Monday, February 20, 2012

Fruits and Fructose - Good or Bad?


I eat a lot of fruit: raisins, grapes, blueberries, apples, strawberries, bananas, orange juice and tomatoes (yes, tomatoes are a fruit.) I always thought they were good for me (well orange juice in great moderation, only to enhance the benefits of green/white tea.)

Lots of research highlights the benefits:

Here are just a few examples:

1. Apples

2. Blueberries
Blueberries Help Build Strong Bones
Blueberries may inhibit development of fat cells
Blueberries: a Cup a Day May Keep Cancer Away
Blueberry’s positive effects on cholesterol

3. Strawberries
Strawberries Boost Red Blood Cells
Strawberries Fight Diabetes and Nervous System Diseases
Strawberries may slow precancerous growth
Strawberries Protect the Stomach from Alcohol

Even the government says fruits are good:

Almost Everyone Needs to Eat More Fruits and Vegetables
A growing body of research shows that fruits and vegetables are critical to promoting good health. To get the amount that's recommended, most people need to increase the amount of fruits and vegetables they currently eat every day. How Many Fruits and Vegetables Do You Need?

Fruits and Vegetables Can Protect Your Health
Fruits and vegetables contain essential vitamins, minerals, and fiber that may help protect you from chronic diseases. Compared with people who consume a diet with only small amounts of fruits and vegetables, those who eat more generous amounts as part of a healthful diet are likely to have reduced risk of chronic diseases, including stroke and perhaps other cardiovascular diseases, and certain cancers.

But a recent article sent to me by a reader/friend says quite the opposite:

A Word about Fructose (a Common Sugar in Soda, Fruit Juice and More) …

You will want to be very careful about the amount of fructose you consume as part of your carb intake, as it is by far the worst type of sugar there is in terms of both your health and your weight:

* After eating fructose, virtually all of the metabolic burden rests on your liver.
*Fructose is turned into free fatty acids (FFAs), VLDL (the damaging form of cholesterol), and triglycerides, which get stored as fat.
* The fatty acids created during fructose metabolism accumulate as fat droplets in your liver and skeletal muscle tissues, causing insulin resistance and non-alcoholic fatty liver disease (NAFLD). Insulin resistance progresses to metabolic syndrome and type 2 diabetes.
* Fructose is the most lipophilic carbohydrate. In other words, fructose converts to activated glycerol (g-3-p), which is directly used to turn FFAs into triglycerides. The more g-3-p you have, the more fat you store. Glucose simply does not do this.
* Consuming fructose is essentially consuming fat!
* The metabolism of fructose by your liver creates a long list of waste products and toxins, including a large amount of uric acid, which drives up blood pressure and can cause gout.
* Fructose has no effect on the hunger hormone ghrelin and by interfering with your brain's ability to use leptin, results in overeating.

If you want to shed excess pounds, maintain a healthy weight long-term, and RADICALLY reduce (and in many cases virtually eliminate) your risk of diabetes, heart disease and cancer, then get serious about restricting your consumption of fructose to no more than 25 grams per day, with a maximum of 15 grams a day from fresh fruit. If you're already overweight, or have any of these diseases or are at high risk of any of them, then you're probably better off cutting that down to 10-15 grams per day -- fruit included.

If you believe you are an exception to this rule then you can measure your uric acid level. If it is below 5 when you are eating loads of fruit then you are metabolically ok with it, as elevated uric acid levels are a strong indication of fructose toxicity.

So what should I do?

Well this article, Fructose: Sweet, But Dangerous, suggests that fruit isn't really so bad:

Fruits and vegetables have relatively small, "normal" amounts of fructose that most bodies can handle quite well... For example, a cup of chopped tomatoes has 2.5 grams of fructose, a can of regular (non-diet) soda supplies 23 grams, and a super-size soda has about 62 grams.

But this table tells me apples, grapes, and especially raisins, are particularly bad.

My conclusion - I'm going to go right on eating most of my fruits but will cut down on raisins, which I use to sweeten my daily oat meal ( the subject of my next, similar, post).

More on Fructose (Some of it quite contradictory):


Fructose produces less rewarding sensations in the brain

Fructose not only results in a lower level of satiety, it also stimulates the reward system in the brain to a lesser degree than glucose. This may cause excessive consumption accompanied by effects that are a risk to health, report researchers from the University of Basel in a study published in the scientific journal PLOS ONE. Various diseases have been attributed to industrial fructose in sugary drinks and ready meals.

