GastroLife

How your body digests fat and absorbs nutrients

Digestion involves much more than your stomach. Before your body can use food, it needs to be broken down and its nutrients absorbed. The pancreas, liver, gallbladder and small intestine each have a part to play. ¹

Understanding their roles can help explain why digestive symptoms sometimes need different investigations—and where a stool test such as faecal pancreatic elastase may be useful.

What does your pancreas do for digestion?

The pancreas sits behind your stomach. Many people associate it with insulin and blood sugar, but it also produces enzymes that help digest food. These enzymes travel through ducts into the duodenum, the first part of the small intestine. ²

Its main digestive enzymes include:

• Lipase, which breaks down fats.
• Amylase, which helps break down starches.
• Proteases, which break down proteins.

The pancreas also releases bicarbonate, which helps neutralise stomach acid as food enters the small intestine. This provides a suitable environment for digestion. ^{2, 3}

Why the pancreas matters more than most people realise

Eating nutritious food is only part of the process: your body also needs to digest it effectively.

When too few pancreatic enzymes reach the intestine, or they cannot work properly, food may not be fully broken down. This is called exocrine pancreatic insufficiency, or EPI. It can lead to poor nutrient absorption and malnutrition. ⁴

Possible symptoms include greasy stools, diarrhoea, bloating, excessive wind and unintentional weight loss. Poor fat absorption can also affect levels of vitamins A, D, E and K. These symptoms have other possible causes, so symptoms alone cannot establish EPI. ⁵

What does your liver actually do?

Your liver is in the upper right side of your abdomen. It processes nutrients arriving from the digestive tract and helps regulate how they are stored and used.

Its functions include:

• Producing bile to support fat digestion.
• Storing glucose as glycogen and releasing it when needed.
• Making proteins involved in blood clotting.
• Processing medicines and alcohol.
• Handling bilirubin, a substance produced when red blood cells break down. ⁶

The liver therefore supports digestion and many other essential functions. A stool elastase test assesses a different process—pancreatic enzyme output—and is not a liver health test.

The role of bile in digesting fat

Bile is made by the liver. The gallbladder, a small organ beneath the liver, stores it and releases it into the small intestine when you eat. ⁷

Bile helps break large fat droplets into smaller droplets, making it easier for pancreatic lipase to digest the fat. Together, these processes support fat absorption and the absorption of fat-soluble vitamins. ²

The liver makes bile, the gallbladder stores and releases it, and the pancreas supplies digestive enzymes.

Can you digest food without a gallbladder?

Yes. Your liver continues making bile after gallbladder removal. Instead of being stored in the gallbladder, bile flows directly into the small intestine.

Most people can live normally without a gallbladder. Some develop softer or more frequent stools after surgery. Persistent changes should be discussed with a doctor. ⁸

Why some people struggle with fatty foods

Feeling uncomfortable after a rich meal does not automatically mean you are failing to absorb fat. Fatty or greasy foods can trigger indigestion symptoms in some people, including fullness, bloating and nausea. ⁹

Other possibilities include:

Gallbladder problems

Gallstones can cause pain when they block a bile duct. Pain is often in the upper right abdomen and may follow a heavy meal. Many gallstones cause no symptoms. ¹⁰

Reduced pancreatic enzyme activity

EPI can interfere with fat digestion and cause greasy stools, diarrhoea and weight loss. ⁵

Problems affecting the small intestine

Conditions such as coeliac disease can damage the intestinal lining and interfere with nutrient absorption. ¹¹

The pattern matters. Occasional discomfort after a large meal is different from ongoing diarrhoea, repeatedly greasy stools or unexplained weight loss. Persistent symptoms deserve medical assessment rather than an assumption about which organ is responsible.

How nutrients are absorbed in the gut

Digestion and absorption are closely connected, but they describe different steps.

Digestion breaks food into smaller components. Absorption moves those components through the intestinal lining so the body can use them.

