The dangers of over-hyping ‘sugar addiction’.

Sugar seems to be frequently vilified in the media. Just a quick google search and headlines report ‘Sugar can destroy your brain’, ‘Sugar is as addictive as cocaine’ and ‘Sugar addiction ‘should be treated as a form of drug abuse’. It’s frequently referred to as an addictive drug, which supports people who build successful careers out of teaching people to avoid the perils of sugar. But how well founded are these claims and should you really cut sugar out of your diet?

Firstly, it’s important to understand that we absolutely need sugar in our diets. Glucose is an essential substance for cell growth and maintenance. The brain accounts for only 2% of our body weight yet uses approximately 20% of glucose derived energy, it’s vital to consume sugar to support basic cognitive functions. Disruption of normal glucose metabolism can have dangerous effects, resulting in pathological brain function. Yet there is concern that overconsumption may lead to a multitude of adverse health effects.

Is it addictive?

The impact of sugar on the brain is partly what has led many people to compare sugar to an addictive drug. Indeed, there are similarities, sugar activates the reward network which reinforces intake. It’s been suggested that ingesting an addictive drug hijacks this reward network and causes addiction. When people mention the reward pathway they are referring to the effect of dopamine on the pathway from the ventral tegmentum (VTA) to the nucleus accumbens and the effect of opioids in the amygdala and VTA. Dopamine underlies ‘wanting’ of an addictive substance whereas opioids underlie ‘liking’. Wanting causes the motivation to find and consume the substance, dopamine can be released in anticipation which increases craving, whereas liking is the enjoyment of actual consumption.

Our preference for sweetness is the only taste we have an innate preference for and can be seen in newborn babies. This is adaptive because it signals the food is likely to be high in calories and therefore valuable, at least in the environment we evolved in where food was hard to find. However, our environment is now full of food cues and feeding opportunities so our natural preference for sweetness is now counterproductive. These cues increase the likelihood of craving and consumption, like in drug addiction. Addicts show a biased attention towards cues related to their addictive substance, this is usually measured as being quicker to detect them and finding it harder to ignore them. This is also seen with food in those who are obese, hungry or have problematic eating behaviours. In our obesogenic environment this is an issue as food cues are so frequently encountered.

Our obesogenic environment offers temptations at every turn.

Despite the potential common mechanisms, addictive behaviours such as increased tolerance and withdrawal syndrome have not been seen in humans (Which the exception of a single case study). Instead most of the research is based on animal models. ‘Sugar addiction’ can be seen in rats, but only when they are given intermittent access, this causes sugar bingeing and anxiety which might be evidence of withdrawal symptoms (although this could also be caused by hunger). This addictive behaviour is not seen in rats given free 24-hour access to sugar, even in those preselected to have a sugar preference. Given that free access is most like our own environment, this evidence is not particularly compelling. Furthermore, you get similar effects when using saccharin (artificial sweetener), so addictive behaviours are more likely caused by the rewarding sweet taste rather than at a chemical level. This makes sense when you consider self-confessed ‘sugar-addicts’ tend to crave sweet foods such as chocolate, cake and doughnuts, not sugar in its purest form.

Whilst these foods are likely to be high in sugar, they are also high in fat as well as other nutrients.

Issues with evidence?

A further issue with claims of ‘sugar addiction’ is that claims are difficult to test. One problem is that human diets are varied, which makes it difficult to isolate the effect of sugar. Effects are usually confounded with lifestyle factors and other nutrients commonly found in the “Western diet” such as fat. If you try to list some high sugar foods, you’ll probably find these are also high in fat. Therefore, studies investigating the overall western diet do not provide compelling evidence for a direct causal link between sugar and negative health outcomes. To directly test this, we would need to put a sample of participants on a high sugar (controlling for all other dietary and lifestyle factors) diet for an extended period time. For obvious practical and ethical reasons, this is not possible (ethical boards tend to object to experiments where you intentionally damage the health of participants).

