PET scan preparation
Eating Sugar Before a PET Scan — Will Not Help — It Makes the Scan Worse
Some people eat sugar deliberately before a PET scan, believing it will attract the tracer to the cancer. The opposite is true. High blood sugar competes with the tracer, reduces the signal from the tumour, and can mean the scan has to be repeated.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026
- The tracer is already a form of sugar — FDG, the radioactive tracer, is a modified glucose molecule. You do not need to add more sugar to attract it.
- Extra sugar competes with the tracer — High blood glucose means the tracer has to compete for uptake into cells, including tumour cells. Less tracer reaches the tumour.
- Breaking the fast can cancel the scan — If your blood glucose is above what the imaging team considers acceptable, the scan is postponed to another day.
- Fasting is not a formality — It directly controls image quality. The imaging team checks your glucose before injecting the tracer for exactly this reason.
17+
Cancer Specialists
on Panel
on Panel
96.9%
Breast Cancer
Survival Rate*
Survival Rate*
15,000+
Patients
Treated
Treated
4.8★
Google Rating
(800+ reviews)
(800+ reviews)
Eating sugar before a PET scan does not help the tracer find cancer — it does the opposite. Your blood glucose rises, competing with the radioactive tracer for uptake into cells. Tumours may appear less active than they are, or not appear at all, which can lead to a missed result or a cancelled scan.
At CION, a whole-body PET-CT starts from Rs 10,499 — among the lowest published prices in Hyderabad. Indicative price, as of September 2026.
Does eating sugar before a PET scan help the tracer find cancer?
If cancer feeds on sugar, eating sugar before a PET scan will help the tracer find it.
The tracer — FDG — is already a modified form of glucose. You do not need to add more to attract it. Eating sugar raises your blood glucose, which competes with the tracer for uptake into cells. The result is less tracer reaching the tumour, not more.
A small amount of sugar before the scan won't affect the result.
Even a modest rise in blood glucose changes how the tracer distributes in your body. The imaging team measures your glucose before injecting the tracer precisely because the difference matters. A reading above the acceptable range means the scan is postponed.
The fasting instruction is just a precaution — the scan will still work.
Fasting directly controls image quality. High blood glucose triggers an insulin response, and insulin pushes the tracer into muscle cells across your whole body. This creates a bright, noisy background that can hide or mask active areas in the scan.
What do the terms on your PET scan preparation sheet actually mean?
- FDG (fluorodeoxyglucose)
- The radioactive tracer used in most PET scans. It is a modified form of glucose that your body treats like sugar. Cancer cells, which use glucose more intensively than most normal cells, absorb more of it — and that higher uptake is what appears as a bright area on the scan.
- Blood glucose at the time of the scan
- The level of sugar in your bloodstream when the tracer is injected. When it is high — because you have eaten — FDG has to compete with ordinary glucose for uptake into cells, including tumour cells. The fasting instruction is specifically to keep this level low.
- Tracer uptake
- How much FDG a tissue absorbs. Higher uptake in a suspicious area appears as a brighter spot on the PET image. High blood glucose reduces the difference in uptake between tumour and surrounding tissue, making it harder to distinguish one from the other.
PET-CT Partner Centres
PET-CT Scan Centres in Hyderabad
CION offers PET-CT scans through 4 trusted partner PET-CT centres across Hyderabad, so you can choose the one closest to you. Call 18002028726 and we’ll guide you to the earliest available appointment.
PET-CT Centre — Punjagutta
PET-CT Centre — Himayatnagar
PET-CT Centre — Narayanaguda
These are partner diagnostic centres within the CION network. Toll-free booking: 18002028726.
Meet the Specialists
17+ senior cancer specialists. One panel for your case.
Trained at AIIMS, Tata Memorial, and leading international centres. Combined 150+ years of experience. Every complex case is reviewed by 3+ of them — together.
Medical Oncologist
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
Interventional Radiologist
Dr. Mohammed Imran
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
Surgical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Get a straight answer from a specialist
45 minutes, your reports reviewed, your questions answered in plain language.
Why does fasting matter so much for a PET scan?
The PET tracer works by going where glucose goes. Cancer cells take it up more than normal cells do — but only when they face little competition. Fasting keeps your blood glucose low so the tracer has a clearer path to wherever activity is highest.
When you eat before the scan, two things happen. First, your blood glucose rises, diluting the tracer in your bloodstream. Second, your body releases insulin, which actively drives the tracer into muscle cells throughout your body. Muscles light up instead of the tumour.
If your blood glucose is above the acceptable range when you arrive, your scan will usually be rescheduled rather than done with a compromised result. A second appointment is an inconvenience. A misleading result is a much larger problem.
How should I prepare for a PET scan?
- Fast from food as your team instructs — no meals, no snacks, no juice, no chai with sugar or milk.
- Drink plain water. It does not raise blood glucose and helps the tracer distribute properly.
- Take your regular medications only as the imaging team instructs — ask in advance, not on the morning of the scan.
- If you have diabetes, contact the imaging team before scan day for specific instructions on glucose management.
- Tell the imaging team immediately if you accidentally ate or drank something — they will check your glucose and decide whether to proceed.
Did you know?
When blood glucose is high at the time of injection, insulin drives the FDG tracer into skeletal muscle throughout the body. A PET scan done under those conditions can show diffuse muscle uptake rather than tumour activity — one of the most common reasons scans have to be repeated.
Reporting your preparation honestly when you arrive protects the value of the result.
Source: EANM/SNMMI Procedure Guidelines for Tumour Imaging with 18F-FDG PET/CT
Book a PET-CT at CION from Rs 10,499 — among the lowest published prices in Hyderabad — with an oncologist-reviewed report and a free Rs 950 consultation, across 4 partner centres. Indicative price, as of September 2026.
