Sardine Fasting - Dom D'Agostino's Protocol & Benefits

In Tim Ferriss’ 2025 interview with Dominic D’Agostino, Dom explained a fasting protocol he calls “Sardine Fasting”.

It stems from an experience he had with his mentor Fred Hatfield, aka “Dr Squat”, who developed metastatic prostate cancer in around 2010, and was given 3 months to live.

Fred experimented with a fasting mimicking diet of the following description:

1 can of sardines per day, for 7 days
Repeating this fast every 1 to 2 months

Fred apparently enjoyed the fasts and said he felt better for them.

Dom says that Fred ended up going into “rapid remission” and didn’t pass away until 8 years later, from something completely unrelated to his cancer.

Dom notes that Fred’s Gleason score at the time was bad, with this being a measure of prostate cancer severity.

Since this, Dom uses sardine fasting situationally. For example if he wants to get his head down and do focused work for a period days or if he’s travelling.

Further notes Dom adds to the topic:

For cancer patients he works with, he suggests a sardine fast over a water fast, as the nutrition from the sardines can help avoid cancer cachexia (muscle wastage).
Sardines provides adequate nutrition for people, and then you create a caloric deficit that comes with some benefits. He says that the protein is low enough that you’re suppressing insulin, mTOR and activating AMP-kinase.
Whilst he says sardines have most of the nutrients you’ll need, he acknowledges you may want to add a little bit of vitamin C or magnesium.
Once in the caloric deficit, over time your glucose levels will decrease and your ketone level will increase. You then want to maintain a glucose to ketone index of 1 to 2 for 3 to 5 days. When measuring that ratio, you want to use mg/dL units for both. Convert units to mg/dL if needed.
If you want to achieve this glucose to ketones ratio quicker, you can use tips I noted down from Tim’s book Tools of Titans. In essence, it’s about adding long walks to deplete glycogen stores quicker.