Therefore, we use animal models, which go some way in addressing this issue as sugar can be isolated more effectively. However, animal studies are also subject to criticism, as models are created from them to demonstrate the effects of sugar in the brain, but they do not necessarily translate to complex human behaviour in the real world. For example, humans can compensate for sugar compensation by choosing less sugary foods later, whereas rats in a controlled environment do not have this option.

How similar do you think your behaviour is to this guy?

Brain imaging studies are another popular method to study the short-term effects of sugar on cognition. There is no shortage of articles describing how the brain ‘lights up’ or is ‘flooded with dopamine’ in response to sugar, like the patterns of activation seen in response to addictive drugs. However, we also see the same patterns in response to listening to music, drawing doodles and cars, but we don’t think these things are addictive. It’s also important to realise fMRI is only measuring increased blood flow to those areas, not neural activity, so the information we get from them is limited. Brain imaging studies provide valuable insights into the underlying mechanisms of behaviour, but the results should not be overstated.

Negative consequences of vilifying sugar

The issue with vilifying one specific substance is that it causes people to adopt overly restrained diets. Restrained eating is an issue because it is frequently linked to diet breakdown, overeating and weight fluctuation. Tightly controlled diets involve a large amount of self-control, which usually fail and result in disinhibited eating. Making a food forbidden increases craving and overeating of that food, particularly in restrained eaters. The breakdown of restraint often causes guilt and leads to an unhealthy psychological relationship with food. In contrast, intuitive eating/flexible dietary control is associated with improved psychological well-being and lower BMI.

Whilst there is no evidence to support ‘sugar addiction’ it’s been suggested that a better term might be ‘eating addiction’. This term would describe the behavioural symptoms of loss of control, intense craving and overconsumption, rather than the substance-based addiction. The criteria for addiction in the most recent version of the DSM-5 (a diagnostic manual for clinicians) has been extended to account for non-substance-based addictions, such as gambling. However, there is concern that the term addiction implies that the behaviour is uncontrollable, which would undermine dieting attempts. Furthermore, there is some evidence that belief in ‘food addiction’ increases food consumption, particularly in those who self-identify as an addict.

To summarise, the causes of obesity are complex and cannot be reduced to a single substance. A combination of biological and psychological influences are involved, and to complicate matters further, the relative power of different factors differ between people. It would be more convenient if we could blame the multitude of potential health issues on sugar consumption, but at present there is no strong evidence to support this argument. Finally, over-hyped headlines and advice to cut sugar out of our diet completely is potentially harmful to our attempts to make positive changes to our diets and achieve long term health goals.


What determines which food you like and how much you enjoy it.

You might think our likes and dislikes are preprogramed, after all don’t we all love chocolate and hate Brussel sprouts? It’s true that there is a biological basis for basic taste preferences. We tend to enjoy sweet food because it suggests that the food will be high energy, which is valuable from a survival perspective. We avoid sour and bitter foods, again this is useful as they are associated with potentially poisonous substances. These innate preferences can be seen in new-born babies, putting sucrose on the tongues of new-born babies causes them to smile, stick out their tongue and smack their lips, all of which indicate liking. In contrast nose wrinkling, frowning and head shaking are observed in response to a bitter solution. These behavioural reactions are also seen in primates, great apes show the most similar responses, which further strengthens the argument that sweet/bitter preferences are innate.

smiling baby
We can observe innate preferences in babies for sweet and bitter tastes.

Technically speaking, taste only refers to what is detected by taste bud receptors on the tongue. When we consume food, we do not experience tastes in isolation, we experience flavour. Flavour is the hedonic experience of eating which involves all the senses: taste, smell, touch, sight and sound. Odour (smell) is a particularly important component of flavour, pleasant odours are thought to enhance flavour and increase liking. However, in contrast to taste preferences, there is no evidence of any innate preferences for different odours. We learn odour preferences through their association with tastes, this explains why we describe many smells with taste words i.e. “It smells sweet in here”. We cannot taste sweetness, but we are remembering previous encounters with that smell where it was associated with an actual sweet taste.

