Is Sugar Really the Enemy?

Sugar has become a hot topic in nutrition. Some call it "toxic" and blame sugar consumption for everything – whether it's weight gain in the short term or chronic illness in the long term. Others say that sugar is misunderstood and just another source of energy.

So, what's the real story? In this post, we will go beyond the social media headlines and provide insight directly from high-quality research studies. In doing so, I aim to provide good, evidence-based information to help you intelligently navigate the sugar debate. As you will find out, "the truth about sugar" is nuanced. Anyone arguing an extreme position is not serving you because they inevitably exclude key information. Let's jump in.

What Is Sugar?

Let us start with straightforward definitions. Sugar is a form of carbohydrate that your body can utilise for energy. It exists in various forms, including:

·       Glucose: The body’s primary fuel source for muscles and the brain.

·       Fructose: Found naturally in fruit and honey.

·       Sucrose: Common table sugar (made up of glucose and fructose).

·       Lactose: Found in dairy (made from glucose and galactose).

So far, so good. But it gets more complicated very quickly. Why? Because there are dozens of hidden forms of sugar in our diet. Hidden sugars refer to different types of sugars added to processed foods or naturally present in forms that might not be immediately recognisable as sugar. Hidden sugars are an issue because they are often listed under other names on ingredient labels, making them harder to spot. Here’s a useful list of hidden sugars you can use as you move forward:

1.    Common Names for Sugar:

·       Sucrose

·       Glucose

·       Fructose

·       Dextrose

·       Maltose

·       Lactose

·       Galactose

·       Trehalose

2.    Syrups:

·       High-Fructose Corn Syrup (HFCS)

·       Corn Syrup

·       Rice Syrup

·       Malt Syrup

·       Golden Syrup

·       Maple Syrup

·       Agave Syrup

·       Glucose Syrup

3.    Natural Sweeteners:

·       Honey

·       Molasses

·       Coconut Sugar

·       Date Sugar

·       Fruit Juice Concentrates

·       Brown Sugar

·       Raw Sugar

·       Evaporated Cane Juice

4.    Less Obvious Sugars:

·       Invert Sugar

·       Cane Crystals

·       Cane Juice

·       Evaporated Cane Juice

·       Turbinado Sugar

·       Demerara Sugar

·       Muscovado Sugar

5.    Alcohol Sugars (Polyols):

·       Sorbitol

·       Mannitol

·       Xylitol

·       Maltitol

·       Erythritol (while technically low- or no-calorie, it’s still considered a sugar substitute)

6.    Ingredients with Hidden Sugars:

·       Barley Malt

·       Maltodextrin

·       Fruit Puree

·       Caramel

·       Diastatic Malt

·       Ethyl Maltol

Given this, successfully monitoring and managing total sugar intake becomes very difficult when one eats a Western diet high in ultra-processed food and beverages.

What are the Dietary Guidelines for Sugar?

The World Health Organisation recommends adults and children consume no more than 10% of daily calories from sugar, and preferably under 5% for extra health benefits (World Health Organisation 2015). That’s 100-200 calories daily from sugar for a typical 2000-calorie diet.

The NHS in the UK advises that free sugars (from the sources of sugar mentioned above) should not make up more than 5% of adults' total calorie intake. This equates to about seven sugar cubes per day.

Now, let’s put these numbers into context with some popular foods on the market:

·       A large caramel Frappuccino with semi-skimmed milk contains over 50 grams of sugar (12 teaspoons of sugar)

·       A Belgian chocolate & hazelnut frappé crème contains 44.5g of sugar (11 teaspoons of sugar) 

·       A standard can of cola contains 39g of sugar (nearly 10 teaspoons of sugar)[LM1] 

This is wild when you think about it: people can consume their entire daily sugar intake with a single drink. It’s perhaps no wonder then that research has found a strong link between sugar-sweetened beverages and weight gain.

For example, a recent meta-analysis found a direct dose-response between sugar and weight in adults and children. In other words, the more sugar-sweetened drinks participants consumed daily, the more overweight they were, and vice versa (Nguyen, Jarvis et al. 2023).

A screenshot from the paper (shown below) highlights the impact of sugar-sweetened drinks on body weight. It displays a forest plot that visually represents the findings of multiple randomised controlled trials in the meta-analysis. At the bottom of the image, a diamond illustrates the net effect of all the studies. As you can see, sugary drinks appear to cause weight gain. 

The Argument that Sugar Is the Enemy

What evidence supports this view? Let’s begin with a massive study: an umbrella review that analysed a whopping 73 meta-analyses and found significant harmful associations between sugar intake and metabolic health, cardiovascular outcomes, seven cancer outcomes, and ten other illness outcomes (Huang, Chen et al. 2023).

The conclusion of the authors was as follows:

“High dietary sugar consumption is generally more harmful than beneficial for health, especially in cardiometabolic disease. Reducing the consumption of free sugars or added sugars to below 25 g/day (approximately six teaspoons/day) and limiting the consumption of sugar-sweetened beverages to less than one serving/week (approximately 200-355 mL/ week) are recommended to reduce the adverse effect of sugars on health.”

At first glance, this paper appears compelling, and the results seem straightforward. It’s also important because meta-analyses and systematic reviews sit at the top of the evidence-based medicine pyramid. Therefore, when dozens of top research papers find sugar problematic, we should sit up and take notice.

However, like many things, it’s not as simple as the headline. In meta-analyses and systematic reviews, you will encounter something called “evidence classification” as part of the write-up. This ranks the quality and reliability of evidence from highest to lowest (I to V). As you might imagine, the higher the ranking, the more trust we can have in the outcomes.   

