Is Fructose in Fruit Bad For You?

There is a hefty amount of confusion about the proper role of fructose in the diet.  Setting aside misleading studies from the food industry for a moment, recommendations from the wellness-friendly community alone can seem all over the map.  Specifically, I wanted to find out once and for all – Is fructose in fruit bad for you?

This post cuts through the sometimes-opposing assertions and answers the question.  Right at the top, I’m going to tell you it depends on where your fructose is coming from and also your physical condition.

Let’s start with an overview of sweeteners so we can see where fructose fits in the grand scheme.

Sweetener Overview

I obtained this list from Dr. Joseph Mercola, who has written extensively about sugar for years.

• Dextrose, fructose, and glucose are all monosaccharides, known as simple sugars. The primary difference between them is how your body metabolizes them. Glucose and dextrose are essentially the same sugar. However, food manufacturers usually use the term “dextrose” in their ingredient list.
• The simple sugars can combine to form more complex sugars, like the disaccharide sucrose (table sugar), which is half glucose and half fructose.
• High fructose corn syrup (HFCS) is 55 percent fructose and 45 percent glucose.
• Ethanol (drinking alcohol) is not a sugar, although beer and wine contain residual sugars and starches, in addition to alcohol.
• Sugar alcohols like xylitol, glycerol, sorbitol, maltitol, mannitol, and erythritol are neither sugars nor alcohols but are becoming increasingly popular as sweeteners. They are incompletely absorbed from your small intestine, for the most part, so they provide fewer calories than sugar but often cause problems with bloating, diarrhea, and flatulence.
• Sucralose (Splenda) is NOT a sugar, despite its sugar-like name and deceptive marketing slogan, “made from sugar.” It’s a chlorinated artificial sweetener in line with aspartame and saccharin, with detrimental health effects to match.
• Agave syrup, falsely advertised as “natural,” is typically HIGHLY processed and is usually 80 percent fructose. The end product does not even remotely resemble the original agave plant.
• Honey is about 53 percent fructose, but is completely natural in its raw form and has many health benefits when used in moderation, including as many antioxidants as spinach.
• Stevia is a highly sweet herb derived from the leaf of the South American stevia plant, which is completely safe (in its natural form). Lo han (or luohanguo) is another natural sweetener, but derived from a fruit.

Fructose turns to fat in the liver

According to Dr. Joseph Mercola, “Unlike glucose, which can be used by virtually every cell in your body, fructose can only be metabolized by your liver, because your liver is the only organ that has the transporter for it.”

According to the Harvard Medical School web site, “The entry of fructose into the liver kicks off a series of complex chemical transformations. (You can see a diagram of these at health.harvard.edu/172.) One remarkable change is that the liver uses fructose, a carbohydrate, to create fat. This process is called lipogenesis. Give the liver enough fructose, and tiny fat droplets begin to accumulate in liver cells (see figure). This buildup is called nonalcoholic fatty liver disease, because it looks just like what happens in the livers of people who drink too much alcohol.”

A 2005 study by by the American Diabetes Association found found that excess fructose consumption resulted in a five fold increase of de novo lipogenesis in only 6 days.

Up to 30% of adults in the United States are affected by nonalcoholic fatty liver disease.  Between 70% and 90% of those who are obese or who have diabetes have nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease is reversible in the early stages, however, eventually the liver can become inflamed.  According to the Harvard publication, “This can cause the low-grade damage known as nonalcoholic steatohepatitis (steatomeaning fat and hepatitis meaning liver inflammation). If the inflammation becomes severe, it can lead to cirrhosis — an accumulation of scar tissue and the subsequent degeneration of liver function.”

These photos from Harvard show what the fatty deposits look like in an actual liver.