So why do people like bitter substances such as vegetables, alcohol and caffeine? Most food preferences are learnt, and this takes time. You might remember the first time you tasted coffee, how pleasant was this experience? Coffee tends to be bitter, which we naturally avoid as it may suggest the substance is poisonous. However, this bitter beverage also contains caffeine, which is rewarding. If you repeatedly consume coffee then you associate the taste with the beneficial effects of caffeine. This is called flavour consequence learning (FCL), it’s based on the basic psychological principle of classical conditioning (you might remember learning about Pavlov’s dogs). In theory we should be able to associate any flavour (conditioned stimulus) with its post-ingestive consequence (unconditioned stimulus). However, evidence is somewhat mixed, and it can be difficult to observe FCL in adults who already have many varied food preferences.

Acquiring a flavour preference through FCL is also dependent on your current motivational state. Pairing caffeine with a novel drink over a period of several days increases people’s liking for that drink, but this is limited to regular caffeine users who were caffeine deprived. What this means is participants only learnt to associate the novel drink, which was fruit tea in this study, with the positive energizing effect of caffeine when they were experiencing a need for caffeine. This may prevent an unnecessary preference being developed, but also from being expressed at inappropriate times. Therefore, you prefer food when you are hungry but enjoy food less as you become full. This might be a useful mechanism the body has to prevent over-consumption, as liking tends to increase immediate intake.

A similar concept is flavour-flavour learning (FFL), where repeatedly pairing a liked/disliked taste with another taste changes liking for the other taste. This explains why people often start drinking coffee with lots of sugar/syrups/milk but as they repeatedly consume it they adopt an actual liking for the coffee taste, because the sweet and coffee flavours are linked. This may also work with increasing liking of foods too. Adding a small about of sugar to vegetables such as broccoli increase liking in children.  The effect is maintained even when the sugar is removed, children are still more willing to taste and consume more of the previously disliked vegetable.

We often start by consuming sweetened versions of naturally bitter substances.

Another reason FFL may work is because it makes it easier to become repeatedly exposed to a flavour, by reducing the intensity of the bitter taste. Studies suggest that 10-15 tastings of a previously disliked food is enough to establish significant liking. It’s thought that we start to like a food after repeated exposure because we have learned it’s safe to eat. However, the opposite is also true; if a new food makes you sick you are likely to develop an aversion for that food. This is an adaptive mechanism from your body attempting to discourage further consumption of the risky substance. Rats tend to treat all new food items as potentially unsafe and at first try only small amounts, consuming larger amounts only if they do not become sick. This approach is referred to as neophobia and is common in children, who are rapidly acquiring flavour preferences. Whilst this ‘learned safety’ explanation is popular and makes evolutionary sense, it does not fully explain flavour preference, as it would suggest we should like all foods that don’t make us ill.

As we develop food preferences, we also learn a huge amount of other information about food. We learn that it’s more usual to eat certain foods in the morning, liquids are less filling than solids, and a fancier label might mean better quality. These form expectations about how a food should be consumed and how it will taste. Altering these expectations can change both the taste of the food and our enjoyment of it. For example, if you give participants smoked salmon ice cream, they strongly dislike it and rate it as very salty and savoury. This is because the salty fish taste conflicts with the expectation of a sweet, fruity flavour generated by the labelling and visual appearance. However, call it smoked salmon mousse and liking significantly improves. This demonstrates that a conflict between expected and actual flavour enhances the perception of unexpected sensory components (saltiness in ice cream), resulting in negative taste experience. In contrast, valid expectations enhance food enjoyment, it’s why we prefer ‘slow roasted tomatoes’ to ‘tomatoes’.

ice cream
Smoked salmon ice cream anyone?

