Intermittent Fasting: What a Doctor Tells People Who Ask

I knocked a boiled egg against the table, and the crack cut through the silence.

We were at a hotel for a week of leadership training. The morning session started at eight o'clock, and so did my eating window, so I came in from the breakfast buffet with eggs and started breakfast in front of everyone.

I understand why the rule appeals. Pick your hours, and you have fewer decisions to make. The problem is expecting that one rule to deliver everything you have heard about fasting.

Two people asked my opinion in the last fortnight. My answer always starts with their goal, and this episode is that answer in full.

In this episode:

Why a year-long trial that gave everyone the same calorie target found the eating window worth an extra one point eight kilos, and why that number did not survive the statistics. I explain what the P value actually means, in plain language, because it is the part most coverage skips.

The trial that settled the timing question more directly, by handing both groups the same food for twelve weeks. The early ten-hour window produced no extra weight loss and no better blood sugar.

The stronger result almost nobody talks about. Four normal eating days a week, three days at about twenty percent of normal intake, and after a year, nearly three kilos more weight lost than daily calorie cutting. It is the version of fasting with the best evidence behind it, and it is the version nobody asking me about 16:8 has in mind.

Autophagy, which is why I came back to fasting in the first place. What the 2016 Nobel Prize was actually awarded for, what has been measured in human white blood cells since 2017, and why the hour figure in your fasting app has no human study underneath it.

What Krista Varady, who runs these trials for a living, says about the hours. It is the most honest sentence in the whole field.

Making weight at sixteen. Weeks of cutting calories, then broth, then nothing, then the sauna to sweat off the last kilogram. It worked. It also belongs to a part of wrestling's history that killed three healthy college wrestlers in the winter of 1997, and I say why that is a different thing from restricting the hours you eat.

Why my priorities changed. An unstable shoulder that has dislocated even after surgery, a back that complains when I skip two weeks of lifting, and what I now put ahead of any eating schedule.

How to read a claim about fasting and muscle, including the difference between a scan's fat-free mass and actual muscle, and why that distinction changes what a well-known twelve-month trial can tell you.

The afternoon crash, the workday test, and the three signs that mean you should stop running a window regardless of what the research says.

What the evidence really supports about finishing dinner before bed, including the trial that hit one of its two main outcomes and missed the other.

The correction. In May 2025 I was too sure about preserving lean mass, and I left out a mortality finding that was already sitting in my research notes. This episode gives the full picture.

Three things to try today, sorted by what you actually want.

Every study mentioned is fully referenced in the written edition at https://www.andreheeg.com