Certain Fruits May Be Linked to a Lower Risk of Type 2 Diabetes
September 16, 2013 |
By Dr. Mercola
You’re probably well-familiarized with my controversial stance on fructose. Compelling evidence shows that fructose is, by far, more harmful to your health than other sugars—especially when it’s removed from whole fruits and highly processed and genetically modified, such as high fructose corn syrup (HFCS) found in most processed foods.I’ve also, as a general rule, warned you of eating too much fruit, as many fruits can be quite high in fructose.This has caused some confusion and consternation among many readers, as fruit has long been promoted as an important part of a healthy diet. That said, there are considerations to take into account when it comes to fruit consumption—some of which are dependent on your individual and specific circumstances.I will seek to clarify some of these points here. I believe there’s more than compelling evidence supporting the concept that high-fructose diets are a primary factor that is responsible for most chronic disease; insulin resistance, type 2 diabetes and obesity in those who eat a highly processed food diet..I’ve long urged those struggling with these health issues, or who have hypertension, heart disease or cancer, to pay extra-careful attention to the fructose content of whole fruit in addition to other sources of fructose. Now, recent research indicates that some fruits may in fact be protective against type 2 diabetes.
Can You Reduce Your Risk of Type 2 Diabetes with Your Fruit Choices?
According to a new analysis of three cohort studies, published in the British Medical Journal,1 whole fruits—particularly blueberries, grapes, prunes and apples—may in fact reduce your risk of type 2 diabetes. Conversely, consumption of fruit juices was associated with greater risk. According to senior author Qi Sun, an assistant professor in the department of nutrition at the Harvard School of Public Health:2"While fruits are recommended as a measure for diabetes prevention, previous studies have found mixed results for total fruit consumption. Our findings provide novel evidence suggesting that certain fruits may be especially beneficial for lowering diabetes risk."The researchers analyzed the dietary records of nearly 190,000 people who had participated in three studies from 1984 to 2008. None of the participants were diagnosed with diabetes, cardiovascular disease or cancer at the outset of the studies.They found that those who ate blueberries, grapes and apples at least twice a week were up to 23 percent less likely to develop type 2 diabetes, compared to those who ate these fruits once a month or less.I find this quite surprising as, grapes and apples are particularly high in fructose (as you can see in the chart below). It’s unclear why the authors observed this benefit here but it’s likely that the phytonutrients found in the apples and grapes are more than compensate for any potential fructose toxicity.Antioxidants and other phytonutrients combat inflammation, which is a hallmark of diabetes and most other chronic disease. Similarly, blueberries, which are much lower in fructose, have in other studies also been found to be of benefit for diabetics primarily due to their high antioxidant content.One antioxidant in particular, called quercetin, could potentially help explain some of the results. Apples for example, while high in fructose, contains this flavonoid, which actually blocks some of the fructose metabolism according to expert Dr. Richard Johnson. If you haven't done so yet, I recommend viewing my "What Are Apples Good For?" information page for a listing of even more benefits of apples.Red grapes, plums and many different berries, including blueberries. also contain quercetin. I have scheduled an interview with Dr. Johnson, in which we’ll delve into this at greater depth. So keep your eye out for that interview, which should be out before year end, if you want to learn more.
Don’t Be Fooled By Fruit Juices and Smoothies
In comparison, the featured study found that those who drank one or more servings of fruit juice each day had a 21 percent higher risk for type 2 diabetes compared to the others. This is a really important point, and I’ve often highlighted the potential harm of drinking fruit juices.
You’re simply getting FAR too much fructose, not to mention the rarely mentioned methanol toxicity in any preserved juice. Furthermore, while whole fruits do contain fructose, they’re also rich in fiber, antioxidants, and a vast array of health-promoting phytochemicals.Fruit juices, especially not pasteurized, commercially-available fruit juices have virtually none of these phytonutrients. The fiber in the whole fruits also plays a large in protecting you from a rapid and exaggerated rise in blood sugar. The fiber slows the rate at which sugar is absorbed into your bloodstream.
This also applies to fruit smoothies, which are often touted as a convenient strategy to boost your fruit and veggie intake. Unfortunately, they too contain excessive amounts of fructose, and perhaps even added sugars on top of that. As reported by the Guardian:3“In the UK, Coca-Cola owns Innocent Smoothies while PepsiCo has Tropicana. Launching Tropicana smoothies in 2008, Pepsi's sales pitch was that the drink would help the nation to reach its five a day fruit and vegetable target.
"Smoothies are one of the easiest ways to boost daily fruit intake as each 250ml portion contains the equivalent of two fruit portions," it said at the time.However, Popkin [professor at the department of nutrition at the University of North Carolina] says the five a day advice needs to change. Drink vegetable juice, he says, but not fruit juice. "Think of eating one orange or two and getting filled," he said. "Now think of drinking a smoothie with six oranges and two hours later it does not affect how much you eat.The entire literature shows that we feel full from drinking beverages like smoothies but it does not affect our overall food intake, whereas eating an orange does. So pulped-up smoothies do nothing good for us but do give us the same amount of sugar as four to six oranges or a large coke. It is deceiving."
