By: Dr. Joseph Mercola

The answer to the question in the headline is fruit juice. But before I explain why fruit juice may be as hazardous to your health as soda, let me first give you some background information.

Fructose has become one of my newest health passions for a number of reasons. It is really not well understood how pervasive a negative influence this sugar has on people’s health, but even more importantly, it is something that we can easily change, by influencing  the food industry to replace it with something healthier.

One of the leading researchers in this field is Richard Johnson, MD, who is the chief of the division of kidney disease and hypertension at the University of Colorado. I’ve previously interviewed Dr. Johnson about his research into the health dangers of fructose, specifically how fructose causes high blood pressure, obesity, and diabetes.

Here, we continue this discussion, and Dr. Johnson also shares new details of the research he’s been involved with since the last interview.

An interesting aside is that at the end of this interview, I was very pleasantly surprised to learn that I had written some of the articles on fructose that he reviewed when he first decided to researched this topic.

It really gave me great joy to know that all the hard work and effort I have put in over the years really is making a difference, not only getting people healthy, but also motivating high integrity scientists to do the right thing.

It is worth noting that Dr. Johnson actually endorses Splenda in his book, The Sugar Fix, which was written prior to us getting to know each other, but I recently sent him my book Sweet Deception, which outlines the many dangers of artificial sweeteners. He’s a true physician and was eager to review the material and update his knowledge on the subject.

There aren’t many doctors out there with this type of integrity. I really like Dr. Johnson and believe he’s an authentically well-intentioned good guy.

It is not often that a health researcher can open up my eyes to a completely novel and new risk factor for health, as he did with uric acid and fructose, and I will always be grateful to him for that and for his willingness to enlighten us in these interviews.

Uric Acid as a Marker for Fructose Toxicity

One of the surprising facts discussed in our first interview was how detrimental the impact of fructose is on your uric acid levels. It appears as though that process is essential to the damage that fructose causes, and it’s actually an excellent marker for toxicity from fructose.

According to the latest research in this area, the safest range of uric acid is between 3 and 5.5 milligrams per deciliter, and there appears to be a steady relationship between uric acid levels and blood pressure and cardiovascular risk, even down to the range of 3 to 4 mg/dl.

Dr. Johnson suggests that the ideal uric acid level is probably around 4 mg/dl for men and 3.5 mg/dl for women.

This is actually the only major biochemical marker that I need to optimize at this point in my life, which most likely suggests that I am particularly sensitive to fructose intake and that it’s best for me to keep my levels as low as possible.

This is most likely due to genetics and would explain why most of my paternal relatives have, or have died from, diabetes. That side of the family is most likely particularly sensitive to fructose.

So I would STRONGLY encourage everyone to have their uric acid level checked to find out how sensitive you are to fructose. (I’ll discuss this strategy further, in just a moment.)

As you know, two-thirds of the US population is overweight, and most of these people likely have uric acid levels well above 5.5. Some may even be closer to 10 or above.

Dr. Johnson has developed a program to help people optimize their uric acid levels, and the key step in this program is complete elimination of fructose.

Results of the Latest Clinical Trial

“We’ve just finished a clinical trial where we gave a low fructose diet to overweight and obese adults from Mexico City.” Dr. Johnson says.

“We tried two different low fructose diets, but first, before we go into that, we think that the effects of fructose are independent of its energy intake. So,table sugar (sucrose) — which contains fructose and glucose — although there is a caloric component, we think that the effects of fructose are not specifically related to the calories but rather to its mechanism, of which uric acid is a driving part.

… [Uric acid levels] being too high seems to really increase the risk for diabetes and high blood pressure, kidney disease and obesity. And in fact, there are more and more papers coming out showing that connection.”

One of the questions that Dr. Johnson sought to answer in his latest trial was whether or not you need to reduce ALL fructose in your diet, or just reduce the fructose primarily in added sugars like high fructose corn syrup and table sugar.

After comparing the two low fructose diets — one that was strictly low fructose, and the other that had low fructose but allowed natural fruits – they discovered that both diets had remarkable effects in reducing metabolic syndrome.

Both diets improved triglycerides, insulin resistance and blood pressure.

A Novel Idea — Using Uric Acid as a Marker of Susceptibility to Fructose Damage

Going back to the issue of genetic variability, it seems that some people may be able to process fructose more efficiently, and the key to assess this susceptibility to fructose damage lies in evaluating your uric acid levels.

Dr. Johnson agrees that using uric acid levels as a marker to identify your susceptibility could be a reasonable approach.

So, for example, if you’re passionate about fruit and typically eat large amounts of fruit, but have a uric acid level above 5 (or better yet, 4 if you’re a man, and 3.5 if you’re a woman), then you may want to consider lowering your fruit consumption until you’re able to optimize your uric acid levels.

