Wednesday, 17 April 2013

Low calorie sweeteners

Gilded sculptures of skeleton cutting thread of life for unfortunate mortal
Asamkirche, Munich, March 2013
We often recommend to people with diabetes that they limit their intake of sugar, but that artificial sweeteners can be used in their place. In fact, I discovered following a bit of research that there are more categories of sweeteners than I had thought, including fruit sugar (fructose), nutritive and non-nutritive sweeteners. And that the advice to avoid sugar may not actually be valid. I haven't yet got the complete picture and I certainly need to do more investigation to understand the claim (by Diabetes UK) that, if the same total amount of carbohydrate is consumed, then "sugar does not raise blood glucose levels any higher than starch."

Fructose is only slightly slower to be converted into blood glucose compared with sucrose, but usually comes neatly packaged inside fruit which has many obvious benefits. Granulated and refined fructose, however, is comparable with sucrose. Nutritive sweeteners are polyols (sugar alcohols), including sorbitol, maltitol, xylitol, isomalt and mannitol. They contain fewer calories than sugar and are better in terms of dental health, but are generally not absorbed consistently from the gut into the bloodstream. This has two consequences: firstly, it is more difficult to estimate their effect on blood glucose and therefore to administer the correct dose of insulin. Secondly, as they are not fully absorbed, then they pass on through the gut causing flatulence and producing a laxative effect.

These nutritive sweeteners are often used in 'diabetic' products, which is why we generally advise people to steer clear of those. As an aside, Diabetes UK is now calling for an end to food labelling as 'Suitable for Diabetics,' saying that it is misleading, since a report from the European Commission in 2008 states that there is no role or benefit from the use of diabetic foods, and specifically:
  • There are no grounds for developing specific compositional requirements for foods intended for people with diabetes;
  • People with diabetes should be able to meet their dietary needs by appropriate selection from everyday foods; so
  • There are no grounds for especially formulated foods for people with diabetes to manage their condition.
But I digress.

There are now five different chemicals that are commonly found in artificial (non-nutritive) sweeteners: aspartame, sucralose, acesulfame K, saccharin and stevia. In the supermarket aisles, you will find Canderel, Splenda, Sweetex, Hermesetas, Sweet & Low and Truvia as well as Silver Spoon, Tate & Lyle and supermarket own brands. There are tablets and granulated sweeteners, types designed for baking, and 'half-and-half' sugar if the transition to sweetener is a step too far. It should be possible to find something palatable.

Sometimes there is suspicion: wasn't there a report about rats getting cancer? Are sweeteners really a suitable replacement for sugar? The European Food Safety Authority (EFSA) has been tasked with reviewing all food additives for safety by 2020.  They were asked to review aspartame as a priority; their report was published in January 2013 and can be found in full on the EFSA website (ref 2013-EN-399). The following highlights are quoted directly from that report.
  • Aspartame is classified as additive E 951. 
  • The molecular shape of aspartame stimulates our taste bud receptors in a similar way to sugar, so we perceive the taste as sweet, but in fact the molecule is broken down to aspartic acid, phenylalanine and methanol in the stomach and gut before absorption. So the actual aspartame molecule does not reach the bloodstream (oral bioavailability is zero).
  • No significant acute or subchronic toxicity has been observed in animal models even at the highest doses of aspartame which could reasonably be administered. 
  • Epidemiological studies have not identified any association between brain tumour incidence and use of aspartame.
  • It is suitable for pregnant women.
So aspartame was found to be safe. And, presumably in response to some other hypothesis, the EFSA review also states that "intervention studies have consistently failed to demonstrate that low calorie sweeteners promote weight gain."

Safe as it is, an Acceptable Daily Intake (ADI) still has to be specified. This has been set at 40 mg per kg body weight per day, which for a person weighing 70 kg (11 stone or 154 pounds) would equate to 140 level teaspoons of sugar. This daily amount would be equivalent to 12 x 330ml cans (4 litres) of diet soft drink containing the maximum permitted amount of aspartame, or 36 or more cans (12 litres) at the usual concentration in diet soft drinks on sale.

Of course, there is one significant proviso - people with the inherited metabolic disorder phenylketonuria need to restrict their intake of phenylalanine, so they should definitely avoid aspartame and aspartame-containing products. The rest of us can do as we wish.

Low calorie sweeteners: Their safety, role in the diet and route to the supermarket shelf, Complete Nutrition Vol. 13 No. 1, Feb/Mar 2013
Review of data on the food additive aspartame, EFSA, 8 Jan 2013 (2013-EN-399)
Position Statement on Sweeteners, Diabetes UK, July 2007
Position Statement on 'Diabetic Foods', Diabetes UK, March 2013

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