Saccharin Solution? Sugar Substitutes May Mess With Gut Bacteria – Causing Obesity In The Process, The Economist, 20 September 2014
A paper just published in Nature1 … provides a big dollop of evidence in support of an emerging idea that artificial sweeteners are not directly bad for people (humans cannot even digest most of them). Rather, they may be bad for the zillions of microbes that live in people’s guts – and this, in turn, may be bad for their human hosts.
Three groups of rodents were given water containing aspartame, sucralose or saccharin, three common commercial sugar substitutes. Three control groups were given plain water or water laced with glucose or sucrose—sugars from which the body can extract energy.
After a week, Dr Elinav and Dr Segal gave their animals a hefty dose of glucose and measured how well they processed it (inability to do so properly is a risk factor for obesity, and is characteristic of diabetes). The mice drinking the artificial sweeteners had higher levels of glucose in their blood than did their confrères who had been sipping water or ordinary sugar.
To check whether the sweeteners were affecting the murine microbiome, the researchers dosed their mice with broad-spectrum antibiotics. Sure enough, killing off the gut bacteria reversed the metabolic changes. To make doubly sure, they transplanted faeces from mice that had been drinking artificial sweeteners into others that had been raised in sterile conditions, and which, therefore, had no gut bacteria of their own. Once the transplanted bacteria had colonised their new hosts, these too began showing signs of glucose intolerance
Gene sequencing confirmed that mice fed artificial sweeteners had a notably different set of bacteria living in their guts from those fed on the natural kind. Intriguingly, the microbiomes of the sweetener-fed mice looked a lot like those found, by other studies, in obese individuals.
Here’s the study’s press release, and an excerpt about the team’s pilot study on humans:
Sugar Substitutes Linked To Obesity, Nature, 17 September 2014
So his team recruited seven lean and healthy volunteers, who did not normally use artificial sweeteners, for a small prospective study. The recruits consumed the maximum acceptable daily dose of artificial sweeteners for a week. Four became glucose intolerant, and their gut microbiomes shifted towards a balance already known to be associated with susceptibility to metabolic diseases.
Why only 4 out of the 7? Back to The Economist:
Unlike those of mice – animals which are enthusiastic eaters of each others’ faeces, and which thereby regularly swap gut bacteria – the microbiomes of humans differ from one individual to the next, says Dr Elinav. It is a lot to hang on one small experiment, but if the unpleasant effects of artificial sweeteners affect only some people, that could explain why the large epidemiological studies have failed to find that they consistently make people fat.
So, eating sugar resulted in lower blood glucose, and a purportedly lower risk for obesity than eating artificial sweeteners – in mice and in some humans. Do the new soda taxes apply to non-caloric sweeteners too?
Another thought … if something as benign, or thought to be as benign as an artificial sweetener can markedly affect glucose tolerance, what are other chemicals doing?
1 Artificial Sweeteners Induce Glucose Intolerance By Altering The Gut Microbiota, Nature, 17 September 2014