“We have some evidence from our laboratory that uric acid actually regulates the sensitivity to fructose,” Johnson says. “So the higher your uric acid, the more sensitive you are to the effects of fructose.

… So I agree with you. If you measure your serum uric acid and it’s very significantly high, you probably will get into more trouble with fruit juices and large amounts of fruit than other individuals would.

That seems to be the take home message from our current research.”

Revisiting Fruit Consumption

So it appears as though whole fruits, even though they contain fructose, may not be nearly as problematic as fructose from added sugars. One of the reasons for this is believed to be because whole fruits contain high amounts of natural antioxidants, as well as other synergistic compounds that may help counter the detrimental effects of fructose.

“When I originally wrote my book, I was concerned that if you eat large amounts even of natural fruits you could get into trouble,” Johnson says, “and I have had cases where people were eating very large amounts of natural fruits.

When I cut it out or reduced it, they’ve had dramatic weight loss.

So I’ve had a number of people like this who are eating almost a pure fruit diet, and I don’t think that that’s particularly good, but I think that the normal individual eating two to four natural fruits a day probably is going to be fine.”

The key here though is WHOLE fruits, but I still remain convinced that many people, especially those that have insulin resistance, such as those with:

• Diabetes
• High blood pressure
• High cholesterol
• Overweight

should be particularly careful about limiting their fructose from fruit to 15 grams per day or less.

How to Know if Fruit May Be a Problem for You

However the NEW appreciation is that if you have your uric acid level checked and have a level of 4 for men, or 3.5 for women, you probably are at a very low risk for fructose toxicity and can be more liberal with these limits.

The higher your uric acid though, the more you need to limit or even avoid fructose until your uric acid level normalizes.

Fruit Serving Size Grams of Fructose Limes 1 medium 0 Lemons 1 medium 0.6 Cranberries 1 cup 0.7 Passion fruit 1 medium 0.9 Prune 1 medium 1.2 Apricot 1 medium 1.3 Guava 2 medium 2.2 Date (Deglet Noor style) 1 medium 2.6 Cantaloupe 1/8 of med. melon 2.8 Raspberries 1 cup 3.0 Clementine 1 medium 3.4 Kiwifruit 1 medium 3.4 Blackberries 1 cup 3.5 Star fruit 1 medium 3.6 Cherries, sweet 10 3.8 Strawberries 1 cup 3.8 Cherries, sour 1 cup 4.0 Pineapple 1 slice (3.5″ x .75″) 4.0 Grapefruit, pink or red 1/2 medium 4.3

Fruit Serving Size Grams of Fructose Boysenberries 1 cup 4.6 Tangerine/mandarin orange 1 medium 4.8 Nectarine 1 medium 5.4 Peach 1 medium 5.9 Orange (navel) 1 medium 6.1 Papaya 1/2 medium 6.3 Honeydew 1/8 of med. melon 6.7 Banana 1 medium 7.1 Blueberries 1 cup 7.4 Date (Medjool) 1 medium 7.7 Apple (composite) 1 medium 9.5 Persimmon 1 medium 10.6 Watermelon 1/16 med. melon 11.3 Pear 1 medium 11.8 Raisins 1/4 cup 12.3 Grapes, seedless (green or red) 1 cup 12.4 Mango 1/2 medium 16.2 Apricots, dried 1 cup 16.4 Figs, dried 1 cup 23.0

What About Fruit Juices?

Fruit juice typically contains very high concentrations of fructose, which will cause your insulin to spike and may counter the benefits of the antioxidants. Previous studies have already clearly demonstrated that drinking large amounts of juice dramatically increases your risk of obesity. Children are at particular risk here, since so many children are given juice whenever they’re thirsty instead of plain water.

For example, research has revealed that 3- and 4-year-olds who carry extra weight and drink just one to two sweet drinks a day double their risk of becoming seriously overweight just one year later.

When buying commercial fruit juice, you need to check the label, as the majority of fruit juices contain high fructose corn syrup and artificial flavors in addition to concentrated fruit juice.

But even freshly squeezed fruit juice can contain about eight full teaspoons of fructose per eight-ounce glass!

Naturally, some fruits are less problematic than others, as the amount of fructose and antioxidants vary from fruit to fruit.

“For example, pear juice and apple juice are very, very low in vitamin C but very, very high in fructose,” Johnson says, “ and so those particular kinds of juices maybe worse than orange juice or grapefruit juice which have high amounts of vitamin C.

Now, apples contain other compounds like quercetin, which is an antioxidant that may block some of fructose’s effects. So, you know, the verdict is still out in terms of which juice is better and which juice is worse.

But in general, with apple juice and pear juice, I would be more concerned about those types of juices because they are very, very high in fructose and relatively low in antioxidants.”

For all these reasons, it is wise for most to limit their intake of fruit juice, especially if your uric acid is above the ideals recommended.

