Fat vs glucose being the energy source depending on diet? Where can I find more info about this?
The difference between a normal person and somebody with insulin resistance is that the latter will feel hungry for longer before starting to burn fat.
Contrary to what the GP says, you need to be low on fat (think extremely skinny) before the body starts scavenging healthy non-fat tissues.
The process of converting muscle tissue into glucose falls under the umbrella of gluconeogenesis.
If you burn up your glucose stores, your body may turn to fat (more efficient than converting muscle to glucose), but the body can "skip" the fat burning and turn to the break down of muscle to convert the amino acids (proteins) into glucose. Hint: its build right into your post...Insulin. If a body burns up glucose, and there are high levels of insulin in the blood, then the body will go into gluconeogenesis to breakdown muscle to convert the amino acids into glucose instead of burning fat.
If you want science/studies I would start maybe with the krebs cycle/ATP, ketogenic diet, ketosis, ketones as a by-product of fat buring. Maybe mix in studies about insulin, blood sugar levels/glycemic index, glucose, glycogen, glucagon/pancreas, amino acids/liver/gluconeogenesis.
For more practical/functional/anecdotal information, usually your interest will be in sports/athletic performance. You might start with more generic blogs about glucose vs fat and then work your way into blogs of individual athletes in the sport you are most interested in. Although I distance run, I don't limit myself to the experiences of just other ultra runners. I also really enjoy reading about the various diets/experiences of body body builders, sprinters, other endurance sports, and mixed martial artists. It is such a wide gap in terms of performance goals and mass/muscle/weight goals.
These videos by the channel "What I've Learned" are great:
- Fasting vs. Eating Less: What's the Difference? [1]
- Longevity & Why I now eat One Meal a Day [2]
The channel [3] also has many other videos on the topic of nutrition, with similar emphasis.
Also see the excellent and readable book "The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting" by Dr Jason Fung and Jimmy Moore [4].
[1] https://youtu.be/APZCfmgzoS0
[2] https://youtu.be/PKfR6bAXr-c
[3] https://www.youtube.com/channel/UCqYPhGiB9tkShZorfgcL2lA/vid...
If 70% or more of your calories come from fat, your body starts increasing its fat oxidation rate, but it also down regulates the carb burning pathway
The video on the page provides a detailed look at how the body breaks down glucose and fat for energy:
https://peterattiamd.com/introduction-to-superstarch-part-i/
I’ve been following a keto diet for some time now and still learned a lot from Peter’s discussion with Joe.
It made me realize, often when we say we are hungry and we are craving something, it's not that we are hungry, it's that we are craving carbs.
Back when I did it, I had two friends that did it with me. One of them got cognitive benefits like I did while the other did not. It might be that we were deficient in or sensitive to something else. In fact the energy was so boundless at the 2-week mark that we actually had a hard time falling asleep at night.
It worked well over couple of months. Actually, I found the chart I made then:
https://www.dropbox.com/s/vdlgazsfjjbqkox/weight-2012.png?dl...
(Measurements are blue, running average (of AFAIR a week) is green. I used the running average as an indicator of progress, to eliminate measurement noise / daily variations.)
That ~8-10kg drop in 3 months is when I was on ketogenic diet. I carried it a bit longer, then I guess at some point I just decided I miss pizza too much. One permanent change this caused though, that I have to this day, is that I switched from sugar to artificial sweeteners in my tea/coffee, and always opt for sugarfree coke/pepsi instead of the regular one.
Following your conversation I have a wild guess...you likely were not exercising and therein likely was.
First, I’ve never meet anyone who did some form of working out/exercising who couldn’t tell if they were in ketosis (good or bad).
If I am right, this may also explain the feeling of mental clarity therein experiences that you didn’t. Glucose is fuel for the brain, but fat isn’t...ketones are which are a by product of fat burning, so the more fat burning/ketones the more fuel for the brain.
Interesting if you both chime in on my theory.
> Glucose is fuel for the brain, but fat isn’t...ketones are which are a by product of fat burning, so the more fat burning/ketones the more fuel for the brain.
That definitely makes sense to me and would even to a certain extent explain the difference between individual experiences with ketogenic diet.
No. You are hungry, not necessarily for carb or protein or fat, you're just hungry. If you wait long enough, your body will switch to burn body fat.
Even after knowing that my body has switched to primarily using ketones via Ketone Measurement Strips used on urine daily, I would find myself wanting to eat something, but once I realized all I had at home that I could eat was food full of fat and protein but not carbs, my craving would disappear or I would become disinterested.
And even after eating, I could still feel that it didn't hit the right spot at satisfying my cravings. I would be really full, and really full of energy-dense food but I would still be dreaming of a slice of bread or even a sip of lemonade next to whatever dish I am eating. I realized what I craved wasn't food but that spike in blood sugar.
I think there is just a difference in the use of "controlling" here. Fat/Glucose will always be used jointly as energy, but the idea is to "control" which is the primary fuel source. A Ketogenic diet or ketosis is part of that, still giving you a fair reading I can understand how you conclude that is not "control", though I would argue it is because I am controlling my fuel source, but to your point I am not eating whatever I want (carb/sugar heavy diet) and controlling my primary fuel source like a light switch.
Separate and apart from the diet, there are other things you can do to "control" or "train" your body to burn fat as the primary fuel source. Again keto is a large part of it, but lets assume I am in ketosis and about to go for one of my runs...in short, aerobic or anaerobic. Is my body going to go for the fat or is it going to go for the available glucose which is the preferred energy source for anaerobic exercise? Also, in anaerobic exercise the muscles produce lactic acid as a by product and as anaerobic exercise can only be maintained for a short period of time, when its over and the body is recovering the lactic acid goes to the liver and is converted into glucose, of course that raises the blood glucose level which in turn may encourage the body to use as the primary fuel source. Keeping my run aerobic I am "controlling" the primary fuel source and burning fat, both in the short term (same run) and long term (over periods of time) I am training my body to be pushed harder and harder while maintaining my aerobic threshold increases.
So training in a glycogen depleted state (back then we called this bonking) is bad news if you want to increase your aerobic threshold, since the kind of training that has been shown most effective in causing the required adaptations involves repeated maximal efforts.
The only training effect you can hope for is nudging your body towards using more fat at lower levels of exertion, thereby saving valuable glycogen. This isn't very relevant for most running events which are typically done at a consistently high VO2max percentage, but beneficial for say cycling races where you have low intensity (riding in the slipstream on the flat) mixed with very high intensity (up a steep grade).
These is a difference between burning glucose as the primary fuel source, depleting it, and bonking vs using fat as the primary fuel source to begin with (there is no bonking).
But basically glucose store empty pretty quickly and if not refueled the body shuts down to conserve the limited glucose for the brain because that is it’s primary fuel source (the body shut down is the bonking).
When in keotsis, the burning of fat produces a by product, ketones, which is a different source of fuel for the brain. So when in ketosis when burning fat as the primary fuel source (which is essentially limitless compared to glucose) there is no bonk because 1. You don’t run out of fat (like you would glucose), and 2. As you burn fat you produce ketones to fuel the brain (which isn’t happening when burning glucose as the primary fuel).
For example my last marathon I ran in ketosis I did with only water and electrolytes (no fuel), I cant do that if I’m not in ketosis.
Your point about being able to more efficiently increase the aerobic threshold while using glucose sounds right.