The biphasic diet is a diet that is claimed to help manage small intestinal bacterial overgrowth (SIBO) symptoms.
In this article, we will discuss the biphasic diet, how it works, the evidence supporting it and the best practices for treating your SIBO in the long term.
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What is the biphasic diet?
The biphasic diet was created by Dr Nirala Jacobi and claimed to treat small intestinal bacterial overgrowth aka SIBO (1).
It combines the low FODMAP diet and the specific carbohydrate diet.
SIBO occurs when you have abnormally high levels of bacteria in your small bowel.
SIBO can result in similar symptoms to IBS, such as bloating, gas and abdominal pain (2).
The biphasic diet is designed to reduce the amount of fermentable carbohydrates and support the growth of beneficial gut bacteria (3).
The Biphasic Diet Stages
The biphasic diet is carried out in 2 phases: the elimination and the reintroduction phases.
It is advised that the diet should be followed for a maximum of 3 months (4).
Firstly, it aims to deprive bacteria of their preferred fuel source.
High FODMAP sources and grains are avoided as they are a food source for bacteria in the small intestine.
Some people will experience some side effects during the “die-off” period.
The “die-off” process is when toxins from dying bacteria are released when they are being eliminated.
These toxins can stimulate an inflammatory response known as the Herxheimer reaction (5).
It can cause symptoms such as bloating, diarrhoea, abdominal pain, and fatigue.
The theory is that using a two-phased approach can limit the side effects during the “die-off” process whilst removing the bacteria.
Phase 1 focuses on reducing fermentable starches and fibres.
This allows bacteria in the small bowel to die off gradually. This phase can be separated into two groups: restricted and semi-restricted diet.
You begin with the restricted diet where these foods are not allowed (6):
- All grains
- Starchy vegetables
- Canned fruit and vegetables
- Garlic, onion, mushrooms
- Agave nectar, artificial sweeteners, maple syrup, xylitol
- Chia seeds, flaxseed, peanuts
- Energy drinks, fruit juices, soft drinks, beer, wine, liquors, spirits (dark), wine
Note: This is not an exhaustive list.
Once the symptoms start to subside, you follow the semi-restricted diet. This diet allows for a few more foods to be included based on your tolerance levels.
Some starches such as rice and quinoa can be added back to the diet.
However, you can revert to the restricted diet if symptoms reappear.
Probiotics may also be used to improve digestion and repair the integrity of the gut lining. This phase can take between 4-6 weeks before phase 2.
In phase 2, you will build on the foods allowed in phase 1. Certain foods will be reintroduced into the diet in phase 2, such as (7):
- Butter, aged cheese
- Small amounts of lentils, lima beans, potatoes
- Raw cacao
- Tamari, miso, fish sauce
Note: This is not an exhaustive list.
The aim of this phase is it remove remaining bacteria and restore motility.
The increased leniency of the diet in this phase will allow some bacterial growth.
So, antibiotics/antimicrobials will be prescribed to eliminate the remaining bacteria.
A prokinetic agent can be prescribed to stimulate your gut to improve gut motility. This aims to prevent SIBO recurrence.
This phase takes another 4-6 weeks to complete.
Does the biphasic diet work?
There is no research to prove that the biphasic diet works as a SIBO treatment.
The biphasic diet can be very restrictive.
We know that restrictive diets have a high risk of nutritional deficiencies. And, the restriction of prebiotic foods in this diet can reduce good gut bacteria.
We do not recommend this diet for SIBO treatment.
Alternative ways to treat SIBO
Antibiotics are the only proven treatment method for SIBO (8). Antibiotics work by killing bacteria (9).
SIBO symptoms can overlap with IBS – Studies have shown that 30-85% of people with IBS have SIBO (10, 11).
However, there is no research yet using the low FODMAP diet to help SIBO symptoms (12).
Probiotics may be useful whilst treating SIBO. People treated with a combination of antibiotics and probiotics have shown greater improvement in SIBO symptoms compared to antibiotics alone (13).
However, it has been shown to provoke symptoms like gas, bloating and brain fogginess in SIBO patients in another study (14).
You can find out more about the management of SIBO here.
The biphasic diet is claimed to treat and eliminate SIBO symptoms.
It involves restricting grains and high FODMAP foods to help kill off bacteria in the small bowel.
There is no proof that the biphasic diet works to treat SIBO. It is also a restrictive diet which may lead to nutrient deficiencies.
Instead, it is important to seek help from a professional for a proper diagnosis and treatment of SIBO. Antibiotics remain the only method to treat SIBO.
Article written by Leeona Lam, Registered Associate Nutritionist, MSc, ANutr, and reviewed by Kirsten Jackson, Consultant Dietitian BSc Hons, RD, PG Cert
Serena is a UK HCPC Registered Dietitian with a keen interest in IBS and gut health. Serena graduated from Coventry University in 2021 with an upper second class in Dietetics and Human Nutrition.
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