Added Sugar

We tend to think of added sugar as a weight issue. A few extra calories. A little indulgence. Something to be balanced out with a walk or a trip to the gym.

But what if the real concern isn't the calories at all?

What if the bigger issue is what happens when one particular component of sugar, fructose, arrives in the liver?

Understanding this changes the conversation. It takes us beyond calories and into metabolism.

Table sugar (sucrose) is roughly half glucose and half fructose.

Glucose is the body's preferred fuel. Every cell can use it. Your muscles use it during exercise, your brain relies on it daily, and excess amounts can be stored for later use. The metabolic workload is shared across the body. 

Fructose follows a very different path.

While glucose can be used almost anywhere, fructose is handled predominantly by the liver. This means that every sweetened drink, dessert, syrup, confectionery product or sugar-laden snack delivers a fructose load that the liver must process.

And this is where things become interesting.

Think of the liver as your body's chemical processing factory.

Every day it sorts, packages, stores, converts and detoxifies thousands of compounds. It's remarkably resilient, but it isn't infinitely adaptable.

When small amounts of fructose arrive, this system works perfectly well.

The challenge arises when fructose arrives in large quantities, repeatedly, day after day.

Unlike glucose, fructose bypasses many of the body's normal regulatory controls. The liver rapidly processes it, and when energy stores are already sufficient, much of that fructose can be diverted into a process called de novo lipogenesis. Literally translated, this means "making new fat." 

In other words, excess fructose can be converted directly into fat within the liver.

This isn't a problem because fat is inherently bad.

The issue is location.

A certain amount of body fat is normal and healthy. Fat accumulating inside the liver is a different story entirely.

Researchers have shown that excess fructose intake can increase liver fat production, elevate triglycerides and contribute to insulin resistance. Over time, these changes may contribute to the development of fatty liver disease and wider metabolic dysfunction. 

This is one reason rates of fatty liver disease have risen dramatically in populations where sugar-sweetened beverages and ultra-processed foods have become dietary staples. 

This is where the comparison that captures so many people's attention comes from.

Researchers such as Robert Lustig have highlighted that excessive fructose and excessive alcohol share several important metabolic pathways. Both are processed primarily by the liver. Both can stimulate fat production in the liver. Both can contribute to oxidative stress, inflammation and fatty liver disease when consumed in excess over time.

Of course, fructose is not alcohol.

It won't impair judgment, affect coordination or leave you with a hangover.

But from the liver's perspective, excessive fructose can create a surprisingly similar workload. This is why fructose has sometimes been described as "alcohol without the buzz." 

One of the biggest misconceptions in nutrition is that nutrients exist in isolation.

They don't.

What matters is how they are delivered.

Our ancestors encountered fructose packaged inside whole fruits, alongside fibre, water and thousands of plant compounds. These naturally slowed consumption and absorption.

Modern food manufacturing has changed that equation.

Today's added sugars are often delivered in forms that are rapidly consumed and rapidly absorbed:

• Soft drinks
• Energy drinks
• Fruit juices
• Flavoured coffees
• Breakfast cereals
• Confectionery
• Sweetened yoghurts
• Snack bars
• Desserts

The result is a fructose load that can arrive in the liver far faster, and in far greater quantities, than would ever occur from eating whole fruit. 

At this point it's important to separate added sugar from naturally occurring sugar.

An apple is not a fizzy drink.

A handful of berries is not a chocolate bar.

Whole fruits contain fibre, polyphenols, water and structure. These elements slow digestion, influence how sugars are absorbed and provide benefits that extend far beyond their sugar content. 

You would struggle to eat six oranges in a few minutes.

You could drink the sugar equivalent of those oranges in one glass of juice.

The fructose molecule may be the same, but the metabolic experience is not.

For decades, sugar was often discussed as a simple calorie issue.

Eat too much, expend too little, gain weight.

But emerging understanding of fructose metabolism suggests the story is more complex than that.

The liver doesn't respond to marketing claims. It doesn't know whether fructose arrived in a sports drink, a breakfast cereal, a smoothie or a fizzy drink. It simply processes what arrives.

And when that fructose load becomes excessive, one of its responses is to turn some of it into fat. 

Perhaps that's why the most important question isn't whether added sugar is "good" or "bad".

It's whether we've normalised levels of sugar consumption that our metabolism was never designed to handle.

• Robert Lustig. Fructose: It’s “Alcohol Without the Buzz”. [advances.n...rition.org], [researchgate.net]
• Robert Lustig: Similar Pathways of Alcohol and Fructose in Fatty Liver Disease Development. [youtube.com]
• Fructose and the Liver. [pmc.ncbi.nlm.nih.gov]
• From fructose to steatosis, fructose-induced inflammation as a driver of hepatic injury and MAFLD progression. [nutrition.bmj.com]
• Fructose and Alcohol Hepatotoxicity: Demographic Overlap and Mechanistic Interactions. [mdpi.com]