8 February 2011,
 1

I am starting to feel like the whole wide world has simplified obesity into a case of Pavlovian conditioning, whereby we simply engage in some kind of See-Food-Eat-It reflex. I feel that this age old adage needs at least little bit of resistance, particularly because…well.. humans are nothing if not incredibly, amazingly complex.

How do we choose how much to eat?

Weingarten (1983) argued that normal meal-control involved an interaction between internal regulatory and learned cues, with external cues relating to food availability promoting both meal initiation and to some extent the size of meals.

So, the food environment has changed drastically since 1983, and we are seeing a leap in obesity. This illustrates the role the environment has on food intake.

But what else? How do we decide what to eat? What does it mean to be full? Can aspartame be used in food, or will we ravenously crave more calories if we incorporate this additive into our diet (a claim made by many a holistic nutritionist, a claim I find a little reductionist. The short answer on the aspartame issue? It’’s complicated).
So, now, I am going to tell you a story about why.

Wild Strawberry and Fresh Banana Porridge

Years ago, before I started my PhD, I was assigned on to a research project to investigate human learning and food preferences. In one of the investigations, we were required to compare how much participants ‘liked’ a novel food, and if they could learn to eat more of it after experiencing it a few dozen times. In many ways, we incubated the idea that exposure-leads-to-consumption, but instead of assessing this in children, we were doing it with grown men. It meant we had to get creative with the food they were eating, in order to determine: can food sweetened with aspartame be as filling as food sweetened with sugar? Also, do we prefer food with sugar or aspartame?

Two interesting questions, no doubt.

The trick with understanding why people eat something, is to try and emulate as novel a situation as possible. In essence, create foods that are so odd, the dependent variable of how much the person ate, has everything to do with how the food tastes, and nothing to do with prior experience. Problematically, we all have variations on the theme of: ‘When I was five, I burnt my mouth on this flavour, so I don’t like anything with it anymore’, or, adult onset 24 hour flus that are paired with a certain food type – you catch my drift. Basically, we had to create a brand new food. From scratch. No recipes!!

You can imagine how much fun it is to create absolutely new foods. If you are eccentric and open minded (yours truly) it is hilarious. If you are obsessed with precision and order, it can be a bit tedious (my world-wary PhD lab mates at the time). So, while I was delighted with the possibility of talking to the kind representatives of Firminich (a Swiss flavour company) for hours, my lab mates were busy in the lab making fish flavoured ice cream, amongst some other gastronomic gems.

The ‘novel food’ we finally settled on, was wild strawberry oatmeal, with a bright yellow colour, and ripe banana oatmeal in bright pink (We didn’’t want to colour the banana in yellow, in case anyone recognized the flavour. Trust me, with enough sugar/aspartame and oats; the banana-ness of something definitely changes. Ditto for wild strawberry). So here we are with two very weird foods, we had to make sure to record whether they were sweetened with sugar or with aspartame, and we also tested two different volumes of oatmeal: 150 g versus 300g.
NB: Bless all of the people in this study who were forced to eat 300 g of banana porridge three days a week, all those years ago. I’’m still not sure if the reimbursement payment really compensates for the experience, but I guess it’’s not worth the debate now.

Back to the porridge.
What flavour was the most popular?
Was sugar or aspartame more popular?

The short answer: we saw a U-shaped curve. Basically, in the case where participants were forced to eat 300 g of Banana/Strawberry porridge (SUGAR), when we let them eat as much as they’’d like, they responded by not eating very much. However, when the other participants in the 150 g (SUGAR) condition were able to eat as much as they’’d like, they responded by eating a lot.

A similar situation happened with the aspartame flavoured porridge but in reverse: people in the 300 g condition ate a lot more volume than in the 150 g condition.

So basically, participants in the 300 g Aspartame condition, and participants in the 150 g Sugar condition ate the most. The critical difference? Calories taken in. In the Aspartame condition (even in the huge bowl of porridge) participants ate significantly fewer calories. They consumed a lot of volume, it was very sweet food, but they did not eat nearly as ‘much’ in terms of energy density. None of the participants were aware of the flavour differences in terms of aspartame versus sugar, either.

The current post was started by investigating why we eat or how we decide: how much should I eat. The data here show us that it’’s not just a case of See Food Eat It: if so, we would have seen all participants in the sugar conditions eating more, and liking it. Instead, we see that aspartame can play a role in reducing the caloric density of a food, unbeknownst to the consumer.

While this is certainly not the last word on the inclusion of aspartame, and the debate will continue for quite a while, here is some empirical data showing that artificial sweeteners, paired with a new flavour, can help you to eat less (in terms of calorie density). It’s an interesting message for the food industry, particularly as we move towards making foods that are lower in calories – people still rated the aspartame foods as pleasantly as the sugar-flavoured foods.

These kinds of novel interpretations of the drivers of human appetite are going to be vital if we are to change the obesity situation. If food was lower in calories, the whole ˊSee Food Eat Itˊ wouldnˊt be such a problem, but as this post demonstrates, the issue of quantity is also a key driver in learning food preferences. Maybe we can start to adapt studies like this into learning how to truly curb our caloric intake without feeling psychologically punishing effects.

Purple porridge in the mean time?
(Yeomans, Gould, Leitch, & Mobini, 2009)
Weingarten, H. P. (1983). Conditioned cues elicit feeding in sated rats: a role for learning in meal initiation. Science, 220(4595), 431-433.
Yeomans, M. R., Gould, N. J., Leitch, M., & Mobini, S. (2009). Effects of energy density and portion size on development of acquired flavour liking and learned satiety. Appetite, 52(2), 469-478.

One response on “How Much Should I Eat?

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