Most nutrient absorption happens in the small intestine. Its lining has tiny finger-like projections called villi, which increase the surface area available for absorption. ^{1, 12}

Simple sugars and amino acids enter the bloodstream. Much of the absorbed fat travels first through the lymphatic system before reaching the blood. The large intestine absorbs water from the remaining material as stool forms. ¹

If food is not adequately digested, or the intestinal lining cannot absorb nutrients properly, deficiencies can develop. Coeliac disease is one example of a condition that can impair absorption through damage to the small intestine. ¹¹

Where does pancreatic elastase testing fit?

Faecal pancreatic elastase testing measures a pancreatic enzyme in a stool sample. It helps assess the pancreas’s digestive enzyme output and is commonly used as an initial investigation for suspected EPI. ^{5, 13}

AGA guidance describes results below 100 µg/g as good evidence of EPI, while results between 100 and 200 µg/g are indeterminate and need further assessment. ⁵

The test should use a solid or semi-solid sample. Watery stool can dilute elastase and produce a falsely low reading, so a repeat sample may be needed. ^{13, 14}

Results need to be considered alongside symptoms and medical history. The test does not directly measure fat absorption or diagnose the underlying cause of a low result. A normal result does not exclude every pancreatic disorder or every cause of malabsorption. ^{5, 14}

What about malabsorption breath tests?

Different tests answer different questions. For example, a lactose breath test investigates whether lactose is being properly digested and absorbed. It does not assess pancreatic enzyme output or overall nutrient absorption. ¹⁵

Choosing an investigation depends on the symptoms and suspected cause. There is no single stool or breath test that assesses every aspect of digestion.

When should you seek medical advice?

Arrange a GP review for persistent diarrhoea, recurrent greasy stools or unexplained weight loss.

Seek urgent medical attention for severe or persistent abdominal pain, especially with vomiting or fever, or for yellowing of the skin or eyes. Pale stools with dark urine can also indicate a bile-flow problem and need prompt assessment. ^{9, 10}

How GastroLife can help

GastroLife provides faecal pancreatic elastase testing and other digestive investigations. Tests examine specific markers or processes and can provide information for your GP or consultant to consider alongside your symptoms and medical history.

GastroLife is a testing centre and does not prescribe or provide treatment. If you are unsure which investigation is appropriate, discuss your symptoms with your GP.

Explore digestive testing at GastroLife

Information provided is for educational use only and should not replace professional medical advice or diagnosis.

References

1. NIDDK. Your Digestive System & How it Works. Read source
2. Johns Hopkins Medicine. The Digestive Process: What Is the Role of Your Pancreas in Digestion? Read source
3. Johns Hopkins Medicine. The Pancreas. Read source
4. NIDDK. Definition & Facts for Exocrine Pancreatic Insufficiency. Read source
5. Whitcomb DC, Buchner AM, Forsmark CE. AGA Clinical Practice Update on the Epidemiology, Evaluation, and Management of Exocrine Pancreatic Insufficiency: Expert Review. Gastroenterology. 2023;165(5):1292–1301. doi:10.1053/j.gastro.2023.07.007. Read source
6. Johns Hopkins Medicine. Liver: Anatomy and Functions. Read source
7. NIDDK. Definition & Facts for Gallstones. Read source
8. NIDDK. Treatment for Gallstones. Read source
9. NIDDK. Eating, Diet, & Nutrition for Indigestion; Symptoms & Causes of Indigestion. Diet and nutrition; Symptoms and causes
10. NIDDK. Symptoms & Causes of Gallstones. Read source
11. NIDDK. Definition & Facts for Celiac Disease. Read source
12. NIDDK. Story of Discovery—Intestinal Stem Cells. Read source
13. NIDDK. Diagnosis for Exocrine Pancreatic Insufficiency. Read source
14. Phillips ME, et al. Consensus for the management of pancreatic exocrine insufficiency: UK practical guidelines. BMJ Open Gastroenterology. 2021;8:e000643. doi:10.1136/bmjgast-2021-000643. Read source
15. NIDDK. Diagnosis of Lactose Intolerance. Read source