Why does whey protein cause constipation?

If you are wondering, ‘does whey protein cause constipation?’ The answer is yes, it may. 

This article will discuss why whey protein may cause constipation and other gut symptoms and if plant-based protein powder has the same effect. We will also suggest to you how to stop protein constipation.

Does whey protein cause constipation?

Yes, whey protein may cause constipation in people with milk protein allergy (1).

Milk protein allergy occurs when the body recognises it as harmful and activates an immune response by producing specific antibodies (2).

Milk allergy is not the same as lactose intolerance. Having an intolerance means the body cannot digest certain food, which does not include an immune system (2). 

People with lactose intolerance lack enzymes which break down lactose. Gut bacteria then digest lactose in large intestines, which causes loose stools.

Some online articles suggest lactose intolerance can cause constipation, but there is no evidence for that.

What is whey protein?

Whey protein comes from milk, it is the watery liquid that separates out during the cheese making process. Thus, whey protein contains lactose. 

There are two types of whey protein including whey protein isolate and whey protein concentrate (3). Whey protein isolate contains a lower amount of lactose only 1 gram or less of lactose per 100-calorie serving (4).

Does plant-based protein powder cause constipation?

No, plant-based protein powders do not cause constipation. However, they may cause other digestive symptoms if they are high in FODMAPs. FODMAPs are types of carbohydrates which can cause symptoms in people with IBS.

You can read more about FODMAPs here.

How do you stop whey protein constipation?

If you have a milk allergy, replace whey protein with other low FODMAP protein powder that does not contain milk. Examples include egg white protein powder and rice protein powder (5).

If you are not allergic to milk but you are still constipated when consuming whey protein, focus on the following:

1. Fibre

General recommendations suggest 30 g of fibre a day (6). Fibre bulks up and softens the stools, which makes them easier to pass. A sufficient amount of fibre is not essential only for regular bowel movements but also (6):

• Lower the risk of colorectal cancer
• Lower the risk of heart disease
• Lower the risk of diabetes etc.

To increase the fibre consumption while enjoying your protein shake, you can add to it:

• Fruits, such as bananas or blueberries
• Oats
• Seeds, such as linseeds

2. Fluid

Sufficient fluid intake has a significant impact on bowel movement (7). Your hydration status is adequate if the colour of your pee is pale yellow, such as lemonade (8).

However, your fluid intake needs depend on your:

• Body weight
• Physical activity level
• Weather etc.

Also, you should increase your fluid intake when adding more fibre to your diet, as fibre absorbs water. Otherwise, fibre can worsen constipation.

3. Physical activity

Physical activity improves colonic activity by speeding up movement through the intestines and reducing water absorption from the stools (9).

General recommendations for adults include 150 min of physical activity per week (10).

Regular physical activity is also associated with reduced risk of (11):

• Heart disease
• Depression 
• Breast cancer in women etc.

How to choose a low FODMAP protein powder

FODMAPs are types of carbohydrates that may cause digestive symptoms in people with IBS.

If you have IBS or are following a low FODMAP diet, you can check out our guide on Low FODMAP protein powders for a comprehensive overview of suitable options.

Summary

Whey protein powder can cause constipation in people with milk allergy. To avoid this, switch whey protein powder with egg white powder, beef powder, or plant-based protein powders like hemp protein powder.

To relieve constipation, increase fibre in your diet, drink plenty of fluids, and add movement to your daily routine.

Written by Barbara Lešnik, Student Dietitian and Rida Mahmood, Dietitian, reviewed by Kirsten Jackson, Consultant Dietitian BSc Hons, RD, PG Cert