Fruit sugar, or fructose, is a carbohydrate that occurs naturally in fruits and vegetables and is generally harmless in this form. Despite their similar structures, fructose and glucose - that is, pure grape sugar - affect the body very differently: an intake of glucose causes a sharp increase in blood insulin within minutes, whereas fructose stimulates insulin secretion to a limited degree only.

Teams of researchers led by Professor Christoph Beglinger from the University Hospital and Professor Stefan Borgwardt from the Psychiatric University Clinics (UPK Basel) have now taken a more in-depth look at how these two types of sugar affect interactions between the gastrointestinal tract and the brain. Their work was funded by the Swiss National Science Foundation. In their study, the researchers used combined pharmacological and imaging methods such as functional magnetic resonance imaging (MRI).

Brain activity examined

In the placebo-controlled, double-blind study, twelve healthy young men were given either fructose, glucose or a placebo by way of a feeding tube. Blood samples were then taken from the subjects to measure satiety hormones. The subjects were also asked about how satiated they felt, and their brain activity was monitored by MRI while at rest.

The findings of the pilot study were as follows. Unlike glucose, fructose is less effective at creating feelings of satiety and stimulating the reward system in the brain. An analysis of the MRIs in fact showed that the two types of sugar differed greatly in terms of network activation within the hippocampus and amygdala areas of the limbic system, i.e. the regions of the brain that regulate emotions and impulses. Furthermore, in contrast to glucose (which stimulated a strong signal) the levels of satiety hormones in the blood barely or only minimally increased following fructose consumption. The subjective feeling of satiety also tended to be less affected by the consumption of fructose.

The problem of fructose

"The study may provide the first key findings about the lack of satiety and rewarding effects triggered by fructose," state lead authors Dr Bettina Wölnerhanssen and Dr Anne Christin Meyer-Gerspach. The role of the differing insulin levels and other effects will have to be demonstrated in further studies with more test subjects. Research is increasingly finding indications that isolated, industrially manufactured fructose - which is increasingly used in sugary drinks, sweets and ready meals - is problematic for the human body. It is suspected that fructose promotes the development of various disorders such as obesity, diabetes, fatty liver disease and gout.

Fructose powers a vicious circle

'Walk through any supermarket and take a look at the labels on food products, and you'll see that many of them contain fructose, often in the form of sucrose (table sugar)' -- that's how Wilhelm Krek, professor for cell biology at ETH Zurich's Institute for Molecular Health Sciences, summarises the problem with today's nutrition. Prepared foods and soft drinks in particular, but even purportedly healthy fruit juices contain fructose as an artificial additive -- often in high quantities. In recent decades fructose spread throughout the food market, due to a reputation as being less harmful than glucose. In contrast to glucose, fructose barely increases blood glucose levels and insulin secretion. This avoids frequently recurring insulin spikes after any glucose consumption, which are judged harmful. In addition, fructose is sweeter to the taste.

But there's a downside: the liver converts fructose very efficiently into fat. People who consume too much high-fructose food can in time become overweight and develop high blood pressure, dyslipidaemia with fatty liver and insulin resistance -- symptoms that doctors group together under the name metabolic syndrome.

Unchecked growth of the heart muscle

A new paper by Krek and his team member Peter Mirtschink describes a further, more troubling side effect of fructose. The researchers have discovered a previously unknown molecular mechanism that points to fructose as a key driver of uncontrolled growth of the heart muscle, a condition that can lead to fatal heart failure. Their study was recently published in Nature.

When a person has high blood pressure, the heart has to grow as it is harder to pump the blood through the circulatory system. These growing heart muscle cells require a considerable amount of oxygen. However, since not enough oxygen is available to adequately supply the increased growth, the cells switch to an alternative energy supply. Instead of drawing energy from fatty acids, they rely more on an anaerobic process called glycolysis -- literally, the 'splitting of sugars'. If the heart muscle cells can access fructose in addition to glucose, this can set off a fatal chain reaction.

Flipping the switch for fructose metabolism

In the study, Krek's research group demonstrates that a lack of oxygen in the heart cells cues the appearance of the HIF molecule. This is a universal molecular switch that flips whenever a pathological growth process is under way, such as cardiac enlargement or cancer. HIF causes the heart muscle cells to produce ketohexokinase-C (KHK-C), the central enzyme in fructose metabolism. KHK-C has a high affinity for fructose and can therefore process it very efficiently. The production of KHK-C also has a reinforcing effect on glycolysis. Since fructose metabolism doesn't involve any negative feedback regulation, a vicious cycle starts that can lead to heart failure.

