Sugar is toxic

Dr. Robert Lustig in his 'Sugar: The Bitter Truth' claims that sugar is toxic. We analyse this material and look into the science in it.

Sugar is killing us. At least this is what Dr. Robert Lustig is telling us in his seminar “Sugar: The Bitter Truth” that accumulated over 6 million views on YouTube. This 90 minutes lecture is worth watching as Dr. Lustig is a skilled speaker.

As Dr. Lustig is addressing mostly medical students, he is using a lot of jargon when talking about chemistry and biology so we decided to give you his findings in more digestible form.

Sugar(s), glucose, and fructose. What’s the difference?

When we say sugar we usually mean a processed product like table sugar or high fructose corn syrup. In other words sucrose – and this usually is roughly 50% glucose and 50% fructose.

Both glucose and fructose are sugars but as Dr. Lustig points out, they are not the same.

Glucose is the energy of life. Every cell in our body can use it to produce energy. Every plant on our planet is producing it as a way to store energy.

From the evolutionary point of view, we are designed to process glucose all the time as we eat it with all the vegetables.

Fructose is not glucose

Fructose metabolic path is different that the one of glucose and Dr. Lustig claims that chronic exposure  to fructose promotes the metabolic syndrome.

Additionally, fructose does not stimulate insulin or leptin and doesn’t suppress ghrelin, hormones responsible for feeling of hunger. The result is overeating.

Metabolic paths of glucose, ethanol and fructose

You might be asking now what is ethanol doing here? This is the most controversial part of Dr. Lustig’s lecture.

But first, let’s have a look on glucose. The energy of life.

If we consume 120 kcal in glucose (two slices of white bread), 80% will be used by all the cells in the body. 20% of glucose will get to the liver where most of it will be turned into glycogen (a non-toxic storage form of glucose). Finally, just 0.5 kcal will end up as fat. As the insulin goes up the brain sees that as a signal to stop eating.

Now to the ethanol. Dr. Lustig calls it a carbohydrate as it’s made from sugar (fermentation).

There is no doubt that ethanol is a toxin. If we consume 120 kcal (a shot of Marker’s Mark) roughly 10% will be metabolised in stomach and intestine, another 10% will be metabolised by kidneys, muscle, and brain. 80% of consumed methanol will hit the liver. And we all know that liver is the first victim of alcohol abuse. At least in our body.

The result that methanol can have for our body are bad. Sclerosis, dyslipidemia, insulin resistance, and inflammation just to name the most severe ones.

If we consume 120 kcal in sucrose (a glass of orange juice) we are consuming 60 kcal of glucose and 60 kcal of fructose.

48 kcal (glucose) will be used by the body, 60 kcal (mostly fructose) will be processed by the liver.

30% of it will end up as fat according to Dr. Lustig. As he point’s out fructose causes insulin resistance, inflammation, dyslipidemia, hyperinsulinemia and high blood pressure.

Fructose is to blame

Dr. Lustig is painting here a grim picture where excess fructose consumption has very similar effects to our health as alcoholism. He even calls fructose ‘alcohol without the buzz’.

He blames high fructose consumption that went through the roof in recent years for the epidemic of obesity. Goal to reduce the amount of fats consumed per capita (that we managed to meet) resulted in the increased consumption of sugar. As fats and sugars are key factors in experiencing taste when you remove fat from food it tastes, as Dr. Lustig describes, like cardboard. That problem has been solved by food industry with added sugar.


As you can imagine those claims are highly controversial and there are people pointing out holes in this theory.

The main one is the amount of fructose that converted to fat. 30% quoted by Dr. Lustig is not confirmed by other studies.  There is a correlation between high fructose consumption and fat creation process in the liver but from what we gathered the process is not very well understood. We definitely need more research in this area to be able to tell with a 100% certainty that fructose is the bad guy here.

What we liked

Controversies aside, one thing that we liked in Dr. Lustigs approach is what he calls a ‘sugar intervention’:

  • get rid of all sugared liquids – drink only water and milk
  • eat your carbohydrates with fiber – fructose in fruit is good for you
  • wait 20 minutes for the second portion
  • buy your screen time (watching tv, playing video games etc.) minute-for-minute with physical activities using those four steps in his daily work with obese children.

Dr. Lustig is using those four steps in his daily work with obese children and his getting great results there.

Should I eat fructose?

At VeryBreakfast, we are big fans of unprocessed food. Fructose in fruit is good for you, but sugar added to most processed food that we find in our shops is what we recommend staying away from.

Of course, a little sugar is not going to harm you but having sugar added to every meal and drink, as it is these days without you even knowing it, is not good. From the evolutionary point of view, we have been eating fructose from ripe fruit for a very long time and our bodies have a way to metabolize it. But as you can easily imagine before the supermarkets and fridges in every home, fruit have been available seasonally.

Moderation is the key here.

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