Food Freedom Friday Edition 304 - Fructose Malabsorption

Fructose is a sugar that is found in fruit and gives it its sweetness. It is also a type of sugar that forms part of table sugar (sucrose) and is one of the leading industrial sweeteners in the form of high-fructose corn syrup.

Over the last 10-15 years, there has been a lot of discussion about the role that fructose plays in many chronic health issues, including obesity, diabetes, non-alcoholic fatty liver disease, and many others. However, most of these discussions are a lot of hype and some hyperbole.

As with most things nutrition-based, there is much nuance and bio individuality with regards to fructose and whether it should be part of your healthy lifestyle.

The Perceived Good

When the Glycaemic Index first hit public awareness in the 1990s, fructose was hailed as the great white hope of diabetics. The index measured the speed at which foods, mainly carbohydrates, were converted into glucose in the body and fructose came very low on the index as it ‘converted’ very slowly into glucose.

Glucose provides energy that the human body and brain to function. It is absorbed from the gut into the blood stream and then into the liver where it is converted and stored as a substance called glycogen. Glycogen is released back into the blood stream to be converted into energy for whichever part of the body when and in the quantities that it is needed. This process is monitored and regulated by the hormone insulin.

If the release is not properly controlled too much glucose (sugar) can end up in the blood and become sticky. Gradually it will clog up the tiny veins in the eyes, kidneys and extremities and, in due course, larger veins leading to the main organs such as the heart. Insulin ensures that the glucose from the food you eat, is converted, stored and released in the right amounts, as needed, to fulfil your body’s and brain’s energy requirements when not running on alternate fuel sources (fats and ketones).

The problem for diabetics is that they either do not produce any insulin, or do not produce the right amount at the right time to ensure the correct release of energy-providing glucose (or glycogen) into the blood stream. When eating a significant amount of sweet and/or high carbohydrate foods that convert very quickly into glucose, the glucose will flood the blood stream making the blood far more sugary and sticky than is healthy. This is why in the past diabetics were advised to live on very low sugar, savoury diets.

The fact that fructose came very low on the glycaemic index and did not convert quickly into glucose was good news for diabetics because it meant that fructose-sweetened foods would not immediately turn into glucose and sending blood sugar levels sky high. Fructose also actually delivered more sweetness that sucrose (table sugar), so technically one would need less of it so had less chance of putting on weight. This theory did not hold water for the vast majority of fructose sweetened products as, once you heat fructose, its sweetness level reduces to that of sucrose.

And finally, as far as the food industry was concerned, fructose was cheaper than sucrose or other sweeteners…

The Bad…

However...

All was not quite what it seemed. Why was fructose so low on the glycaemic index? What made it different from other sugars?

Unlike glucose, fructose is not controlled by insulin, nor can it be converted, as can glucose, into energy in any part of the body. Fructose can only be processed by the liver.

Unlike glucose, eating fructose does not suppress the release of the stomach hormone, ghrelin. Ghrelin is the hormone that controls feeling hungry, and if suppressed when eating, you may continue to feel hunger and continue eating fructose-sweetened foods whereas you might have stopped eating glucose-sweetened foods because you felt full.

Strangely, although it is a carbohydrate or sugar, fructose is processed by the liver as a fat. This means that rather than being stored in the liver as glycogen, it gets stored as potentially harmful fat. Excess fructose consumption leads to excess fat being stored in the liver which can cause inflammation (with all its attendant ills) and liver disease.

Although theoretically fructose may help diabetics keep their weight down, it might actually add to the risk of obesity. Because excess fructose is stored by the body as excess fat, excess fructose consumption could cause problems right across the population in terms of obesity, heart disease, stroke and other chronic illness.

The food industry and fructose supporters in general defend fructose on the grounds (quite correct) that if fructose is ingested in equal quantities with glucose (which it is in sucrose, made up of 50% glucose, 50% fructose) it can be metabolised perfectly safely. But the most widely used sweeteners, because of the relative cheapness of fructose, use a higher proportion of fructose than glucose.

But what about fruit?

Yes, fruit does contain fructose (along with glucose) although in varying amounts depending on the fruit. But in fruit the fructose comes bound up in fibre and other carbohydrates which need to be broken down in the digestive system before the body can access the fructose. This prevents you getting the pure fructose ‘hit’ of high fructose sweetener.

Frucose Malabsorption

There are, however, two other health problems relating to fructose which have nothing to do with any of the above!

