Ok I’m looking to nerd out a bit here, and I’ll see if some of the more biologically sophisticated amongst us can chime in…many of you know I’ve been here for a while- on the forum and in the Facebook group years before. Keto/LCHF for 5 years. I’ve done every iteration of this “way of eating” you can imagine. And I still think of questions after all this time! Anyway…as a personal trainer that specializes in keto nutrition strategies, energy substrate/utilization is particularly fascinating to me. I am obviously quite fat adapted, and do all my running and workouts fasted. I’m quite lean- sub 10% body fat- and have settled into a mostly OMAD template that’s about 95% carnivore. I have coffee with almond/coconut milk creamer, spices, maybe some condiments and “incidental” vegetables. But the bulk of my diet is fatty beef, eggs, bacon, fatty pork and lamb. My question is this…while I strongly disagree with the CICO model of energy utilization, there’s the nagging issue of how to know I’m taking in sufficient energy to fuel my body and my physical activity. Since I am so lean- I have about 10-12 lbs of body fat by weight according to the fairly reliable InBody machine at my gym, and with the limit of about 35 calories of energy that can be drawn from a pound of body fat daily, I can really only use about 350ish “calories” of energy from my fat stores- and here is one confounding issue…since I am so lean as a female, does my body maybe release less energy from my fat stores as someone who has more body fat? Because I am “underfat.” So I wonder if I have low leptin levels and maybe that keeps my body from releasing any of its energy stores?? And stemming from that, aside from counting “calories” to make sure I’m getting in sufficient energy, how do I gauge how much fat I need to eat during my meal to fuel my body for the next 20 to 24 hours? Because I don’t measure or weigh anything. And I refuse to. I just eat to satiety and sometimes I’m very hungry and eat at 2 and have more like a couple meals. Sometimes I eat at 5 and have one big meal of a crap ton of ribeye…so, eating primarily carnivore keto, how do I know I’m getting enough fat to account for my low endogenous energy stores?
Not CICO...how about FAT IN, FAT OUT?
I’m confused. Do you mean to say you ‘eat to satiety’ at meal time? Then later you’re unexpectedly hungry again, when previously you would not have been hungry. For example, you mention at 2 and sometimes later when you might eat a couple times again.
I’m just an average guy who really knows next to nothing about how so much is so different for women and men physiologically. So for what it’s worth (which may be diddly 
): maybe you’ve just reached a point where OMAD and ‘eating to satiety’ at meal time doesn’t work any more. You seem to have an extremely low body fat % for anyone, man or woman, but especially for a woman. You’re obviously measuring that, yet you refuse to measure nutrient and calorie intake that would likely give you very relevant information.
I don’t mean to sound negative or derogatory so please don’t take offense. You describe yourself as ‘quite lean’. I guess that’s one way to frame it positively. Have you considered that you may have taken it a bit too far and your hunger is the relevant message? Most of the posters here who advocate eating to satiety advise against being hungry. Have you ever read Kafka’s A Hunger Artist?
I’m no expert but I would just go by how I felt. You’re definitely riding the edge Erin with little headroom to spare. I would think that you would be running out of gas if you weren’t meeting those energy needs which it sounds like you’re doing just by eating to satiety and listening to your body. You’re about 4 1/2 years further down the keto trail than I am, you’re obviously fit and body conscious. If I were you I would just keep going with what’s working so well for you apparently. I actually should be asking you for advice. 
This is what I was thinking too. But I do understand you are trying to “geek out” and figure out a formula. Should prompt some good discussion.
