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The low-FODMAP Diet

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The low-FODMAP Diet

The low FODMAP diet is not really a diet, more a way of analysing what foods may be causing IBS, colitis or worse; and it needs an expert who understands it to monitor patient progress.

What is FODMAP?

FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. These are all short-chain carbohydrates (sugars) that may be poorly absorbed by the small intestine in some people. As a result, those people can develop diarrhoea, constipation, pain, gas and flatulence, cramping, and/or bloating – symptoms often described as Irritable Bowel Syndrome (IBS). In particular, we are talking about:

Fructose – high fructose corn syrup, honey, certain fruits

Oligopolysaccharides – beans, lentils, onions, garlic, wheat

Lactose – especially cows’ dairy products

Polyols – found in sweeteners e.g. sorbitol, some fruits and some vegetables

What is the FODMAP Diet?

In one respect it is not really a diet, more like an old-fashioned eating ‘regime’ where you restrict certain foods and then add them back one by one to analyse what may be causing you problems. It’s more like a personal reality check than a diet. In fact, most people are actually encouraged to use the Rainbow Diet as the basic diet.

What form does the FODMAP diet take?

First, you eliminate all the foods that might cause a problem for 6 weeks. So, this may well appear to be a very restrictive diet. This usually results in all the symptoms going.

Then, you add back in foods one by one, until you develop a reaction.

And finally, you know what to avoid and you can return to a Rainbow Diet but avoiding one or two items (or maybe more). Research shows that this works for 86% of people who previously had problems. 

What foods must I avoid on the FODMAP diet?

The first issue is that there seems to be some conflict between the ‘Don’t eat’ and the ‘Can eat’ lists. 

Don’t eat:

  1. Dairy milk, yoghurt, and ice cream
  2. Pulses/legumes such as lentils
  3. Wheat products – bread, biscuits, cereals
  4. Vegetables such as garlic and onions, artichoke, asparagus
  5. Fruits such as apples, pears, peaches, cherries

Can eat:

  1. Almond milk
  2. Grains such as quinoa, oats and rice
  3. Meat and eggs
  4. Cheeses such as Feta, camembert, brie and cheddar
  5. Vegetables such as potatoes, aubergines, tomatoes, cucumbers
  6. Fruits such as grapes, blueberries, pineapple, strawberries, oranges 

If you are a little confused or bemused at this point, so am I. 

Apparently, there are nutritionists who understand why milk is not allowed but camembert is!

Beneficial bacteria issues 

While your gut may have a problem absorbing foods like garlic and onions, to your gut bacteria, these are their favourite foods or Prebiotics. Unfortunately, our friends produce hydrogen and methane when they ferment these foods and the gut retains water, the totality leaving you bloated.

So a FODMAP-rich meal leaves you bloated and even in pain, while your good (commensal) beneficial bacteria thrive.

And here’s the rub. A low FODMAP diet might leave you with a calmer gut lining, but the restrictive list of foods you can eat leave you nutritional weaker and your gut bacteria unhappy.

Once symptoms have have stabilised participants need to re-introduce the missing foods as soon as possible; 2-6 weeks is the norm. 

There is no need for a healthy person to try a FODMAP diet – only those with gut problems like IBS, colitis or diverticulitis.

How can the FODMAP DIET help?

The part of the gut that is particularly under scrutiny is the Small Intestine. This is the part of the gut where the largest absorption of nutrients from your food takes place. Situated between the stomach and the large intestine, bile and pancreatic enzymes flow into it through the pancreatic duct. Although it is called the ‘small’ intestine, it is actually about 6 metres long. What can happen in the small intestine is what’s called SIBO, or Small Intestinal Bacterial Overgrowth. 

SIBO means you can have too many bacteria in this part of your gut, and/or the wrong sort. Various theories abound for this. SIBO occurs when your food just doesn’t move through you quickly enough. This can be the result of:

  • surgery, 
  • Is there any research?diverticulitis, colitis or lupus
  • scar tissue from radiotherapy, 
  • A build-up of amyloid,
  • HIV, diabetes
  • Drugs such as antibiotics or PPIs and ironically those used to treat IBS
  • Poor peristalsis – the nervous contractions that move food through the gut, occurring every 90 minutes to 2 hours.

SIBO is linked to other illnesses in the body. For example, people with SIBO are more likely to develop Hashimoto’s, a condition of the thyroid, supposedly an autoimmune disease.

Is there any Research?

Yes, but it is somewhat inconclusive.  A 2017 meta-analysis of nine studies felt there was a high degree of bias and concluded the benefits might be due to the placebo effects. However, a study (1) by Monash University in Melbourne did conclude that there was a benefit to 7 out of 10 people with IBS. But, then, they came up with the FODMAP diet.


  1. Gibson, P. R., Halmos, E. P., & Muir, J. G. (2020). Review article: FODMAPS, prebiotics and gut health-the FODMAP hypothesis revisited. Alimentary Pharmacology and Therapeutics, 52(2), 233-246. https://doi.org/10.1111/apt.15818