Fructose intolerance

The first is a rare but potentially life-threatening condition, hereditary fructose intolerance, in which the liver does not produce the enzyme (fructose 1-phosphate aldolase) essential to metabolise fructose. As a result, the fructose accumulates in the liver and prevents the conversion of glucose into glycogen starving the body of glycogen/energy and causing severe hypoglycaemia or low blood sugar. If this is not treated it can lead to coma and, ultimately, death. Its incidence is thought to be about 1 in 22,000.

The only treatment for genuine fructose intolerance is strict avoidance of fructose.

Fructose Malabsorption – or Fructmal

Far more common (thought to affect as many as 30-40% of the population to a greater or lesser degree) is fructose malabsorption.

In this condition, which greatly resembles what is known as lactose intolerance but is in fact also a malabsorption problem, the sufferer is deficient in the ‘transporting protein’ GLUT-5 which, in a healthy person, enables the fructose to be absorbed through the gut and into the liver. This results in the fructose traveling on through the intestines and ending up in the colon where bacteria break it down into short chain fatty acids and gases. This results in the bloating, flatulence and diarrhoea that are typical of fructose malabsorption.

Absorption of fructose through the gut is greatly improved if the fructose is taken with glucose (one molecule of glucose will ‘transport’ one molecule of fructose with it through the gut into the liver). Sucrose, or ‘normal’ sugar, is made up of equal parts of fructose and glucose. So those with fructose malabsorption can often tolerate normal sugar when they cannot tolerate fruit or high fructose sweeteners such as honey, maple syrup or HFCS.

But, sugar alcohols (sorbitol, mannitol, xylitol and all other sweeteners ending in ‘ol’) actually make fructose absorption more difficult, and can cause further problems. The sugar alcohol sorbitol can also occur naturally – in fruit such as apples –making these types of foods doubly lethal for ‘fructmal’s.

Causes

As with lactose malabsorption, you can inherit the condition but it can also be caused by:

·       Over use of high fructose foods (especially those sweetened by high fructose corn syrup – HFCS)

·       Bacterial abnormalities in the gut

·       Celiac disease

·  Treatments (such as chemotherapy or radiation) that damage the lining of the small intestine.

You can develop fructose malabsorption at any time in life but, more encouragingly, although it can be a lifelong condition, for most people it will resolve as general health and, particularly, their digestive health improves.

Symptoms and Diagnosis

Mainly digestive – bloating, flatulence, gurgling, abdominal pain and diarrhea

Less commonly – depression, anxiety, fatigue, headache, brain fog, constipation, weight loss or sugar craving and, as a result of constant diarrhoea, anaemia and nutrient deficiencies.

Formal diagnosis is via a hydrogen or a methane breath test. Since the gut produces neither of these gases naturally, if they are present in the breath it normally comes from fermentation in the large intestine as a result of the breakdown of fructose (or lactose) by gut bacteria.

Fructans

However, it may not only be fructose, and therefore fruits and sweeteners, that are problematic

Fructans are chains of fructose molecules which end in a glucose molecule and can cause the same problems to a fructose mal-absorber as fructose itself.

Fructans are found in many grains and vegetables including:

·       wheat, spelt, kamut and brown rice

·       many members of the onion family (alliums), artichokes, asparagus, green beans and tomato paste.

The glucose/dextrose formula does not work with fructans.

As with fructose, only trial and error will determine tolerance and in what quantity.

Treatment or Management

As with most non-organic digestive complaints the best approach is to identify and then eliminate the problematic foods for a period of time. Once some degree of stability has been achieved, you can establish your own thresholds and triggers. These will vary from person to person. Although some high-fructose foods (most fruits and many sweeteners) will cause reactions in most people, there are no hard and fast rules and trial and error is the best determinant.

The most successful way to establish your tolerance levels is to go ‘cold turkey’ 30 (or more) days, excluding all foods that contain either fructose or fructans. Assuming that you feel better (if you do not, consult with your health care provider as there may be some other cause for your un-wellness) then introduce foods containing fructans or fructose one by one, giving yourself several days on each new food before you try another as it can sometimes take 72 hours or more for the reaction to work through your system.

Remember also that a glucose (also known as dextrose) molecule will ’transport’ a fructose molecule through the gut wall, so you may be able to tolerate certain relatively high fructose foods provided you combine them with high glucose/dextrose food – such as a dextrose tablet. However, this only works if the levels of glucose/dextrose are as high, if not higher than the levels of fructose – if lower, the excess fructose will still not be absorbed – and you can end up by consuming a good deal more sugar than you might wish to.

At the same time, it is important to improve intestinal function. Consulting a nutritionist/nutritional therapist who would test your gut function and suggest appropriate supplementation or dietary manipulation can be very helpful and support your transition to an eating plan that is ultimately supportive of your health goals