Why your brain craves sugar – and how to control itby Donna Chisholm
You may think your sweet tooth dictates what you eat. But can you stop your brain tricking you into wanting sugary food that’s dangerous for your health?
Because of genetics, culture and upbringing, we all have different bliss points for flavours, but now scientists are discovering how those thresholds determine what food we like, and how much of it we’ll eat.
We’ve long known that we are hard-wired to like sweet food. We need glucose to survive, and sweetness is an evolutionary signal for food safety – sweetness generally marks a safe source of carbohydrate, whereas sour and bitter tastes may indicate toxicity. But much less is known about how much the liking for sweetness drives food choices dangerous for health.
As Professor John Prescott, the former director of the Sensory Science Research Centre at the University of Otago, notes in his book Taste Matters, “It’s unfortunate that the list of most of those things that our body innately registers as good to ingest – sugar, fat, salt – reads like a set of disease-risk factors. This seems to put our biological drives at odds with the nutritional advice we hear about every day.”
So, why do we go ahead and have that muffin with our coffee when nutritionists tell us that even a medium “healthy” blueberry muffin has nine teaspoons of sugar and almost 150 calories?
Taste researchers have understood for some time that adults can be classified as likers or dislikers of sweet tastes – although the disliking is relative and not absolute. The big question has been whether “likers” eat more sweet foods than “dislikers”. Now, Massey University nutrition researchers say they’ve found evidence that the intensity at which people perceive sweetness is linked to their intake of sugary foods: those who perceive sweetness more intensely than others, and dislike the taste at relatively lower levels, eat less. They say the work, published last year in the international journal Nutrients, has important ramifications for the food industry.
Nutrition researchers distinguish between homeostatic and hedonic eating: the former is driven by nutritional need, the latter by the urge for pleasure regardless of nutritional deficit.
Your internal homeostatic system is guided by your body’s need to survive. “Internal levels of nutrients and hormones, such as leptin and ghrelin, send signals between the brain and the gut telling you you’re hungry or you’ve had enough to eat,” according to a new Harvard Medical School report.
“Your brain is constantly monitoring levels of these hormones: leptin acts like a fuel gauge and tells you when you’ve got enough fuel on board; ghrelin works the opposite way, telling your brain when you need more fuel. It’s basically the system that makes your stomach start growling when you haven’t eaten for hours.”
To complicate things, ghrelin levels increase when you lose weight, prompting you to eat more and simultaneously slowing your metabolism.
And, as the report points out, your brain’s reward system adds to the challenge by encouraging you to seek out high-fat and high-calorie food – often full of sugar. The hedonic system, which is driven by external factors such as liking sweet, processed food, is responsible for the insatiable cravings that make it so hard to avoid the impulse to eat an extra piece of chocolate, say, even though your leptin is telling your brain you are already stuffed.
Remarkably, and confirming how big a role the brain plays in telling us we are hungry, we can be fooled into secreting hunger hormones. Yale University researchers offered study volunteers a 380-calorie milkshake on two occasions, once telling them it contained an “indulgent” 620 calories and the other time saying it was a “sensible” 140-calorie drink. When ghrelin was then measured, the levels in those who thought they were drinking the high-calorie shake dropped sharply; the drinkers who believed their shakes were “sensible” showed little or no change – suggesting they had gained little satisfaction.
The good news is that the Massey research, led by professor of human nutrition Bernhard Breier and his PhD student Shakeela Jayasinghe, challenges the findings of several other international studies that found no relationship between intake and hedonic liking for sweetness.
“Manufacturers can be assured their sales won’t drop much if the sugar in their product is reduced, because people will get used to it,” says Breier, “and some people may even like it better when there is less sugar.”
Sausage roll or brownie?
Massey dietetics student Beatrice Drury, 23, had always described herself as having a sweet tooth, but after some of the perception tests, researchers found her “bliss point” was set at a low level of sweetness – in the bottom 25% of women tested. The results surprised her. “If there was a choice between a sausage roll and a brownie,” she says, “I’d choose the brownie.”
