‘Puppet master’ in gut makes us crave chocolate
THE next time you succumb to an irresistible craving for a late-night burger, a bowl of ice cream or a bar of chocolate, it’s not down to a lack of willpower – it could be due to microscopic bacteria in your gut.
Experts believe that groundbreaking findings from two new studies could change the way doctors look at preventing obesity, diabetes, heart disease and cancer. Previous efforts have concentrated on educating people about lifestyle changes.
Dr Carlo Maley, of the University of New Mexico, who led one of the studies, says: ‘Like microscopic puppet-masters, microbes in the gut may control our eating behaviour in a number of ways, including production of toxins that alter mood, changes to taste, and the hijacking of nerves between the gut and the brain.’
Trying to resist cravings for junk foods that are high in sugar and fat is an everyday challenge for many people.
A lack of self-control is often blamed, but researchers now suggest another possibility – an evolutionary tussle between consumers and the bacteria in their gut.
‘The carbohydrate cravings I sometimes feel might not even be my own, but my system being hijacked by my gut microbiota – microbes controlling the mind,’ says Dr Anna Zakrisson, who has analysed the evidence for a second new study reported in the journal Acta Physiologica.
The findings have echoes of the storyline of Sky Atlantic’s hit thriller Fortitude. In the series, which starred Sir Michael Gambon, parasitic wasps took control of the inhabitants of an Arctic town, leading them to kill.
But far from being a work of fiction, the influence of some gut bacteria, which change the behaviour of their host, is well established in science.
The process is known as host behaviour modification, and the parasite toxoplasma gondii is the best-known example.
Once in the brain of rodents, the bug can change their behaviour to make them more impulsive and less defensive, making them more vulnerable to cats – the only animals in which the bug can sexually reproduce.
Research on mice has shown that infected animals develop a preference for more exposed, open areas, increasing the risk of coming into contact with a cat.
Humans, who acquire the bacteria through contact with domestic animals or through eating contaminated meat, rarely experience any symptoms due to a strong immune system. However, if this is compromised through illness, infection can take hold and some studies suggest those people become more impulsive and prone to reckless behaviour.
Bacteria genes outnumber human genes by 100 to one in the digestive system, and 70 per cent of the cells that make up the body’s immune system are found there. Different types of bacteria have different needs – bacteroidetes, for example, feeds on fat, while roseburia favours sugar.
One possible way bacteria in the gut may influence behaviour is through their effect on brain chemicals known as neurotransmitters. Other possibilities looked at by researchers include manipulation of hormones, and even interference with signals travelling along the vagus nerve between the gut and brain.
According to Dr Maley, there is some evidence for a connection between cravings and the gut in humans. People who desire chocolate have different microbes in their urine from people who are indifferent to confectionery.
‘The struggle to resist cravings for foods that are high in sugar and fat is part of daily life for many people,’ he says. ‘We suggest that evolutionary conflict between the host and microbes in the gut leads to a difference in interests over eating behaviour.
‘Gut microbes may manipulate our eating behaviour in ways that promote their fitness at our expense.’