A PET Scan is an advanced medical imaging technique used to detect cancer, brain disorders, and heart diseases with high accuracy.
However, to ensure correct scan results, your diet before the PET scan plays a crucial role.
Because eating the wrong foods or not following instructions can interfere with the tracer (FDG) and lead to inaccurate images, it’s important to follow all guidelines properly.
Therefore, if you are scheduled for a PET CT scan in Chandigarh Panchkula or Mohali, We will help you to understand why diet matters and what steps you must follow before, during, and after the scan.
Why Diet is Important Before PET Scan?
Most PET scans use FDG (Fluorodeoxyglucose) – a radioactive glucose-based tracer that helps detect abnormal metabolic activity in the body. Since cancerous cells and diseased tissues consume more glucose than normal cells, the FDG tracer highlights these active areas on the scan.
However, the way FDG distributes in the body depends directly on blood glucose levels. Therefore, if you eat high-sugar or carbohydrate-rich foods before the scan, your blood sugar may rise significantly. As a result, the tracer may get absorbed by normal muscles or tissues instead of the target disease-affected areas.
Consequently, important abnormalities might get hidden or appear less intense on the image. In many cases, this can lead to inaccurate results or the need to reschedule the scan, which delays diagnosis and treatment.
That is exactly why doctors strongly recommend a strictly controlled diet before the PET scan – to ensure the tracer works effectively and the imaging results are reliable for clinical decisions.
General Dietary Guidelines (24 Hours Before PET Scan)
Diet Rules Before a PET Scan (Expert-Approved)
To ensure clear and accurate imaging, it is necessary to follow a low-carbohydrate and high-protein diet for at least 24 hours before the scan. This diet helps keep your blood glucose levels stable, which allows the FDG tracer to target abnormal tissues effectively.
Low-Carbohydrate, High-Protein Diet
You should focus on foods that do not spike blood sugar.
Therefore, choose:
- Paneer, Tofu, Eggs (if allowed)
- Dal, Beans, Chickpeas
- Green leafy vegetables
- Nuts and seeds
- Soy products
Non-starchy vegetables (Broccoli, Cauliflower, Capsicum, Cucumber)
These foods provide energy without disturbing the tracer uptake.
Avoid Sugary Foods and Drinks
Additionally, avoid foods that cause a rapid glucose spike, such as:
- Sweets, Chocolates, Ice-cream, Cakes
- Sugar, Jaggery, Honey
- Bread, Rice, Chapati, Pasta, Oats, Cornflakes
- Soft drinks, Juice, Energy drinks, Milkshakes
- Fruits (especially banana, mango, grapes)
Because sugary and high-carb foods overload the bloodstream with glucose, they compete with the FDG tracer and may reduce scan sensitivity.
Drink Lots of Water
Meanwhile, staying well-hydrated helps FDG circulate properly in the body and improves scan quality.
So, keep drinking plain water before fasting begins (no flavored water, no coconut water, no juices).
Hydration also helps reduce radiation exposure after the scan, as the body flushes out the tracer faster.
Hydrate well: Plain water is best
Follow Strict Fasting as Advised
Doctors commonly recommend 6 hours of fasting before the PET scan (only water is allowed).
This is crucial, because fasting stabilizes insulin levels and makes the tracer accurately locate hyper-active cells like cancer cells or inflammation.
During fasting:
- No chewing gum
- No coffee/tea
- No milk or protein shakes
- No smoking or alcohol
Any calorie intake can disturb metabolism → poor scan results → repeat scan required.
Special Instructions for Diabetic Patients
Because diabetic patients have fluctuating blood sugar levels, they must follow personalized diet + insulin guidance from their doctor.
- Keep glucose levels under control
- Inform the staff about insulin timing and dosage
- Do not adjust medication without medical advice
If glucose levels are too high on scan day, the scan may be postponed to avoid inaccurate imaging.
Foods to Avoid Before PET Scan
Avoid carbohydrates, sugars, and heavy exercise 24 hours before:
- Rice, Roti, Bread
- Fruits, Fruit Juices
- Potatoes, Sweet Potatoes
- Sweets, Chocolates, Ice-cream
- Cold drinks / Soft drinks
- Alcohol
- Pasta, Noodles, Pizza, Bakery items
- Sugar-based beverages (Tea/Coffee with sugar)
- Fast food and Fried foods.
Avoid strenuous physical activity (gym, running, sports) because muscles may take up too much tracer.