Drury always adds sweet flavours to her morning porridge, in the form of berries or a banana, and her snacks often include bliss balls or smoothies. She does, however, water down her orange juice because she finds it too sweet, and also rejects very sweet treats such as doughnuts.
“The dichotomy is that she says herself she has a sweet tooth, but even though she likes it, she ends up not overeating it,” Breier says. “It means she can safely enjoy her sweet tooth because she won’t overdo the caloric intake.”
Breier and Jayasinghe’s research has superseded the findings of a study at Deakin University in Victoria, published in the same journal in 2016, which found no link between sweet-taste perception, diet and body size. Breier believes the Massey results are more reliable, because of the way participants recorded what they ate; they had to weigh and list everything they ate daily, whereas Deakin used a “much less accurate” food-frequency questionnaire that asked participants roughly how many times over a year they’d eaten various foods.
In the Massey study, the most commonly eaten sweet foods were fruit, chocolates, biscuits and cakes, followed by smoothies and soft drinks, then yogurt and cereals. Participants ate foods that were either naturally sweet or with added sugars on average seven times a day.
But Jayasinghe says those who found higher levels of sweetness very disagreeable ate significantly fewer carbohydrates and sugars. The study involved only 40 participants, and Breier says that although the findings need to be replicated in bigger groups, the food-intake measurements are “very robust” and have never been done to that standard before.
New Zealand research into sweet taste gained a big boost last July when Massey appointed the internationally renowned scientist Professor Joanne Hort to a new Fonterra-Riddet chair in consumer and sensory science. Hort, who came from the University of Nottingham, will lead a team aiming to better understand consumer responses – including emotional reactions, perceptions and biases – to dairy foods. She hopes to get funding this year for research into the drivers of preferences for different levels of sweetness, examining cultural, genetic and ethnic factors.
Unsurprisingly, Fonterra’s funding involvement means that Hort’s work will be directed at developing dairy products that consumers want, varying sweetness levels for different markets, as “we already do with coffee strength”. But she says it will also have implications for public health. “If we can better understand how people perceive these sensations in different populations, we could try to identify people who might be at risk of consuming too much sugar and fat, and intervene.”
The Massey findings don’t surprise her, but she says it’s important the research is done using a range of foods, rather than sugary solutions.
Like Drury, Hort is a “sweet disliker”, which puts her in the majority. Studies suggest that only 35% of people are “sweet likers”, although manufacturers commonly add sweeteners to food. “I went to the US a couple of months ago,” says Hort, “and it drove me mad, because everything was too sweet. Your ice cream here is also too sweet for me.”
Food manufacturers around the world have been working for years to reduce sugar levels in food, but because sugar affects the structure of a product, it’s no easy task. Reducing salt has been easier: what Hort calls a “stealth approach” of gradual reduction has cut back the salt in many foods without consumers even noticing.
When it comes to sugar, however, it seems the biggest changes have been in marketing and product size. In November, Consumer NZ announced the recipients of the Bad Taste Awards, which highlighted the way some companies market their products as healthier choices than they really are.
Winners included the Pump range of flavoured waters advertised as being “low in sugar” when each bottle contained more than four teaspoons of sugar, and Pam’s and Countdown’s toasted muesli, the sugar contents of which have increased 44% and 20% respectively since 2012.
Kiwi baker and patissier Dean Brettschneider, who has 10 businesses in Singapore, three in Manila and is about to open in Saudi Arabia, says in his experience, sweet products aren’t becoming less popular, even though people now say they prefer healthier options.
“The bran muffin everyone wants to have? They actually want the blueberry muffin. I make the bran muffin because that’s what people are telling me, but I’m actually throwing them out.”
For a baker, reducing sugar is a trade-off in terms of the aeration and “tenderness” of the goods produced. “I could make a blueberry muffin with less sugar, but if I take sugar out, I lose my tenderness. Imagine making a boston bun [sally lunn] without sugar in the dough. I can tell you how much I think people want a healthier boston bun: they don’t.”
