Alternate-Day Fasting
A very low intake “fast day” alternating with an unrestricted day — a research protocol, not a product.
Compiled by Nidari Nutrition from the Atlas dataset · pending clinical review by Maryam Shabbir, DN.
This is an Atlas entry — a short reference overview, not one of our long-form diet guides. Educational, not medical advice; personalized and clinically reviewed at your consult.
What is Alternate-Day Fasting?
Alternate-Day Fasting is a modern, commercial diet from Chicago, Illinois, USA. Nidari rates it hard to keep up day to day, and rates the weight of peer-reviewed evidence behind its main claims as moderate.
Family: Modern & Commercial · Origin: Chicago, Illinois, USA · Era: 2009 · Difficulty: Hard · Evidence rating: Moderate evidence
Where does Alternate-Day Fasting come from?
Alternate-day fasting is a laboratory protocol that became a public diet. Early work in 2005 showed strict every-other-day fasting was feasible but hungry; Krista Varady’s group then developed modified ADF — about a quarter of energy needs on the fast day, unrestricted eating the next — first published in 2009. Unlike almost every other entry in this family, nobody owns it: no company, no membership and nothing to buy, which is precisely why the trial evidence is comparatively clean.
Originator: Krista Varady PhD, University of Illinois Chicago · Region: Chicago, Illinois, USA · Era: 2009 · Atlas map pin: 41.87° N, 87.65° W
How does Alternate-Day Fasting work?
- Alternate fast days and unrestricted days
- About 25% of energy needs on fast days
- Eat freely, not doubly, on feed days
- No food groups excluded on either day
What do you eat on Alternate-Day Fasting?
✓ Eat freely
- One substantial meal on fast days
- Protein and vegetables to hold satiety
- Normal, unrestricted eating on feed days
✕ Limit or avoid
- Compensatory bingeing on feed days
- Fasting on consecutive days
- Attempting it on diabetes medication unsupervised
Who is Alternate-Day Fasting for?
The goals this pattern is most often used for. In a consult we confirm whether it actually fits your body and life.
Is there good evidence that Alternate-Day Fasting works?
Nidari rates the evidence behind Alternate-Day Fasting’s primary claims as moderate — that is the current weight of peer-reviewed research for those claims, and nothing more.
The pivotal trial (Trepanowski, Varady et al., JAMA Intern Med 2017, 100 adults, 12 months) found 6.0% weight loss against 5.3% for daily calorie restriction — not statistically significant — with 38% dropout in the fasting arm. A 2025 BMJ network meta-analysis of 99 randomised trials found ADF was the only fasting strategy to beat continuous energy restriction, by about 1.29 kg, at moderate certainty.
Is Alternate-Day Fasting safe, and who should avoid it?
Better studied than most fasting patterns, but not benign. The landmark 12-month trial recorded high dropout in the fasting arm and a significant rise in LDL cholesterol relative to daily calorie restriction — worth watching in anyone with existing cardiovascular risk. Contraindicated in pregnancy and breastfeeding, in children and adolescents, in anyone underweight or with a history of an eating disorder, and it demands prescriber supervision for anyone on insulin or sulfonylureas.
How does Nidari adapt Alternate-Day Fasting?
This is the fasting pattern with the cleanest independent evidence, and it costs nothing. It is also the one most people abandon — the landmark trial lost 38% of its fasting arm. We would rather build a rhythm you can hold.
Book a free 15-minute intro callReady to discuss Alternate-Day Fasting?
Fifteen minutes with one of our dietitians. We’ll tell you honestly whether Alternate-Day Fasting fits you — or point you to the diet that does. Halal and home-kitchen ready. No pressure.