut feelings’; that unproven yet instinctive sense we have about particular events, people and places. 

In the pursuit of health amongst the well, in addition to the sick, maintaining a healthy gut is crucial. Yet most modern Western diets don’t support microbial diversity, which is crucial to our well-being; loss of diversity is particularly linked to obesity. The over-consumption of chemically-produced and enhanced food, in addition to the over-use of antibiotics and antibacterial products, restricts and damages our gut flora, arguably making us more susceptible to allergies, infections and systemic problems.  

We can combat this erosion of healthy gut bacteria by eating probiotics that help defeat 'bad' bacteria, and prebiotics that enable 'good' bacteria to flourish. Naturally fermented foods, organic fruit and vegetables, ‘live’ cultures all point in the right direction. 

There is much that can be said about the militaristic battle lines drawn in the gut, as everywhere else, between the bacteriological forces of good and evil. Crucially, though, for theorising medicine and the mind/body relationship, listening to our guts turns conventional scientific ideas upside down, a theme I have discussed in This Mortal Coil: The Human Body in History and Culture It destabilises the brain from its pedestal as the dominant organ of the body in the neurocentric age, and creates a more holistic vision of the body. 

A focus on the gut challenges the idea that experiences like stress are transmitted just one way, from the brain to the belly, e.g. in conditions like Irritable Bowel Syndrome (IBS). In an alternative model, the  physical condition of the stomach and guts, and their nutritive and hormonal makeup, can be seen to run the show, sending information to the brain and even influencing mental health and brain structures.

As a historian of emotion and the body, I am interested in the imaginative and literary meanings of the body turned upside down. And in the fact that - as with with other anecdotal ideas about the body (like the emotional heart and transplantation) - science often finds material explanations for anecdotal or metaphysical concepts.

Many hormones and chemicals previously thought to exist only in the brain are now identified in the gut. About ninety-five per cent of the body’s serotonin, for instance, a neurotransmitter linked to appetite, sexual behaviour, pain and happiness, is found in the gut. So is dopamine, the 'pleasure hormone'.

If the gut/brain relationship is being re-jigged, however, it is at the expense of gender. We might not think of the gut as being gendered, but it is. Gender, like obesity, age and lifestyle, influences the hormones that are produced in the gut, and therefore the kinds of gut flora that might flourish. Whether or not there are ‘natural’ differences in gut flora is under-researched, though it is likely, given the role of hormonal influence.  It is known, for instance, that taking the contraceptive pill dramatically affects women’s gut bacteria, and that gut bacteria is gendered in BMI-specific ways - could this be a clue to the gender differences in metabolic and intestinal inflammatory disease? 

Why is gender missing from discussions of gut bacteria? And does it matter? Drugs and therapeutics have historically been developed for theoretically genderless (though inherently male) patient. According to the Institute of Medicine, women and men are perceived as different at the level of each individual cell. Each cell line is derived from a single donor and contains 23 pairs of chromosomes. Included in this group are the sex chromosomes, XX (female) and XY (male). Since 5% of the human genome 'resides on these chromosomes - 1846 genes on the X and 454 on the Y' - male and female cells are genetically different, a theme recently explored in the American Journal of Physiology.

Molecular biology is beginning to show how genes expressed on cell chromosomes 'impact cell function, and how they react to all sorts of stimuli'. For instance,female neurons uptake dopamine more quickly than male neurons, and female liver cells may metabolise drugs differently to male.

These cellular differences are rarely considered in medical studies or drug development. Since the 19th-century birth of scientific medicine, there has been a significant gender bias in favour of men. Yet the gender bias affects women's and men's experiences of healthcare in key ways. 

It remains to be seen how much difference gender will make to scientific understandings of the gut. There is a cultural stereotype that women are more able to access 'gut-feelings', though this ability is usually framed as 'intuition'.  Intuition has not historically been regarded credibly, but as evidence of women's connection with the emotional and the mystical (by contrast to men's reliance on reason and logic). Might it one day be re-imagined as a product of bacteria?

Electron micrograph of a common gut flora: Escherichia coli. Image courtesy of Wellcome Images

Electron micrograph of a common gut flora: Escherichia coli. Image courtesy of Wellcome Images