[PurpleRamen]

> instead of being irritable when hungry, you mind feels clear and focused.

From my experience, it's a delusion. The focus is there for some while, but the actual abilities decline very fast without you even realizing it because of this supposed clearness. It might be even that the clearness comes exactly because of your mind limiting itself to a shorter attention and horizon, removing all the complex and complicated things. It's basically being in the zone, but the zone itself is so limited that you might not do good work if you need to have a "big zone". Though, it depends on your type of work if this can be beneficial. But as a knowledge worker, I consider it harmful for my work.

> When I was a kid, I recall the teachers always telling us to have a good meal before a test. Even then I felt that was silly, as a big lunch always gave me brain fog.

Depend on the type of food, size of meal and how long before the test you were eating.

[throwaway290]

From my experience, I think clearest when my body is not busy digesting.

Just as you say my experience is a delusion I can suggest that perhaps your feeling of expanded attention and horizon could be a fallacy caused by your attention in fact becoming more limited as your body diverts blood (and so oxygen) from your brain to your stomach and gut for food processing (which takes hours, so if you eat 3 meals this is basically your entire day).

[PurpleRamen]

> From my experience, I think clearest when my body is not busy digesting.

Exactly. Digesting is also kind of a burden to your focus, which is why one should not work directly after eating, especially if it was a heavy meal. But digesting ends at some point, after which you do have excessive energy available. So the point is to know roughly how long each meal will burden your body, and plan accordingly when you will reach a performance-high.

[andai]

One thing I found quite astounding while fasting is how keen my sense of smell is. I normally don't smell much at all, but while fasting I can smell every restaurant in a 2 mile radius.

I guess it's mostly my brain filtering out "irrelevant data" (the location of food becomes relevant when you're hungry!)

That made me wonder if my other senses might be sharper while hungry too. As hunters, I imagine our ability to plan might also benefit.

Has any research been done on the effects of hunger on cognitive performance?

[andrem]

Do you suffer from allergies/chronic rhinitis by any chance? I have hyposmia because of rhinitis.

But I get the same - go without food for a while and my sense of smell increases until I eat and become satiated.

Now whether it’s related to certain allergens that I eat or the body/senses becoming less sharp I do not know.

Probably worth investigating a bit more, I never really dug deeper into this.

[distantaidenn]

Agreed. When I first started IF so many years ago, it was a shocker how much my sense of smell increased. In the sense of evolutionary biology, it makes sense. If you are hungry, you better be able to find your next food source and maximize every sense you have to get it done.

[distantaidenn]

I can't agree with it being a delusion. Again, my personal experience is just that -- personal.

Ketones are associated with fasted states and/or restricted carbohydrates. The average person holds about 400-500g of glucose (1600-2000 calories) in their bodies. Once that is depleted, through fasting or carb restriction, you will switch to ketogenesis to provide fuel. There are numerous studies that show a positive correlation with ketone production and cognitive performance.

Few examples: > https://pubmed.ncbi.nlm.nih.gov/25404320/ > https://pubmed.ncbi.nlm.nih.gov/27528626/

If I am doing serious deep work, I can go 8 to 10 or so hours without even thinking about food. However, once I do eat, I'm done with any serious work for a few hours. Keep in mind, I'm operating from a 20 year experience of intermittent fasting (before it was cool).

To reiterate, I don't think it's a delusion. We evolved in a feast or famine state. Dense carbohydrate sources and constant satiation were rare when our base metabolic pathways evolved.

[dist1ll]

> There are numerous studies that show a positive correlation with ketone production and cognitive performance.

Do you have a source? Your second link measures cognitive performance in rats, not humans.

[distantaidenn]

> Castellano, C.A., Nugent, S., Paquet, N., Tremblay, S., Bocti, C., Lacombe, G., Imbeault, H., Turcotte, E., Fulop, T., & Cunnane, S.C. (2015). Lower brain 18F-fluorodeoxyglucose uptake but normal 11C-acetoacetate metabolism in mild Alzheimer's disease dementia. Journal of Alzheimer's Disease, 43(4), 1343-1353. doi: 10.3233/JAD-141952

-- This study found that the brain's uptake of ketones was preserved in patients with mild Alzheimer's disease, and that higher levels of ketone metabolism were associated with better cognitive performance.

