Why Is Fructose Bad For You?

Written by Dr. Steve Chaney on . Posted in Fructose

Is It The Sugar, Or Is It The Food?

Author: Dr. Stephen Chaney

 

why fructose bad for youI don’t usually report on studies done in mice, but this study sheds light on a particularly puzzling question: Why is fructose bad for you?

The studies are clear-cut. High fructose consumption is associated with inflammation, obesity, non-alcoholic liver disease, insulin resistance, type 2 diabetes, kidney disease, increased LDL cholesterol and triglycerides, and heart disease. Based on these associations, fructose appears to be deadly. Why would anyone want to consume it?

Yet fructose is found in virtually every fruit. In fact, fructose, also known as fruit sugar, was first isolated from fruits. Hence the name fructose. Humans have been eating fruits safely for thousands of years. Fruits are very good for us. That raises the question: “If fruits are good for us, how can fructose be bad for us?”.

An important clue can be found by looking at what the food industry has done to the American diet. Because fructose imparts a pleasurable, sweet taste to foods, the food industry keeps adding it to more and more foods. As a result, dietary intake of fructose has increased 100-fold over the past two centuries. It has reached the point where fructose now accounts for almost 10% of the caloric intake in the United States.

 

Is It The Sugar, Or Is It The Food?

 

Let me expand the discussion by using a couple of graphics I developed for my book, “Slaying The Food Myths.”  

There Are No Sugar Villains. There Are No Sugar Heroes:

why fructose bad for you sugar foodVirtually all sweeteners are primarily a mixture of fructose and glucose. The graphic on the left compares high fructose corn syrup (the current villain) with other “natural” sweeteners used in foods (our current heroes). High fructose corn syrup ranges from about 40% fructose to 55% fructose. The exact percentage depends on what kind of food product is being made with it. Honey and coconut sugar are about 45% fructose. Sucrose and grape juice concentrate are around 50% fructose. Apple juice concentrate is around 60% fructose, and agave sugar comes in at a whopping 80% fructose.

In other words, if fructose is the culprit that everyone makes it out to be, “healthy” sugars are no better than high fructose corn syrup. Simply substituting a “healthy” sugar for high fructose corn syrup is unlikely to provide any meaningful benefit.

 

Is It The Sugar, Or Is The Food?

why fructose bad for you fruitsThis graphic shows us what a nutrition label would look like on a medium apple. I am sure that label is a wake-up call for many of you. The amount of sugar and the percentage of fructose and glucose are about the same as in an 8-ounce soda sweetened with high fructose corn syrup. The same is true for virtually every other fruit you can think of.

Now let me share one more thing you won’t hear from what I refer to as “Dr. Strangelove’s Health Blog” (You probably know the ones I am referring to). Virtually all the studies showing the bad effects of fructose consumption have been done with sodas and sugary junk foods. They haven’t been done with apples.

In fact, virtually every study looking at fruit and vegetable consumption has shown they are incredibly good for us. They lower inflammation and reduce the risk of obesity, diabetes, heart disease, and cancer. And, the more the better. One study found that the health benefits of fruit and vegetable consumption topped out at around 10 servings a day.

With this background, you should now fully understand why the question “If fruits are good for us, how can fructose be bad for us?” is so perplexing.

My simplistic explanation has always been that whole foods like fruits have fiber, which slows the absorption of fructose from the intestine. Our bodies were designed to handle fructose in a safe manner when it enters the bloodstream slowly. Sodas and junk foods, on the other hand, have little to slow the absorption of fructose. When fructose enters the bloodstream rapidly, our “safe” metabolic pathways for handling it are overwhelmed, and it is forced into the pathways that are harmful. For example, the “excess” fructose is converted to fat by the liver, which causes inflammation, obesity, fatty liver disease, and triglyceride production.

This is, of course, simply my hypothesis for explaining the different effect of fructose in fruits and sodas. It is based on sound metabolic principles, but it is far from proven. That is why I found the current study (C. Jang et al, Cell Metabolism, 27: 351-361, 2018 ) so interesting. It provides a metabolic rationale for my hypothesis.

How Was The Study Done?

Mice were fed a 1:1 mixture of fructose and glucose at doses that approximated the ranges of typical human fructose consumption. The fructose was isotopically labeled so that fructose and its metabolites could be identified by LC-MS (liquid chromatography – mass spectrometry). After feeding the mice the labeled fructose, the investigator measured the amount of fructose and its metabolites in various organs and in the portal vein, which transports sugars from the intestine to the liver for additional metabolism before they enter the bloodstream.

 

Why Is Fructose Bad For You?

why fructose bad for you intestine liverThe first surprise was that most of the fructose was metabolized by the intestinal mucosal cells that line the small intestine rather than the liver. Previous reports had assumed that fructose was primarily metabolized by the liver because that was where most of the bad effects of fructose metabolism had been observed.

These investigators observed that fructose was primarily converted to glucose and small molecular weight metabolites by the intestinal mucosal cells before being released into the portal vein, where they were transported to the liver. However, there was a strong dose response effect.