Excess fructose can cause Metabolic Syndrome

In addition to the buildup of fat in the liver, an excess of fructose also has the following impacts:

• Rapidly leads to weight gain and abdominal obesity (“beer belly”) – 30% more fructose was turned to fat compared to glucose in a 1996 study on medical students
• Elevates triglycerides quickly – doubled in 6 days
• Can double Insulin resistance in 6 days.  Insulin resistance is a precursor to diabetes.
• Decreases HDL (good cholesterol)
• Increased harmful LDL (so-called bad cholesterol)
• Promotes the buildup of fat around organs (visceral fat)
• Increases blood pressure – elevates uric acid, which decreases nitric oxide, raises angiotensin, and causes your smooth muscle cells to contract
• Increased uric acid also leads to chronic, low-level inflammation
• Increases the production of free radicals, energetic compounds that can damage DNA and cells.
• Turns off the body’s appetite-control system – does not appropriately stimulate insulin, which in turn does not suppress ghrelin (the “hunger hormone”) and doesn’t stimulate leptin (the “satiety hormone”)
• Elevated blood sugar
• Eventually, the pancreas will become unable to secrete sufficient insulin to drive blood glucose into cells. At this point, blood sugar levels elevate significantly, resulting in a diagnosis of diabetes.

These symptoms constitute classic metabolic syndrome.

Like alcohol, fructose serves as a substrate for converting carbohydrates into fat, which promotes insulin resistance, dyslipidemia (abnormal fat levels in the bloodstream), and fatty liver.  This is not surprising, given that ethanol is fermented fructose.

One of the foremost experts on fructose, Robert H. Lustig, M.D, says, “fructose is ethanol, but without the buzz.” He says, “Fructose creates habituation, and possibly dependence; also paralleling ethanol”. This happens by “stimulating the ‘hedonic pathway’ of the brain both directly and indirectly,”

Robert Lustig is Professor of Pediatrics in the Division of Endocrinology at University of California, San Francisco, and Director of the Weight Assessment for Teen and Child Health (WATCH) Program at UCSF. According to wikipedia, “On May 26, 2009, he delivered a lecture called “Sugar: The Bitter Truth” which was posted on YouTube the following July and “went viral” with some 5.8 million viewings (as of August 10, 2015). In his lecture, Lustig calls fructose a “poison” and equates its metabolic effects with those of ethanol.” His findings were published in the Journal of the Academy of Nutrition and Dietetics.

General Fructose Strategies

Dr. Lustig offers four general strategies to avoid consuming excess fructose:

• Get rid of all sugared liquids.  Drink only water and raw dairy.
• Eat your carbohydrates with fiber. Dr. Lustig said, “When God made the poison, he packaged it with the antidote.”  He went on to clarify that eating fruit is okay because the fiber limits the fructose. Fiber also limits the rate of carbohydrate absorption, induces satiety and suppress insulin.
• Wait 20 minutes for second portions.
• This applies especially to children… Buy your screen time minute-for-minute with physical activity.  In other words, if you watch 30 minutes of television, try to also have 30 minutes of being active. Dr. Lustig explained that activity is not for the purpose of burning calories.  The true benefits are:
  • improves skeletal muscle insulin sensitivity
  • reduces stress and cortisol release
  • makes the TCA cycle run faster, which detoxifies fructose and improves hepatic (liver) insulin sensitivity

Context is everything with fructose

Studies indicate the problems with fructose, or any sweetener, occur when consumed in excess.  So how much fructose is okay and what’s the limit?  The answer is: It depends.

The source of your fructose greatly determines how it is metabolized

When people eat whole foods that contain fructose or glucose, they naturally tend to reduce their calorie intake, simply because the stomach can only hold so much.  There is an automated compensation to reduce overall daily calories as well as all the benefits of fiber.  Not so, when consuming a beverage sweetened with fructose or glucose.  The one or two soft drinks per day easily lead to inadvertent overfeeding.

The condition and activity level of the individual impacts how fructose is metabolized 

Kris Gunnars, BSc of Authority Nutrition sums it well: “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 (study).”