Why does this matter? None of the meta-analyses in this massive umbrella review received the highest evidence classification (I). Instead, the majority were rated III or IV, indicating potential study design and methodology issues. In short, while the study is impressive, certain questions remain, which should caution us before making too many blanket statements about sugar.

This issue goes to the heart of a much broader problem you will find when you go to PubMed and look to research the effect of sugar on our health. Many times, on social media, you see things like “sugar is deadly” or are told that “sugar is as addictive as cocaine”.

However, these memes about sugar are rarely based on evidence from tightly controlled human randomised controlled trials. Instead, they come from much lower-quality studies, like animal studies. Here’s one problem with that: humans are not mice!

Even if an animal study finds something interesting, we should not automatically assume the results apply to humans. Studies comparing oral glucose tolerance tests (OGTTs) in humans and mice reveal highly divergent metabolic responses due to differing physiology (Bruce, Hamley et al. 2021).

Equally important, the vast majority of studies examining the effects of sugar on human health are “epidemiological” studies that monitor individuals over time in natural living conditions, asking participants to keep a food diary or recount their diet during telephone interviews.

You may already recognise the problem with this type of study: humans going about their daily lives naturally make mistakes. We can forget what we eat, underestimate portion sizes, and make various mistakes in diet recall. Indeed, one study found that in these types of studies, people could underestimate energy intake by up to 30% when comparing food diaries to gold-standard calorie measurements (Burrows, Ho et al. 2019).

I am spending time on this because numerous claims are often made against sugar on social media. However, these frequently stem from animal studies (which do not always apply to humans) or epidemiological studies (which are open to errors) and cannot establish direct causation (Le, Faeh et al. 2006). These details matter.

The Argument that Sugar Is NOT the Enemy

Let’s take the opposite approach and try to steelman the argument that sugar is NOT the enemy. This is a good exercise because it shows we are at least seeking to be neutral, thorough, and scientific.

First, the brain runs on glucose. Research shows that glucose is the brain's primary fuel source (Mergenthaler, Lindauer et al. 2013). In this respect, sugar is not innately toxic; it’s a key substrate that helps us live, work and play. This does not mean we can eat sugar with reckless abandonment because the body tightly regulates glucose metabolism in the brain. It just means it is not innately “toxic”.

Secondly, research shows that athletes who enjoy endurance training can benefit from taking on dietary sugars at the right time to fuel their performance (Tiller, Roberts et al. 2019, Viribay, Arribalzaga et al. 2020, Leaf, Rothschild et al. 2024) . As we push ourselves in a hard training session or race, our muscles become progressively more reliant on carbohydrates as an energy source. This makes periodised carbohydrate supplementation essential for performance and energy availability.

To give but one example, a very recent study found that supplementing with a high dosage of 2:1 maltodextrin fructose formulation (sugar) before, during, and after a 15-kilometre run reduced post-workout inflammatory biomarkers (Righetti, Medoro et al. 2024). In this context, sugar is not the enemy but a valuable tool for hitting PBs.

Reconciling the Research

So far, we have looked to steelman the argument that sugar is the enemy, and some significant studies show its adverse effects on our health. We have also looked to go the other way, and research shows it can be a valuable tool to get the most out of our fitness.

Are these differing points of view reconcilable? Absolutely! And this is a key takeaway for you: understanding the effect of sugar on human health requires nuance and context. Whether sugar has a positive impact on a person’s health and performance depends on many factors, such as:

·       How much sugar they consume (dose)

·       When they have it (timing)

·       The underlying health and fitness of the person consuming it (physiology)

Everything gets easier when you look at the sugar debate through this lens. In this sense, sugar is not inherently “toxic”. It’s just a source of energy. However, if we get the dosage, timing and context wrong, sugar can cause adverse effects. To bring this to life, let’s use a few examples.

A study of overweight teenagers who reduced their sugar intake to under 10% of calories saw improvements in triglycerides (blood fats), TNF-a (inflammation), and pancreatic function (Schmidt, Mokhtari et al. 2023). This makes sense: they had pre-existing health issues, reduced dosage to recommended levels, and saw results. A healthy, fit population doing extensive endurance training might not see the same results—context matters.

Here's another example. A study of IBS (irritable bowel syndrome) patients found that reducing sugar intake improved physical and mental symptoms, with almost one-third of patients experiencing near-full remission in a month (Nilholm, Roth et al. 2019).

These results are excellent, and they show how limiting sugar can benefit specific groups. Yet, context matters here, too. Before the study, this population ate excessive amounts of sugar and had pre-existing gastrointestinal imbalances. In other words, things become easier to understand once you look at sugar through the lens outlined above (dose, timing, and existing physiology).

Final Thoughts

The debate around sugar is highly polarised, with some labelling it toxic and others considering it a misunderstood energy source. However, the reality is nuanced, and understanding sugar’s impact requires personal context and understanding how scientific research is done.

Whether sugar has adverse effects on someone’s health will depend on:

·       How much sugar they consume (dose)

·       When they have it (timing)

·       The underlying health and fitness of the person consuming it (physiology)

Sugar is not innately harmful but must be managed carefully based on individual needs and health contexts. It is easy to overdo sugar in a world of ultra-processed foods and sweetened beverages. Focus on the bigger picture—a balanced, nutrient-rich diet that supports training, recovery, and long-term health—and seek to limit processed foods to no more than 10% of your diet. With this awareness and approach, you will be set up to win.