At nearly 50, Brettschneider says he’s eating more savoury foods than he used to, particularly when he was growing up in north Canterbury where his mother and grandmother kept the biscuit tins full. His next cookbook, which will be published this year, is more influenced by savoury flavours than sweet.
“That’s about the range of ingredients we have now. Take watermelon – it used to be something you sliced and put on a plate and ate. Now you make a salad with a pomegranate dressing, feta cheese and microgreens and it looks amazing.”
James Kane, the New Zealand head of Mondelez International, which owns confectionery-maker Cadbury, says the premium chocolate flavours, which have higher cocoa content and a more bitter taste, are becoming more popular. He believes that’s the result of a preference for healthier chocolate.
“The population is ageing, so you have a more mature palate. It’s also seen as more indulgent, more of an experience to savour.” But he says the confectionery market is growing strongly, driven by innovation and new products in the premium category.
Last year, Cadbury removed two flavours – the unpopular Cherry Ripe-flavoured Cherry Heaven and Vanilla Butter Caramel – from its Roses chocolates, replacing them with salted caramel and dark mocha, which were more “on trend”. Kane says he doesn’t know what people didn’t like about the more “traditional” cherry flavour. He says the company is trying to reduce sugar content in its products without sacrificing taste and quality, but that was mainly in powdered drinks and gum, rather than chocolate.
In November 2016, the global chocolate and confectionery giant Nestlé announced that its scientists had found a way to structure sugar differently, so the tongue perceived virtually no loss in sweetness when much less was used. The company’s chief technology officer, Stefan Catsicas, said the research had the potential to reduce total sugar by up to 40% in its confectionery, but more than a year on, however, the technology has still not made its way into any products the company sells.
Nestlé has a global commitment to reducing the added sugar in products by 5% by 2020. Last year, it cut the sugar content of its KitKat bars by 10% by increasing the cocoa and milk content. But it’s not easy to get consumers to accept the reformulated products, says Australia-based Nestlé nutritionist Anne-Marie Mackintosh, who’s working on sugar reduction in cereals.
In response to consumer demand, the company launched a low-sugar (1.5%) Cheerios cereal in New Zealand last year – but it isn’t selling well. “Consumers say they want reduced-sugar products, but when it comes to buying them, they can be fickle.”
Sugar does more to cereal than just make it sweet. It forms a protective barrier that stops the granules or flakes from going soggy as soon as milk is added, and it improves the intensity of the other flavours. It also affects structure: when some Uncle Toby’s muesli bars, reformulated to contain less sugar, were released, they failed to stick together properly.
Accurately assessing how consumers will respond to food is not an exact science, as the reaction to some reduced-sugar products shows. For Roger Harker, science group leader of consumer and product insights at the crown research institute Plant & Food Research, it’s less about liking or disliking the sweetness and more about a consumer’s emotional reaction.
“A consumer is often better at telling you what they feel emotionally about a product, and in what circumstances they’d drink or eat it. We’re interested in what represents uniqueness in flavour.”
Much of the institute’s work is with fruit producers. “It’s taught us that everybody likes something different and you have to take that into account."
Manufacturers often aim products at different markets. Northern Europeans, for example, traditionally prefer tarter apples – probably because that’s what they ate growing up in countries with shorter growing seasons. Consumers generally want crisp, juicy apples, with some preferring types that are sweeter and others tarter. The sweeter apples don’t necessarily contain more sugar – the difference in taste often stems from higher or lower acid levels, so sweeter-tasting fruit is just as good for you.
“In manufactured food, when you add a teaspoon of sugar to a muesli bar, you’re just adding sugar, but [to add sweetness] in a fruit, we have to change the way carbon is moved around the tree,” says Harker.
A decline in kiwifruit sales in Japan in the 1990s was linked to the way fruit was grown here. More fruit on each vine meant less carbon and more water was going into the fruit and weakening the flavour. “They changed the way they grew the fruit; the taste and flavour went back up and so did the sales.”
