Sweetness can be more addictive than Cocaine

14 07 2010

While reading an article by Stephan Guyenet on super-stimuli (such as MSG and excitotoxins), I found the link to a study on a subject that had caught my attention a few weeks ago. In a recent discussion, someone mentioned seeing cases of depression when people began a low carbohydrate ketogenic diet (LCKD). Seems odd, as LCKD may have mood stabilizing properties and may be useful in the treatment of depression.

So what is happening? The first thing that came to my mind was that carbohydrate intake increases the release of serotonin in the brain, which in turn produces a feeling of wellbeing. By lowering or removing carbohydrates from the diet, a disruption of this pattern occurs and depression and adverse effects could appear  (similar to the abstinence syndrome*).

However, an important point is that the feeding pattern of overweight and obese people is not characterized by a high consumption of low glycemic carbohydrates and cardboard-like tasting  foods (such as “healthy” whole grains and cereals). On the contrary, excessive carbohydrate consumption is from sugary and sweet sources. And it seems that the sweet taste is the responsible for addiction to carbohydrates and sugars, not sugar per se.

Food reward shares brain pathways with other pleasurable activities such as sex and drug administration (as well as the same behavioral paradigm with other addictions, like binging, withdrawal, craving and cross-sensitization), and consists of two branches: sensory (gustatory pathway – mediated by receptors on the tongue and the mesolimbic dopamine system) and postingestive (mediated by the metabolic products of the food). When we eat a caloric sweet food (think sodas), we stimulate the two branches of the system, both the sensory and postingestive.

As our genome, the receptors responsible for sweet perception evolved in an environment poor in sugars and probably arent adapted to high concentrations of sweet tastants, like nowadays. This access to high amounts of sugar and sweet could be producing a supra-physiological reward, with the potential to override self-control and homeostasis mechanisms, creating addiction. A chronic intake of foods high in sugar and/or sweet flavors can cause exaggerated release of dopamine (DA) in the nucleus accumbens (NAc) in response to sweet, and a delayed acetylcholine (Ach) satiation response as shown in rats that are dependent on sucrose.

Moreover, behavioral cross-sensitization (defined as an increased locomotor response to a different drug or substance) between a high sucrose diet and low dose of amphetamine has been observed, and sugar and amphetamine seem to share the same mechanism to trigger hyperactivity. This suggests that addiction caused by sweetness occurs through a mechanism similar to other drug addictions: excessive and repeated increases in extracellular DA with subsequent brain adaptation due to chronic exposure, which in turn, raises the dose needed to exert the same effect. In addition, withdrawal of drugs such as morphine, nicotine and alcohol is accompanied by alterations in DA/ACh balance in the NAc; (DA goes down and ACh goes up) and the same effect is seen during withdrawal in sucrose-dependent rats.**

But the study that caught my attention was not referring specifically to sugar, but to sweetness. The authors allowed a group of rats to choose between saccharin-sweetened water (no calories) and intravenous cocaine (a highly addictive and harmful substance). 94% of the rats preferred the sweet taste of saccharin (preference that was also observed with sucrose). Surprisingly, this behavior was also seen in rats sensitized and addicted to cocaine, which, despite increasing the cocaine dose, continued to prefer saccharin. This preference was maintained even when increasing the “cost” for saccharin, so that rats were willing to “work harder” to get it.

Unlike natural sweeteners, artificial sweeteners with no (or very few) calories as saccharin, stimulate the reward system only at the sensory level, and not the postingestive; that is, there is a partial activation of the food reward pathways. The failure to activate the postingestive component may further fuel the food seeking behaviour (and cravings for sweetness). They may also activate the sweet taste receptor in a different manner than natural sweeteners.

Repeated exposure to sweet substances (both caloric and non-caloric) could trigger a vicious and addictive cycle, in which every time a larger amount of sweet is needed. Intense sweetness (even in the abscence of calories) may act as a supra-stimuli to cells, leading to severe cravings for sweet and difficulty to give up these foods ***.

So when going into a low carb approach, some people who are addicted to sugar and sweetness may show withdrawal symptoms, like depression. In this patients, cutting carbohydrates cold-turkey could lead to severe problems.

* Indeed, enhanced responding for sugar has been observed in sugar-dependent rats after abstinence, similar to other drugs of abuse.

** For a more thorough explanation, check this review.

*** This is very important during childhood, where repeated exposure to a particular taste could influence future preferences.

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9 responses

15 07 2010
Dave

Interesting. I wonder if there’s something similar at work with wheat foods? When I talk about low carb with my high carb friends, they seem to be able to handle the idea of giving up sugar, but are absolutely aghast at the thought of not having “healthy whole grain” bagels etc. Blogged about it here:

http://sparkofreason.blogspot.com/2010/05/why-do-you-eat-grains.html

16 07 2010
somatotropin

Hello Dave, it is a really interesting topic. I think it is related to a. Preconceived ideas (as whole grains are healthy) and b. Satiety (by starch and fiber). You feel more satisfied with a starch-rich meal than with other meals.

16 07 2010
Dave

Sure, but WHY do these foods cause a greater sense of satiety? What is the physical mechanism?

17 07 2010
somatotropin

Activation of vagal mechanoreceptors by stomach distension. Satiety is a complex inter-related process, but starch and fiber increase meal volume and intragastric pressure, thus activating volumetric satiation signals.

17 07 2010
Dave

Stomach distension is part of the picture, but I suspect a rather small one in terms of reinforcing feeding behaviors. Otherwise ingesting high energy-density foods would not be preferred over low energy-density foods, e.g. you could eat a whole lot of grass repeatedly, fill your stomach, and wind up starving to death. So I would presume that macro/micronutrient content of food more strongly determines which feeding behaviors are reinforced.

BTW, this is one of the reasons I conjecture (and I emphasize “conjecture”) that fiber cannot be as crucial to health as generally assumed.

18 07 2010
Dave

I’d also guess that “preconceived ideas” need to start someplace and grow. I’ll bet there’s a difference between performing a behavior (eating grains) and avoiding a behavior (eating saturated fat), in that the former requires some internal reinforcement. Many “health” fads have come and gone, but some seem to stick, even when we understand they really aren’t healthy. Cigarettes were once promoted as healthy, now we know better, but still many people smoke. Why? Because nicotine reinforces the behavior.

19 07 2010
somatotropin

Maybe gluten/exorphin/opiate related?

15 07 2010
hans keer

You’re very right Sugar is addictive. Sugar causes, like nicotine, cocaine, speed and alcohol, a strong response in the reward centre of the brain. I wrote a post on the subject too. You can read it here: http://bit.ly/a9SJeB VBR and good luck with this new blog. Hans

26 07 2010
katharine

Have artificial sweeteners been used to wean addicts off cocaine?

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