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The LOW FODMAP diet
A diet low in fermentable carbohydrates known as FODMAPs is frequently recommended for the management of irritable bowel syndrome (IBS). (1, 2)
Several studies have suggested that avoiding high FODMAP foods can help manage bloating, stomach pains, flatulence, diarrhea and constipation. (3, 4, 5)
Bacteria in the gut help break down food through a process called fermentation. When this occurs gas is released.
For some IBS sufferers, certain high FODMAP foods are thought to increase gas production in the gut, leading to distension and discomfort, because they are rapidly fermented and can be poorly absorbed.
This is likely to be exacerbated in the presence of a small intestinal bacterial overgrowth (SIBO), as there is more bacteria available for fermentation.
With SIBO, the type of bacteria in excess can also impact stool consistency. Those with predominantly methane gas-producing bacteria tend towards constipation. Those with mainly hydrogen gas-producing bacteria are more likely to have loose stools or diarrhea. (6)
What does FODMAP stand for and which foods are high FODMAP?
FODMAP stands for fermentable oligo-, di-, mono-saccharides and polyols. (7)
The four groups of FODMAPs and their main dietary sources include:
Oligosaccharides: fructans (FOS) and galacto- oligosaccarides (GOS) are subsets. Wheat, rye, legumes, lentils and various fruits and vegetables, such as garlic and onions.
Oligosaccharides are poorly absorbed in everyone, because humans lack the enzymes to break these carbohydrates down. Those with IBS tend to be more sensitive to their consumption and the gas produced.
Disaccharides: Lactose is the main carb and is found in milk and milk products, like yoghurt and cheese. People who lack the enzyme lactase will malabsorb lactose.
Monosaccharides: Fructose is the main carb. Found in various fruits including pear and mangoes, sweeteners such as honey and agave nectar, and products containing high fructose corn syrup.
Polyols: Certain fruits and vegetables including blackberries and lychee, as well as some artificial sweeteners like those in sugar-free gum and low calorie processed foods and drinks. Sorbitol and mannitol are the most common polyols in the diet.
A large range of foods contain these fermentable carbs, making a low FODMAP diet complicated and often very restrictive. (8)
How do you know which high FODMAP foods trigger symptoms?
Determining which of the four groups is the most triggering requires a 3 step process over many months. This is usually done with the help of a dietician and the Monash University mobile phone app. (8)
Stage one involves strict restriction of all high FODMAP foods for 2-6 weeks.
Stage two requires systematic reintroduction of specific high FODMAP foods one by one for three days each. This is a 6-8 week process.
During stage three foods that didn't trigger symptoms are reintroduced and a modified low FODMAP diet is continued, but is tailored to personal tolerance. (8)
Could a low FODMAP diet do more harm than good?
Along with being complex and challenging, there are thoughts a low FODMAP diet could do more harm than good. This is because most FODMAPs are prebiotic fibre, meaning they support the growth of good, healthy gut bacteria. (8, 9)
Healthy bacteria in our gut not only help digest food (10), but they strengthen the integrity of the gut (11), produce vitamins (12), harvest energy (13), protect against infection (14), regulate our immune system (15), make neurotransmitters essential for a stable mood (16), and so much more.
Furthermore when healthy bacteria are starved of prebiotic fibre, production of a key short chain fatty acid called butyrate is reduced. Butyrate helps to protect the gut lining, lower inflammation, heal a damaged gut, fuel the processes in the gut, aid insulin function, and even activate anti-oxidants. (17, 18, 19, 20, 21, 22)
Going low FODMAP may reduce symptoms in some, but is it addressing the root cause?
If SIBO or a bacterial overgrowth from poor gut motility (motion) is an underlying factor, avoiding low FODMAP foods could be considered a Band-Aid if not addressed.
Also, could any improvement be due to a reduction in gluten when on the diet?
Gluten containing wheat, barley and rye are high FODMAP or high fructan food groups. Is it possible that the gluten protein triggers symptoms and not just fructans?
Given that the low FODMAP diet allows for small quantities of wheat, barley and rye to be consumed, IBS symptoms may still occur if gluten sensitive and it is not strictly removed from the diet.
Intolerances to lactose and/or fructose are thought to be common in those with IBS symptoms. So avoiding these sugars may definitely prove helpful. But many don't complete the reintroduction phase of the low FODMAP diet correctly and end up on a diet low in all high FODMAP foods indefinitely just to manage symptoms. As already mentioned this does not support the growth of healthy bacteria in the gut.
The causes of irritable bowel syndrome can be multiple, and diet is certainly a major contributing factor, but it pays to be aware that a small intestinal bacterial overgrowth or a previous bacterial or viral infection are underlying reasons for IBS that can and must be addressed if being symptom free with a healthy gut is a long term goal.
Learn more about IBS and the root causes by visiting What is IBS & what causes it?
