The sugar wars: Is fructose really toxic?

 

There is very little doubt that drinking sugary drinks regularly is associated with obesity, type 2 diabetes, hypertension and heart disease.

But does drinking sugar just make us consume too many empty calories, or is there something inherently unhealthy about sugar? Is high fructose corn syrup (HFCS) the villain? Is old fashioned sugar any better or just as bad? Will agave (with its low glycemic profile) save us? And what’s all this talk about fructose being toxic?

Food sugar 101

Our foods and drinks are usually sweetened with sugars that are a combination of the simple sugars glucose and fructose. Sucrose (table sugar) is a two-sugar molecule with one glucose and one fructose bound together, and is therefore exactly 50 percent glucose, 50 percent fructose. HFCS is about 45 percent glucose, 55 percent fructose. Fruit juice concentrate's sugar composition (stripped down concentrated fruit juice is really just sugar!) will depend on the fruit source: Apple juice concentrate is about 30 percent glucose, 70 percent fructose, while orange juice concentrate is about 50 percent glucose 50 percent fructose.

Agave syrup, favored by those adhering to a low glycemic diet, is about 70-75 percent fructose.

What you need to remember is that practically all forms of caloric sweeteners used in food processing are a glucose/fructose mixes. Although only HFCS has fructose in its name, all our commonly added sugars contain both fructose and glucose. Corn syrup stands apart as a pure glucose sweetener, but since pure glucose is less sweet than HFCS or sucrose, it isn’t economic – or tasty -- to use.

Is fructose more harmful than glucose?

A study from the University of California at Davis, led by Peter Havel, made headlines a couple of years ago when it showed that drinking 25 percent of daily calories in fructose for 10 weeks increased triglycerides and cholesterol and caused insulin resistance in people, while drinking the same amounts in glucose didn’t. And while both the fructose and the glucose groups gained weight during the study, the fructose group gained more belly fat.

The study concluded that drinking lots of fructose led to unique adverse effects on lipid metabolism, insulin resistance and abdominal obesity, effects not seen when drinking the same amounts in glucose.

What explains our body’s different reaction to these two sugars? The authors hypothesized that since fructose is metabolized in the liver, fructose sweetened beverages affect the liver’s metabolism of fats; glucose is metabolized in every cell of the body, doesn’t need as much of the liver’s attention, and therefore the adverse metabolic effects weren’t seen in the glucose beverage drinkers.

But one question lingered: Could high levels of blood sugar and blood insulin explain fructose’s adverse metabolic outcomes?

To answer that question the authors went back to study the blood samples of the people enrolled in their initial study. They published the findings of their new research in the American Journal of Clinical Nutrition. Havel’s group found that the 17 people who were drinking 25 percent of their calories in fructose were actually consuming a diet with a lower glycemic index, and their blood glucose and insulin after meals were lower than the fluctuations seen in the 15 people consuming 25 percent of calories in glucose.

To conclude, in this 10 week study, drinking fructose caused dislipedimia and insulin insensitivity unrelated to blood sugar and insulin levels. On the other hand drinking glucose caused rollercoaster peaks and troughs of blood glucose and insulin, while not causing dislipedemia.

The dose makes the poison

Fructose is metabolized by the liver, and this study supports the notion that its excess consumption plays a part in causing insulin resistance (which leads to diabetes), high cholesterol and triglycerides (all risk factors for heart disease) and the tendency to accumulate belly fat (a risk factor for a myriad of diseases, including heart disease, high blood pressure and cancer).

While drinking glucose may not affect our fat metabolism in the same way fructose does, glucose causes spikes in blood sugar and blood insulin – which are not good either.

If you’re concerned about fructose, you should be concerned with the intake of all the sweeteners that contain fructose -- that includes not only HFCS, but also cane and beet sugar (table sugar), molasses, agave, brown sugar, fruit juice concentrates and honey.

I don’t personally believe glucose or fructose are evil. Our body, especially our brain, runs on simple sugars, and sugars, including fructose, are a natural part of very healthy foods, such as fruits and veggies.

It is excess sugar – of any kind – that is harmful. The dose makes the poison. 

Excess sugar is hard to come by in nature unless you run into a beehive and the bees are willing. It takes a lot of berry picking to hit your liver with the fructose dose that is anything similar to what’s in a can of soda. Only processed foods, and especially sugary drinks, hit your liver with that much fructose at such high speed. Fructose containing foods in nature have fiber (and much less sugar) and break down slowly. On the other hand processed foods and especially sugary drinks have no fiber – just lots of fructose – and we’ve shown a tremendous capacity to chug them down real quick.

Does the study’s experiment resemble real life? On one hand, the study group drank 25 percent of daily calories in sugar. We’re bad but not that bad: A recent study shows that our teens consume 21 percent of their daily calories from added sugar.

On the other hand, the study lasted for 10 weeks. Our kids are ingesting a large proportion of their daily calories as glucose/fructose mixtures for years and years.

Considering the current evidence, this is not an experiment we should be conducting.

Dr. Ayala

Full disclosure: I’m vice president of product development for Herbal Water, where we make organic herb-infused waters that have zero calories and no sugar or artificial ingredients. I’m also a pediatrician and have been promoting good nutrition and healthy lifestyle for many years.

Further reading/viewing:
• Dr. Robert Lustig explores the damage caused by sugary food in this controversial & much viewed video: Sugar: The Bitter Truth.
• Gary Taubes’ New York Times Magazine article: Is Sugar Toxic?