If you suffer from any of the four health problems I just listed above, you would be best off avoiding fruit juices altogether until you’ve normalized your uric acid and insulin levels.

Is Glucose a Safer Alternative Sweetener?

Although you cannot buy “glucose” commercially, it’s available under the name of “dextrose.”

It’s relatively inexpensive, priced at about a dollar a pound. It’s not as sweet as table sugar or fructose, but it also doesn’t seem to cause the same health problems – at least for those who are not diabetic or insulin resistant.

Dr. Johnson explains:

“It is absolutely true that if you take a laboratory animal and you feed it glucose or dextrose or starch, it will not get into trouble. It will stay skinny. It will stay healthy.  Rice diets are high in starch and historically have been associated with being lean.

In contrast, if you give sugar or fructose to an animal, they’ll rapidly develop features of metabolic syndrome, obesity, and so forth. And you can pair-feed animals, so one animal gets exactly the same number of calories as the other one, but it’s only the sucrose- or sugar- or fructose-fed animals that develop the features of metabolic syndrome. This makes one believe that starches safe, and this is in fact what I wrote in the book.

Now, as we’ve done more studies, (obviously if you’re a diabetic, glucose is not good because in diabetes you cannot handle glucose metabolism)… one of the things that we’re just discovering in the laboratory — actually it’s been known but we’re trying to figure out how important it is — people who are diabetic, and people who are severely insulin resistant… can make fructose from the glucose through a pathway called “the polyol pathway.”

We are now studying it and we do think that there is an endogenous fructose pathway.

We don’t know how important it is yet, but we do know that you can make fructose from glucose, especially if you’re diabetic or if you’re severely insulin resistant.

Since a lot of people who are very, very overweight and are trying to lose weight, some of them can be insulin resistant. This does throw a new twist into the story… We’re trying to figure out the impact of this.

But certainly if you’re not insulin resistant, dextrose or starch will be ok.”

According to Dr. Johnson’s data, which he claims is “unequivocal,” starch and dextrose (glucose) do NOT cause obesity or diabetes, whereas fructose does.

Interestingly, animal studies have discovered that if an animal eats lots of fructose, over time they become diabetic. Part of this process, however, is that once they become insulin resistant, they activate the polyol pathway and begin to make fructose from other sources of food as well!

This is quite remarkable, and a strong testament to the need to severely limit your fructose intake.

It’s also offers an explanation for how and why the obesity epidemic has flourished the way it has since the introduction of HFCS into most of our processed foods.

“It’s a little bit more complicated than we had originally thought,” Johnson says, “but the bottom line is: If you’re trying to avoid gaining weight; if you’re trying to avoid becoming obese or diabetic, the best thing you can do is to cut back on foods that raise uric acid, particularly sugar, fructose and high fructose corn syrup (HFCS).

That’s by far the best approach. Starch in general appears to be safe unless you’re severely insulin resistant, in which case perhaps isn’t quite as safe as we had originally thought.”

Defining Insulin Resistance

Ideally you’ll want to have a fasting insulin level below 2. In addition, Dr. Johnson recommends using a simple glucose test to check your fasting glucose.

“The fasting glucose, under 100, suggests that you’re not insulin resistant,” he says. “If your fasting glucose is between 100 and 125 mg/dl, you probably are insulin resistant to a mild extent, or you have impaired glucose tolerance.

You have what we would call mild insulin resistance and slightly elevated glucose levels for what you would expect.”

I agree with Dr. Johnson that this is typically true, however it’s still possible to have low fasting glucose yet have significantly elevated insulin levels.

Dr. Johnson explains: “Yes, if you have hyperinsulinemia, in general what happens is that as you become insulin resistant, your insulin levels go up to help keep your blood sugar down. So if you have a particularly robust insulin response, you could keep your glucose in the normal range for some time.”

So, in this case, you’re essentially pre-diabetic and need to take steps to improve your insulin sensitivity, and the most potent way is to reduce or eliminate fructose.

A Word on Agave

I got a lot of push-back after I published my report on agave, which many health conscious people believe is a safe, all-natural, healthy sweetener. However, agave can contain anywhere between 55 to 90 percent fructose!

Some companies were very upset with our article and refuted the information so much so that we actually purchased three of the most popular “natural” agave products and had them independently tested, at our expense, at a commercial laboratory.

The results came back last week and they support what I said, that they were high in fructose. The range was 59 to 67 percent fructose. I am in the process of writing an entire report on it that should be published in the next few weeks.

Fructose content is also high in honey, which contains about 70 percent on average.

In addition, many, if not most of the commercial supplies of agave are processed in a way that’s not too dissimilar to the processing of high fructose corn syrup.

“We have not done any specific research with agave or with honey,” Johnson says. “But I do believe that those two compounds, because they’re so high in fructose, probably will engage the same pathways that we see when we give fructose or sugar to animals.

So I would not recommend those as sweeteners to use daily.”