Toxicity & Aphrodisia – The Chemistry of Chocolate

With Valentine’s Day looming, it seemed an appropriate time to look into the chemistry of chocolate for the latest food chemistry graphic. In particular, here we focus on the two frequently referenced effects of consuming chocolate: its supposed aphrodisiac effect, and its harmful effects on dogs (and to a lesser extent, cats). The graphic gives a brief overview, whilst the text below gives a more detailed picture.

Chocolate as an aphrodisiac

Chocolate has had a reputation as being a potent aphrodisiac for decades – this can be traced back, at least contemporarily, to a psychiatrist at Colombia University, Dr Michael Liebowitz. Liebowitz wrote a book in 1983 entitled ‘The Chemistry of Love’, in which he emphasised the aphrodisiac properties of chocolate, and linked them to the chemical phenylethylamine (PEA).

PEA is a chemical produced naturally in the brain, but also present in relatively high concentrations in chocolate (0.4-6.6 micrograms per gram). In the brain, it acts as a stimulant, increasing the actions of the neurotransmitter dopamine and leading to an elevated mood and feelings of pleasure. It was suggested that, since it was present in significant concentrations in chocolate, PEA could well have an aphrodisiac effect on the brain. However, PEA is broken down, when ingested orally, by the enzyme monoamine oxidase (MAO); this breakdown means that very little PEA will pass into the central nervous system in its unmetabolised form, and consequently it is unlikely that it has any significant aphrodisiac action on the brain.

Another chemical which has been suggested as a possible contributor to an aphrodisiac effect is tryptophan. Tryptophan is an essential amino acid for humans – the body cannot manufacture it, so it must be obtained from food instead. It plays an important role in the synthesis of the neurotransmitter serotonin in the body, which is associated with feelings of well-being. As it happens, chocolate also contains tryptophan, but again it is likely that very little of it remains unmetabolised after ingestion, and therefore it too is unlikely to contribute an aphrodisiac effect. So, it seems that, if chocolate does have any aphrodisiac effects, they’re more likely to be a placebo effect than of a chemical nature.

Theobromine & Toxicity

Theobromine is another stimulant compound found in chocolate; in fact, it comes from the same family of compounds as caffeine, and its structure is very similar. It also acts in a similar manner to caffeine, blocking adenosine receptors in the brain and reducing sleepiness. 100 grams of milk chocolate contains around 200 milligrams of theobromine; the darker the chocolate, the higher the concentration.

Theobromine is, in fact, the culprit when it comes to chocolate’s toxicity. This isn’t a cause for alarm; many chemicals we consume normally are toxic in large amounts, but perfectly benign in the quantities usually consumed, an example of the toxicology adage ‘the dose makes the poison’. In humans, the median lethal dose (the dose required to kill 50% of a test population) has been quoted by some sources as 1000 milligrams per kilogram of body weight. So, for a average human, of say, 70kg, you’d need to consume 70g of theobromine in order to reach this dose, which would work out at 35kg of milk chocolate – unlikely, to say the least. In truth, we don’t really have an accurate idea of the median lethal dose for humans, as no-one’s ever come remotely close to eating enough chocolate at once!

If you compare this to the median lethal dose for dogs, it’s easy to see why chocolate is far more toxic for canines. The figure stands at 300 milligrams per kilogram of weight; assuming we’re talking a relatively small dog of around 10kg, it’d need to consume 3 grams of theobromine to reach this dose, which equates to 1.5kg of milk chocolate. This still sounds quite large, but bear in mind that in dark chocolate, theobromine content can be as high as 600 milligrams per 100 grams, so the figure required to reach the dose here drops to around 500 grams. It’s also worth mentioning that the symptoms of theobromine poisoning (vomiting and diarrhoea) would probably kick in well before this.

So, there you have it: chocolate’s bad news for dogs, and not even likely to have a chemical aphrodisiac effect on them.

Bonus graphic! For Chocolate Week 2015, I’ve added an extra graphic on the cannabinoid compounds found in chocolate, and their suggested effects:

An edited version of this graphic and article appear in the Compound Interest book, “Why Does Asparagus Make Your Wee Smell?”, available now!

Click here to download the graphic as a high resolution PDF.

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

References & Further Reading

• ‘Chemistry in its Element – Theobromine’ – Chemistry World, RSC.
• ‘Chocolate – Food or Drug?’ – K. Bruinsma, Journal of the American Dietetic Association.
• ‘The Poisonous Chemistry of Chocolate’ – Deborah Blum, Wired Science.