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Inside Our Food

Does Sugar Damage Our Health?

Over the past few decades, a rapid increase in sugar consumption has grown parallel with the development of an obesity epidemic in Western countries. It’s now well established that sugar helps us develop cavities and gain weight. But what about all the other diseases that we have heard sugar is responsible for?

Public health institutions such as the WHO1 and the US Dietary Guidelines Advisory Committee2 are clear in their recommendations: free sugars should not make up more than10% of our total energy intake, and an ideal diet wouldn’t include more than 5-6% of calories coming from sugar. This means that a man on 2500 daily calories would ideally eat around not more than 30g of sugar per day. For a woman eating a diet including 2000 daily calories, sugar should be less than 25g. This may still sound like a lot, but it’s much less than the current European average, which surpasses 80g per day.

When presenting their recommendations, public health institutions thoroughly review current evidence and rank it on a spectrum, from “very strong” to “insufficient”. From their most recent reviews, it would appear that the evidence linking high sugar consumption to overweight and dental cavities is very strong. However, the evidence behind other theories looking at sugar’s links to other health issues  – addictions, inflammation, diabetes, cancer, and cardiovascular disease – is still insufficient.1,2

Let’s first take a look at the current evidence and misconceptions behind various theories, and then we’ll delve into why the science around sugar’s impact on our health is still hard and limited.

Does sugar cause diabetes and cardiovascular disease?

In particular when it comes to diabetes, a condition determined by too high blood sugar levels, it’s easy to think that eating too much sugar would be an obvious cause. But things are a bit more complicated, as evidence linking sugar consumption directly to diseases such as diabetes and cardiovascular disease is still insufficient.1,2

However, even if sugar is not directly responsible for an increased risk of developing heart disease and type 2 diabetes, obesity is a well-established risk factor for both of these conditions.4,5 This means that if we eat too much sugar and become overweight as a result, we are also going to increase our risk of developing those diseases.3

Is sugar addictive?

“Sugar affects our bodies like cocaine” so the saying goes, but let’s check whether this theory is backed by solid evidence. An independent review, published in 2016, found little evidence to support the theory that humans become addicted to sugar. Furthermore, findings from mice studies suggested that addiction-like behaviours, such as bingeing, happened only when the animals were given intermittent access to sugar.6

“The addiction literature is complicated,” comments Marion Nestle, NYU Professor of Nutrition, Health Studies, and Public Health (who has nothing to do with the Nestlé food company). Nestle also adds that “Many people believe that they are addicted to sugars and report symptoms similar to those of addicts to other substances. Whether sugar ‘addiction’ meets standards of addiction to other substances is debatable. My understanding of addiction is that if people believe they are addicted, they should be treated as such.” So while the science might conclude that we don’t become neurochemically addicted to sugar, there are still people who develop addiction-like symptoms who might need treatment.

Does sugar feed cancer?

Some people say that cancer cells live off sugars, so many people believe that eating sugar will lead to feeding cancer cells. There are a few conceptual mistakes behind this belief. Cancer cells indeed live off one specific type of sugar, glucose, but that’s also true of healthy cells. All the cells in our body get energy from glucose. It’s also important to note that all the food we eat is converted into glucose in one way or another in our body - not just foods that contain glucose. This aside, scientists have concluded that there’s no evidence that “sugar-free” diets lower the risk of getting cancer or boosts the chances of surviving if you’re diagnosed.7

Does sugar cause inflammation?

Some researchers have suggested that dietary sugar intake could trigger more inflammation in our bodies, which could be linked to the development of various diseases. However, the studies trying to answer this question were often small and ended up reaching opposite conclusions. To draw more confident conclusions, further studies need to be carried out, with larger sample sizes and longer follow-up periods.8 

The Problem With Sugar Research

But why are so many studies inconclusive? Current nutrition science still faces many challenges, and sugar industry-backed studies have added some level of confusion in this field for decades.

