Medical Oncologist
Water and hydration
Coconut water and buttermilk
Both are genuinely useful. They carry fluid and salts, they go down when plain water tastes metallic, and they are cheap and familiar. Two cautions: coconut water is high in potassium, which matters with reduced kidney function, and buttermilk from outside carries the usual hygiene risk.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
Are coconut water and buttermilk good during chemotherapy?
Both are genuinely useful. They carry fluid and salts, they go down when plain water tastes metallic, and they are cheap and familiar. Coconut water straight from a tender coconut and buttermilk made at home from safe curd are two of the better drinks available during treatment.
Two cautions. Coconut water is high in potassium, which matters if your kidney function is reduced or you take certain heart or blood pressure medicines. And buttermilk from outside carries the same water and hygiene risk as any loose drink.
They count towards your fluid
Families often think only plain water counts. It does not work that way. On the days when water tastes wrong, these two plus thin dal, soup and kanji are frequently what actually keeps somebody hydrated.
Neither replaces a rehydration sachet
After vomiting or loose motions, a proper rehydration solution replaces salts in the right proportions. Coconut water and buttermilk help, and they are not the same thing when someone is genuinely losing fluid.
Ask your team about potassium if your kidney reports are abnormal or you take a heart medicine.The detail
What to know about each
- Tender coconut water
- Best straight from a coconut opened in front of you, drunk soon, with no ice added. Naturally sterile inside the shell, which makes it one of the safer drinks available outside the house.
- Packaged coconut water
- Acceptable if sealed and within date, and often has added sugar. Check the seal, and refrigerate after opening. It is convenient rather than better than the fresh version.
- The potassium question
- Coconut water is high in potassium. For most people that is harmless and useful. With reduced kidney function or certain heart and blood pressure medicines, high potassium is a real risk and needs asking about.
- Home-made buttermilk
- Made from curd set with boiled or packaged milk and mixed with safe water. Add a little salt, jeera and curry leaf. Cool rather than iced, and drunk fresh rather than kept.
- Buttermilk and lassi from outside
- Avoid. The water, the ice, the curd and the handling are all unknown, and these are among the commonest sources of a bad stomach during a cycle.
- During the low-count days
- Ask your team about live-culture drinks such as buttermilk for those days specifically, since some units restrict them and others do not. Coconut water from a freshly opened coconut is generally fine.
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Ask an oncologistPractical
How to use them well
These are everyday drinks rather than treatments, and used sensibly they do real work.
Reach for them when water tastes wrong
Metallic taste is one of the commonest reasons people stop drinking enough. Buttermilk with salt and jeera, or coconut water, often go down easily when plain water does not.
Also try
- Water with a little lemon
- Thin dal water or kanji
Cool, not iced
Cool drinks soothe a sore mouth; iced drinks can be painful, particularly with drugs that cause cold sensitivity. And ice from outside is its own risk. Skip the ice entirely.
Make buttermilk at home
From curd you set yourself with boiled or packaged milk, thinned with safe water. Make a small quantity each day rather than keeping a jug, which is how it sours in the heat.
Keep it simple
- Salt, jeera, curry leaf
- No chilli if the mouth is sore
Buy coconuts opened in front of you
Rather than pre-cut or poured into a glass at a stall. The water inside an unopened coconut is sterile; once it has been decanted into an unknown container it is not.
!
Contact your team the same day for these
Muscle weakness, unusual tiredness, tingling around the mouth or a slow, irregular or racing heartbeat in someone with reduced kidney function or on heart medicines · no urine since the morning · persistent vomiting or severe loose motions · a fever, or shivering uncontrollably · dizziness or fainting on standing · swelling of the legs with breathlessness. Say that the person is on chemotherapy and mention how much coconut water they have been drinking, because potassium can be measured.
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Being straight with you
What this page cannot tell you
It cannot tell you how much coconut water is safe for you. That depends on your kidney function, your potassium level and your medicines, and it is a question your team can answer from your own reports rather than a general figure.
It also cannot tell you whether buttermilk is permitted on your low-count days. Units differ on live-culture foods for those days, and both positions are held by reasonable doctors. Ask yours specifically.
Neither is a treatment
These are good drinks, not remedies. Coconut water does not raise platelets, cleanse the blood or reduce side effects, whatever is claimed for it. Enjoy them for what they are and do not let them replace food or prescribed medicines.
They do not replace protein and calories
Someone living on coconut water and buttermilk is hydrated and losing weight. Both belong alongside proper food rather than instead of it, particularly on the days when appetite returns.
What to do next
Make buttermilk at home from curd set with boiled milk, fresh each day. Buy coconuts opened in front of you and skip the ice. Ask your team about potassium if your kidney reports are abnormal. Ask about buttermilk on the low-count days. And keep rehydration sachets for when fluid is actually being lost.
Commonly believed
Four beliefs about these two drinks
"Coconut water raises the platelet count."
It does not. It is a good source of fluid and salts and nothing more. Low platelets during chemotherapy are managed with monitoring and, where needed, transfusion. Do not let a drink substitute for reporting a low count.
"Coconut water is natural, so you cannot have too much."
It is high in potassium. For most people that is harmless, and with reduced kidney function or certain heart medicines high potassium is a genuine risk. Ask your team if your kidney reports are abnormal.
"Buttermilk is cold and sour, so it should be stopped."
Neither is a medical reason to avoid it. Home-made buttermilk from safe curd is one of the easier drinks during treatment. Ask about the low-count days specifically rather than dropping it on a relative's advice.
"Only plain water counts towards fluid."
Buttermilk, coconut water, thin dal, soup, kanji, curd and watery fruit all contribute. This matters a great deal on the days when water tastes metallic, because that is when people quietly stop drinking enough.
Questions we are asked
Common questions about coconut water and buttermilk
Is coconut water good during chemotherapy?
Yes, as a source of fluid and salts, and it often goes down when plain water tastes metallic. Buy coconuts opened in front of you, drink it soon, and skip the ice.
Can you have too much coconut water?
It is high in potassium, which matters if your kidney function is reduced or you take certain heart or blood pressure medicines. Ask your team for a sensible limit based on your own reports.
Is buttermilk safe?
Made at home from curd set with boiled or packaged milk and safe water, yes. Avoid buttermilk and lassi from outside entirely, where the water, ice and handling are unknown.
What about during the low-count days?
Ask your team about live-culture drinks such as buttermilk for those days specifically, since units differ. Coconut water from a freshly opened coconut is generally fine throughout.
Do these replace rehydration sachets?
No. After vomiting or loose motions, a proper rehydration solution replaces salts in the right proportions. These two help with everyday fluid but are not the same when fluid is actively being lost.
Can I have them with kidney problems?
Ask your team first, particularly about coconut water, because of the potassium. You may also have been advised to limit fluid overall, in which case general advice to drink more does not apply to you.
Should they be taken cold?
Cool rather than iced. Cool soothes a sore mouth; very cold can be painful, particularly with drugs causing cold sensitivity. And ice from outside is a separate risk worth avoiding entirely.
Can these replace meals when appetite is poor?
No. They carry fluid but little protein or calories, so somebody living on them is hydrated and losing weight. Use them alongside food, and ask for a dietitian if eating has become difficult.
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Sources
- Cancer Research UK — Diet problems and cancer
- Macmillan Cancer Support — Eating problems and cancer
- National Cancer Institute — Eating Hints for Cancer Patients
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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