Although fruit growers have tended to breed sweeter-tasting fruit varieties over the years, it’s unlikely that this will drive the population’s preference for sweeter foods overall. “In food-addiction rankings, pizza and chocolate are at the top, and apples near the bottom.”
Research suggests that our taste for sweet things declines after childhood, but as we age, we tend to prefer the food we ate as kids. Harker says a US study showed that the type of apple people preferred in their early to mid-twenties was usually the same as they ate as children.
Sell the smell
Scientists have regular conversations with growers about how odour can be used to manipulate consumers’ perceptions of sweetness. In 2007, a paper co-authored by Prescott reported on a study in which participants given a sweet solution that smelt like strawberries took 1.5 seconds to recognise it as sweet, compared with 1.7 seconds when it smelt like grapefruit. “If you want to reduce sugar concentrations, you can play around with the aromas because they affect the same part of the brain.”
Harker says there is international concern about the negative perceptions around sugar, but so far, there haven’t been many responses other than searching for alternative sweeteners.
Plant & Food scientists are starting to incorporate psychological factors when they test consumers’ sensory perceptions, including the environment in which a given food might be eaten, impressions of the novelty of a flavour and reactions to the complexity of the taste.
“There are opportunities to play around with some of these things to give an eating experience that is pleasurable, but doesn’t have a lot of sugar,” says Harker. “Ninety per cent of new products released into the market, including food, fail, so we are trying to understand consumers’ beliefs and attitudes and how those alter whether a product will succeed.
"When we measure flavour, if we talk about sweetness or acidity, it’s not an easy conversation. By the time you add melon and strawberry and vanilla flavour, each person might have a completely different understanding of those, and some they may not even recognise. But some flavours may make them feel happy or feel nostalgic, so we’re starting to find a profile based on the emotional response.”
In the science of sugar, then, the measurement now is not “how sweet is this?” but “how does this make you feel?” As Prescott points out in his book, the sensory pleasure that motivates us to consume high-energy, sugary foods has given us huge adaptive advantages in our evolutionary past – it’s what has kept us alive as a species. But increasingly, it’s making us unhealthily fatter.
“If our eating habits follow our food preferences with enthusiasm, we cannot blame those preferences if we do not use up the energy that they encourage us to consume. More to the point, we ought to give thanks to them for providing us with some of life’s greatest pleasures.”
Research into sweet taste preferences has spawned dozens of academic papers. Here are some of the findings:
- New Zealanders consume an average of 37 teaspoons of added sugar a day each, six times the recommended amount.
- Studies suggest men prefer higher intensities of sweetness than women.
- The liking for sweetness may be higher before a meal than after it.
- Sweetness preferences in different adults tested in 1973 and 1983 were similar, suggesting later generations do not necessarily prefer sweeter foods.
- A study of people tested at the ages of 11-15 and again at 19-25 found the preferred level of sweetness decreased over the intervening years.
- High-sugar foods trigger a spike in an opioid-like chemical in the brains of rats. The stronger the rise in the brain chemical, the faster the rats race to eat sugary food.
Trying to cut down your sugar intake? We asked several dietitians for tips.
- Physical activity burns glucose, and you’re likely to get more of a “sugar rush” if you’re inactive. Going for a short walk helps control blood-sugar levels – even a 10-minute walk up and down the stairs helps to flatten out the spikes.
- A gradual transition will help your taste buds adapt over time. Reduce the sugar in your coffee or tea by half a teaspoon or less at a time.
- At mealtimes, eat vegetables first – they’ll help to fill you up and reduce your intake of less-healthy food at the same sitting.
- A cereal with a low glycaemic index, such as porridge, will keep you feeling full for longer than a highly processed, sweetened cereal.
- It’s important to factor in portion size when calculating your intake from the figures on food labels. For example, soft drinks may have only 8g of sugar per 100g, but the average drink is more than three times that size.
This article was first published in the January 20, 2018 issue of the New Zealand Listener.
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