Evidence-informed. Fred-translated.

Methodology & Sources

Content standard last reviewed: June 13, 2026

This tool provides educational rules of thumb. It does not diagnose, predict an individual glucose response, or replace medical advice.

What a verdict means

"Breaks a fast" means that an item does or does not fit the fasting rule selected in the tool. It is not a claim that insulin, ketosis, fat burning, or autophagy behaves like an instant on/off switch.

• Green: generally compatible with the selected fasting rule when used as described.
• Yellow: a small or product-dependent grey zone.
• Yellow / Red: likely incompatible, with serving size or context still relevant.
• Red: contains meaningful energy, protein, amino acids, sugar, or food.
• Check first: medical context, medication, dose, or interactions matter more than fasting purity.
• Use now: follow an emergency care plan immediately and do not delay treatment for a fast.

How the lenses work

The practical lens prioritizes meaningful energy, adherence, and appetite. Sugar and carbohydrate awareness emphasizes label reading but does not predict glucose readings or manage diabetes. The clean and strict lenses are deliberately simple house rules, not separate medical states.

How items are assessed

Fred checks calories, sugar and carbohydrate, protein and amino acids, product form, serving size, and whether medication or health context could change the answer. Brand formulations vary, so the current product label always outranks a generic database entry.

Safety boundary

People who are pregnant or breastfeeding, have an eating-disorder history, manage diabetes or another medical condition, or take medicine that may require food should discuss fasting with a qualified professional. Prescribing instructions and emergency care plans always outrank the fasting tool.

Primary references

• National Institutes of Health: To Fast or Not to Fast
• NIDDK: Low Blood Glucose (Hypoglycemia)
• NIH Office of Dietary Supplements: Potassium
• NIH Office of Dietary Supplements: Vitamin D
• MedlinePlus: Sodium Bicarbonate
• U.S. Food and Drug Administration: How Much Caffeine Is Too Much?
• U.S. Food and Drug Administration: Aspartame and Other Sweeteners

Corrections

Products and evidence change. To flag an unclear or outdated entry, use the feedback form in the search tool or email hello@fastedfred.com.