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Friday, July 4, 2014

Sugar addiction: The myth re-visited

I have previously blogged on the myth of sugar addiction[1] but I return to that subject today on foot of some recent publications. The first is a chapter in a new book on sugars and health and the section that attracted my attention was an explanation of the rat studies, which first suggested that sugar was addictive[2]. The late Barley G. Hoebel carried out these studies. Rats were given either a 24-hour access to a 10% sugar solution or a 12-hour access to the same solution. Both groups of rats had access to a standard rat diet, perfectly balanced for the nutritional needs of this species. Rats live with a “dark” and “light” cycle of about 12 hours each and it is only during the dark period, when the lights are switched off, that rats eat. In this particular study, the rats in the 12-hour arm of the experiment, only received their sugar, some four hours after the start of the dark cycle. It was well known that if during this dark eating cycle, a rat is deprived of food for the first few hours, then, when presented with the food, the rat will gorge itself on the food and will fully compensate for the period of denial. So when the rats were offered their 10% sugar solution, having spent four hours without access to this highly palatable food, they did precisely as predicted: they gorged.  In fact, during this period of gorging, they amassed 30% of all their daily calories. Thus, without knowing the subtleties of rodent dining protocol, one would happily conclude that when rats were given a sugary solution for a limited period of time, they behaved like alcoholics let into a free bar after a period of booze restraint. Now what about the rats that had access to this sugary solution over a 24-hour period? Well, they consumed exactly the same amount of sugar as their binging, apparently addicted fellow rats that had just 12-hour access. And just to cap it all, neither group of rats went on to become obese as they simply reduced their intake of the standard rat diet. The “addicted” rats showed all the classic neurological signs of addiction including opioid withdrawal when the sugar is removed or when they are treated with opioid blocking drugs. However, the relevance of these studies to humans using this bizarre model is zero.

Which brings me to the second study led by Professor Gary Frost from Imperial College London[3]. This study used the Yale Food Addiction Score  (YFAS). Most criteria to measure addiction are based on clinical models but the Yale version is specifically designed to examine the hypothesis of food (fat and sugar) addiction. The researchers conducted a weight loss intervention study in 178 severely obese subjects (mean BMI of 36.1 kg/m2) taking part in a weight loss programme, which used behavioural therapy to reduce body weight over a 6- month period. They hypotesised that those patients that showed signs of food addiction according to YFAS would be the least successful in weight loss and that significantly more of those with food addiction would drop out. Both hypotheses were shown not to be valid. There was no difference in weight loss between the two groups and there was no difference in attrition. This is by far the largest study to examine food addiction in relation to weight loss.

Consider a study in which alcoholics and social drinkers are compared for their ability to abstain from alcohol or to minimise their alcohol intake. The predicted outcome would be that the alcoholics would fare much worse because their addiction to alcohol is so strong. But that doesn’t happen with this measure of food addiction. In all, some 15% of subjects were declared food addictive at baseline which tallies with the general range seen among the obese population seeking treatment (15-20%). Their “addiction” to food as measured by the Yale scale is so weak that it is simply over-ridden by a behavioural therapy programme.

All in all, while the concept of food addiction might seem attractive, the biology just doesn’t stack up. But, in the area of public health nutrition, why lets the facts spoil a good media story!

[2] Are Sugars addictive? Perspectives for practitioners, by Rebecca LW Corwin and John E Hayes in “Fructose, High fructose corn syrup, sucrose and health, edited by James M. Rippe and published by Humana Press (2014) 
[3] Lent MR et al (2014) Obesity, 22, 52-55

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