A positron emission tomography (PET) scan is a specialized diagnostic tool used to examine how your body tissues are functioning. Unlike scans that simply display the body’s structure, PET scans reveal metabolic activity—looking at blood flow, oxygen use, and how your body processes sugar. This ability to see metabolic activity makes PET scans invaluable for diagnosing and monitoring a wide range of conditions, from heart disease and cancer to neurological disorders and infections.
During a PET scan, a small amount of radioactive glucose (a type of sugar) is injected into the patient’s bloodstream. This radioactive tracer allows doctors to observe how your body uses glucose, highlighting areas of unusual activity – for example, cancerous tumors, changes in the heart, or problems in the brain – that may not be visible through other imaging techniques.
To ensure accurate results, following specific dietary instructions before your PET scan is crucial. These guidelines help regulate glucose distribution throughout your body, preventing interference with the scan’s ability to identify metabolic changes.
Understanding Different PET Scan Types
Several types of PET scans are available, each with slightly different applications:
- Fluorodeoxyglucose (FDG) PET Scan: This is the most common type, used for diagnosing heart conditions, detecting tumors, identifying brain disorders, and evaluating infections. FDG is the most frequently used radiotracer.
- PET-CT Scan: This combines the benefits of a PET scan with a computerized tomography (CT) scan. PET scans show how tissues and organs are working, while CT scans provide detailed 3D images of their structure.
- Myocardial Perfusion PET Stress Test: This test assesses blood flow through the coronary arteries to the heart muscle. It often involves the use of rubidium or adenosine as the radiotracer.
It’s essential to confirm the specific type of PET scan you are scheduled for with your doctor, as different types may require slightly different dietary preparations.
Foods to Focus On: What to Eat Before a PET Scan
In the 24 hours leading up to your PET or PET-CT scan, prioritize hydration and a diet rich in protein and low in carbohydrates:
- Protein-Rich Foods: Include lean meats like beef, chicken, turkey, or fish. Eggs, raw nuts (in moderation), tofu, and unsweetened peanut butter are also good choices.
- Low-Carb Vegetables: Load up on green beans, broccoli, celery, lettuce, spinach, and zucchini.
- Low-Carb Dairy: Stick to butter and hard cheeses.
- Low-Carb Condiments: Use oil and vinegar.
Foods to Avoid Before a PET Scan
To ensure the scan accurately reflects your body’s metabolic activity, it’s important to restrict certain foods and beverages for up to 24 hours before your scan:
- Grains: Avoid bread, breaded foods, cereals, crackers, oats, pasta, and rice.
- Starchy Vegetables: Limit corn, peas, and potatoes.
- Fruits and Fruit Juices: These are high in natural sugars.
- High-Carb Dairy: Skip yogurt and ice cream.
- High-Carb Condiments: Avoid jams, gravies, and most salad dressings.
- High-Carb Snack Foods: Say no to chips, pretzels, and other processed snacks.
- Candy: Eliminate all sources of added sugar.
- Caffeine: Avoid beverages containing caffeine.
- Alcohol: Refrain from alcohol consumption.
Beyond these dietary restrictions, avoid strenuous activity, such as exercising or heavy lifting, for 48 hours before a myocardial perfusion PET stress test.
Final Preparations
For the eight hours preceding your scan, strictly adhere to a fasting schedule, consuming only water. This final period of hydration is critical for optimizing scan results.
The goal of these dietary guidelines is to ensure that the radioactive glucose tracer can accurately highlight areas of metabolic activity in your body, leading to a more reliable diagnosis.
Editorial Sources
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content. Resources utilized include peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
- PET Scan. Cleveland Clinic. October 19, 2022.
- Ashraf MA et al. Fludeoxyglucose. StatPearls. August 28, 2023.
- PET/CT. Radiology Info.
- Myocardial Perfusion PET Stress Test. Cedars-Sinai.
- PET/CT Scan Preparation Guidelines. Florida Cancer Specialists and Research Institute.
- FDG-PET Scan. Cedars-Sinai.
- Before Your PET Scan. Stanford Medicine Health Care.
- PET/CT FDG Scan for Patients With Diabetes. UW Medicine.
Meet Our Experts
Simran Malhotra, MD, and Gordon Kerr, Author, contributed their expertise to ensure the accuracy and clarity of this article.
Simran Malhotra, MD, is a triple board-certified physician specializing in internal medicine, hospice and palliative care, and lifestyle medicine. Gordon Kerr is a health and nutrition expert.
By following these guidelines, you can help ensure the success of your PET scan and contribute to a more accurate diagnosis.
