Sweeteners influencing gut bacteria behaviour

If you're someone who prefers diet fizzy drinks over their full sugar versions, you'll be used to the taste of artificial sweeteners like aspartame. These compounds provide the same sweet taste with none of the calories or sugar, which can be especially useful if you have diabetes. But might these sweeteners have OTHER impacts on our health? A new study just out suggests they can change the behaviour of bacteria that live in our intestines, turning them from helpful Dr Jekylls into aggressive Mr Hydes. Anglia Ruskin University’s Havi Chichger spoke with Eva Higginbotham...

Havi - So we found with our study that if we take two bacteria, that are most commonly seen in our guts, that are happy, healthy bacteria, they help us metabolise what we eat and break down some of the foods, when we add artificial sweeteners to them, such as saccharin or sucralose, we see the behaviour of these bacteria change and they become more likely to cause damage to us, so more likely to stick to our own gut cells, more likely to invade our gut cells and in some cases more likely to kill our gut cells.

Eva - And what do you think is in the sweetener that's causing the bacteria to change its behaviour all of a sudden?

Havi - Well, we think it's definitely something to do with that ability to sense sweetness or sweet taste. And when we sort of inhibit that ability to taste sweetness, the bacteria don't respond. So there's definitely something in that. And we don't know exactly what it is, we're looking at the mechanism. There's lots of different possibilities because bacteria have lots of different ways they can rapidly change their genetic makeup to respond in different ways.

Eva - So does that mean the bacteria think that the aspartame tastes sweet in the same way that we think the aspartame tastes sweet?

Havi - We think so, and that's what the data indicates. We can't prove what that sweet taste receptor is, there's no documented ability for bacterias taste sweet before our study. So we think they have some kind of sensor and that would make sense because bacteria need to respond to their environment, just like we need to respond to our environment.

Eva - And do we know if it's the sweetener directly changing the behaviour of these bacteria? Or is it that it's having some impact on the local gut cells that would then change the behaviour of the bugs?

Havi - Well, we've shown previously that taking bacteria out of the equation, sweeteners can cause damage to our gut cells. But what we're seeing when we add bacteria to the equation is that we almost have an exacerbation of that. And that more closely mimics what we see in our gut, where we have gut microbiota and our own gut cells usually working in symbiosis.

Eva - And do we know if it would happen with sugar itself or is it something special about the sweetener?

Havi - That's a really good point. So there's lots of work done on things like a low in fat or a low in animal protein diet or a low sugar diet causing a good diversity of gut bacteria. And that's what we want, we want good diversity. The more diverse our microbiome is, usually the more happy and healthy we are. So we do know that sugar decreases the diversity of the gut bacteria, and there have been studies with artificial sweeteners showing the same thing. What we're showing that's a little bit different to that is that it actually takes that good microbiome and turns some of the bacteria into something quite pathogenic, not able to respond to antibiotics, not able to function as we'd want it to.

Eva - Do we know if this would work the same in an actual human body though, as in a dish like you've shown?

Havi - It's a really good point. So we used a human cell model, but actually we took 2 bacteria out of the many millions that we find in our guts. So in fact, it could well be that it's a worse scenario than we're seeing in our dish. It could be that actually there's compensation and over time it's not having such a dramatic effect. And so we really need to look at the whole system to be sure of that.

Eva - And what do you think this means then for people who like their fizzy drinks with their aspartame on the side?

Havi - It's a really boring answer, but I think actually if we think about sweeteners as a compensation for sugar, and we know sugar can be very damaging for our health, the ideal is water I'm afraid. And that's what we looked at, we looked at water versus sweeteners as what you'd expect to see. I think it's just being aware that sweeteners aren't without some effect on us, and we're really starting to understand what those effects are.

Eva - And what if you were someone who, you know, you might have a bit of a diet Coke addiction for a few weeks, but then you go back to the water. Is this change permanent? Or is it something that would come and go as your intake of sweetness goes up and down?

Havi - Well, fortunately there are a lot of studies which show that our gut microbiota can revert back to a sort of healthy environment. So over time, taking sweeteners, taking some of the higher fat out of our diets can help our gut microbiome return to normal. And hopefully that shift can be temporary, but still, as I say, just understanding what that is, how long that takes.

Eva - And is there any way, just speaking for myself here, that we can kind of balance it out. If you have enough salad at lunchtime, does that mean you can have a few diet cokes in the evening?

Havi - Wouldn't that be nice if we could! I think we're better off maybe reducing our overall intake throughout the day, rather than top heavy sweetener loading. I think it's especially worth noting, it's not just drinks. Sweeteners can be found in lots of different parts of our diets, sometimes without us even realising it's there.