How Sugar Messes up Your Liver and Gives You Diabetes

Modern man is plagued with many diseases that you will not find in some “primitive” populations like modern hunter-gatherers.

These include obesity, heart disease, some cancers and last but not least, type II diabetes… which has reached epidemic proportions in the past few decades and now afflicts about 300 million people worldwide.

This disease is a common cause of early death, blindness, amputation and a severely decreased quality of life… and it is advancing rapidly, every single year.

In the video above, Dr. Robert H. Lustig and Dr. Elissa S. Epel explain how excess sugar can mess up liver metabolism and ultimately lead to diabetes.

Excess Sugar is Associated With Diabetes

Diabetic Shooting Insulin

Dr. Lustig recently took part in a study where they examined the associations between sugar consumption and diabetes in 175 countries (1).

They found very clear associations, where each 150 kcal (about one can of soda) per day of sugar increased the prevalence of diabetes by 1.1%.

To put this number in perspective, if all of the U.S. added one can of soda to their daily diet, almost 3.5 million more people would become diabetic.

In this study, added sugar was the only part of the diet that correlated with diabetes when they adjusted for confounding factors.

These types of studies are so-called observational studies, which can not prove that one thing caused another, it can only show that they are correlated.

However, there are other lines of evidence linking sugar to the development of type II diabetes and this specifically involves how sugar affects the liver.

How Fructose Messes up Your Liver

Glass Full Of Sugar Cubes

Sugar is composed of two molecules… glucose and fructose.

Glucose can be metabolized by every cell in the body and if we don’t get it from the diet, our bodies make it.

However, fructose is different. The only organ that can metabolize sugar is the liver, because only the liver has a transporter for it (2).

Athletes or highly active individuals can eat quite a bit of fructose without problems, because their livers will turn the fructose into glycogen – a storage form of glucose in the liver.

However, when someone’s liver is already full of glycogen (which is true of most people), the fructose will be turned into fat (3).

Some of the fat gets shipped out as blood triglycerides while part of it remains in the liver, contributing to non-alcoholic fatty liver disease (4, 5).

At the same time, your liver becomes insulin resistant. This causes elevated insulin all over your body, which can lead to obesity, metabolic syndrome and many other diseases (6, 7).

Eventually, the pancreas will become unable to secrete sufficient insulin to drive blood glucose into cells.

At this point, blood sugar levels elevate significantly… and that’s when a diagnosis of diabetes is made.

This Does NOT Apply to Fructose in Whole Fruits

Teenage Girl Eating Fruit

Fructose is harmful in the context of excess calories. If we eat small amounts or we are already in a calorie deficit, fructose will not cause harm.

Fruits are a real food with a low energy density, lots of water and significant chewing resistance. It is almost impossible to overeat fructose by eating whole fruit.

There are a few instances where minimizing fruit might be a good idea.

If you are:

a) Diabetic.
b) Very carb sensitive.
c) Eating a very low-carb ketogenic diet.

…then you should probably avoid fruit as much as possible, except perhaps for the occasional berries.

But for healthy people trying to stay healthy, there is no proven reason to avoid natural, whole fruit.

What Dr. Lustig says applies to excess fructose from added sugars. It does NOT apply to moderate consumption of fruit.


  1. You could teach a biochemistry course just following the errors in this talk. Intestine, kidney and even muscle have transporters for fructose. Twenty percent of glucose goes to the liver? That depends entirely on how much you take in. But it’s beyond the errors in biochemistry. A close colleague of mine recently died from liver failure from alcholism. To suggest that alcoholism is in any way related to eating too much sugar is completely without perspective.

    • Did I miss something? I didn’t see anything at all suggesting that alcoholism is in any way related to eating too much sugar. However, the info concerning insulin resistance and diabetes is spot-on with what my doctor told me when I was diagnosed as pre-diabetic. I have been able to lower my A1C numbers significantly by following a low-carb, low-sugar diet. Thanks for ANOTHER great article, Kris!

      • I wasn’t clear. Lustig has continually made the association between sugar and ethanol. My point was that aside from being incorrect (they are not metabolized by similar mechanisms as he claims), it trivializes alcoholism. Your doctor is correct. In fact, if you lower sugar as a means of lowering carbohydrate that is obviously good. The best treatment for diabetes and pre-diabetes is carbohydrate reduction.