Revisiting Fruit Consumption
I recently interviewed Dr. Brian Clement of the Hippocrates Institute, where they teach raw veganism. Interestingly enough, they also strongly advise most people avoid eating fruits. One of the primary reasons for their stand against fruits is because of the hybridization of fruits, which has made them up to 50 times sweeter than their ancient ancestors. Many fruits have been selectively and purposely bred for increased sweetness, which has also resulted in reduced phytochemical content. This hybridization and subsequent deterioration of healthful nutrition in whole foods was highlighted in a New York Times4 article published earlier this summer.The dramatically increased fructose content of otherwise natural and “wholesome” fruits is the primary problem with high fruit consumption, and this is why I’m leery of very high-fruit diets.Many of the most beneficial phytonutrients found in fruits actually have a bitter, sour or astringent taste, but to satisfy the palate, farmers have, throughout time, opted to selectively breed the sweetest varieties. Today, the “candification” of food is being taken to a whole new level, and if you’re stuck on the idea that all fruit is good for you, you may end up in a real metabolic pickle... For example, according to a recent report in the Los Angeles Times,5 one fruit breeder has created a type of grape called the Cotton Candy grape, which is absolutely bound to be just as problematic as any other junk food!“Bite into one of these green globes and the taste triggers the unmistakable sensation of eating a puffy, pink ball of spun sugar,” the article states. “By marrying select traits across thousands of nameless trial grapes, Cain and other breeders have developed patented varieties that pack enough sugar they may as well be Skittles on the vine. That's no accident. "We're competing against candy bars and cookies," said Cain, 62, a former scientist at the US Department of Agriculture who now heads research at privately owned International Fruit Genetics in Bakersfield.”In light of these issues, let me restate my recommendations on fruit and fructose consumption as simply as possible:
- If you’re insulin- or leptin resistant (are overweight, diabetic, hypertensive, or have high cholesterol), which includes about 80 percent of Americans, then it would be advisable for you to limit your fruit intake. As a general rule, I recommend limiting your fructose intake to a maximum of 15 grams of fructose per day from ALL sources, includingwhole fruit.
- If you are not insulin/leptin resistant, (are normal weight without diabetes, hypertension or high cholesterol) and regularly engage in strenuous physical activity or manual labor, then higher fructose intake is unlikely to cause any health problems. In this case, you can probably eat more fruit without giving it much thought.
- However if you are in category two above you might benefit from a further refinement. Fruit will still increase your blood sugar and many experts believe this will increase your protein glycosylation. So my approach is to consume the fruit typically after a workout as your body will use the sugar as fuel rather than raise your blood sugar.
- Additionally ,if you’re an endurance athlete, you can probably get away with eating fairly large amounts of fruits, since your body will use most of the glucose during exercise, so it won’t be stored as fat. (That said, I still believe athletes would be well-advised to consider becoming fat adapted rather than relying on quick sugars. This is outside the scope of this article, however, so for more information, please see this previous article).
- If you’re still unsure of just how stringent you need to be, get your uric acid levels checked, and use that as a guide. I’ll review this in more detail in the section below.
Using Your Uric Acid Level as a Marker for Fructose Toxicity
I’ve previously interviewed Dr. Richard Johnson about his research into the health dangers of fructose, specifically how fructose causes high blood pressure, obesity, and diabetes, revealed in his excellent book, The Sugar Fix. He’s also the chief of the division of kidney disease and hypertension at the University of Colorado.Dr. Johnson’s research suggests that your uric acid levels can be effectively used as a marker for fructose toxicity; meaning, an indicator of just how significant of an impact fructose has on your individual body and health. As such, it can help you gauge just how careful you need to be in your food selections.According to the latest research in this area, the safest range of uric acid is between 3 and 5.5 milligrams per deciliter (mg/dl), 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. What this means is that if you have a level of 4 mg/dl for men and 3.5 mg/dl for women, you probably are at a very low risk for fructose toxicity and can be more liberal with the fructose limits given above. The higher your uric acid though, the more you need to limit, or even avoid, fructose until your uric acid level normalizes.Using this biochemical marker, I came to realize that I am particularly sensitive to fructose, and that it’s best for me, personally, to keep my fructose consumption 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 probably particularly sensitive to fructose. 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, until your levels are within the ideal range of 3-5.5 mg/dl.
Helpful Fructose Chart for Common Fruits
Again, most people will need to limit your fructose to 25 grams of fructose per day from all sources, or less, while endurance athletes could have more. The chart below is excerpted from Dr. Johnson’s book, The Sugar Fix, which contains more details on the fructose content of common foods. His latest book, The Fat Switch, also gives further details on HOW fructose impacts your body, contributing to excess weight and chronic health problems.
What About Fruit Juices?
One of the profound highlights revealed in the featured study was the dramatic difference in health outcome between eating whole fruits versus drinking fruit juice. It’s important to realize that 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 fruit 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.Furthermore, 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. That said, even freshly squeezed fruit juice can contain about eight full teaspoons of fructose per eight-ounce glass! So, as a general rule, it’s wise for most to severely restrict your consumption of fruit juice, especially if your uric acid is above the ideals recommended. Also, if you suffer from type 2 diabetes, hypertension, heart disease or cancer, you’d be best off avoiding fruit juices altogether until you’ve normalized your uric acid and insulin levels.
Within Certain Limits, Fruit is OK for Most People
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. I believe this is an ideal way for most people to personalize the recommendations on fructose intake.Aside from that, I believe most will benefit from restricting their fructose to 25 grams a day; and as little as 15 grams a day if you’re diabetic or have chronic health issues. This includes fructose from whole fruits. So I’m not advocating fruit avoidance for everyone; I’m simply placing fruit in the category of a fructose-rich food that needs to be included when you’re calculating your fructose intake.If you choose low-fructose fruits, such as blueberries, you can eat more of it than if you choose a fruit high in fructose. Other low-fructose fruits include fresh apricots, lemons, limes, passion fruit, plums and raspberries. Also remember that avocado is actually a fruit too. It’s very low in fructose, and high in healthful fat, making it an excellent choice. Endurance athletes and others who engage in strenuous activities and who are neither overweight nor have chronic health issues probably do not need to concern themselves too much with their fruit consumption however.