Portion control: tips from behavioural science

Behaviour Change Adviser at Bupa UK
10 January 2018

Obesity in the UK is at crisis levels, according to the Organisation for Economic Co-operation and Development. It has increased by 92 per cent since the 1990s, with around 27 per cent of adults classified as obese in 2015.

If you’re looking to lose weight, or even maintain a healthy weight, controlling how many calories you eat is essential. Often this will be through being careful with how much you put on your plate– known as portion control. Of course this is no great secret, but it’s often easier said than done. Sometimes resisting that extra scoop of ice cream, or the last slice of pizza, can take what feels like a huge amount of self-discipline.

A portion of fish and chips

This Obesity Awareness Week, I’ve looked into some aspects of behavioural science and portion control. Here are some ideas as to how you can tweak your habits to try and reduce your daily calorie intake.

Portion control and the ‘portion size effect’

Did you know that the amount of food you eat can be strongly influenced by the size of the portions you’re given? One scientific review in 2014 brought together the findings of many other studies on this. It concluded that – when it comes to shops and food outlets such as restaurants – larger portion sizes lead to an increase in the amount eaten. The reasons behind this aren’t clear, but it does seem as though we tend to just finish what we’re given, rather than considering the size and potential calorie content of what’s put in front of us.

On top of this, food outlets are serving increasingly larger portions. So you don’t always have control over how much food is on your plate. In the US, The Centre for Disease Control and Prevention estimates that the average restaurant meal is now more than four times larger than they were in the 1950s. So it’s no wonder obesity is such a rising problem.

Another study has suggested that even if you’re made aware of this ‘portion size effect’, it doesn’t necessarily mean you’ll make better choices. So reading up to this point probably won’t help you!

Use your imagination

It may seem strange, but one study has suggested that imagining or visualising eating your food, before your start eating, can help with portion control. This is because it can actually reduce the portion size effect I’ve just described. Participants were told to imagine in a lot of detail the experience of eating their whole food portion. This included not just the taste, but the feeling of the food in their mouth, how it looked and smelled. They then appeared to be satisfied by smaller amounts of food, regardless of the size of the portion they were actually given.

So when you’re waiting for your food in a restaurant, or heading home to cook your dinner, why not give this a try? Take some time to really imagine and anticipate the experience of eating. You might just find it’s then a little easier to eat less!

Don’t get stuck in the middle

When we’re presented with choices, we have a tendency towards choosing the middle option. This is called extremeness aversion – sometimes known as the ‘Goldilocks effect’. This phenomenon comes into play when we’re choosing portion sizes. Think how often you’ve been in a fast-food restaurant or coffee shop and pondered whether to go for small, medium or large (or ‘primo, medio and massimo’).

In 2008 a study was carried out in a McDonald’s. Some customers were offered drinks in portions of 12, 16 and 21 ounces. Others were offered 16, 21 and 32 ounces. Both sets of customers gravitated towards the middle option, even though the middle option for the first group of customers was the same as the small option for the second group. This suggests they weren’t making their decisions based on the actual size of the serving, but on where it fell on the scale of available options.

So the next time you’re weighing up your options at a fast-food outlet, coffee shop, or when getting your movie popcorn, stop and consider this Goldilocks effect. Look closely at the sizes and actively exercise portion control, rather than subconsciously opting for a medium. If the sizes aren’t advertised, ask about them, and see if you can find out the calorie count as well. You may find that a‘small’ portion is enough to satisfy you.

Read between the lines

European Union rules mean that most pre-packaged food sold in the UK must display key nutritional information on it. So we’ve become used to seeing small tables of data, claims of being low in certain substances, or the traffic-light systems that some supermarkets use. In theory we should be more empowered than ever to make informed choices and control our portions well.

But sometimes this information can be confusing, or even appear to be misleading, especially when it comes to portion sizes.

For example, something could be labelled ‘no added sugar’, but still be high in naturally occurring sugars, meaning it’s not as healthy as you’d thought.

Or take breakfast cereals for example. Many will base their nutritional information around a portion size of 30g. Not only will you be surprised how small this is (try it at home!), but it may also be at odds with the image on the front of the pack. Think how many times you’ve seen a picture of a bowl overflowing with cereal and milk ... you’d be hard pushed to find a bowl too small to hold a 30g serving.

Another favourite is displaying nutritional information for only a proportion of the product, when you’d think it would be for the whole thing. For example, a chocolate bar or cereal bar might be made up of two or three biscuits, but the nutritional information for only one biscuit is shown on the label.  Or if you look closely you’ll see that the nutritional information displayed on some oven pizzas is actually just for half the pizza.

All of the above can undermine people’s attempts to make healthy decisions when it comes to choosing products and portion control. But being wise to these tricks of the trade may help you during your next shop. If you’re tempted by a new product, look closely at the nutritional values, and keep in mind the standard portion sizes for different foods. 




Do you know how healthy you truly are? Bupa health assessments give you a clear overview of your health. You’ll receive a personalised lifestyle action plan with health goals to reach for a healthier, happier you.

Juliet Hodges
Behaviour Change Adviser at Bupa UK

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