Explore 62 more Family Support, Myths, Follow-Up and Emergencies topics
Myths & Misinformation
- Ayurvedic and Alternative Alternatives to a PET Scan
- Myth: A Normal PET Scan Means You Are Cured
- Myth: A PET Scan Can Cause Cancer
- Myth: A PET Scan Detects Every Cancer
- Myth: A PET Scan Spreads or Worsens Cancer
- Myth: A Positive PET Scan Means You Definitely Have Cancer
- Myth: A Scan From a Cheaper Centre Will Not Be Accepted
- Myth: An Expensive Scan Is Always a Better Scan
- Myth: Eating Sugar Before a Scan Will Show Up Cancer
- Myth: PET Scans Are Only for Terminal Cancer
- Myth: The Tracer Injection Is a Kind of Chemotherapy
- Myth: You Should Avoid Water After a PET Scan
- Myth: You Should Get a PET Scan Every Year to Be Safe
- Myth: You Stay Radioactive for Days After a PET Scan
Caretaker & Family Guide
- A Printable PET-CT Day Checklist for Families
- After the Scan: What the Family Should Know
- Collecting and Storing the Report and Images
- Coordinating a Scan for a Parent in Another City
- Explaining a Parent's Scan to Children
- Explaining the Scan to an Anxious Patient
- Getting an Elderly Parent to and From the Scan
- Helping Someone Fast Before a PET-CT
- Managing Cost and Payment as a Family
- Preparing Questions for the Post-Scan Consultation
- The Family's Complete Guide to a PET-CT Scan Day
- What the Attendant Can and Cannot Do During the Scan
Emergencies & Red Flags
- Accidental Radiation Exposure: Pregnancy Discovered After a Scan
- Breathing Difficulty During or After a Scan
- Delayed Contrast Reaction Hours After the Scan
- Emergencies Around a PET-CT Scan: What Needs Immediate Care
- Fainting or Collapse at the Scan Centre
- Low Blood Sugar (Hypoglycaemia) During Fasting
- Panic Attack During the Scan
- Severe Contrast Reaction: Recognising It
- What to Do If the Cannula Site Swells or Hurts After
- When to Call the Centre After Your Scan
Follow-Up & Surveillance Scanning
- Can You Refuse a Follow-Up PET Scan?
- Follow-Up Scanning During Long-Term Treatment
- How Often Will You Need a PET-CT After Treatment?
- Is Routine Surveillance PET Actually Recommended?
- Keeping a Personal Scan Log
- Reducing Radiation Across Years of Surveillance
- Scan-Based vs Symptom-Based Follow-Up
- Surveillance Scanning by Cancer Type: A Reference Table
- The Annual Cost of Cancer Surveillance Scanning
- Transferring Surveillance to a Centre Closer to Home
- What Happens If a Surveillance Scan Shows Something?
- When Can You Stop Having Scans?
Scanxiety & Emotional Impact
- Fear of What the Scan Will Find
- Getting Bad News From a Scan Report
- Getting Good News: Why Relief Is Complicated
- Living Between Scans: The Six-Month Rhythm
- Making the Most of Your Post-Scan Consultation
- Recurring Scanxiety in Long-Term Surveillance
- Scanxiety: The Fear Before and After a PET-CT
- Should You Look Up Your Results Online Before the Consult?
- Supporting Someone Through Scan Day
- Telling Family About Scan Results
- The Night Before a PET-CT Scan
- Waiting for PET-CT Results: How to Get Through It
- When a Patient Refuses to Have the Scan
- When to Seek Counselling Around Scans
Your next step
Talk to an oncologist about your scan
Your PET-CT report read by a senior oncologist, explained in plain language, with a free 45-minute consultation.
Common questions
Frequently asked questions
Does cancer really feed on sugar, and should I avoid sugar completely during treatment?
Cancer cells do use glucose more intensively than most normal cells — this is a genuine biological observation, and it is what makes PET scanning possible. However, this does not mean that eating sugar in daily life meaningfully accelerates cancer growth, and neither ASCO nor ESMO recommends eliminating sugar as a treatment strategy. The PET fasting instruction is a separate matter: it is about scan conditions, not your everyday diet. If you have questions about nutrition during treatment, ask your oncologist about seeing a registered dietitian.
What happens if I accidentally eat something before a PET scan?
Tell the imaging team immediately — do not try to conceal it. They will check your blood glucose and decide whether to proceed. If your glucose is above the acceptable range, the scan will usually be rescheduled rather than done with a compromised result. A rescheduled scan is inconvenient, but a misleading result is far more harmful. Honesty about your preparation protects the usefulness of the scan.
I have diabetes. How do I prepare for a PET scan?
Diabetes requires specific preparation that your oncology and imaging teams should plan together before scan day — not on the morning of the appointment. The right approach depends on whether you manage your glucose with insulin, oral medication, or diet alone. Contact the imaging centre in advance and ask for written instructions. Do not adjust your diabetes medication on your own on the day of the scan.
Can I drink water during the fast before a PET scan?
Yes, and you should. Plain water does not raise your blood glucose and does not interfere with the tracer. Staying well hydrated actually helps the tracer distribute properly. Avoid anything with sugar, calories, or flavouring — that includes juice, chai, flavoured water, and most glucose or electrolyte drinks.
If my scan is affected by high blood glucose, will the cancer still be found?
High blood glucose at the time of scanning affects the reliability of that particular scan, not your cancer itself. If your team suspects the result was compromised, they will rescan. A missed finding on one scan is a reason to investigate further, not a reason to assume you are clear. This is why preparation matters: a good scan gives your team information they can actually use.