Treating Small Intestinal Bacterial Overgrowth Using the Elemental Diet

In short: an elemental dietElemental diet A liquid diet of pre-digested nutrients (amino acids, simple sugars and easily absorbed fats). They are absorbed in the upper small intestine, which starves bacteria further down. is a liquid formula of pre-digested nutrients that replaces all food for about two weeks. In a 2004 study of people with IBS and an abnormal breath test, 80% had a normal test after 14 days and 85% after up to 21 days¹. A 2025 trial of a better-tasting formula found 73% normalized their breath test, including people with methane overgrowth, and all 30 participants completed it². It is demanding, can be expensive, and does not prevent relapse on its own.

The elemental diet is one of the main treatment options for SIBO, alongside antibiotics and herbal antimicrobials. It is often considered when antibiotics have not worked or cannot be used. For a side-by-side overview, see our comparison of SIBO treatments.

How it works

Elemental formulas contain nutrients in their simplest forms: free amino acids instead of whole protein, simple carbohydrates, fats and the full daily requirement of vitamins and minerals, but no fiber or fermentable carbohydrates. They are almost entirely absorbed in the upper part of the small intestine, which leaves little food for bacteria further down³. Elemental diets are also used in Crohn’s disease, chronic pancreatitis and eosinophilic esophagitis³.

What the studies show

In the 2004 study, about 11% of those who started dropped out because they could not tolerate the formula³. Taste has been the main barrier; the 2025 trial was designed to test whether a better-tasting formula would solve that, and every participant completed it². In that trial, levels of the methane-producing microbe Methanobrevibacter smithii in stool also fell, in line with lower breath methane². See our guide to methane SIBO.

SIBO practitioners report that the elemental diet typically needs fewer treatment rounds than antibiotics or herbs⁵. There are no trials comparing them head to head.

Types of formula

• Commercial elemental formulas use free amino acids, simple carbohydrates and fats. Vivonex Plus was used in the 2004 study¹; newer products aim to taste better².
• Semi-elemental formulas use small protein fragments (peptides) instead of free amino acids. They usually taste better but need a little more digestion, and they have not been tested for SIBO.
• Homemade formulas combine amino acid powder, a simple sugar and oil. They cost less but require careful measuring; the only published SIBO report is the single case above⁴.

The 2-week protocol

The studies used the formula as the only source of nutrition for 14 days, with the amount based on each person’s calorie needs, followed by a repeat breath test¹². Water is allowed. In the 2004 study, people whose test was still abnormal on day 15 continued for 7 more days¹.

How to drink it is debated. Sipping slowly through the day can smooth out blood sugar swings from the simple carbohydrates. On the other hand, the migrating motor complexMigrating motor complex (MMC) A wave of muscle contractions that sweeps the stomach and small intestine between meals, roughly every 90 to 120 minutes, pushing leftover food and bacteria into the colon. Eating interrupts it., the wave of contractions that sweeps bacteria out of the small intestine between meals, only runs while fasting and is interrupted by eating⁶. For this reason, many practitioners recommend drinking the formula as separate meals a few hours apart rather than sipping constantly.

Side effects and who should be careful

The 2025 trial reported no serious or severe side effects². Common complaints in practice include hunger, fatigue, headache, and changes in stool, especially in the first days. Because the formulas are high in simple sugars, people with diabetes need medical supervision. Anyone who is underweight, pregnant, or has other medical conditions should only do an elemental diet under the care of a doctor or dietitian.

After the elemental diet

The 2025 trial reintroduced a regular diet over 2 weeks after the formula². Many practitioners start with simple, easily digested meals and add more fermentable foods gradually; our SIBO diet guide and low-FODMAP guide cover the options.

Relapse is common after any SIBO treatment. In a 2008 study, 44% of people had SIBO again within 9 months of successful antibiotic treatment⁷, and in the 2021 case report, methane returned within 4 months⁴. A prevention plan that addresses the root causes, often including a prokinetic, is usually recommended.

Common questions

How long does the elemental diet take to work?

The main studies used 14 days, with some people continuing to 21 days¹².

Does the elemental diet work for methane SIBO?

The 2025 trial included people with methane overgrowth and found large drops in breath methane and in M. smithii in stool². The study was small and had no comparison group.

Can I eat anything during the elemental diet?

In the studies, the formula was the only nutrition, apart from water¹². Adding food would feed the bacteria the diet is meant to starve.