New polling for the charity Nesta shows that UK adults significantly underestimate the number of calories in popular snack foods, and also don’t realise that small changes in what we eat can have a significant long-term impact.

For the average UK adult, eating 240 more calories per day over the course of a year –⁠ equivalent to a large ‘grab bag’ of crisps –⁠ would lead to weight gain of around a stone (6.35kg). However, three quarters (74.7%) of us underestimate the impact of such small daily changes, with nearly 1 in 10 (9.6%) believing that they would lead to no weight change at all.

“Small changes to our eating habits, if sustained, can make a profound difference,” explains Hugo Harper, Director of Nesta’s health team. “Our environment has a real impact on what we eat, from adverts and supermarket promotions to what’s available in our local corner shop. If we had fewer cues to snack, or were pushed to buy fewer high calorie snacks, we should be able to see real change. Rather than putting the burden on consumers, our food environments need to change so it’s easier for us to eat more healthily. Fad diets and personal calorie counting aren’t the answer, as they tend to lead to short-term weight changes and can be bad for our mental health.”

The data comes from a representative poll of 2,000 UK adults, conducted by Opinium for Nesta, which asked respondents to estimate the calories in a range of popular food and drink items, as well as the annual weight change associated with small daily changes. The fieldwork was done in March and April 2022, before the new calorie labelling legislation was implemented in England.

While most people were broadly accurate at guessing the calorie content of meals and drinks, they significantly underestimated the calories in snack foods including crisps, chocolates and sausage rolls. Pre-pandemic data shows that snacks make up a fifth of all the calories that people eat at home – around 370 calories per day – and the pandemic is likely to have only increased at-home consumption. This figure doesn’t include food eaten outside the home, so the true figure is likely to be closer to 500 calories per day.

“While nobody will be surprised that popular snacks like crisps and chocolates tend to be high in calories, we found that most people tend to significantly underestimate just how calorific they are,” says Hugo. “For example, 95% of respondents underestimated the calories in half a sharing bag of tortilla chips. The average guess was 214 calories, less than half the true value of 447 calories. This sort of difference is significant, as eating 240 more calories per day for a year would cause the average person to gain about a stone.”

In the survey, people were broadly accurate at guessing the calorie content of certain meals and even slightly overestimated the calories in popular fast foods. Nearly half (46%) of respondents overestimated the calories in a Big Mac with medium fries, with an average guess of 1,000 calories compared to the true value of 870. However, 75% of respondents underestimated the calories in a sausage roll, with an average guess of 228 calories for a product that actually contains 328 calories.

“We seem to have a blind spot when it comes to snacking,” says Hugo. “In reality, a big bag of tortilla chips has more calories than a Big Mac and fries, but we think it has fewer than half. With snacks making up a significant portion of the British diet, they present a massive opportunity to improve the nation’s health. When we walk into a shop, snack foods are often promoted, discounted and prominently displayed to push us towards buying them on top of what we actually went in for.

“The soft drinks levy was successful at nudging manufacturers to reformulate their products with less sugar. The upcoming restrictions on supermarket promotions are a welcome step, and we may see some manufacturers making popular snacks healthier in response to the legislation. We’re always looking for interested food manufacturers, retailers, charities and local authorities to test and scale ways to make it easier for people to eat more healthily.”