Thread by @BStulberg

Intermittent fasting (IF) is the latest nutrition, health, and, in some circles, performance—both physical and mental—trend out there.

Here are some thoughts, based on evidence and theory.

(Short thread.)

For most people, intermittent fasting reduces calories. If you don't have the option to eat all day you'll end up eating less calories. Eating less calories is associated with weight loss. Being at a healthy body weight is associated with less disease and enhanced longevity.

Other claims about IF tend focus on health and especially longevity benefits *beyond* the practice's potential positive affect on weight control.

Research has shown IF activates certain pathways in the body, but no study (yet) has gotten to real-world outcomes we care about.

An outcome study is challenging because you'd essentially have to have two groups of people eat the exact same diet and daily calories but one group only eats in certain windows. And you'd have to track for years—virtually impossible to do in a rigorous experimental setting.

If you zoom out a little, it is true that the body responds well to stress—so long (and this is a big so long) the stress is at the right dose.

The theoretical benefits of IF (beyond weight control) all center around it's role as a stressor to which the body adapts.

This is sensible, and there are related areas we can look to for patterns.

Physical activity is great and very well-studied example.

No physical activity, and you get sick. Too much physical activity, and you get sick (or injured).

The key to physical activity (for heath) is to stress yourself just enough over and over again.

If you believe intermittent fasting offers stress-related benefits, it'd be wise to consider the "just enough over and over again" approach here too.

Be a little hungry most days.

Being a little hungry most days translates to something like don't eat for 12 hours. Stop eating at 8 PM and have breakfast at 8 AM, for example.

This feels like about the same hunger stress as would be a healthy workout stress. A little hard but not too hard. Very repeatable.

The beauty of this approach is that you get some stress AND won't be grumpy and miserable because you are always hungry. Also, you probably won't develop an eating disorder, something that sadly gets more and more common the longer you intermittently fast in the name "health."

But what about the very hard workouts you do once in a while? Well, those are as much for your mind as for your body. Doing hard things every so often is good. But you better do them with knowledge or coaching, otherwise you get hurt.

A full day fast once or twice a year? Fine.

But don't think that full day fast is doing anything for your physical health. If that's how you want to experience a challenge, however go for it—again, so long as you have proper knowledge and coaching. I know I'd personally rather just train really hard a few times a year.

Bottom line:
-Intermittent fasting is a way to control calories.
-Any other benefits are still theoretical.
-The main theories are around positive stress-related adaptations, such as with exercise.
-Take a similar approach. Hard but not too hard. Be a little hungry most days.

Longer periods of fasting carry risks:
-Burning out
-Binge eating in the windows you do eat
-And by far most dangerous, eating disorders

Based on everything out there:
-Avoid processed foods.
-Eat lots of plants.
-Consider a 12-hour window: be a little hungry most days.

(End.)