What is a clear diet? Why do you need one? And how do you eat for it?

Written by Catherine Saxelby on Wednesday, 12 September 2018.
Tagged: clear diet, health, healthy eating, healthy lifestyle, nutrition

What is a clear diet? Why do you need one? And how do you eat for it?
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A clear diet is needed to cleanse the bowel (colon or end of the digestive tract), usually in preparation for a colonoscopy, abdominal x-ray, bowel surgery, bowel evacuation of any sort, and intravenous pyelogram. 

So, what actually is a clear diet?

I’m often asked about a “Clear Fluids” diet and have even had to embark on one myself in preparation for a routine colonscopy, so that the gastroenterologist doctor can see inside my bowel clearly. 

 If this is you, you’ll be given detailed instructions by the doctor on how to prepare for a colonoscopy plus you’ll have to buy a bowel prep powder e.g. PicoPrep or MoviPrep  that you mix into water and drink.

What does the bowel prep powder do?

The bowel prep powder produces a watery stool or bowel motion that empties and cleanses the inside of the bowel. They usually taste pretty awful after one glass or slightly acidic due to the high amounts of citric acid they contain (a harmless compound - you’re already eating it from lemons or oranges; and it’s a common acidity regulator additive no: 330). 

It may also be lightly sweetened with a sweetener such as aspartame which is clear. However, this sweetener may not agree with you if you have phenylketonuria. If you have any other food allergy, check the ingredients and ask your doctor for another brand.

What do you need to do?

You must drink this bowel prep and lots of clear fluids in order to stay hydrated and prevent dehydration. You will experience lots of bowel motions, and they gradually become more watery and clearer.  

You will need to visit the toilet frequently, so don’t go out. It’s best to stay home or near a toilet you can get to quickly if you need to. You will have diarrhoea and maybe even tummy pains at times. 

Clear Fluids Coffee Black

Which clear fluids should you drink?

  • Water, flat mineral water or soda water, flat lemonade, flat tonic water
  • Black tea, herbal teas, black coffee - no milk
  • Clear salted soup like broth, consommé or stock
  • You can make up a clear soup from commercial liquid stock (prob the best taste) or using stock cubes dissolved in hot water e.g. Bonox, Bovril or similar
  • You can use commercial vegetable soup or chicken noodle soup as long as you strain away the bits - you only want to drink the clear stuff.
  • Avoid fizzy (carbonated) drinks. Unless you have diabetes or need to shed weight, there is no need to avoid all sugar. You may need a little if you are underweight or very active
  • Clear fruit juice e.g. 100% apple juice
  • Sports drinks
  • Electrolyte-replacement drinks e.g. Gastrolyte, Hydralyte 
  • Clear cordial e.g. clear lemon, clear lime (no red, purple or green colourings that could create weird artefacts or interfere with the inside appearance of your bowel) 

Try for a combination of these clear fluids to give you a variety of drinks so you’ll drink enough. You want to replace the fluid lost through diarrhoea and avoid dehydration. 

Clear Fluids Water with Lime

Warning: Don’t just drink water, especially filtered water. You may lose too many electrolytes and cause a condition called hyponatremia - very low sodium concentration. This can cause extremely bad headaches, nausea and vomiting, confusion, seizures and eventually loss of consciousness. So make sure you have a variety of fluids with electrolytes.

In addition to these fluids you can have barley sugar, boiled lollies or eucalyptus balls to suck (no red, purple or green colours) as well as plain jelly (no red, green or purple colours). 

Suggested clear fluid intake 

(Say for the day before a bowel scan the next morning) 


Drink 2 cups of clear soup 

Then drink at least 1 cup of any other clear fluid each hour; the more the better. e.g.

1 cup black coffee 

1 cup water

1 cup clear cordial

1 cup flat soda water 


Drink 2 cups of clear soups e.g. chicken or vegetable 


1 cup apple juice

1 cup flat lemonade

1 cup water

1 cup black tea  


Drink 2 cups of clear soup e.g. beef consommé

Eat 1 bowl jelly cubes 

jelly cubes in bowl yellow


1 cup hot water with lemon slice

1 cup herbal tea

1 cup apple juice

1 cup water 

No food or drink on the day of the exam (or 6 hours before) 

Your goal: take in 1.5 to 2 Litres of fluid or 6-8 cups (1 cup = 250 mLs)  

The bottom line

A clear diet is needed so a doctor can view your insides without any hindrance. It’s meant to be a temporary diet to prep your bowel – not something you stay on forever.

Clear Fluid diets vary a lot so this is my take on what you can and cannot eat and drink.

Catherine Saxelby About the author

About the Author


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Catherine Saxelby has the answers! She is an accredited nutritionist, blogger and award-winning author. Her award-winning book My Nutritionary will help you cut through the jargon. Do you know your MCTs from your LCTs? How about sterols from stanols? What’s the difference between glucose and dextrose? Or probiotics and prebiotics? What additive is number 330? How safe is acesulfame K? If you find yourself confused by food labels, grab your copy of Catherine Saxelby’s comprehensive guide My Nutritionary NOW!