Thursday, September 3, 2009

Who says artificial sweeteners don't help you lose weight?

 Is the love-affair over?
So who is saying that artificial sweeteners don’t help you lose weight?

Answer : Professor Soraya Shirazi-Beechey, who is a veterinary science researcher at the University of Liverpool.  She claims that "our bodies cannot distinguish between them and sugar."  So what's wrong about that, you might say?  We all know that artificial sweeteners - saccharine, aspartame etc - are no magic wands. But is the body totally fooled,  indeed traduced by them, even in the lower regions of the small intestine, as she claims?

Well, see the article by Chris Irvine in today’s Telegraph (Health Section) and judge for yourself. To say I read it with a growing sense of incredulity, indeed bafflement, would be a gross understatement. Little if any of it makes sense to me.

Let's  begin with the statement that “artificial sweeteners do nothing to help weight loss”. It does not appear to be a  finding of the Professor’s research. Indeed, from googling her other work, it would appear to be more by way of an article of faith.

Whilst I’m no expert on weight loss strategies – and am fighting a losing battle – that statement offends the most basic scientific principles. If somebody is on a dietary regime that just maintains body weight, and they then replace the sugar in that diet with artificial sweetener – then they are almost certain to lose weight, since their calorie intake is reduced. Now the cynics or defeatists may say differently, claiming, for example, that sweeteners increase one’s appetite for real sugars. But that does not permit the bald statement that artificial sweeteners do nothing to help weight loss. We all know, or should know, that any slimming aid has to be  part of a “calorie-controlled diet”.  We are constantly warned about that on the side of food packaging.

She then says that our bodies cannot distinguish between the sweeteners and sugar. Here’s where it starts to get scientifically a bit complicated, but bear with me, and see if you can follow the lady’s chain of reasoning.

We have at least two different sensor  locations for real sugars - sucrose, glucose etc - in our bodies. One is in the taste buds,  which detect “sweet”. These we know can be fooled, so that an artificial sweetener, with a chemical structure entirely different from real sugars, registers as “sweet”, making that cup of coffee more appealing to those of us with a sweet tooth.

But there's another place too -  down in the intestine -  where we have clever systems in the wall of the gut  concerned with selectively absorbing sugars into the blood stream. The important one where this post is concerned  deals with ordinary cane sugar ie “sucrose”, in our diet. There is an enzyme in the wall of the gut that recognizes and binds sucrose, and then cleaves it into two halves – glucose and fructose. There is then another system that recognizes and binds these sugars and then transports them across the wall of the bowel into the bloodstream. The glucose transporter works in conjunction with sodium uptake, and is called the sodium-dependent glucose transporter.

So where does the Professor’s research change our picture of this well-established digestive physiology?  She claims to have found yet another system in the bowel comparable to the one in our taste buds that recognizes “sweetness”.  In other words it  is activated not just by natural sugars but by artificial sweeteners. She herself has described that as “surprising”. Indeed, it is surprising. What’s a receptor for one’s perception of whether food is nice to eat or not doing way down in the bowel?  Down there one would expect molecules to be recognized purely by size, shape, chemical make-up – nothing so subjective as taste.

Now here’s where things start to get really bizarre. The prof' says that these new sweetener receptors are the reason why sweeteners don’t allow us to lose weight. She claims that the sweetener receptors fool our ordinary sugar-transporters into thinking there's an abundance of real sugar about, and send a signal to our sugar-transporters to work more efficiently. End-result – we absorb more glucose and other sugars from the diet than we normally would. Result: the sweeteners make our bodies more efficient at absorbing sugar calories, with the result that we fail to lose weight, and indeed are at risk of putting on weight

Hold on a minute. There’s a weak point in that argument – and that’s all it is – an argument – a far cry from doing  scientifically-controlled experiments.. It’s the assumption that sugar absorption from the gut is inefficient in normal individuals, and that sweeteners improve that efficiency.

Well, I personally know of no evidence that we are inefficient at absorbing sucrose. OK, it may not be 100% efficient – small amounts may reach the lower bowel where it would be fermented to hydrogen, short chain fatty acids etc. But if sucrose were just 95% absorbed,  with a "mere" 5% reaching the lower bowel, we would quickly know about it to our gross discomfiture, with bloating, wind, intestinal cramps – in other words all the symptoms suffered by those with the distressing and socially-embarrassing  "malabsorption syndromes".

Sorry, Professor , but your story does not make sense. To be honest, there seems to be just a little science, and a whole lot of conjecture. What’s more, it’s conjecture in an area in which consumers are already bombarded with a lot of conflicting information from scientists and health professionals. Someone has to act as watchdog. Who better than a retired biochemist/nutritionist with time on his hands? I would send a brief critique to the Telegraph, but there’s unfortunately no facility for doing so. But there is this ability now to attach comments and critiques to Google links. Tally ho!

PS   The Mail has opened a thread on this topic 

Update Sun 5th September. Who says that personal blogs are a waste of time, unless one is besieged daily by comments?

I've just been googlin', and find my humble observations as a "retired biochemist/nutritionist" have been picked up across the pond by an Atkins Diet/Low Carb forum.  Here's what "OregonRose" has to say:

"A few thoughts:

First, is this "real" research? There doesn't seem to be an actual paper or published findings associated with Shirazi-Beechey's alleged research; it's somehow "on display" at a Food Museum. That doesn't sound too awfully rigorous to me, although I might not be qualified to judge that. Also, in the articles I Googled up on her (Soraya Shirazi-Beechey + artificial sweeteners), I found lots of sound-bitey quotes from her but no mention of actual experiments and actual results. And there's this guy, a retired biochemist/nutritionist, who takes issue with what he labels her bald assertion, noting that there doesn't seem to be any experimental data to back up her claim:


Second: As to the problem of where the "extra" absorbed glucose in a low-carb diet might come from--assuming for the sake of argument that her claim might have merit--what about glucose generated by the liver from protein? Supposing she's right, maybe somehow AS prods the liver to produce more?

And finally, the whole claim sounds weakly supported to me. Sure, I think avoiding AS is a good idea in general, along with any other frankenfoods, since we just don't know enough about them (heck, we know barely anything about our own physiology, and here we as a species are throwing hundreds of thousands of years of accumulated food wisdom away and eating who knows what...). Nevertheless, during my first year of LC, they helped assuage many a dessert craving, and I'm glad they were available."

I'd have left a comment, but not only is the site not open to those who are not registered, but I'm fundamentally opposed to the Atkins diet - not because it doesn't help lose weight - it almost certainly does - but because I consider it to be  misconceived - biochemically, physiologically and medically. The Atkins diet takes a huge liberty with one's cellular biochemistry - the subject of a forthcoming post.


Fazila said...

Non-caloric artificial sweeteners such as stevia, saccharin and aspartame can help with weight loss, simply because they contain no calories...


ColinB ("sciencebod") said...

I can't disagree with that, Fazila. Provided the artificial sweetener replaces sugar, and is not being used as a psychological crutch ("I use sweeteners in my tea and coffee, therefore I'm allowed an extra spoonful of sugar on my cornflakes").

Thanks, btw. Yours is the first real comment on my now blog :-)

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