> Krikorian, R., Shidler, M.D., Dangelo, K., Couch, S.C., Benoit, S.C., & Clegg, D.J. (2012). Dietary ketosis enhances memory in mild cognitive impairment. Neurobiology of Aging, 33(2), 425.e19-27. doi: 10.1016/j.neurobiolaging.2010.10.006

-- This study found that a ketogenic diet improved cognitive function in patients with mild cognitive impairment.

> Taylor, M.K., Sullivan, D.K., Mahnken, J.D., Burns, J.M., & Swerdlow, R.H. (2018). Feasibility and efficacy data from a ketogenic diet intervention in Alzheimer's disease. Alzheimer's & Dementia, 4, 28-36. doi: 10.1016/j.trci.2017.11.002

-- This study found that a ketogenic diet was safe and feasible for patients with Alzheimer's disease, and that it improved cognitive function in some patients.

Granted, these are studies for people with existing cognitive impairments. However, given how new the science is, I can see why it hasn't been done with healthy individuals, yet.

[dist1ll]

Thanks for providing those references, I'm pretty curious about this topic.

[andirk]

I believe that pushing the body to limits such as fasting, hot/cold baths, intense workout can help us in the longterm. But for when we need our brains to work at its highest potential in the immediate such as software engineering all those things, how is having a hindrance such as hunger anything but a distraction?

[spirit557]

Hunger could be a distraction perhaps but being fat adapted means your brain is primarily burning ketones for fuel instead of glucose. Ketones burn cleaner in the brain with less reactive byproducts than glucose. Dementia eases when patients are fasted or given exogenous ketones. Being metabolically healthy and in a fasted state also means you're not distracted from dopamine snack cravings which many confuse with real hunger and I think has a worse effect on mood and cognition. In addiction your frontal lobe fights for control over your lizard brain. Addiction means your lizard brain is winning over self control.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8840718/ "The Implication of Physiological Ketosis on The Cognitive Brain: A Narrative Review"

https://pubmed.ncbi.nlm.nih.gov/33103819/ "A ketogenic drink improves cognition in mild cognitive impairment: Results of a 6-month RCT"

[Silverback_VII]

Another perspective would be that when your body switches to survival mode due to adverse circumstances (such as cold or hunger), it mobilizes all its physical and cognitive resources. When the body is fighting for survival, it's about everything. This is probably the reason why many people report that they are capable of peak performance in this state. The body usually doesn't give more when it has more, but does the opposite. It saves and conserves its resources for worse times.

[ilyt]

With intermittent (as in "eat one meal a day") fasting you can set your intake to align for when you need most brain work done.

Also, at least from my own experience, after some time you just get used to that and are hungry later and not as hard. When I eat around noon I only start getting hungry in the evening

[PartiallyTyped]

You don’t feel hunger.

If you adapt to a 18:6 or even 20:4 schedule, you don’t feel hunger.

[Retric]

I ate once a day for years. You can easily ignore hunger, but your body/brain isn’t going to preform as well.

It’s like being mildly dehydrated or sleep deprived, yes you can still function but no it’s not optimal.

[andai]

I feel lethargic after eating. I find it hard to concentrate when hungry. I'm only productive in those 1-2 hours between the brain fog wearing off and the next hunger wave coming on.

I tried the meat diet for a few days (yes, I know that's too short! I couldn't get through the "keto flu") and I was blown away by how stable my mood and energy level was after having steak for breakfast. I wouldn't get hungry at all for the next 8-10 hours.

[reitanqild]

I tried multiple times 1-4 days around 25 - 23 years ago and

1. I didn't feel hunger and I don't think everyone needs to feel it

2. I focused a lot better,

I would probably do it a lot of I lived alone.

In practice I often end up with some kind of intermittent fasting: skip meals between 1700 and 1200 (lunch next day) and even then I happily minimize my lunch.

It helps me.

[throw10920]

> From my experience, it's a delusion.

You say this, implying that you got some objective outside measurement to confirm you were being deluded - what was it?