        What we know, however, is that starch is worse than sugar for people with diabetes. If you lower sugar and put back in starch with all that healthy fiber, (which is what is really being recommended by Lustig) you will probably not accomplish much. What we don’t know is what causes diabetes although carbohydrates are likely involved. But we won’t make progress if we go with non-scientific hysteria of the type that we have not yet given up with fat and cholesterol.

        Lustig’s study showed nothing at all — see my comments at the PlosOne site. The most important thing is that without understanding the biochemistry — fructose is incorporated into glucose metabolism and if we make it out to be a poison (Lustig’s words), we will not make progress.

        • Betty W says:

          Doesn’t the starch turn to sugar once it’s digested? I know it raises blood sugar levels…

          • Two simple sugars (monosaccharides) are glucose and fructose. Sucrose (“sugar,” or “table sugar” is a dimer of glucose and fructose which breaks down to the two monosaccharides. When we talk of “blood sugar” we usually mean glucose because that is the main stimulus for secretion of insulin. That is why it is not good to jump to conclusions on fructose and sucrose because, for people with diabetes or metabolic syndrome, glucose will cause insulin secretion whose fluctuations are what makes things worse.

            I will have a blogpost coming up with an introduction to simple sugar if you are interested. Watch this space:

            On the note below, Sugar is NOT the only calorie source that correlates with the increase in diabetes. Starch went up more than sugar. Actually, most foods went up including fruits and vegetables. The only things that went down during the increase in diabetes are red meat and eggs.

  2. Mike McCarthy says:

    The degenerative diseases from metabolic syndrome – insulin resistance match those from alcoholism. You have alcoholic and non alcoholic fatty liver disease. Carbon, Hydrogen and Oxygen go together in different combinations to make different sugars and alcohols. Who can guarantee there are no enzymes or gut flora to make these conversions! That would be a rash guarantee indeed.

    Winter 2012
    Issues in Liver Health
    Are you feeding your liver too much sugar?

    Alcohol has always been considered the liver’s worst enemy. Lately however, there is increasing evidence that refined sugar and its manufactured cousin – high fructose corn syrup — may actually do just as much damage to the liver when consumed in excess.

  3. Ralwattar says:

    Hi Kris, I always read and learn from your articles–keep them coming! Can you write something about fried food (without batter, of course). We’ve always been taught that it’s very unhealthy to fry food and I would like to know how frying fits in the HFLC diet. Thanks

  4. Happy to report that I have NOT had added sugar in 10 YEARS!!

  5. Peter Murray says:

    While total calorie consumption has contributed to increases in diabetes rates around the world, they don’t explain the whole story. Here’s something that you many don’t know or get all mixed up – a calorie isn’t just a calorie. Researchers in 2010 discovered that it’s the increase in total fats and carbohydrates specifically that’s causing the massive weight gain in people around the world. One product that metabolizes in your body as both fat and carbohydrate is sugar.

    Sugar is the only calorie source that correlates with the increase in diabetes. In 1985, when the world-wide sugar consumption was 98 million tons, diabetes affected 30 million people. By 2010, sugar consumption had risen to 160 million tons, and global diabetes prevalence reached 346 million people. Overall, sugar is 50 times more potent than calories, in terms of causing diabetes. And the answer lies in its unique composition.

  6. This article is incredibly insightful. I feel like never touching sugar ever again. During my childhood sugary sodas and candy was practically force fed to myself and my peers. I am now realizing that it could be setting me up for a lifetime of illness. Is there any way to reverse the damage before it’s too late? I’m in my early 20′s and hoping I can transform my health status into something positive. Keep up the good work!

  7. Practically speaking, Kris is right that moderate amounts of fructose (or, depending on who you are, any carbohydrate) are not going to hurt you. And, as he says, if you have diabetes or metabolic syndrome, you want as little carbohydrate (sugar or starch) as you can. The reason fructophobia is worse than lipophobia is that nobody really wants to say that a lot of sugar is good but that is way different from saying it is a toxin. And, Andy, your body has long since forgotten the sins of your childhood. But as Colin Powell use to say to Karl Rove: “On the floor, private. Give me twenty push-ups.”

  8. Hi.

    I have been following Kris for 5 months now. No sugar or gluten.

    I have just been checked by my gp and my insulin resistance and elevated glucose is gone. My liver function and cholesterol profile were perfect as well. Have lost 17 kgs as well.

    My doctor was very happy and so am I.

    I am never going back to high carb eating.

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