  • At low fructose doses, 90% of fructose was metabolized by intestinal mucosal cells before being released to the liver.
  • At high fructose doses, only 70% of fructose was metabolized by intestinal mucosal cells.
  • That means at high fructose doses the amount of fructose reaching the liver unchanged increases from 10% to 30%. That is a 3-fold increase!

The authors concluded:

  • “Based on these findings, we propose that the small intestine shields the liver from fructose and that excessive doses of fructose overwhelm the small intestine, spilling over to the liver where they cause toxicity.”
  • “A key difference between the health effects of fiber-rich fruits (and perhaps even fiber-rich prepared foods) and juices/sodas is their rate of intestinal fructose release.”
  • “It is likely that the appearance rate of free fructose in the small intestine plays a critical role in dictating its metabolic fate. Like the lower doses in our experiments, a slower rate of fructose appearance will result in more complete intestinal clearance, whereas higher doses and faster rates result in fructose overflow to the liver.”

This study needs to be confirmed, and the mechanism may be entirely different in humans. However, whether the mechanism is the same in mice and humans is immaterial. We already know that fructose in sodas and junk foods exerts a very different effect on our health than fructose in fruits and other fiber-containing foods.

The Bottom Line

 

Previous studies have clearly shown that fructose in sodas and junk foods is bad for us, while fructose in fruits is good for us. A recent study in mice provides a metabolic explanation for this difference. The study found:

  • At low fructose doses, 90% of fructose was metabolized by intestinal mucosal cells before being released to the liver.
  • At high fructose doses, only 70% of fructose was metabolized by intestinal mucosal cells.
  • That means at high fructose doses the amount of fructose reaching the liver unchanged increases from 10% to 30%. That is a 3-fold increase!

The authors concluded:

  • “Based on these findings, we propose that the small intestine shields the liver from fructose and that excessive doses of fructose overwhelm the small intestine, spilling over to the liver where they cause toxicity.”
  • “A key difference between the health effects of fiber-rich fruits (and perhaps even fiber-rich prepared foods) and juices/sodas is their rate of intestinal fructose release.”
  • “It is likely that the appearance rate of free fructose in the small intestine plays a critical role in dictating its metabolic fate. Like the lower doses in our experiments, a slower rate of fructose appearance will result in more complete intestinal clearance, whereas higher doses and faster rates result in fructose overflow to the liver.”

This study needs to be confirmed, and the mechanism may be entirely different in humans. However, whether the mechanism is the same in mice and humans is immaterial. We already know that fructose in sodas and junk foods exerts a very different effect on our health than fructose in fruits and other fiber-containing foods.

For more details, read the article above.

 

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

 

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Latest Article

Can Plant-based Diets Be Unhealthy?

Posted September 10, 2019 by Dr. Steve Chaney

Do Plant-Based Diets Reduce Heart Disease Deaths?

Author: Dr. Stephen Chaney

 

plant-based diets vegetablesPlant-based diets have become the “Golden Boys” of the diet world. They are the diets most often recommended by knowledgeable health and nutrition professionals. I’m not talking about all the “Dr. Strangeloves” who pitch weird diets in books and the internet. I am talking legitimate experts who have spent their life studying the impact of nutrition on our health.

Certainly, there is an overwhelming body of evidence supporting the claim that plant-based diets are healthy. Going on a plant-based diet can help you lower blood pressure, inflammation, cholesterol and triglycerides. People who consume a plant-based diet for a lifetime weigh less and have decreased risk of heart disease, diabetes, and cancer.

But, can a plant-based diet be unhealthy? Some people consider a plant-based diet to simply be the absence of meat and other animal foods. Is just replacing animal foods with plant-based foods enough to make a diet healthy?

Maybe not. After all, sugar and white flour are plant-based food ingredients. Fake meats of all kinds abound in our grocery stores. Some are very wholesome, but others are little more than vegetarian junk food. If you replace animal foods with plant-based sweets, desserts, and junk food, is your diet really healthier?

While the answer to that question seems obvious, very few studies have asked that question. Most studies on the benefits of plant-based diets have compared population groups that eat a strictly plant-based diet (Seventh-Day Adventists, vegans, or vegetarians) with the general public. They have not looked at variations in plant food consumption within the general public. Nor have they compared people who consume healthy and unhealthy plant foods.

This study (H Kim et al, Journal of the American Heart Association, 8:e012865, 2019) was designed to fill that void.

 

How Was The Study Done?

plant-based diets studyThis study used data collected from 12,168 middle aged adults in the ARIC (Atherosclerosis Risk in Communities) study between 1987 and 2016.

The participant’s usual intake of foods and beverages was assessed by trained interviewers using a food frequency questionnaire at the time of entry into the study and again 6 years later.

Participants were asked to indicate the frequency with which they consumed 66 foods and beverages of a defined serving size in the previous year. Visual guides were provided to help participants estimate portion sizes.

The participant’s adherence to a plant-based diet was assessed using four different well-established plant-based diet scores. For the sake of simplicity, I will include 3 of them in this review.

