I found something similar too -- and I'm nowhere even near that thin.

I successfully lost 50 lbs a few years ago doing keto and brought myself to exactly the middle of normal BMI.

While I was losing the weight, keto was easy -- I always had energy (more than ever before), felt great, wasn't getting sick.

But once I hit my target weight... all of a sudden keto became miserable. I had brain fog all the time, except for about the window of 2-4 hrs after each meal when my digestion seemed to peak. I started getting colds all the time.

Once I switched back to eating carbs, I felt great.

My theory is that your body burns fat proportionally to the amount of fat you have... and that it's fine to fuel yourself until you just don't have enough fat anymore to keep it going to even things out between meals.

I was pretty bummed actually to discover that keto doesn't work for me anymore, when I'm already at a healthy weight. I just loved the constant energy. But for however my body's built, it's just not an option for me anymore.

Oh that sounds difficult. Were you eating enough fat & protein each meal, that you needed to burn off? Since your body didn’t have the fat stored...

You are an extreme outlier. Even for men, bf% under 7 is in or getting into the unhealthily low range. Fasting is not for you.

Intermittent Fasting, as described on the internet, doesn't involve eating less food but rather eating within a narrower time window. You can get 16-23 hours of fasting in a 24 hour day, and suggestions are that useful changes happen around 12 hours after eating, and (e.g. work of Prof. Sachin Panda) that fasts of this kind of length can do significant good for animal health.

Are you talking of this kind of thing, low body fat makes even this difficult, or are you talking of multi-day fasting?

I don't understand Intermittent Fasting from a digestion point of view. The fast usually starts when you end your last meal, however you'll be busy digesting your food for hours, can those hours really be counted as "fasting".

Fasting, to me, begins when all previous meals are digested

FWIW, the time window of Intermittent Fasting usually leads to eating less food.

Although there are other benefits to IF, the weight loss is principally from calories in, calories out, because it’s much harder to cram an excess of calories into a small time window unless you purposefully eat beyond satiation.

> the weight loss is principally from calories in, calories out

Is it? Study [1] claims "Mice fed an FS [fat and sugar] diet ad libitum (FSA) consumed the same amount of calories as mice fed within a 9 hr window of the dark phase (FST) [fat and sugar, time restricted] (Figure S2A, i), yet the FST [time restricted] mice gained less body weight"

and then "to investigate the therapeutic potential of TRF [Time Restricted Feeding], we tested whether TRF could reverse or arrest body weight gain [..] Within a few days the mice were habituated to the new feeding paradigm and continued to consume equivalent calories (Figure S2A, iv). The 13:12 FAT mice showed a modest drop in body weight"

[1] https://www.cell.com/cell-metabolism/fulltext/S1550-4131(14)...

From related work of https://www.salk.edu/scientist/satchidananda-panda/

I think "it has to be calories in/calories out because it's just common sense" is not nuanced enough for biological systems.

I do intermittent fasting frequently. I can't fast from food for long periods, or go below a certain calorie count in a day. As long as I get the nutrition I need, I'm ok, I just run on thin margins.

A lot of "conventional wisdom" about health seems to be targeted at people who are sedentary, which is kind of counterproductive, since being active is the most effective way to improve your health. When you're highly active, things like intermittent fasting start to make a lot less sense.

I disagree completely. Regular caloric restriction has its place, exercise has its place, and intermittent fasting has its place.

My wife and I are long distance hikers. That means carrying 10-15kg up and down mountains for 10-14 hours per day every day for 3-6 months.

It also means literally counting every calorie--because you have to plan it in week-long intervals and also optimize it for minimal weight and sufficient nutrients.

Sounds like a perfect recipe for weight loss right? Enter 'hiker hunger.'

Appetite is completely elastic. Your ability to perform depends on your brain's ability to produce happy endorphins and satisfaction signals etc.

That's where intermittent fasting is crucial. You exercise your body's regulatory functions. It's not just some belief or willpower or placebo I mean: at a chemical level you transform the function of your neurochemistry to improve your metabolic process.

