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Monday, February 27, 2012

Sugar ~ Pure, White and Misunderstood

Few of the nutrients in food attract a more negative agenda than sugar. I recall early in my career a famous or, in hindsight, an infamous book entitled “Pure, White and Deadly” written by John Yudkin, then Professor of Human Nutrition at the University of London. Not a year has gone by since then, that sugar and its attendant industry, has not been strapped to the whipping post for a thorough reminder of its evil properties. One of the most recent was a ‘Comment’ in Nature which equated sugar with alcohol as a substance of abuse and addiction meriting the guiding hand of Miss Nanny State to help us free ourselves of its dangers, through tax and other regulatory measures. In relating sugar to alcohol, the first parallel is that there is now unfettered access to a high sugar diet, which according to the authors, is a new phenomenon. They write thus: “First, consider unavoidability. Evolution­arily, sugar was available to our ancestors as fruit for only a few months a year (at har­vest time), or as honey, which was guarded by bees. But in recent years, sugar has been added to nearly all processed foods, limiting consumer choice”[1].   If I got that in an essay from an undergraduate, I would have annotated it with the letters “WTF”. (If you don’t get that, then simply Google it [2].)

The missing bit is somewhere in between “our ancestors” and “in recent years”. Honey, was one of the great luxury foods, bees or no bees, for centuries. Virgil wrote about it thus: “Next I come to the manna, the heavenly gifts of honey…one that can load me with fame”. The God Zeus was fed from childhood on honey. Sugar cane came later but well over 1,000 years ago, first recorded in T’ang dynasty (AD 766 to 790). The first known industrial sugar cane refinery was built on the Greek island of Crete in 1000 AD, the island of Crete being known as Qandi in Arabic, hence the name Candy[3] (bet you didn’t know that)!!!  So sugar didn’t suddenly appear in the last few decades.

One of the problems linking sugar with health is that the term sugar is a chemical term referring to a very specific group of chemicals called “saccharides”: “Any of a series of compounds of carbon, hydrogen, and oxygen in which the atoms of the latter two elements are in the ratio of 2:1, especially those containing the group C6H10O5”. Glucose is the most abundant saccahride and because it is alone, single in the sugar world, it is a monosaccharide. Fructose is next and then we meet disaccharides where sugars are paired off. The most abundant pairing is glucose with fructose and that is what we know as “sugar”, in the sense of the white crystalline material in the sugar bowl. Simple? You would think so but my UK colleagues have managed to create quite a complex issue from this, fortunately not followed by many other countries. Let me explain. Here I am at my breakfast table. In front of me is a bowl of oranges, which contains one less orange that two minutes earlier, since I took one of the oranges, cut it in two and used a manual juicer to extract the juice. That juice is in a glass on my right. Now according to the UK authorities, the sugar in the orange in the bowl in front of me is an “intrinsic” sugar, a natural part of the plant. The fact that I made juice from it means I changed the sugar from being intrinsic to being “extrinsic”, that is a sugar outside its natural plant environment, which now lies in the glass to my right. The UK decision to adopt these definitions was not based on extensive epidemiology, which showed that intrinsic sugars were “good” and extrinsic sugars were “bad”. Rather, it was based on the general negative nutritional view among some (ideological rather than scientific in my analysis) that “sugars are just plain bad” and the need to square that stance with the belief that some foods, which were definitely “good”, such as fruits had sugar in them. So there had to be good sugars  (intrinsic) and bad sugars (extrinsic).

When the epidemiological evidence linking sugar intake to obesity emerged as completely inconclusive, a new concept evolved to the effect that glucose, one item of the sucrose pair, was probably ‘ok nutritionally” (they had little choice here since starch is digested and absorbed as glucose and starch was a very “good” carbohydrate) but that the other half of sucrose, namely fructose was the real culprit.  According to the Comment in Nature, sugar compares almost precisely with alcohol in its effects on humans. In a table entitled “Excessive consumption of fructose can cause many of the same health problems as alcohol” they list conditions such as high blood pressure, heart disease, impaired glucose function, obesity, pancreatitis, liver disease (fatty liver) and addiction (habituation) to chronic fructose intake. Frankly, these are extreme views based largely on (a) the extrapolation of animal studies with extreme diets to humans and (b) association studies in human nutrition epidemiology, which have not been subject to verification with dietary intervention studies. Take one example, chronic fructose intake and obesity. A major study, which reviewed all known intervention studies (n=41 studies) of the chronic effect of dietary fructose on obesity in humans, was recently published by some of the world’s most respected specialists in carbohydrate nutrition, a study fully funded by the Canadian Institutes of Health Research with zero industry funding[4]. I report their conclusion in full: “Fructose does not seem to cause weight gain when it is substituted for other carbohydrates in diets providing similar calories. Free fructose at high doses that provided excess calories modestly increased body weight, an effect that may be due to the extra calories rather than the fructose”. So this independent review of the direct effect of chronic intake of fructose on obesity finds the villain innocent. Will that placate the naysayers of sugar in human nutrition? Not at all. However, I would once again remind them of my favourite quotes to those who resolutely adhere to pet theories. Addressing the Assembled Church of Scotland, Oliver Cromwell exorted them so: “Gentlemen, in the bowels of Christ, I beseech thee, think it possible you may be wrong” or Sir Peter Medawar, Nobel Laureate in immunology who wrote in his book “Advice to a young scientist”: “The intensity with which an hypothesis is held to be true has no bearing on its validity”. And finally, from Professor Rose Frisch, the subject of last week’s blog whose work was always controversial when she was asked how did her work finally reach acceptance, she replied: “Funeral by funeral”!!

Whipping sugar is popular. It makes people feel good, it is good media friendly and it is a joy to ministers for health who would rather discuss anything bar waiting lists.  But it is rooted in atrocious science with one exception, dental caries. Sugar is to be enjoyed and if you’re watching your weight, artificially induced sweeteners are to be enjoyed. My religious friends tell me, that sugar hasn’t yet reached the sinful threshold.

[1] Lustig, RH et al (2012) “The toxic truth about sugar”. Nature, 482, 27-28
[3] “History of Food” by Maguelonne Toussaint-Samat, Blackwell, Oxford
[4] John L. Sievenpiper, et al (2012) Effect of Fructose on Body Weight in Controlled Feeding Trials - A Systematic Review and Meta-analysis. Ann Intern Med. 156:291-304.

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