On the Day of PET Scan – Do’s & Don’ts
| Do’s | Don’ts |
|---|
| Wear warm, comfortable clothing | Avoid jewelry, metal items |
| Carry medical reports & prescription | Avoid bringing children along |
| Reach on time | Don’t drive long distances or workout |
Is a Blood Test Required Before a PET Scan?
Yes, a blood glucose (sugar) test is required before a PET scan.
Since PET scans use a glucose-based tracer FDG (Fluorodeoxyglucose), the body’s blood sugar level must be within a specific range for accurate results.
Why is Blood Sugar Check Important?
- High sugar levels can reduce tracer absorption
- Cancerous or abnormal cells may not appear clearly
- Increased chance of repeating the scan
- Accuracy of diagnosis may get affected
Ideal Blood Sugar Level for PET Scan
Patient Type Acceptable Level
| Patient Type | Acceptable Level |
|---|---|
| Non-Diabetic Patients | 70 – 150 mg/dL |
| Diabetic Patients | Below 200 mg/dL (as per doctor’s recommendation) |
If sugar is high, the scan may be delayed or rescheduled.
Other Blood Tests Sometimes Needed
Depending on the doctor’s prescription, the center may ask for:
| Test | Why Required |
|---|---|
| Kidney Function Test (KFT) | For patients with kidney issues before contrast use |
| HbA1c | To assess long-term sugar control in diabetics |
| CBC | General health evaluation if needed for cancer patients |
Not all patients need these – it depends on medical history and treatment stage.
Important Tips
- Avoid sugary food & drinks 24 hours before scan
- 6 hours fasting before the scan (only plain water allowed)
- Inform the team if you are diabetic or on insulin
People Also Ask About PET Scan
Is the PET scan safe? Will I be exposed to radiation or side-effects?
A PET/CT scan does involve a small amount of radiation (since PET uses a radioactive tracer, and CT uses X-rays), but the dose is generally considered low, especially when the benefits outweigh the risks.
Side effects are rare – the tracer injection is similar to a routine blood test (small needle prick), and most patients don’t feel anything unusual.
For women who are pregnant or breastfeeding, it’s extremely important to inform the doctor/technologist, as special precautions will apply.
What happens during the PET scan procedure?
Roughly, the process is:
- First your blood sugar is checked
- Then a small amount of radioactive tracer (often F-18 FDG) is injected via IV.
- After injection, you will wait quietly (often 30–60 minutes) for tracer to distribute in your body – during which you should relax, avoid movement, reading, or strenuous mental activity (especially in brain scans) to avoid altering results.
- Then the scan itself takes place: you lie on a table that moves through the PET/CT scanner, and you must stay still until imaging is done (approx. 20–45 minutes depending on scan type).
- Total time at centre may be about 2 hours (including preparation, uptake waiting, scan, and check-out).
After the scan – any restrictions or precautions?
After the PET scan, most people can resume normal activities immediately.
You are usually advised to drink plenty of water – to help flush out the radioactive tracer from your body
If contrast dye or special radiotracers were used (or you are pregnant/breastfeeding) – follow any additional instructions given by the centre.
How soon will I get the results?
Typically, a radiologist (specialist in interpreting PET/CT) reviews the images and sends the report to your referring doctor within 24–48 hours.
Your doctor will then discuss the report with you and suggest further steps (if any).
Will the PET scan show cancer definitively?
PET/CT is a powerful diagnostic tool – it can show metabolic activity (how tissues use glucose) and highlight abnormal areas that may indicate cancer, infection, inflammation, or other disease.
However, a PET scan alone may not definitively “diagnose” cancer. Your doctor usually considers PET results together with other tests, biopsy (if needed), clinical history, and sometimes other imaging (CT, MRI) to reach a final diagnosis.
Tips for Patients in Chandigarh / India Going for a PET Scan
- Always confirm preparation instructions with your diagnostic center – dietary / fasting, blood sugar control, medication advice, etc.
- If diabetic – inform the centre ahead; maintain stable sugar levels and follow their special instructions.
- Wear comfortable clothes, avoid metal items.
- Stay hydrated (plain water), avoid heavy exercise or stress 24 hours before scan.
- After scan, drink water and follow your doctor’s advice; ask when & how you’ll get your report.
Following the right diet before a PET scan ensures accurate results and a smooth scanning experience. If you have any concerns or medical conditions like diabetes, always speak to your doctor or the diagnostic team in advance.
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