fructose… victim or villain?
- Fructose (a.k.a “fruit sugar”) is used to sweeten many modern processed foods due to its sweetness and low cost.
- On the plus side, fructose has a lower glycemic index value than glucose and does not require as much insulin to metabolise.
- On the downside, fructose is processed directly by the liver, does not trigger appetite signaling hormones such as leptin, and in excess can lead to increased triglycerides and LDL, and can lead to fatty liver.
- If we focus on nutrient dense foods that don’t spike blood glucose levels will mean that we largely avoid empty calories, including foods high in fructose.
it all started when…
Not so long ago people with diabetes were advised to use fructose rather than glucose as the sweetener of choice.
More recently though the reputation of fructose has become tarnished.
Let’s look at what happened and what it means for us now.
At first glance, fructose appears to have a number of positive qualities.
- With a Glycemic Index (GI) value of 19, fructose raises blood glucose less than other sweeteners such as sucrose (table sugar) (GI = 66) or pure glucose (GI = 100). 
- Fructose requires less insulin to metabolise than other carbohydrates. 
- High fructose corn syrup is cheaper than other sweeteners (though this is largely due to government subsidies).
- Calorie for calorie, fructose is sweeter than sucrose so you don’t need to use as much to get the same effect.
These days the list of negatives attributed to fructose is increasing.
- Excess fructose increases triglycerides and LDL cholesterol more than glucose.
- Excess fructose can lead to fatty liver, insulin resistance and type 2 diabetes. 
- Fructose does not trigger appetite the signalling system hormones insulin and leptin so it is easy to overeat foods sweetened with fructose.
- Fructose over consumption may be at the heart of metabolic syndrome which has also been linked to a wide range of cancers.
foods highest in fructose
The foods highest in fructose are listed below. With soft drinks at the top of the list, it is also interesting to note that a range of naturally occurring foods are not far behind.
|food||% calories from fructose|
|salad dressing (fat-free)||48%|
For our ancestors, high fructose, low satiety fruits would have been an effective way to store some extra fat in preparation for winter.
In our modern environment though, foods high in fructose are available all year round and can easily lead to excess consumption of “empty calories”.
Fruits do contain vitamins, however most fruits are typically not as nutrient dense as vegetables. Avocados and olives are the only fruits that routinely make it into the lists of nutrient dense foods.
High Fructose Corn Syrup (HFCS) was developed in the 1950s and was incorporated into our diet in processed foods between 1975 and 1985. HFCS now represents more than 40% of the caloric sweeteners added to foods and beverages and is the sole source of sweetener in soft drinks in the USA.
The low nutritional value of soft drinks combined with the fact that they are easily over consumed makes for an ominous combination.
fructose, glucose, sucrose, starch… does it really matter?
There has been a lot of discussion about the perils of added sugar (e.g. That Sugar Film and I Quit Sugar) as well as dire warnings about high fructose corn syrup. However in the end I’m not sure there is a big difference.
Fructose is processed directly by the liver and converted to triglycerides and LDL, largely without insulin.
Glucose that isn’t burned immediately raises blood sugar and is mopped up by insulin and stored as body fat and triglycerides in the blood.
So in the end, excess carbohydrate, whether it comes from fructose or glucose, ends up as stored body fat or fat in your blood stream (i.e. cholesterol).
The table below shows a comparison of the types of sugars contained in a number of foods along with their nutrient density score (note: a ND score of zero corresponds to the average of the foods in the USDA foods database, less than zero means that it’s less nutrient dense than average).
|food||% calories from carbs||% starch||% maltose||% glucose||% fructose||Nutrient Density / cal|
In his Perfect Health Diet Paul Jaminet says:
“A nourishing, balanced diet that provides all the required nutrients in the right proportions is the key to eliminating hunger and minimising appetite and eliminating hunger at minimal caloric intake.”
While cola and apple juice may have the highest percentage of calories from fructose they also have the lowest nutrient density values. So if you’re not worried about the carbs it’s going to be better to have the sweet potato or the bread from a nutrient density point of view.
Although at the same time you’ll notice that the sweet potato and bread both have less nutrients per calorie than the average of all the foods analysed. There are a going to be better food options if you’re interested in nutrient density and / or blood glucose control.
the bitter truth
While Robert Lustig has drawn a parallel between the toxic effects of alcohol and fructose on the liver, it is not entirely clear whether the overall effect of fructose is actually worse than any other form of carbohydrate, particularly if not eaten in excess.
If you are insulin sensitive and have excellent blood glucose control should you avoid all apples and grapes just because they contain fructose? I’m not sure.
Perhaps naturally occurring fructose with the fibre packaging it came in is not going to be such a big deal. A quick check with a blood glucose meter will tell your whether your body can tolerate that banana or orange.
What we do know is that substituting carbohydrates with fat, particularly omega 3 (fish) and oleic acid (olive oil), will provide positive outcomes in terms blood markers such as HDL and LDL (see the Good Fats, Bad Fats).
Even the gurus though are divided on the topic of fructose. Dr Richard Feinman says:
“Dietary carbohydrate restriction remains the best strategy for obesity, diabetes and metabolic syndrome. The specific contribution of removal of fructose or sucrose to this effect remains unknown.”
fructose and the food insulin index
If you have read much of my blog you’ll know that I’m interested in using the food insulin index data to refine our understanding of our insulin response to food. So what does the fact that fructose requires less insulin than glucose mean for predicting our insulin response to food?
As shown in the plots below, our insulin response to food is loosely related to carbohydrate content and the glycemic load of our diet. When we look a little closer though we see that high protein foods require insulin while fibre containing foods require less insulin than we might have expected.
Once we account for the effects of fibre and protein we are better able to predict our blood glucose and insulin response to food. However even after we account for fibre and protein the outliers that require less insulin than we might have anticipated seem to be foods higher in fructose (e.g. Coke, corn, raisins, bananas, and oranges).
We know that fructose requires less insulin than other carbohydrates. Once we account for this fact the correlation improves even further. The high fructose foods move back towards the trend line. The best correlation is achieved when we assume that 72.5% of fructose does not require insulin. This aligns with the observation that fructose has a lower GI and our understanding that fructose can be converted to glucose via gluconeogenesis.
useful for diabetes or just a ‘fun fact’?
For people with type 1 diabetes this additional understanding of the way fructose affects insulin demand could be used to more accurately calculate insulin doses. Rather than simply assuming that all carbohydrates require insulin we can better predict the insulin demand by considering protein, fibre and fructose.
However, in practice this is probably a little over the top. The simplest approach for people trying to manage insulin and blood glucose levels is to simply avoid or limit non-fibre carbohydrates, including fructose containing foods.
what does this it all mean?
But what does this mean for the rest of the population who do not routinely pay attention to their blood glucose levels?
I think the take home of all this is that if we focus on nutrient density and maximising nutrient dense foods the foods that are highest in simple carbohydrates (like fructose, glucose and sucrose) will fall off our shopping list.
Fructose, glucose, sucrose, maltose or starch? Which one is worse? Personally, I’m not sure, but I think if you focus on nutrient dense foods that normalise your blood glucose the question largely becomes irrelevant.
Excess low satiety empty calories are a disaster regardless of their source.