Is fructose evil? What's all the fuss about sugar contained in fruit?Back to Blog
30 July 2015
Google “Fructose” and you’re bound to get search results to articles like “Why is Fructose Bad For You” and “Fructose: Can Fruit make you Fat?”
There’s been a small wave of variations on sugar-free diets with some people deeming fruit now ‘bad’ since it’s high in fructose. How have we arrived at this rather bizarre conclusion?
At the risk of oversimplifying things, it seems to have begun with two particular professors.
Fructose is 'poison'?
It all started in 2009 with Professor Lustig from the University of California and his YouTube video: “Sugar: The Bitter Truth”.
With almost 6 million hits for a 90 minute lecture (we’re not joking…), Professor Lustig argues sugar is a toxin that harms our organs and disrupts our body’s natural hormones. Excessive consumption of sugar therefore causes obesity, diabetes and heart disease. He, along with other journalists like Gary Taubes and Mark Bittman (New York Times) emphasise that sugar is a toxin because of its evil child, fructose.
Sugar comes in the form of sucrose, glucose or fructose. Glucose travels quickly to our cells to convert to energy. It also makes the pancreas secrete the hormone insulin, which removes excess glucose from our bodies and triggers the hormone leptin, which stops us from being hungry.
Fructose on the other hand, needs to be broken down into glucose by the liver so our body’s cells can use it as energy. In addition, it doesn’t trigger insulin production. Instead, it raises the hormone ghrelin, which makes us hungry. So, the argument is, if you eat too much fructose, you poison yourself (because it taxes your liver) and are hungrier, so you end up eating more and gaining weight.
Because of Professor Lustig’s findings, people have jumped on the anti-sugar bandwagon and reject fruit, which is filled with naturally-occurring fructose.
Not all fructose is equal
Meanwhile, Professor Ludwig of Harvard Medical School reminds us it’s not that simple and how we consume fructose needs to be considered. If we consume fructose by downing soft drink or ice cream, then we flood our insides with ‘loose fructose’ which reaches the liver all at once. This then has the effect Lustig describes, of ‘poisoning’ ourselves.
However, if we consume fructose via fruit, the fibre in fruit enormously slows down digestion. This means that sugar is released into the body much more slowly, and as Ludwig argues, it has a much lower glycaemic index than chugging a bottle of Coke.
In fact, a South African study had 17 adults eat a diet of 20 servings of fruit a day (approximately 200 grams of fructose), for 24 weeks. None of the adults gained weight, developed high blood pressure or had any imbalance to their insulin and lipid levels.
So what's all the fuss about?
Consuming loads of fructose isn’t great if it’s primarily through highly processed foods (soft drinks, desserts, snacks, sugary cereal). But consuming fruit and similar whole foods is good, as they contain an immense amount of fibre and other necessary nutrients which change the way fructose is processed.
It’s simplistic to say that fructose is bad, and you should stop eating fruit. That would be akin to throwing the baby out with the bath water. The lesson from this is that we should approach nutrition and health holistically – eating more whole foods as part of a balanced diet and training/exercising well. There really is no quick fix.