Modern Diet Myth No. 4: Fructose turns to fat

Fructose – the dietary villain de jour – is currently giving rise to more myths than anything else and they all seem to relate to fat. Fructose supposedly leads to fatty liver and too much fat in the blood. To top it off, fructose is said to be uniquely fattening! Where do we start?

Fat in your liver

Most of the carbohydrate we eat ends up in the bloodstream as either glucose or fructose. The myth goes that glucose is the good sugar as it is used to power the brain, the muscles and most of the cells in the body. And the fructose is the bad sugar which is quickly taken up by the liver and turned into fat, giving rise to fatty liver.

Unfortunately for the myth-makers, no reputable health authority in the world agrees. Fatty liver is certainly a common problem but the experts see it as part of the metabolic syndrome – a cluster of abnormalities linked to central obesity and insulin resistance, where the cells of the body become less sensitive to insulin.

There is no recommended diet for fatty liver. Instead, health authorities encourage people with fatty liver to lose some weight and increase their physical activity, both of which improve insulin resistance.

Fat in your blood

Our liver certainly has the ability to turn both glucose and fructose into fat – it’s the perfect way to turn any excess carbohydrate calories into a form that can be stored for later use. And sooner or later this fat appears in the blood as ‘triglycerides’.

However, the idea that all the fructose we eat turns to fat pushing up the level of triglycerides in the blood is just plain wrong. If you are a healthy, normal weight person eating enough food to maintain your body weight your liver only turns a tiny fraction of fructose into fat, about 1-3%. Most of the fructose taken up by the liver is actually turned into glucose – supposedly the good sugar, so it’s much more accurate to say ‘fructose turns to glucose’ than it is to say ‘fructose turns to fat’.

It’s a different story if you overeat thereby forcing the body to turn excess sugars into fat. But the underlying problem here is not fructose; it’s overeating.

The best ways to lower the level of triglycerides in the blood are to lose some excess weight, increase physical activity and limit alcohol intake.

Image: source

Fat on your body

The silliest myth about fructose is that it is uniquely fattening. You would have thought that we would all have learned something from the fat-makes-you-fat fiasco, where the blame for the obesity epidemic was laid at the feet of just one nutrient – fat. This focussed everyone’s attention on the third of our calories that came from fat and allowed us to ignore the rest. And the nation got fatter.

Does it make any sense to target fructose, which typically provides just 10% of calories? Do the other 90% of calories not count?

None of the nutrients is uniquely fattening. People put on weight when they regularly eat more calories than their bodies need.


7 thoughts on “Modern Diet Myth No. 4: Fructose turns to fat

  1. I recently took an on-line drubbing for making the outrageous claims that there is fructose in fruit and that the very word fruct-ose means “fruit sugar”. Apparently, fructose is only synthesized from corn, GMO, no doubt. I suspect that not everyone was paying attention in 9th grade life sciences the way that I did. Thanks Mrs. Post, for leading me astray!

  2. Does anybody know that having 2 eggs for breakfast cooked with a tea spoon of butter every day one slice of whole grain bread toasted butter thinly spread have a negative affect on cholesterol level thanks

    • Enrico, your statement makes no sense. When you say “having 2 eggs for breakfast cooked with a tea spoon of butter every day one slice of whole grain bread toasted butter thinly spread have a negative affect on cholesterol level”, it begs the question: compared to what? Regards, Bill

  3. Unlike glucose, fructose doesn’t trigger two key satiating hormones. “The digestion, absorption, and metabolism of fructose differ from those of glucose,” researchers in a review published in The American Journal of Clinical Nutrition wrote. “[U]nlike glucose, fructose does not stimulate insulin secretion or enhance leptin production. Because insulin and leptin act as key afferent signals in the regulation of food intake and body weight [to control appetite], this suggests that dietary fructose may contribute to increased energy intake and weight gain.” George A Bray, Samara Joy Nielsen, and Barry M Popki – Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity1,2 – Am J Clin Nutr April 2004 vol. 79 no. 4 537-543

  4. So Dr Robert Lustig who was on RN’s The Health Report and has at least one Youtube video is talking nonsense?

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