Dr. Lustig wrote this for The Guardian: “The food industry is fond of referring to a 1999 study showing that liver fat generation from oral fructose occurs at a very low rate (less than 5%). And that’s true, if you’re thin, insulin sensitive, fasting (and therefore glycogen-depleted), and given just fructose alone (which is poorly absorbed). Conversely, if you’re obese, insulin resistant, well fed, and getting both fructose and glucose together (like a sizable percentage of the population), then fructose gets converted to fat at a much higher rate, approximating 30%. In other words, the toxicity of fructose depends on context.”

Chris Kresser doesn’t agree that we need to take as strong a stance against fructose. Nevertheless, I still hear him summarizing about the same way.  In a blog post Chris states, “Fructose-sweetened beverages like soft drinks and juice cause metabolic problems when calories are in excess, and studies have shown that people are not likely to compensate for the additional calories they get from such beverages.”  Chris doesn’t see a problem with an occasional glass of fruit juice, “unless you have a pre-existing blood sugar issue.”

Dr. Mercola advises:  “Four out of five Americans have insulin and leptin resistance. This also includes people who are overweight, diabetic, hypertensive, or taking a statin drug. If you fall into this category, it would be prudent for you to restrict your fructose consumption to about 15 to 25 grams of fructose per day from all sources. Those who are normal weight and relatively healthy may also benefit from reducing their intake of fructose, particularly from foods containing high fructose corn syrup or sugar, as the effects of high sugar and HFCS intake may have effects that build up over time.”  Of the advised 25 g daily limit, Dr. Mercola says, “If you are a raw food advocate, have a pristine diet, and exercise very well, then you could be the exception that could exceed this limit and stay healthy.”

Dr. Richard Johnson is the head of nephrology at the University of Colorado and is actively engaged in clinical research.  According to Dr. Johnson, if you exercise on a regular basis, a small amount of fructose can actually be quite beneficial. The fructose will accelerate glucose absorption in your gut and improve muscle performance. That said, it really depends on how your body metabolizes the fructose. The human body normally cannot absorb fructose well. But the more fructose a person eats, the more the transporters that allow for fructose uptake in the gut are enabled… and the more fructose the body will absorb. As an example, lean children tend to only absorb about half of the fructose they consume, whereas obese children who have fatty liver disease absorb close to 100 percent.

Is it okay to eat fruit?

The quick answer is: Yes!  Physically fit and active people can eat more but those with some belly fat to lose should aim for moderation and stick with lower fructose fruits like berries.

Here’s what the experts say.

Chris Kresser: “I don’t think there’s any basis for avoiding whole fruit simply because it contains fructose.” “…there’s nothing uniquely fattening or toxic about fructose when it isn’t consumed in excess. And since whole fruit contains fiber and other nutrients, it’s difficult to eat a lot of fruit without simultaneously reducing intake of other foods.”

Dr. Mercola: “Fruits also have fructose but contain many beneficial nutrients and antioxidants. For someone who is obese, one has to be careful with eating fruits that have substantial fructose content. Some fruits, such as lemons and limes, have minimal fructose content and are safe. Other fruits, such as grapefruit, kiwi, and berries, also have relatively low fructose content and high levels of nutrients. However, fruit juices, dried fruits, and some fruits that are rich in fructose (such as pears, red apples, and plums) should be eaten relatively sparingly.”

Kris Gunnars: “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.”

Fructose in fruit can be a problem if you are FODMAP intolerant, but that’s a topic for another post.

The amount of fructose in fruit

Credit to Dr. Johnson for providing the data.

I was surprised to learn bananas pack a little less fructose than an apple and that apples have more fructose than dates.  The Wellness Repair Diet advises an emphasis on berries because most people following the diet are trying to lose weight.  Berries, in general, tend to have less fructose.

I would love to know what stood about about fructose to you!  Please leave a comment below or join the conversation on my Facebook page.

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Thanks for reading!
Jeff

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