10% Human by Alanna Collen

10% Human by Alanna Collen

Author:Alanna Collen
Language: eng
Format: epub
Publisher: HarperCollins
Published: 2016-03-23T00:00:00+00:00


SIX

You Are What They Eat

As I sit down with Dr Rachel Carmody for a cup of tea at Harvard University, she tells me about the moment she realised we were looking at the human diet in completely the wrong way. She had just finished her Master’s dissertation on the effect of cooking on the nutritional value of food, and was presenting her work in her viva examination. At the end of the meeting, the examiner sitting at the far end of the long table from Carmody stood up and slid a stack of newly published scientific papers towards her. As they fanned out in front of her, Carmody caught sight of ‘microbiome’ and ‘intestinal microbiota’ among the titles. ‘You might want to have a think about how this would affect your conclusions,’ the examiner said.

‘The amount of energy that we can extract from the diet drives all of biology,’ Carmody explains. ‘Chances are that the way an organism looks and behaves has to do with how it procures its food. The trouble was, as a human evolutionary biologist looking at how humans digest their food, I was studying only half of the problem.’ Carmody had been focused on the digestive processes going on in the small intestine, but as prestigious journals like Nature and Science began to publish special issues about the role of the gut microbiota in nutrition and metabolism, she realised that her research, and that of others studying human nutrition, could never yield all of the answers. ‘What we had,’ Carmody tells me, ‘was a system of thinking about the diet that was distressingly incomplete.’

Our entire perspective on nutrition has shifted. Until recently, what went on in the small intestine was all that mattered. This long, thin tube that leads off the blender-like stomach is where it all happens, as far as ‘human’ digestion is concerned. Enzymes pumped in from the stomach, pancreas and the small intestine itself break down the large food molecules into smaller ones that are capable of crossing through the cells of gut lining into the bloodstream. Proteins, like twisted and folded pearl necklaces, are cut into single beads, called amino acids, and shorter chains of these building blocks. Complex carbohydrates are sliced into more manageable chunks called simple sugars, such as glucose and fructose. And fats are pruned into their parts: glycerols and fatty acids. These smaller units go about their business in the body, making energy, building flesh and being repurposed for our own use.

Human nutrition, according to dogma at least, essentially stops at the end of the seven-metre-long tube that is the small intestine. It’s followed by the much shorter, but wider, large intestine, but this relatively mucky section of bowel has been neglected up until now – as if it’s simply an outsize waste pipe. At school, many of us were taught that, while the small intestine was there to absorb nutrients, the large intestine was supposed to absorb water, and to gather up the leftovers of our food ready to be egested.



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