To investigate this mechanism, the researchers used not only mouse models but also biological samples from patients with pathological heart enlargement accompanied by a narrowing of the aortic valve. Samples of heart muscle cells taken by surgeons during heart operations provided the ETH researchers with the means for proving that such cells really do have more HIF and KHK-C molecules. In mice that were suffering from chronic high blood pressure, the researchers turned off the KHK enzyme, which indeed inhibited enlargement of the heart.

One gene, two enzymes

Another fact worthy of note is that the body also contains KHK-A, an enzyme very similar to KHK-C except that it has poor preference for fructose. Both these enzymes have the same genetic code; the difference between them comes from how a molecular cutting tool tailors their construction blueprint -- their messenger RNA, which is a transcript of the relevant gene. Depending on requirements, one of two blueprints can be generated from the same gene to produce either of two different enzymes. The expert term for this process is 'alternative splicing'. Krek explains, 'About 95 percent of all human genes are alternatively spliced. It's a major way to create the extraordinary variety of proteins, enzymes and regulators in the human body.'

Normally primarily liver cells produce the fructose-friendly KHK-C enzyme; other organs produce almost exclusively KHK-A. Now for the first time, the ETH researchers are showing that even an organ like the heart is capable of producing KHK-C, the more efficient of the two enzymes, if it is exposed to pathogenic stress factors. In the process, HIF activates the molecular cutting tool, or splicing factor, SF3B1. This molecule is often genetically altered in many types of cancer, which possibly indicates that even the growth of cancer can be affected by fructose.

Normal fruit consumption safe

Large volumes of fructose are added to many foods, but especially to sweet beverages and soft drinks. This practice drove up per capita consumption of high fructose corn syrup in the USA between 1970 and 1997, from 230 grams per year to over 28 kilograms.

But Mirtschink provides reassurance that eating a normal amount of fruit daily is safe and healthy. 'Besides fructose, fruit contains plenty of important trace elements, vitamins and fibre,' he says. People should, however, avoid overly sweet soft drinks and fruit juices -- these often have sugar added -- as well as ready-made meals and other foods to which large amounts of fructose are added as a flavour carrier. 'Just this surplus of fructose can help trigger the mechanism we have described if one of the stress factors is present, such as cardiac valve disease or high blood pressure,' Mirtschink emphasises.

Fructose contributes to weight gain, physical inactivity, and body fat

In the last 40 years, fructose, a simple carbohydrate derived from fruit and vegetables, has been on the increase in American diets. Because of the addition of high-fructose corn syrup to many soft drinks and processed baked goods, fructose currently accounts for 10 percent of caloric intake for U.S. citizens. Male adolescents are the top fructose consumers, deriving between 15 to 23 percent of their calories from fructose--three to four times more than the maximum levels recommended by the American Heart Association.

A recent study at the Beckman Institute for Advanced Science and Technology at the University of Illinois found that, matched calorie for calorie with the simple sugar glucose, fructose causes significant weight gain, physical inactivity, and body fat deposition.

The paper, "Fructose decreases physical activity and increases body fat without affecting hippocampal neurogenesis and learning relative to an isocaloric glucose diet," was published in Scientific Reports.

"The link between increases in sugar intake, particularly fructose, and the rising obesity epidemic has been debated for many years with no clear conclusions," said Catarina Rendeiro, a postdoctoral research affiliate at the Beckman Institute for Advanced Science and Technology and lead author on the study. "The reality is that people are not only consuming more fructose through their diets, but also consuming more calories in general.

"One of the key questions is whether an increase in fructose intake contributes to obesity in the absence of excessive calorie intake."

The researchers, under the direction of Justin Rhodes of Beckman's NeuroTech Group and professor of psychology at Illinois, studied two groups of mice for two-and-a-half months: one group was fed a diet in which 18 percent of the calories came from fructose, mimicking the intake of adolescents in the United States, and the other was fed 18 percent from glucose.

"The important thing to note is that animals in both experimental groups had the usual intake of calories for a mouse," said Rendeiro. "They were not eating more than they should, and both groups had exactly the same amount of calories deriving from sugar, the only difference was the type of sugar, either fructose or glucose."

The results showed that the fructose-fed mice displayed significantly increased body weight, liver mass, and fat mass in comparison to the glucose-fed mice.

