Wednesday, April 12, 2017

An Apple a Day Keeps the Diabetes Away?

A new study from China finds that people who eat at least one piece of fruit a day are less likely to develop diabetes and its complications. If that seems a little odd in light of the alleged evils of fructose, here's an explanation.

Eating fresh fruit every day was linked with a lower risk for diabetes and diabetes-related vascular complications in a Chinese epidemiological study that included half a million people.

Among individuals without diabetes at baseline, daily fruit consumption was associated with a 12% lower risk for getting diabetes compared to never or rarely eating fresh fruit (hazard ratio 0.88; 95% CI 0.83-0.93; P<0.001); this corresponded to a difference of 0.2 percentage points in 5-year absolute risk, said a research team led by Huaidong Du, MD, PhD, of Oxford University in England.

Among individuals with diabetes at baseline, eating 100 grams per day of fresh fruit was associated with lower risks of all-cause mortality (HR 0.83; 95% CI 0.74-0.93), microvascular complications (HR 0.72; 95% CI 0.61-0.87), and macrovascular complications (HR 0.87; 95% CI 0.82-0.93) (P<0.001 for trend), the study found.

"To our knowledge, this is the first large prospective study demonstrating similar inverse associations of fruit consumption with both incident diabetes and diabetic complications. These findings suggest that a higher intake of fresh fruit is potentially beneficial for primary and secondary prevention of diabetes," Du and colleagues wrote.

But if fruit and fructose are practically toxic, how can any of this be? As I wrote in Healing without Medication:

Fructose, as its name suggests, is the most abundant sugar in fruit. Gram for gram fructose is actually sweeter than other sugars such as sucrose (table sugar, or cane sugar) or glucose (the sugar to which our bodies convert most carbohydrates). The sweetness in fructose is sensed on the tongue more quickly than the sweetness of table sugar, and the sensation of sweetness induced by fructose is more intense than that generated by any other kind of sugar. We humans are pre-programmed to enjoy the taste of fruit.

If fruit was the only place we got fructose, there probably would not be a problem. In the modern world, we don't just get fructose in the fructose we eat in fruit or, if you happen to drink them, soft drinks sweetened with high-fructose corn syrup.

Fructose is also a component of the table sugar sucrose. Chemically, each molecule of sucrose consists of a molecule of fructose joined to a molecule of glucose. Digestive enzymes break down sucrose into fructose + glucose, and then specialized transporter proteins called GLUT2 and GLUT5 carry the fructose into the bloodstream.

If we don't eat fructose on a regular basis, however, our small intestines don't make the carrier proteins that take it into the bloodstream. Depending on how often we consume fructose, our bodies can only absorb 5 to 50 grams (20 to 200 calories) from fructose per day. That's a good thing, because any level of fructose consumption over 25 grams (100 calories) per day is mildly toxic.

The portal hepatic vein sends fructose from food and drink to the liver, where it is absorbed without the help of insulin. (For this reason, fructose was long considered a safe sweetener for diabetics—but only if it is consumed in amounts of 2 to 3 teaspoons per day. ) Glucose from food gets sent from the liver to other parts of the body, but fructose is quickly converted into dihydroxyacetone phosphate and glyceraldehyde. With the right enzymes, the liver can burn these forms of “sugar” to make energy.
Excesses of these two byproducts of the liver's processing of fructose can form triglycerides, cholesterol, and fat, but most of the resulting fat stays in the liver, sometimes (diabetes expert Mark Hyman says in about 30% of people) accumulating to cause a condition called fatty liver.
But dietary fructose consumed in excess can cause many other problems.

• Fructose may actually increase appetite, by elevating bloodstream concentrations of a hormone called ghrelin.
• Fructose may suppress the brain's appetite control system, by decreasing bloodstream concentrations of a hormone called leptin.
• Fructose increases the permeability of the lining of the small intestine. This increases the likelihood of problem proteins (such as certain proteins in wheat, meat, tomatoes, citrus, chocolate, and dairy products) entering the bloodstream.
• Fructose doesn't activate the brain's satiety centers. There isn't any kind of signal to or from the brain that tells us when we have had enough. That's not a problem when we eat a single piece of fruit or we use a single teaspoon (or maybe two) of fructose to sweeten a beverage, but there is no natural way for the brain to put the brakes on the consumption of fructose. It's natural to eat and eat and eat without feeling full.
• Fructose can enter the same metabolic processes that use glucose. Fructose doesn't require insulin, so cells that use fructose shut down their receptor sites for insulin carrying that glucose. At a later meal, when the energy source is glucose rather than fructose, cells are too insulin-resistant to receive the glucose efficiently. This leaves insulin free to store fat, and elevates blood sugar levels.
• Fructose can undergo the Maillard reaction. In cooking, this would be seen as caramelization. In the human body, fructose accelerates glycation, the process of “sugar coating” red blood cells and nerves.
• Because the body's disposal of fructose generates uric acid and uric acid aggravates gout, which is also aggravated by diets that are high in purines, found in meat and beans.
Small amounts of fructose, however, are actually beneficial:
• Athletes can “pump up” muscles after a workout faster when their post-workout beverages are sweetened with a mixture of about 70% glucose and 30% fructose (or galactose. This would be especially important during an athletic competition or during a race.
• Tiny amounts of fructose, from 3 to 10 grams (about half a teaspoon to two teaspoons) per meal, the equivalent of a single piece of fruit or a single serving of berries, activate the liver to respond more completely to the other sugars released from starch, so that insulin levels are kept down and the body can burn more fat—assuming one doesn't overeat and one gets at least some exercise.

The bottom line about fructose is that a little not only is OK, it's healthy. A “little” is up to the equivalent of a single serving of fruit at each meal, or no fruit at meals and two or three fruit snacks. Diabetics actually get slightly better control over their blood sugars when they consume small amounts of fruit. 

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