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Wednesday, October 2, 2013

Food addiction: Myth or reality

Animal models appear to show that certain foods (usually the so-called “high-fat, high-sugar and high-salt foods) can be addictive. However, this experimental model of addiction bears no relationship to addiction in humans. In his book “An End to Over-eating”, David Kessler comments on this animal model of food addiction, one he incidentally finds attractive to human obesity. Citing work from Italian researchers, which showed that in the short term, a cheese flavoured snack food increased levels of dopamine in rat brains he writes thus: “Over time, habituation set in, dopamine levels declined and food lost its capacity to activate their behaviour. But there’s more to the story. It turns out that if the stimulus is powerful enough, or administered intermittently enough, the brain may not curb its dopamine response after all. Desire remains high. We see this with cocaine use, which does not result in habituation”. Effectively one can trick the mouse and then make a quick jump to human cocaine addiction. Simple isn’t it?

Not so, according to a recent review by researchers at the Department of Psychiatry at the University of Cambridge[1],[2] In their review, they begin by distinguishing between behavioural addiction such as gambling, which doesn’t have an additive agent (betting slips per se are not addictive) and substance addictions, which are agent-dependent. Alcohol and cocaine are examples of agents that can be addictive. Thus the first challenge to the food addiction model is to identify the agent. It can’t be “fat” since effectively a totally fat-free diet is lethal to populations – reproduction becomes impossible. It can’t be “high-fat” since olive oil, the elixir of all our ailments according to many, is pure, 100% undiluted fat ~ the real thing. The normal brain relies solely on glucose as a fuel so if “sugars” are the agent, we have a problem. If it’s a specific cocktail of fat-sugar-salt, then that needs to be articulated in terms of the human diet and as of now, no such norms exist, let alone exist in some unproven state. So the putative addictive agent in food is utterly ill defined. The authors go on to point out that the so-called addictive hyperpalatable foods are widely available and widely consumed but as yet, are not a widespread public health problem. Thus they argue that in addition to some vague and as yet undefined cutoff above which addiction may occur, they will have to find other factors to explain why some people might become addicted whereas others will not. It could be a genetic factor or an addiction, dependent on alcohol intake, or on a sedentary life style or on stature or age or gender or all of the above. The concept of food addiction, particularly in relation to obesity might be popular with the wannabe celeb scientists but it is as imprecise a concept as one could possibly imagine.

 The clinical management of addiction uses a standardised guideline to define substance dependence based on the “Statistical Manual of Mental Disorders, fourth edition (DSM-IV)”. There are 7 criteria to be considered within this tool, all of which help in judgment on addictions. The first deals with “tolerance” and specifically the need for the user to seek ever-increasing amounts to reach the desired level of intoxication. This is impossible to apply to food addiction since we know neither the exact agent or its dose or its physiological, genetic, social or lifestyle dependencies. The second relates to withdrawal symptoms and no such data exists for humans and their food habits. The manual refers to symptoms such as shakes and sweats! The third is a persistent desire for and unsuccessful attempts to cut drug use. Overweight persons certainly wish to rid themselves of excess fat and try repeatedly to do so but linking this concept to a specific and putative food addiction agent is not supported by scientific data. The fourth describes the taking of larger amounts of the drug than intended. This is impossible in food since we don’t know the agent or its intoxicating dose. The fifth recognises that a great deal of time is spent getting, using and recovering from the drug. Take a walk in Tesco or Wal-Mart! The sixth deals with the effect the drug has on the pursuit of important social, occupational or recreational activities.  It’s hard to think of work absenteeism arising from the pursuit of highly palatable and putatively “addictive” foods. The seventh and final area deals with the continued use of the drug with the user well aware of its dire consequences for health and social well-being. Again, it is impossible to see how this can apply to food.

The authors do however, point out that certain eating patterns are nearing the DM-IV criteria, most specifically Binge Eating Disorders (BED) which they say is characterized by: “ …recurrent episodes (‘binges’) of uncontrolled, often rapid consumption of large amounts of food, usually in isolation, even in the absence of hunger. This eating behaviour persists despite physical discomfort and binges are often associated with feelings of guilt and disgust”. This is the closest that psychiatrists see food as approaching addiction but researchers in Yale are working on an adaptation of DSM-IV to score and quantify food addictions[3]. This blogger’s read of this adaptation of the DSM-IV clinical guidelines is that it will be quite significant adaptation, if not a total re-write. Like it or not, this will sustain the nutrition-psychiatry gulf in understanding and characterizing addiction.

Food addiction has now begun to attract the interests of other groups, most notably the legal & ethical researchers[4]. If, and it is a big if, research were to point to a possible addiction among some to a particular food or nutrient or cocktails thereof, then how do we deal with this legally? Do we expect to see certain foods removed from the supermarket shelves and driven into the underworld of dodgy dealing such as the illegal cheesecake (high fat, high, sugar, High salt food par excellence) the Cambridge scientists refer to? Of course this is farcical but where else would a regulatory and policy framework go to tackle this problem, if indeed, such behaviour is deemed to be a problem in the first place?  For those who want to explore this further, watch the You Tube video of a stand up comedian (lead author of references 1& 2 above) who is also a board certified psychiatrist on the subject of food addiction[5].

[1] Ziauddeen H & Fletcher PC (2013) Obesity Reviews, 14, 19-28
[2] Ziauddeen H et al (2012) Nature Neuroscience, 13, 279- 286
[3] Gerhardt A et al (2009) Appetite, 52, 430-436
[4] Gearhardt A et al (2013) J Law Med Ethics. 41 Suppl 1:46-9

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