@amwassil I can respect what you’re asking and your concerns about me not listening to my hunger. I’m very open about having struggled with a restrictive eating disorder previously, a fee years ago, while doing keto. It was not intentional (this is a very complex issue so I can’t really go into the detail I’d need to in order to really give an accurate description of the biological basis of eating disorders) but I was a guest on the Keto Woman podcast and talked about it there…long story short, I was not fueling my body sufficiently as I was undergoing a lot of personal stress- I regained some weight with the help of a counselor and have settled back into keto with the help of my doctor, making sure I am staying healthy. And I am. I have my cycle now whereas I didn’t before. I only know my BF % because I’m a personal trainer, as I mentioned, and calibrate myself on the machine I use before I measure a client. I’m not especially concerned or make a concerted effort to stay that low- my body seems to settle into that range eating this way. I am very active, but not to the degree I was when i was really suffering a few years ago. Mentally I am in a much healthier place as well…so, that’s a little of my background. And to address my lack of clarity, I meant that some days I’m hungry at 2 pm, and I’ll eat then and a couple hours later I’ll eat again. So my “eating window” will include a couple meals. Some days I eat later because I’m not hungry until 5 or so and I’ll eat a bigger meal. But I am very responsive to my hunger. I literally cannot ignore it, I cannot and will not fast for longer than I’m able. It really irritates me that there’s so much emphasis on fasting in the keto community. I hear all the time how these fitness types, guys who are gym bros and do keto or carnivore and they say you have to push through the discomfort of the first day of fasting and anyone can do extended fasts, even lean people…no!! It’s ridiculous- and somehow no one calls them out for promoting restrictive eating behaviors. But when i say I’m sub 10% body fat I get all sorts of criticism. But I’m honest about what I’ve been through and I monitor myself. But fasting is like some kind of super power apparently, even though it can have negative repercussions even for someone with a higher body fat percentage…
@KBG I am very, very aware of when my body needs to refuel. I can feel it and I make sure I eat as soon as I notice- but yes, I’m really looking for a good way to get an idea of how the body uses fuel from a meal to provide energy for the hours that follow until I eat again- or really for anyone that is lean and active and runs on fat 
@David_Stilley well, I don’t know everything but I’ve been around here for a while and have a lot of success transitioning people I work with to keto and seeing great benefits in doing so. I always, always eat to satiety, and on a more carnivore template the satiety is different than when I eat plant foods, nuts, etc…it’s a very definitive sense of having had enough whereas when I eat a of of vegetables and nuts and things like that, I can just keep eating but I end up feeling both not completely satisfied and also kind of nauseous. So I’m trying to stick with the base of meals being as much fatty meat as it takes to get me feeling just right
Thank you for further details. Something occurred to me after posting previously. After whatever amount of energy intake occurs at a meal has burned through the system, remaining energy requirements must then be fulfilled (or not) by internal supply. Insufficient internal supply results in hunger signals. At sub-10% your internal supply is quite low, ergo hunger signals. HOWEVER:
You report as a ‘nagging issue’ how to know if you’re taking in sufficient energy to meet your needs. Does that mean you have ALWAYS felt hungry and are only now asking for suggestions about dealing with it? If so, I’d say eat more. If you can’t eat more OMAD then do it twofers, 3-fers or whatever it takes. If you’ve only started getting hungry recently, then the question becomes what has changed the previous equation where OMAD was sufficient?
i would like to know, why OMAD?
eat when hungry, just not before workout. it is anyway unlikely to gain weight with carnivore - if you dont force yourself to eat over!
i do not see, that your workout suffers. so why change?
and cause of your low bodyfat: as long as you have muscles, there is nothing wrong with that. congratulations!
I don’t think this is a leptin resistance issue. Low leptin is normal when you don’t have inflamed adipose cells.
Could be your catabolizing lean body tissues (your own protein) after glycogen stores are depleted rather than catabolizing lipids (ketones) if no outside source of carbohydrates, dietary fat or protein is being steadily supplied frequently enough in adequate amounts to compensate for the lack of lipids for fuel, the body works like this regardless if your fat or under-fat.
Glycogen can be used when you physically exert and contract muscle tissue or it can be used and converted back into glucose when your body needs it by eating a little protein (only) to stimulate glucagon to release glycogen stores from the liver and muscle tissue.
Looking at the notes below kind of give mixed messages?
Notes
[1] Glycogen Stores Versus Fat for Energy: Your body can store about 600 grams of glycogen? 100 grams in the liver and 500 grams in your muscles. However, when you’re exercising, the glycogen in your muscles fuels your workout. Glycogen is converted into energy more easily than fat, which is why it’s used first. To start burning fat, you need to diminish your glycogen stores so your body has no other choice than to use stored fat for energy. …More
Question: If only eating protein by itself converts glycogen back into glucose and gluconeogenesis does not occur or is prevented from occurring by carbing up or eating less protein (good timing?) does that result in weight loss? Ketogenic fat adaption; muscle tissue goes into glucose refusal mode or glucose sparing (physiologic insulin resistance). Can fat cells go into glucose refusal mode, that may explain high levels of glucose? (“…However, while muscles are in “refusal mode” for glucose the least input, from food or gluconeogenesis, will rapidly spike blood glucose out of all proportion. This is fine if you stick to LC in your eating. It also means that if you take an oral glucose tolerance test you will fail and be labelled diabetic. …” …More) DOES HIGH LEVELS OF BLOOD GLUCOSE EVEN MATTER IF YOUR KETOGENICALLY FAT ADAPTED? (“…If your blood sugar is 5.7 but your fasting insulin is under 9 μU/mL, you are insulin sensitive and likely in glucose refusal mode from a low-carb diet. …” …More)
[2] Muscle: The major fuels for muscle are glucose, fatty acids, and ketone bodies. This glycogen is readily converted into glucose 6-phosphate for use within muscle cells. Muscle, like the brain, lacks glucose 6-phosphatase, and so it does not export glucose. …More
…it does export glycogen to be converted back into glucose? Notice all three are being turned into glycogen?