"In previous studies, the increases in fructose consumption were accompanied by increases in overall food intake, so it is difficult to know whether the animals put on weight due to the fructose itself or simply because they were eating more," Rhodes said.

Remarkably, the researchers also found that not only were the fructose-fed mice gaining weight, they were also less active.

"We don't know why animals move less when in the fructose diet," said Rhodes. "However, we estimated that the reduction in physical activity could account for most of the weight gain."

"Biochemical factors could also come into play in how the mice respond to the high fructose diet," explained Jonathan Mun, another author on the study. "We know that contrary to glucose, fructose bypasses certain metabolic steps that result in an increase in fat formation, especially in adipose tissue and liver."

The precise mechanisms are still being investigated, but one thing is certain: high intake of fructose by itself adds pounds.

"We designed this study based on the intake of fructose by adolescents in the United States," said Rhodes. "Our study suggests that such levels of fructose can indeed play a role in weight gain, favor fat deposition, and also contribute to physical inactivity. Given the dramatic increase in obesity among young people and the severe negative effects that this can have on health throughout one's life, it is important to consider what foods are providing our calories."

Not so bad

Fructose does not impact emerging indicator for cardiovascular disease

Fructose, the sugar often blamed for the obesity epidemic, does not itself have any impact on an emerging marker for the risk of cardiovascular disease known as postprandial triglycerides, new research has found.

However, overconsumption of calories from fructose can have substantial adverse effects on health, said Dr. John Sievenpiper, a researcher in the Clinical Nutrition and Risk Factor Modification Centre of St. Michael's Hospital.

"This is more evidence that fructose has adverse effects only insofar as it contributes to excess calories," said Dr. Sievenpiper.

Fructose, which is naturally found in fruit, vegetables and honey, is a simple sugar that together with glucose forms sucrose, the basis of table sugar. It is also found in high-fructose corn syrup, the most common sweetener in commercially prepared foods.

Dr. Sievenpiper conducted a meta-analysis of existing studies on fructose and its impact on the level of triglycerides, a fat found in blood, after eating. Testing for these triglycerides—in addition to the standard testing for blood glucose levels—is becoming more common for people trying to determine their risk for cardiovascular disease, although health care professionals remain divided on its usefulness.

Dr. Sievenpiper's results appear in the January 2014 issue of the journal Atheroclerosis.

"Fructose doesn't behave any differently than other refined carbohydrates," he said. "The increases you see are when fructose provides extra calories."

Scientists conclude high fructose corn syrup should not be blamed for obesity

A new article published today in International Journal of Obesity found there is no evidence to suggest the current obesity epidemic in the United States can be specifically blamed on consumption of high fructose corn syrup (HFCS).

The commentary concludes that after an extensive review of all available HFCS research, there is overwhelming evidence showing HFCS is nutritionally equivalent to sugar. This opinion is in-line with the American Medical Association and the Academy of Nutrition and Dietetics, both of which concluded that HFCS is not a unique cause of obesity.

The authors state that while there has been a large amount of debate in the media about the impact of HFCS on obesity levels, the fact is "Sucrose (sugar) and HFCS are very similar in composition….and are absorbed identically in the human GI tract."

"The public discussion about HFCS will likely continue to rage on and more studies will be conducted," said James M. Rippe, M.D., Founder and Director of the Rippe Lifestyle Institute, and Professor of Biomedical Sciences at the University of Central Florida, one of the article's authors. "However, at this point there is simply no evidence to suggest that the use of HFCS alone is directly responsible for increased obesity rates or other health concerns."

The article goes on to discuss a number of research trials that have been conducted on the issue of HFCS and obesity, and concludes that at this time the evidence shows no short-term health differences between the use of HFCS or sugar could be detected in humans. Weight gain, glucose levels, insulin and appetite were not adversely affected by the use HFCS over sugar.

The commentary was co-authored with Dr. Rippe by David M. Klurfeld, Ph.D. of the USDA Agricultural Research Service, John Foreyt, Ph.D. of Baylor College of Medicine, and Theodore J. Angelopoulos, Ph.D., MPH Professor and Director, Laboratory of Applied Physiology Department of Health Professions at University of Central Florida.

HFCS was developed in the mid-1960's as a more flexible alternative to sugar and was widely embraced by the food industry. The use of HFCS grew rapidly from 1970-1999 where usage peaked. Since 1999, the use of HFCS has declined while obesity rates have continued to rise. Sucrose is still the dominant sweetener worldwide with over nine times the consumption of HFCS.

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