Magazine

Why do people put on differing amounts of weight?

  • 26 January 2016
  • From the section Magazine
Detail of woman eating salad Image copyright iStock

Foods that make some of us put on weight can have little effect on others, according to research being carried out in Israel. It might be time to rethink the way we diet, writes Dr Saleyha Ahsan.

Like most of the population, I must admit that I am on an eternal quest to lose weight. For me it's more to do with concerns about health than aesthetics. I have polycystic ovary syndrome and a family history of type 2 diabetes and that puts me into a high risk category for developing diabetes myself.

I have always watched what I eat - and yet I never seem to shift the weight, while friends seem to eat what they want without putting on a single bulge. It seemed like they could just "break all the rules". But perhaps that's just because we have been wrong about what "the rules" of diets are.

Last month, I travelled to Israel for Trust Me, I'm a Doctor to take part in a vast new research study being carried out there by a team at the Weizmann Institute of Science. They are in the process of monitoring 1,000 people in absolutely minute detail to see exactly how their bodies react to food - and their first results are rewriting the textbooks on our relationship with food.

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.

Once I arrived in Tel Aviv, the team not only took all my vital statistics and medical history, but they gave me a little implanted glucose monitor under my skin, which would monitor my blood sugar levels constantly for the next week. The team's nutritional experts had prepared me six days of menus specifically designed to test my body's response to a few standardised meals, mixed in with some of my personal staple foods.

I'm an accident & emergency doctor, which is something that undoubtedly has an effect on my diet. Rushing around on my feet all day with strange working patterns has meant that eating times can be erratic - and unless I have been super-organised, I am at the mercy of the hospital canteen.

I never buy bread - it's an aisle I just don't even go down in the supermarkets and I live in fear of sandwiches - but I see other people living on them.

I do, however, reach for the grapes - I love them. I can eat bunches of them and feel guilt-free doing so. They are my go to "healthy" snack. Another guilt-free grab is sushi - especially after a day's filming. I snatch a box of salmon nigiri and am off. Now, though, had come my chance to find out what each of these foods was really doing to my body.

Image copyright iStock

Other things, such as 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.

Most importantly, though, because their initial data had suggested that different individuals responded differently to foods, I teamed up with another volunteer of the same gender and age - Leila.

For the next week, Leila and I did and ate exactly the same things together - eating in the same restaurants and carefully weighing our food to ensure that it was as identical as possible. Textbooks said that our bodies should respond to them in a similar way. The Israeli researchers suspected that we wouldn't.


Find out more

Trust Me I'm A Doctor is broadcast on BBC Two at 20:00 GMT on Wednesday 27 January - catch up afterwards on BBC iPlayer.


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.

Image copyright iStock
Image caption Doughnut or vegetables? The healthy choice may not be so simple

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.


What is polycystic ovary syndrome?

The three main features of PCOS are:

  • Cysts that develop in your ovaries (polycystic ovaries)
  • Your ovaries not regularly releasing eggs (ovulating)
  • High levels of "male hormones" called androgens in your body

The condition is associated with an increased risk of developing health problems in later life, such as type 2 diabetes and high cholesterol levels.

More from NHS choices


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.

Over the next month, I shall be sending regular little parcels to Israel for analysis, and hoping to see that change as I adapt my diet.

The team at the Weizmann 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.

As they say, the widespread obesity and diabetes epidemics show that whatever we're trying now to improve our relationship with food simply isn't working. It could well be that they have hit upon the key to this - that until now we have completely misunderstood our own bodies and how food affects us.

So, as I chomp on a chocolate bar and ice cream (although the researchers hasten to add that a nutritionally balanced diet is still as important as ever), I am looking forward to seeing whether I can start to lose weight and become healthier as a result.


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