This is an overview of just some of the factors that contribute to the development of food preferences and momentary food liking. Whilst there are biological mechanisms for a few basic tastes (Sweet and bitter), most of food preference is learnt. This influences how you experience food and is rooted in our environment, insects for example are readily enjoyed in cultures other than our own. We acquire preferences through a combination of exposure, associating flavour with nutritional/behavioural benefits and by associating them with already accepted flavours. In addition, these mechanisms can be used to increase liking for new and even disliked foods, perhaps even insects!





Five reasons why we overeat

We tend to think that we stop eating when our stomachs are full. Science shows otherwise. Here are five reasons we often overeat without realising it.

1. Portion size

Visual aspects of a meal, such as portion size, have been shown to influence how much we eat. In an American study on satiety, participants were seated at a table and instructed to eat soup. Half of the bowls were slowly and imperceptibly refilled, via a tube beneath the table, as their contents were consumed. The participants whose bowls were covertly refilled consumed 73% more soup than those who refilled the bowls themselves, but they didn’t believe they had consumed more, nor did they feel more full than those eating from normal bowls.

It’s unlikely that someone is secretly refilling your bowl under the table, but it’s important to be aware that you are likely to eat however much food is on your plate.


2. Variety

Usually, when eating, we get used to the taste of the food, which means we get less pleasure from it and so stop eating. This effect is called “sensory-specific satiety”. It essentially means we get full for that specific taste. However, when we eat a varied plate of food, switching between the foods continues to renew their palatability.

When researchers tested this effect, they found people ate four times as much when given multiple different foods. The sensory-specific satiety effect tends to be enhanced the more different the foods are to each other. This variety means you will enjoy the food for longer and keep the feeling of being full at bay.

Although nutritional advice suggests a varied diet for good health, you should be wary of situations that result in lots of different food items on your plate at the same time, such as buffet meals.

3. Distraction

People often eat while doing other things, such as watching TV, working or catching up on social media. But eating while distracted interferes with mechanisms that normally stop an eating session, such as liking a food less after consuming a certain amount of it, meaning that it will take longer to feel full. Also, when distracted you are less aware of becoming full and so need to consume more food to reduce hunger.

You’ve probably already heard that eating while distracted tends to increase intake, but what you might not know is that this effect continues throughout the day. Distraction can disrupt both your awareness of fullness when eating and your memory of the food eaten, which makes you more likely to eat more later in the day.

4. Alcohol

Alcohol increases the likelihood of overeating for several reasons, including reduced self-control and increased impulsivity. It can even make food tastier. Recent research suggests it may also disrupt your ability to monitor your body’s signals, so-called interoception.

Interoception can be measured by a heartbeat tracking task. People who are better at this task are more likely to be a healthy weight and have healthy eating habits. Just two alcoholic drinks significantly decreases a person’s ability to track their own heartbeat on this task.

5. Eating with others

Eating a meal with other people increases the amount you are likely to eat. The foods you choose to eat are also likely to be influenced – you are more likely to choose similar food to those around you.

This effect is enhanced when we have close relationships with the people we are eating with as we feel a stronger need to identify with them. This is primarily a social effect, where we use others’ eating behaviour as a guide for our own. However, recent research suggests this phenomenon may also affect your experience of eating. If people you identify with are enjoying a particular food, it suggests to you that the food will taste good. Expecting a food to taste good increases how much it is liked which in turn increases the amount eaten.

So, what can we do to combat overeating if we are not aware of it. Research shows that eating attentively (focusing on the food without any distractions) reduces current and subsequent intake by increasing awareness and memory for the food eaten. Other research has shown that a smartphone-based attentive eating app, which involved photographing, answering questions and being reminded about food consumed, can help with weight loss. So, even when it is not possible to eat attentively at the time of eating, it might still be worth taking a photo of your food to avoid overeating throughout the day.


This article was originally published on The Conversation. Read the original article.