Yule tired
So, Christmas was fun, right? It’s always filled with lights hearts and good humour! And the food – turkey is such a surprise and so creative and delicious! If, at this stage, you are nodding, then you may very well be in a minority. We know that family tensions increase at Christmas, and so do suicides. For whatever reasons, many of those who celebrate Christmas day without the company of their parents or extended family view themselves as having a lucky escape. It’s not about being in the depths of winter either. Those in the USA sensibly organize their Christmas meals in early November to coincide with the date when local indigenous tribes took pity on the local settlers from England, recognizing that they were Puritans and hence unlikely ever to organize their own celebrations. If you are raised in an Anglo-Saxon culture in the southern hemisphere, it is even worse of course. A huge winter meal during a 35oC day is not culinary experience one dreams about. And yet it is commonplace, and produces similar emotional consequence.
Of course, children love Christmas – there’s lots of colour and movement, there are presents to break, and lots of cakes, puddings and pies to ramp up blood sugars to maximum. Sometime around puberty, though, the presents start to become less exciting (more Lego …. great!) and there comes a belated realization that the food is most likely exactly what it was last year and at every previous Christmas. In Victorian times and in northern hemisphere winters there was probably nothing nicer than tucking into a goose (where’s the meat?) or turkey (is it really meant to be this dry?). But does anybody really now look forward to such foods that we could eat at any time of the year, but interestingly choose not to? And let’s not forget the groans that commence after the meal. Who’s more stuffed – you or the turkey?
This brings me to the point that popped into my own head during a recent mince pie and Madeira binge. We have a pretty good idea of how food preferences are formed (if you don’t, may I recommend [1]), namely through different forms of associative learning following a small number of innate preferences and dislikes present at birth. It is pretty easy to see how children would learn to love the Christmas feast. But let’s look at the context for the meal, since we know that this is an important factor in preference development [2]. Given the unreasonable expectations of the day, the family feuds, the obnoxious drunk uncle, the disappointing presents, why do we clearly want to eat the same foods again and again?
Perhaps it’s comfort food? (see: Tastes Like Home) Certainly, that might be part of it, but why isn’t this undermined by the often uncomfortable context and the questionable gastronomic qualities of the food itself? If emotions are so important in determining food preferences [3], why don’t Christmas family feuds produce food dislikes?
In fact, we know far less about acquiring food dislikes than we do about how our preferences are formed in the first place. And one good reason for this is that … perhaps surprisingly … acquired food dislikes are not very common. Of course, pairing flavours with illness produces long-lasting ‘taste’ aversions, but this accounts for only a small fraction of the foods people say they don’t like. The effects of dietary monotony or boredom with particular foods are well known [4], but this seems to be about regularity of consumption and not the development of an actual dislike. Something similar occurs during a meal (sensory-specific satiety) when the first sip or bite of a food tastes best.
When we consider most food dislikes we are really talking about those foods that either haven’t been tried more than once or that are disliked for purely moral or cognitive reasons such as meat for a vegetarian (or tofu for everyone else). It becomes quite difficult to acquire a food dislike once it has been regularly eaten and a preference has formed because the body has learned through these eating occasions both that the food will not poison us and also that it carries calories or some other valued nutrient. Even ‘empty calories’ are still calories.
The learning processes through which food preferences are formed are known as evaluative conditioning (EC). EC is much like classical (aka, Pavlovian) conditioning (CC) in that it involves pairing of something neutral with something to which we already have a like or dislike. The effect is to make the neutral thing into something that evokes a response. So, the sound of a bell paired with an electric shock repeatedly leads to the bell eliciting a response as though a shock were about to be delivered, initially even when the shock is removed. Similarly, a novel flavour paired with sugar produces a liked flavour. Pairing flavour with bitter tastes might be expected to produce dislikes, but if we do this often enough then the food’s energy will offset this effect and increase liking for the flavour (known as post-ingestive or flavour-calorie learning).
One of the few ways in which EC and CC differ may account for the relative lack of learned dislikes. When the pairing is stopped, a process known as extinction (n CC) occurs. Having established that the bell is a useful signal for an upcoming shock, repeatedly presenting the bell without the shock will eventually lead to a recognition that it has stopped being a good signal and there’s no point in responding as though a shock were about to happen. In contrast, once a flavour has been paired with a liked sweet taste it remains liked, even if it is never (as far as we know) again paired with sugar [5]. Your first thought will be that it’s all down to the relative importance of these processes to survival. Unfortunately, this doesn’t work. EC occurs not just with food flavours but even in cases where there is no survival advantage (e.g., pairing a like picture with one that is neutral); conversely, predicting that red lights signal oncoming traffic clearly helps avoid an untimely demise.
There is some very limited evidence that post-ingestive learning – that is, a flavour paired with calories – can extinguish. In one study with humans, considerably reducing the energy content of a familiar, preferred meal led to a pronounced decline in liking over repeated eating occasions, as compared to the same meal without the energy reduction [6]. This seem s to suggest that, as with CC, the participants in the study were learning something new about these food flavours and their ability to signal upcoming energy.
But in the absence of low-cal turkey and pudding, it appears we are stuck with our Christmas preferences and food habits. Which suggests very strongly the power of early learning against anything that the adult yuletide experience can throw at it.
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1. Prescott, J., Taste Matters. Why we like the foods we do. 2012, London: Reaktion Books.
2. Meiselman, H.L., et al., Demonstrations of the influence of the eating environment on food acceptance. Appetite, 2000. 35: p. 231-237.
3. Spinelli, S., et al., Emotional responses to branded and unbranded foods. Food Quality and Preference, 2015. 42: p. 1-11.
4. Meiselman, H.L., C. deGraaf, and L.L. Lesher, The effects of variety and monotony on food acceptance and intake at a midday meal. Physiol. Behav., 2000. 70: p. 119-125.
5. Baeyens, F., et al., Once in contact always in contact: Evaluative conditioning is resistant to extinction. Advances in Behavioural Research and Therapy, 1988. 10: p. 179-199.
6. O’Sullivan, H.L., et al., Effects of repeated exposure on liking for a reduced-energy-dense food. Am J Clin Nutr, 2010. 91: p. 1584-1589.