> That's where intermittent fasting is crucial

Would you be able to use IF during a thru hike? I suspect that the answer is no. The weight gain problem for distance hikers is after the hike is finished and we reduce activity significantly. I've solved that by training for distance races when I'm not hiking.

Zach Bitter, the current 100 mile record holder, put it in a way that makes a lot of sense to me[0]. For a mere mortal, fasting for 6 hours puts you in the hole for about 700 kcal. A world class athlete like him is at more like a 2000+ kcal deficit. It's impossible to catch up once you get that far behind, and you end up losing weight and injuring yourself. I only burn about 800 kcal during training on an easy day, but I still find it nearly impossible to catch up if I miss a meal. I'm already eating 5x a day. It's hard to cram 5 full meals into a few hours.

[0]: https://zachbitter.com/blog/2014/04/06/intermittent_fasting_...

Of course not.

And weight gain is not contained to "after the trail"

And weight loss is not guaranteed.

It's great that you've found something that works for you. Like I said, it works for me too.

Bodies are different though.

"I've hacked around this problem" != "This problem is illusory"

Being active is one factor, but doesn't fix obesity. It's also difficult or even potentially harmful to start doing some kinds of activity when you're extremely obese.

Highly active is something you can be when you're at or approaching a healthy weight; the causality is IMO almost backwards from what you've described.

You can't outrun a bad diet. It's way too easy to overeat in our modern world, even if you're active.

> You can't outrun a bad diet

In spite of jamming as much junk food down my throat as I possibly could, I struggled to maintain weight on the Appalachian trail. You can definitely outrun a bad diet. (Not that it's a healthy way to live either.)

Not everyone can. Genetic factors and how your body handles insulin determine almost everything about how your body will gain or lose weight and in what conditions.

Gary Taubes book “Why we get fat,” is a great read on this subject.

I agree that outrunning a diet is something that outliers do, but has Gary Taubes found a way for his foundation to confirm his claims after it refuted them? There's little doubt that genetics and how your body handles insulin have influence, but the variations still don't compare with how many calories you consume versus how much you move, given a healthy diet.

You can eat a lot of calories and lose weight.

I have lost weight like that before, but can't maintain a 2 hour a day exercise routine.

I imagine you can't stay on the Appalachian trail forever.

So eventually a bad diet will lap us.

I had the same problem on the AT.

But, yknow, HYOH

My mom used to regularly fast for "religious" purposes. One day during a week long fast she passed out in the shower. According to the doctor it's because we're not supposed to keep a full schedule while fasting.

Was it a wet fast or a dry fast?

> According to the doctor it's because we're not supposed to keep a full schedule while fasting.

That's a standard answer that likely does not draw on his medical knowledge. People pass out even when not fasting (women more so than man, something to do with vagus nerve IIRC), and thousands of people do long wet fasts while keeping a full schedule with no ill effects.

The feeling ill part is a n=1.

As mentioned from fasting you still get major benefits from autophay, sirtuin activation, longevity, low insulin variability.

Some of the top fitness and health practitioners who are big on fasting are very low body fat, incredible shape.

If you are highly active and have a low bodyfat percent, then you are just catabolizing your own muscle by fasting, and you become very injury prone. There's no upside.

You seem out of touch with the scientific literature, and have hand-waved all the real health benefits I've listed.

Leading figures like Peter Attia, Tim Ferriss, Ben Greenfield, David Sinclair, Kevin Rose to name a few, all pro fasting, all in top shape/low body fat.

> and you become very injury prone

No, you become temporarily weaker, and that's only if you're fasting multiple days. It's recommended you work out during fasts... your body remains anabolic to muscle (barring other variables like elevated stress).

With the exception of Ben Greenfield, none of these people seem to have a sports science background. In the realm of athletics, things like intermittent fasting and keto diets are something of a meme. Some people do advocate for training with depleted muscle glycogen first thing in the morning, but there's no consensus that this does anything.

Autophagy for me is my muscles eating themselves for energy. Not healthy, and it feels like being beaten.