Manu Mehrotra
Founder, iFast
Manu builds iFast, an intermittent fasting tracker for iPhone. They are not a clinician. Everything on this site is sourced to published research, human studies are distinguished from animal ones, and where the evidence is weak the article says so rather than guessing. Corrections are welcome and get made.
Articles
- Why your calorie deficit stops working, and what to do about it
The 3,500-calorie rule predicts weight loss that never stops. Real loss slows and plateaus. What the dynamic models show, and how to set a target that survives it.
- Body fat percentage: every way of measuring it is wrong, differently
Tape measures, smart scales and calipers all have known error bars, and most of the numbers people quote are convention. What each method can honestly tell you.
- How much water do you need? The honest answer is a range
The eight-glasses rule has no evidence behind it, and neither does the ml-per-kg formula. What the reference bodies actually publish, and why it is a range.
- The best intermittent fasting apps in 2026, honestly compared
Zero, Simple, Fastic, DoFasting and iFast compared on what each is actually built for. Written by the people who make one of them, and clear about it.
- The first two weeks of intermittent fasting: what to expect
Headaches are real and mostly caffeine. Hunger may not fade the way you have been promised. What the trials found about the early weeks.
- How to use iFast, in the order that works
A practical order for setting up an intermittent fasting app: what to do on day one, what to leave until week two, and what to ignore at first.
- Fasting while on a GLP-1: what the guidance says
The advisories on fasting with semaglutide or tirzepatide do not rule it out, but name low blood sugar first. What they say, and where surgical guidance disagrees.
- What happens during a fast, hour by hour
A sourced hour-by-hour account of fasting physiology, including where the popular timeline is wrong and where the human evidence simply does not exist.
- Autophagy and the 16-hour fast: what is real, and what is marketing
Autophagy is real and fasting influences it. No study has found the hour it switches on. What is measured, and the effects you can count on instead.
- Hours 12 to 24 are where fasting does its real work
Most of the measurable change in a fast happens between hours 12 and 24. Here is what shifts, by how much, and why it argues for a 16 to 20 hour window.
- Are you losing fat or muscle? How to tell, and how to keep it
Fasting can cost lean mass, but mostly when protein is low and you are not lifting. What the trials found, and the three things that protect muscle.
- 16:8 vs 18:6 vs OMAD: which one actually suits your day
No trial has shown one fasting window beats another for weight loss. What the research does suggest is that timing matters more than width. How to choose.
- Do women need to fast differently? What twice the ketones at 30 hours means
Women reach roughly twice the ketone level of men at the same hour. The physiology differs; the popular rules about it are mostly invented. What holds up.
- What breaks a fast, and what the 50-calorie rule gets wrong
The 50-calorie threshold appears in no trial or guideline. What the research actually shows about coffee, cream, sweeteners and what interrupts a fast.
- Your TDEE: what the number means, and how wrong it can be
TDEE estimates how many calories you burn a day. The equations are good on average and meaningfully wrong for a sizeable minority. How to use one properly.
- BMI: what it can and cannot tell you
BMI was built to describe populations, not people. What it is useful for, where it fails, and why NICE now asks for your waist-to-height ratio as well.