Ethical issues

Think, for example, about ethical limitations. It would be nutrition scientists’ dream to carry out precise experiments where they feed thousands of people with an ingredient they think could be responsible for causing some diseases. But as we can imagine, not many ethical panels would give the green light to these methods, and not many volunteers would be happy to serve as guinea pigs. 

Issues with observational studies

For this reason, scientists often have to resort to carrying out observational studies – instead of feeding people the foods they’re interested in investigating, they ask people about what they eat normally and then follow up with them for years to see which people go on to develop some diseases. But when you do this kind of research, it’s really hard to unpack one factor from the rest of a person’s lifestyle: for example, scientists can’t be sure whether sugar intake is causing the disease instead of smoking or lack of exercise. 

Also, participants often don’t report very accurately what they eat: they might under- or over-report how much sugar they eat, making the scientific conclusions imprecise. Complicating things even further, many nutritional studies often have limited resources and as a result can only deal with very small cohorts of patients, making it impossible for them to represent the impact of sugar on a wide population.9

Issues with animal studies

Animal studies are helpful to identify new directions for research on humans, but they are poor predictors of human reactions to exposure. The results from animal experiments can’t always be reproduced in human trials, and that’s why the evidence stemming from them is often considered “low”. The gold standard of scientific research would be randomised controlled trials on humans. More of these studies are being carried out, but not many large-scale studies of this kind are around yet.10

Read more about how the sugar industry has been skewing science.

Reviewing sugar research: advantages and limitations

That’s why for now reviews – and even better, meta-analyses – are one of our safest bets. They look at the literature and compare all studies to draw conclusions, and so are useful to overcome the confusion stemming from contradictory results. They can help us spot patterns among many small studies that would bear little significance on their own. However, we should be wary of glorifying these studies too much for a couple of reasons. 

Issues with industry-funded studies

First of all, some of these studies are still funded by the industry, so we need to be careful and always check a study’s conflict of interest section. Industry-funded reviews and meta-analyses might downplay the strength of evidence linking sugar to specific diseases. Some researchers found that most industry-funded studies tend to favour sponsors and find fewer risks associated with the consumption of the sponsor’s product.11 When looking at sugar-sweetened beverages, researchers found that industry-funded studies were eight times more likely to produce favourable conclusions than those funded by non-industry sources.12

Not enough scientific literature

Secondly, if the literature is limited or has been skewed, then a review won’t magically give us the answer. At best, it will tell us that there aren’t enough good studies to draw any conclusions – as we’ve seen happening with the link between sugar and certain diseases. At worst, it will perpetuate the findings of the individual studies without much critical interpretation. Only when large randomised controlled trials will have been carried out, we can be more confident that the conclusions reached by meta-analysis will be really strong and significant.

Limiting our sugar intake

Sugar is an interesting example of how scientific claims can be misused to influence policy and public opinion.

On the one hand, the sugar industry attempts to make us believe that sugar is not linked to any negative side effects, not even oral health and obesity. On the other, some researchers (and individuals or companies who don’t even research the topic in a systematic way but could benefit from demonising this ingredient) identify sugar as the sole culprit for many diseases.

The reality sits, as it is often the case, somewhere in between. Many diseases stem from the complex interactions of different factors in our lifestyles and diets. But the negative impact of the overconsumption of sugars is clear enough that we can be at least sure of something: diminishing our sugar intake can only be good for us.

How do you limit your sugar intake? Let us know in the comments below!

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  1. Diabetes UK. Sugar and Diabetes. Accessed on 29 October 2020.
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  8. Michael B. Bracken (2009). Why animal studies are often poor predictors of human reactions to exposure. Journal of the Royal Society of Medicine. Accessed on 25 October 2020.
  9. Lenard I Lesser et al. (2007). Relationship between funding source and conclusion among nutrition-related scientific articles. PLoS Medicine. Accessed on 10 October 2020.
  10. Maira Bes-Rastrollo et al. (2013). Financial Conflicts of Interest and Reporting Bias Regarding the Association between Sugar-Sweetened Beverages and Weight Gain: A Systematic Review of Systematic Reviews. PLoS Medicine. Accessed on 10 October 2020.
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