IBS, Depression, and Skin Problems in Fructose Malabsorption

There is one problem with the Paleo diet for oh, about 30-50% of Europeans and maybe 15-20% of Americans – the low starch approach that encourages eating more fruit and sweet potatoes exacerbates many digestive, mood, and skin problems.

You hear about it often. “I’ve made all these positive dietary changes and suddenly I’m more sensitive to everything.” A possible reason for this might be that they have included in their diets more fresh foods that include more fructose and fructans.

What Is Fructose Malabsorption?

According to Wikipedia “Fructose malabsorption, formerly named “dietary fructose intolerance,” is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine’s enterocytes.”

This means that our ability to break down fructose is impaired and so fructose molecules travel down to the colon undigested. When anything makes its way down to the large intestine without first being broken down, the situation can get pretty ugly.

Many people with fructose malabsorption experience digestive troubles such as diarrhea or constipation, rashes, melancholy or anger, among others.


Symptoms of fructose malabsorption vary from person to person. Many of the symptoms are IBS- like symptoms and, in fact, fructose malabsorption may be one of the leading causes of irritable bowel syndrome.

  • Bloating
  • Cramping
  • Gas
  • Diarrhea
  • Constipation
  • Headaches
  • Itching and rashes
  • Acne
  • Eczema
  • Depression and low serum tryptophan concentrations
  • Carbohydrate cravings
  • Colic in babies


The test for fructose malabsorption is a simple hydrogen breath test – the same test used for lactose intolerance.

The poor man’s way to test for fructose malabsorption is by eliminating fructose and observing symptoms. This method works just as well since there are so many symptoms associated with the condition. If relief of all of these happens, you’ve figured it out.

Fructose Can Cause Depression

Surprisingly, the undigested fructose molecules in the intestine does a whole lot more damage to the body than just some annoying bloating, gas, and rashes. I mean, as if that weren’t enough, researchers have found that those free floating fructose molecules actually react chemically with tryptophan – the precursor to serotonin, one of the neurotransmitters that helps us feel happy – degrading it and lowering serum levels. Without tryptophan we feel depressed and irritable and weepy.

Researchers from the University of Innsbruck in Austria found a high correlation to depression and women with fructose malabsorption, although the same was not found in men. Another Spanish study found that 71% of the depressed adolescents they studied had sugar intolerance, compared with 15% of controls. A huge margin like this should not be overlooked.

Lactose and fructose malabsorption disorders combined were found to result in an even greater instance of depression.

Depression is more common in women with FM
We can thank Emily Deans, an MD with interests in evolutionary psychiatry, for clarifying the cause of the connection between women with fructose malabsorption and depression. Why not men she asked? The answer is because men have more tryptophan than do women.

“The researchers postulated that estrogen made the big difference. Estrogen activates an enzyme called hepatic tryptophan 2,3 dioxygenase that shifts the metabolism of tryptophan from making serotonin (happy) to making kynurenic (not happy). Women already have lower serum levels of tryptophan than men do (which may be part of the reason why we are more vulnerable to depression in the first place), so screwing up whatever available tryptophan in the diet with fructose may lead to even lower levels, and thus depression.”

Looks like if you’re a woman and you’re depressed, you had better get yourself tested for fructose malabsorption.

Safe Foods List

Not all fruits and sweeteners are created equally. Some of them have more fructose than others, and so some of them are safer than others.

Foods which can be eaten liberally:

  • Meat
  • Eggs
  • Milk – if lactose malabsorption is not also an issue
  • Yogurt
  • Cheese
  • Nuts (soaked is best for nutrition)
  • Olives
  • Leafy green vegetables
  • Broccoli
  • Lemons and limes
  • Coconut water (not milk!)
  • Butter and oils
  • Kiwi
  • Pomegranate
  • Glucose
  • Yams but NOT sweet potatoes (although yams are said to be high in anti-nutrients)
  • Plantain
  • Tapioca – same as yuca or casava
  • Potato
  • White rice

Foods to Avoid List:

Not only do fructose malabsorbers need to avoid fructose but they need to avoid something called fructans too. Fructans are long chain fructose molecules and they usually do the same damage as fructose. The amount of fructans vary in the following foods so add after eliminating all fructose and fructan containing foods, try adding some of these back one at a time and in small amounts to observe tolerance. Many of these such as coconut, onions, and wheat are quite high in fructans and usually don’t work for any of us FMs.


  • Most fruit juice
  • Dried fruit
  • Fruit concentrates
  • Apples
  • Pears
  • Apricots
  • Watermelon
  • Cantaloupe
  • Cherries
  • Grapes
  • Mango
  • Honey
  • Agave
  • Tomato paste
  • Corn syrup and high fructose corn syrup
  • Wine – dry wines might be ok in moderation


  • Wheat
  • Onions
  • Garlic
  • Leeks
  • Coconut milk and meat
  • Jerusalem artichoke
  • Asparagus
  • Chicory root

For a long list of sugar content of fruits check ThePaleoDiet.com. For the book on FODMAPs and fructose malabsorption, with a more complete list of fruits vegetables, fructose and fructans read The Complete Low FODMAP Diet.

Tips for Avoiding Fructose

The last and very important thing to know about fructose is that table sugar (sucrose) contains 50% fructose and 50% glucose. This sounds scary at first but, interestingly, glucose helps carry fructose through the intestines. So, when you eat table sugar, the glucose helps the fructose get absorbed. Since they get absorbed together, even if you don’t break down fructose, you can still absorb it aided by glucose. Now, f you eat a whole heck of a lot of sucrose, some of the fructose will probably escape down to the colon, unaided by the glucose, so don’t go overboard.

This little fact about glucose can be very useful when accidentally (or intentionally) eating something which contains a small amount of fructose. We can simultaneously eat some glucose (I use NOW brand dextrose) to avoid the ill effects of fructose. But remember, this only works in small amounts. If you decide to eat a whole entire mango, for example, adding glucose isn’t going to help you absorb that amount of fructose. As far as I know, the glucose trick does not work for fructans. You’ve just got to avoid those.

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