High-fructose and high-fat diet damages liver mitochondria, study finds

Your liver is one of the most vital organs in the body. Although it often does not get as much attention as the heart or the lungs, the liver performs over five hundred functions. For this reason, it is important that you keep your liver- and more importantly, your liver mitochondria- healthy. 

New research has found that consuming a large amount of fructose along with a high-fat diet can damage your liver, and lead to other health problems.

What Does Your Liver Do?

Before we get to the study, lets first discuss what exactly this vital organ does for you. Your liver helps you to digest everything you eat and drink. One of its main functions is detoxifying your body. It absorbs everything you eat, drink, breath, or rub into your skin and processes it. In general, it keeps what you need and gets rid of what you don’t [1]. Other functions of the liver include:

• Cleansing your blood: your liver turns harmful substances like alcohol, drugs, and environmental toxins into a form that can be excreted [2].
• Regulating your fuel supply: your liver stores some of the carbohydrates you eat as glycogen. It releases some of that later when you need it- between meals, or when you’re sleeping- to fuel your brain, muscles, and other parts of the body [3]. Your liver also processes and stores fat for energy [4].
• Producing proteins: proteins transport substances like iron, calcium, and thyroid hormone in your blood. Your liver produces some of these proteins, including albumin, which maintains water balance in your body, and proteins that help clot your blood, and proteins that help fight infection [5].
• Keeping your hormones balanced: the liver makes sure your sex hormones, thyroid hormones, cortisol, and other adrenal hormones, as well as many more, stay organized [1].
• Regulating cholesterol: your liver produces cholesterol and converts it into other substances like vitamin D, testosterone, and estrogen [6].
• Producing bile: bile is how your liver gets rid of toxins. It emulsifies fats so your body can absorb fat-soluble vitamins like vitamins A, D, E, and K. The liver removes any toxins and by putting them into that bile, which is eventually excreted in stool [7].

Read: Gut Bacteria Linked to Cardiovascular, Other Health Conditions

Study: Sugar and Fat Damage Liver Mitochondria

It goes without saying that we must keep our livers healthy. One major way to do this is through a healthy diet. Unfortunately, the typical North American diet is not supporting liver health. Researchers at the Joslin Diabetes Research Center discovered new information regarding how our diet affects our livers. Specifically, they found that high levels of fructose in the diet inhibit the liver’s ability to properly metabolize fat [8].

C. Ronald Kahn, Chief Academic Officer at Joslin and the Mary K. Iacocca Professor of Medicine at Harvard Medical School and lead author on the study, explained that fructose makes the liver accumulate fat. 

“It acts almost like adding more fat to the diet. This contrasts the effect of adding more glucose to the diet, which promotes the liver’s ability to burn fat, and therefore actually makes for a healthier metabolism.” [8]

Despite the fact the glucose and fructose have the same number of calories, fructose appears to have a much more damaging effect on the body. When you add more fructose to the diet, the liver stores more fat. This is bad for both the liver and for whole body metabolism.

“Surprisingly, when you switch the sugar in the diet from fructose to glucose, even though they’re both equally caloric, the glucose doesn’t have that effect. In fact, if anything, overall metabolism is somewhat better than if they just were on plain high-fat diet,” said Kahn [8].

The researchers performed a series of animals studies that evaluated a number of diets:

• High-fructose
• High-glucose
• High-fat
• High fat with high fructose
• High fat with high glucose

To determine the effects of each diet, they looked at markers of fatty liver. One of these is the presence of acylcarnitines, which are produced when the liver burns fat. High levels of these mean there is a lot of fat being burned in the liver.

Animals on the high-fructose high-fat diet had the highest levels of acylcarnitines. Animals on the high-fat high-glucose diet had the lowest- even lower than the plain high fat diet. This shows that glucose actually helps the liver burn fat [8].

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Fructose and Your Mitochondria

Researchers also looked at another marker for fatty liver, CPT1a. CPT1a is an enzyme that is critical for burning fat. High levels indicate that the mitochondria are working effectively. In the study, animals on the high fructose high fat diet had very low levels of the enzyme. This means their mitochondria were not functioning properly.

“When mitochondria are healthy, they have this nice ovoid shape and crosshatching,” says Dr. Kahn. “In the high-fat plus fructose group, these mitochondria are fragmented and they’re not able to burn fat as well as the healthy mitochondria.” [8]

The high-fat high-glucose group, however, had mitochondria that looked more normal, because they were burning fat properly.

This research is building off of another study from 2017, in which researchers gave mice a high-fructose high-fat diet. These mice all developed obesity, glucose intolerance, and enlarged livers. Like with the more recent study, adding glucose to their diets did not produce the same negative effects [9]. While these are only animal studies, the results are not encouraging and lends to the notion that excessive fructose from processed foods should be avoided.

Read: Choline Deficiency Can Trigger Fatty Liver Disease

Eat to Support Your Liver

So where is all this added fructose in our diets coming from? While it can come from a variety of places, the most common source is sugar-sweetened beverages. This, combined with the typical high-fat western diet, is very damaging to your liver.

Luckily, keeping your liver healthy is well within your control. While eating a balanced diet rich in whole nutritious foods is extremely important, there are some foods that particularly good when it comes to supporting liver health. The following foods are great for supporting liver health:*

• Coffee
• Green, black, and white tea
• Grapefruit
• Fish and seafood
• Berries
• Nuts
• Leafy green vegetables
• Beets and beet juice
• Cruciferous vegetables
• Olive oil
• Eggs
• Dark orange vegetables
• Onions, garlic, and shallots
• ginger

Why are these foods so good for your liver? They all contain certain vitamins, minerals, and chemical compounds that reduce inflammation and oxidative stress [1].

Foods to avoid include deep fried foods, foods high in refined or added sugar, highly processed foods, and red meat. Alcohol is also detrimental to your liver health, because it breaks down into a highly toxic compound called acetaldehyde. The less alcohol you drink, the better.

*For more info on exactly why these foods are so good for your liver, check this article out by Doug Cook, RDN.

Read: 14 Ways Low Glutathione Levels Could Be Affecting Your Health

A Word on Detox Diets

There is a lot of hype around “detox” diets, but unfortunately, they don’t work. The truth is, your liver is detoxifying all the time. There is nothing that you can consume that can remove toxins from your body.

The best way to remove toxins from your body is to provide your liver with all the nutrients that it needs in order to function properly. Detoxes, which often hinge on eating next to nothing, do not provide much in the way of nutrition. For this reason, they are doing nothing to help your body [1].

The best thing you can do is avoid sugar-sweetened beverages and other processed foods that contain added fructose, avoid excessive saturated fats and avoid trans fats (small amounts naturally in dairy are ok), and eat a healthy diet that supports your liver. Do this, and you’re doing what you can do to support your liver and to allow it to function optimally.

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