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Why do people put on differing amounts of weight?

Stashed in: Awesome, Nutrition!, Diabetes, Nutrition, Microbiome, Microbiome, Weight Loss

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Personalized nutrition is gonna be huge! Especially if, like this guy, it tells you that you should eat ice cream but not grapes.

Yeah, this goes against everything I've been taught:

When we eat, our blood sugar level rises - and both the speed at which it peaks, and then how quickly our bodies deal with that and get it back to normal, is very important to our health. Constant high spikes can lead to type 2 diabetes, as well as us laying down more fat and increasing our risk of other diseases. 

Foods have, therefore, been traditionally classified by how much of a blood sugar spike they cause - with "high GI" (Glycaemic Index) foods being thought of as bad for us, and "low GI" as good. Every nutritionist would tell you this. But the Israeli research, led by Dr Eran Segal and Dr Eran Elinav, suggests that it is simply not so.


Stress levels, exercise and sleep can all affect our blood glucose responses, so the research team made me log everything I did throughout the day on a little phone app.


A fortnight later when our results came through I could not have been more flabbergasted. Virtually all my "healthy snacks" such as grapes and sushi caused me big blood sugar spikes, as did a chicken sandwich, and cereal. On the "good" menu, though, was chocolate, ice cream and regular cola. 

For Leila, the results were very different. Whereas pasta was "bad" for me, it was fine for her. Yoghurt was good for me, but bad for her, and our responses to bread and butter were also complete opposites.

No-one seems to have suspected this degree of individual variation existed, simply because such a controlled study on so many people has never been done before. There is, it seems, no such thing as a "high GI" or "low GI" food - it depends entirely on your own body. But why do our bodies vary so much? Well, the team also have a handle on that now too - and it's an answer that has exciting implications.

What is the major defining factor? The microbiome!

Along with our roster of health tests, Leila and I both also gave the researchers a stool sample. From this, their laboratory was able to discover the composition of our gut microbes. We all carry thousands of different bacteria, viruses and fungi in our guts, which not only help break down the food that we eat, but also produce a huge range of compounds that our bodies absorb and which can influence almost every aspect of our lives, from our immune system, to our metabolism, to our neurotransmitters. 

Because of technological breakthroughs in gene sequencing in recent years we have started to get to grips with the diversity and importance of these communities that are very much part of "us".

By comparing the gut microbes of the hundreds of study volunteers with their blood sugar responses, Segal and Elinav have been able discover that our microbes might be the key to why our blood sugar spikes with different foods are so individual. The chemicals they produce, it seems, control our bodies to this extent. What is particularly exciting about that fact is that - unlike our gene - we can actually change our microbes. And that is very good news indeed for any of us who find that our favourite foods turn out to be "bad" for our blood sugar levels.

When it comes to my own microbes, at the moment I have a mix of good news and bad. The variety of different types of gut bacteria I have is limited and that's not ideal. 

Healthier people, it seems, have a wide diversity. However, the ratio between two of the main ones I do have is in the good category. I also found it interesting that I had a lot of a gut bacterium associated with polycystic ovary condition. It was a huge surprise to me that there could be such a link between microbes living in my lower gut and a condition like that.

Elinav and Segal assured me, though, that by adhering to the diet of foods that my gut bacteria like, I should actually be able to change the composition of them. This in turn would have wider impacts on the rest of my health and wellbeing.

So, armed with my list of "good" foods, I am now embarking on a second phase of the study. I am going to see if I can change my own gut microbes. My results showed that although I do have a good balance between two major groups of bacteria, I am missing a third group almost completely, which could be a key to a healthier weight, and I am also lacking in microbe diversity.


The team at the Weismann Institute are continuing their work with a huge year-long study now into how people can improve their gut microbes. Their dream is that anyone, from anywhere in the world, will soon be able to send in a small stool sample, have their microbes analysed, and - without the need for a week's blood sugar monitoring - be sent a personalised diet plan that will stabilise their blood sugar levels and improve their gut microbes.

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