[3] When an overweight or obese person on a low carb diet eats too much fat, they gain weight? Difference between a High Carb Diet and a High Fat Diet When people consume diets high in carbs it stimulates insulin to be released. In response to all the insulin, energy that is not immediately needed for activity is stored as glycogen in the liver and muscle cells, and the remainder is shipped off to our adipose cells (fat cells), to be stored as fat. When eating a high carb diet, getting excess calories into fat cells is easy, getting the fat out of fat cells, not so much. When people eat a diet high in fat and low in carbs, the fat is absorbed in the intestines as chylomicrons and is shuttled through the lymphatic system to the thoracic duct, going directly into the blood circulation. From there, the fat is either burned for energy or goes into our fat cells, to be stored. It is important to note that the fat does NOT go to the portal circulation of the liver and as a result, fat needs no help from insulin to be absorbed. That’s good, but if excess fat gets stored in fat cells, doesn’t eating fat make one fat? Not for lean people, because lean people are leptin sensitive and obese people are leptin resistant. When overweight or obese people eat excess fat, it is a different matter. …More
Question: There is a difference between therapeutically eating more fat than just simply being a case of “eating too much fat”? Eating more fat is a temporary thing, to help with hunger ghrelin, leptin hunger signaling when restricting carbohydrates or fasting?
It sounds like what you’re doing is working
Are you asking to better understand the mechanics of how your body is working?
@atomicspacebunny, these are really interesting links, and one study in particular, the FASTER study, was a very thorough and ground breaking study of long time fat adapted athletes that demonstrated how we burn almost twice the amount of fat per minute as previously seen in athletes eating a mixed diet. In other words, those of us who engage in a high volume of exercise (the study tested endurance athletes) and are sufficiently fat adapted, burn a greater proportion of the energy we use as fat, even at higher heart rate zones which are typically glycolytic. I think maybe my question wasn’t exactly worded the way I’d intended since I’m hearing people respond more to their concern that they think I’m hungry and not eating when I feel hunger- which is not the case, I definitely eat when I’m hungry- but I’m looking at this from the angle of: Rather than those stupid calorie calculators that tell you how how many calories to eat, how do I gauge the amount of FAT my body uses on an average day?? I mean, this is pure curiosity, like I said I refuse to measure or weigh anything I’m eating, but I’m just very curious to know, based on something like the FASTER study, if I can peek into my body somehow and see where the fuel I eat goes and how it’s utilized.
Along those lines, maybe Dave Feldman’s model, where eating fat lowers LDL cholesterol and fasting raises it, it should be safe to assume your body deals with fat-in fat-out by regulating blood lipids as a labile pool. This is just his hypothesis, but am fairly convinced of it, despite the lack of direct evidence. Yet.
So, given the extremes of cholesterol manipulation, 24 hours is a relatively short span compared to the 3 day turnaround in lab tests.
If your body fat is constant, then your metabolic rate = your energy intake. You may be superficially cycling fat in your body (like a tank of fuel), but it’s in balance.
The protein feeds the amino acid Nitrogen urea cycle. You lose X protein every day through catabolism and your body replenishes it with food protein sources. If lean mass is constant, then you’re in balance there.
The fat feeds your energy metabolism, so you consume Y fat and use the same if your fat mass is constant. That may pass through your endogenous fat stores if you’re fasting for too long, but if you return to the same fat mass, then it’s in equilibrium.
Without measuring RMR, lean mass and fat mass - it’s all subjective based on what you think your macros are… unless you measure.
Per my own testing and comparison. Yes, there can be a huge difference in accuracy vs a DEXA
See my post “ DXA Scan vs InBody 270”
You can link it here if you want
Didn’t want to hijack your post 
Depending on availability and cost for you
I say you go for the “ combo deal “
Up size 
DEXA + RMR
locally for me it’s $75+$45
Good Luck
Good deal. It’s $75+$75 for me!
Still worth it to know what you are working with
i measure myself with caliper. there are different ways to do it, but they all are very close! some need a second person, but not worth it.
the only thing you could say now: i am totally wrong! well, i am not a professional bodybuilder, so i dont care!
its just a number, at least mine is analog, not digital 
I can’t use the calipers properly. Maybe it’s because I have too much loose skin?
@Tmdlkwd I should specify that I know the InBody isn’t as accurate as a DEXA but it is helpful for giving a general range- I have calibrated the InBody against my body fat scale at home (also bioelectrical impedance) and it is pretty close- what matters for me as a personal trainer is trends for my clients- I can see if they are trending downward in body fat % and gaining lean body mass. But I know I am in the range of 9 to 12% as I consistently get those readings- whatever the case, even if I were actually 14% I’m still very lean
I understand
What about looking in to getting an RMR Scan?
Just a suggestion
Fun, geeky stuff…for me at least.
Besides the cost of the scan , you will get s beautiful info printout😄
Why get an RMR test?
YMMV
An RMR test answers the question,
How much should you eat?
Your RMR is your body’s baseline caloric requirement. Knowing your RMR enables you to:
- Set accurate individualized calorie targets to help you lose, gain, or maintain your weight
- Verify if a training or nutrition program has increased or decreased your metabolism
- Compare the speed of your metabolism to others of your gender, age, height and weight