  • The PDI (Plant-Based Diet Index) categorizes foods as either plant foods or animal foods. A high PDI score means that the participant’s diet contains more plant foods than animal foods. A low PDI score means the participant’s diet contains more animal foods than plant foods.
  • The hPDI (healthy plant-based diet index) is based on the PDI but emphasizes “healthy” plant foods. A high hPDI score means that the participant’s diet is high in healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, coffee and tea) and low in animal foods.
  • The uPDI (unhealthy plant-based diet index) is based on the PDI but emphasizes “unhealthy” plant foods. A high uPDI score means that the participant’s diet is high in unhealthy plant foods (refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts) and low in animal foods.

For statistical analysis the scores from the various plant-based diet indices were divided into 5 equal groups. In each case, the group with the highest score consumed the most plant foods and least animal foods. The group with the lowest score consumed the least plant foods and the most animal foods.

The health outcomes measured in this study were heart disease events, heart disease deaths, and all-cause deaths. Again, for the sake of simplicity, I will only include 2 of these outcomes (heart disease deaths and all-cause deaths) in this review. The data on deaths were obtained from state death records and the National Death Index. (Yes, your personal information is available on the web even after you die.)

 

Do Plant-Based Diets Reduce Heart Disease Deaths?

plant-based diets reduce heart deathsThe participants in this study were followed for an average of 25 years.

The investigators looked at heart disease deaths over the 25 years and compared people with the highest intake of plant foods to people with the highest intake of red meat and other animal foods. The results were:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, coffee and tea) had a 19-32% lower risk of dying from heart disease than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods (refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts) had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

When the investigators looked at all-cause deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had an 11-25% lower risk of dying from any cause than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

What Else Did The Study Show?

The investigators made a couple of other interesting observations:

  • The association of the overall diet with heart disease and all-cause deaths was stronger than the association of individual food components. This underscores the importance of looking at the effect of the whole diet on health outcomes rather than the “magic” foods you hear about on Dr. Strangelove’s Health Blog.
  • Diets with the highest amount of healthy plant foods were associated with higher intake of carbohydrates, plant protein, fiber, and micronutrients, including potassium, magnesium, iron, vitamin A, vitamin C, folate, and lower intake of saturated fat and cholesterol.
  • Diets with the highest amount of unhealthy plant foods were associated with higher intake of calories and carbohydrates and lower intake of fiber and micronutrients.

The last two observations may help explain some of the health benefits of plant-based diets.

 

Can Plant-Based Diets Be Unhealthy?

plant-based diets unhealthy cookiesNow, let’s return to the question I asked at the beginning of this article: “Can plant-based diets be unhealthy?” Although some previous studies have suggested that unhealthy plant-based diets might increase the risk of heart disease, this study did not show that.

What this study did show was that an unhealthy plant-based diet was no better for you than a diet containing lots of red meat and other animal foods.

If this were the only conclusion from this study, it might be considered a neutral result. However, this result clearly contrasts with the data from this study and many others showing that both plant-based diets in general and healthy plant-based diets reduce the risk of heart disease deaths and all-cause deaths compared to animal-based diets.

The main message from this study is clear.

  • Replacing red meat and other animal foods with plant foods can be a healthier choice, but only if they are whole, minimally processed plant foods like whole grains, fruits, vegetables, nuts, legumes, coffee and tea.
  • If the plant foods are refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts, all bets are off. You may be just as unhealthy as if you kept eating a diet high in red meat and other animal foods.

There is one other subtle message from this study. This study did not compare vegans with the general public. Everyone in the study was the general public. Nobody in the study was consuming a 100% plant-based diet.

For example:

  • The group with the highest intake of plant foods consumed 9 servings per day of plant foods and 3.6 servings per day of animal foods.
  • The group with the lowest intake of plant foods consumed 5.4 servings per day of plant foods and 5.6 servings per day of animal foods.

In other words, you don’t need to be a vegan purist to experience health benefits from adding more whole, minimally processed plant foods to your diet.

 

The Bottom Line

A recent study analyzed the effect of consuming plant foods on heart disease deaths and all-cause deaths over a 25-year period.

When the investigators looked at heart disease deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had a 19-32% lower risk of dying from heart disease than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

When the investigators looked at all-cause deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had an 11-25% lower risk of dying from any cause than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

The main message from this study is clear.

  • Replacing red meat and other animal foods with plant foods can be a healthier choice, but only if they are whole, minimally processed plant foods like whole grains, fruits, vegetables, nuts, legumes, coffee and tea.
  • If the plant foods are refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts, all bets are off. You may be just as unhealthy as if you kept eating a diet high in red meat and other animal foods.

A more subtle message from the study is that you don’t need to be a vegan purist to experience health benefits from adding more whole, minimally processed plant foods to your diet. The people in this study were not following some special diet. The only difference was that some of the people in this study ate more plant foods and others more animal foods.

For more details on the study, read the article above.

 

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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