How does the body burn fat?

I’ve been fasting now for a few days (nothing but water thus far). I would assume that by now I must be in ketosis, so I should be using fat reserves for energy, by my simplistic understanding.

How does that work? Is it fundamentally different than, say, eating a spoonful of lard? Or do the same processes come into play either way?

Your body is using fats *and *muscle for energy during your fast, which is one of several reasons why fasting is not a great weight loss strategy.

The biochemistry of using fat stores during fasting is not the same as using dietary fat when in normal energy balance. When fasting or avoiding carbs, your body uses ketogensis to make glucose from fatty acids, something it doesn’t have to do when you’re eating (carbs).

Mine doesn’t. :frowning:

FWIW, I’ve been restricting carbohydrates to between 40 and 60 g per day since mid-March. For a while, I was walking 3.4 miles per day, five days a week, or else doing physical labour for a couple of hours. (I’ve been lazy for the past several weeks.) I’ve also reduced portion sizes. I’ve lost over 60 pounds.

I’m going to ask for a cite on that. Here’s a link https://idmprogram.com/fasting-and-muscle-mass-fasting-part-14/ to a graph showing carbohydrate, protein, and fat oxidation during fasting. Protein oxidation drops off pretty rapidly. Sure, your body burns fat, that’s what the fat is there for, for energy storage.

Well your body is using fats and muscle for energy during all weight loss. Not sure that there is any quality data that one method or another results in more from one or the other compartment end of day of a complete weight loss program. My WAG is that bigger controller of the body composition impact is the amount and sort of exercise done during the program. If time allows later I’ll try to search some …

Not sure I am understanding the question of the op though.

Digesting fat breaks into into glycerols and fatty acids which get absorbed and transported to cells which use them, for energy (via oxidation in muscles mainly), for synthesis (such as in the liver), so on. They travel in certain packages.

Metabolizing fat also produces glycerols and fatty acids which get transported to cells which use them … which also travel in certain packages.

The process of breaking down the fat that occurs digestively uses lipases that are secreted into the the intestine. Likewise mobilizing fat stores starts with lipase and that cellular lipase activity level is the rate controlling step.

Is that what the op was asking about?

Resistance exercise is definitely the primary determinant of the proportion of weight loss from muscle or fat. We have good data on that.

My claim above was that fasting, as compared to simply having a small but sustainable energy deficit, leads to proportionally more muscle loss for any given amount of weight loss.

This is absolutely true. What also important, in terms of muscle sparing, is to combine that sustainable deficit in energy with an increased protein consumption. This is the ideal way to lose weight while preserving muscle mass. It’s how bodybuilders do it.

I spent a week in the hospital recently. No food for 6 days straight. I think I lost 6#. I have lost 30# since August, both by watching my diet and having stomach issues. I feel like I have lost a lot of muscle. My neck and shoulders seem to have gotten a lot smaller, not so much my stomach but it did shrink some.

Well actual fasting is clearly not sustainable, and adequate protein is of course required to preserve muscle and well to live, but making it a more realistic we can look at very low calorie diets (VLCD) that are protein sparing.

This one for example compared diets ranging from 800 down to 420 kCal/d with no differences at the end in body composition (or weight loss).

I can’t find a good meta-analysis or even study comparing longer term body composition changes differences between VLCD and other diets … but long term they clearly do not result in great weight loss even if the initial phase is faster.

No idea why our op is fasting but not a great long term plan!

If the OP wants to know if he’s in ketosis, KetoStix or a similar test strip are available at just about any pharmacy, and only require a urine specimen to test.

Sorry for not returning!

The fasting was not really intentional, just a result of some pretty major stress I’m facing right now.

What prompted the question might be a bit TMI…

I suddenly started having bowel movements that were very reminiscent of what I would face after eating, say, a big order of greasy food (I have no gallbladder). So I was curious if there might be any link, like if fat is moved from storage and then sort of runs through the normal digestive processes, or if there was something entirely different going on.

Tangentially, I wonder if a medium-term ketogenic diet might help with fatty liver disease. I will have to dig (and ask my doctor, of course) but does anybody have any ideas on that?

https://www.cell.com/cell-metabolism/fulltext/S1550-4131(18)30054-8

It sure can. But why would you try it medium term? Do you want your NAFLD to come back after a while?

FWIW here are what I think are the most recent guidelines and that article Bill Door says less than I think you think it does. “Can” for sure. Does? Bottom line is that current evidence is not enough to state that it does better over any clinically meaningful time period than any other mean of losing fat mass.

If anything the Mediterranean Diet has the most evidence as the best for this specific indication.

IF that specific nutrition plan is what works best to get and keep fat off, for a specific individual both short, medium, and long term, then it is the best for that individual.

Crash diets are of potential specific harm in this context.

I certainly didn’t suggest a crash diet. In fact, I asked why he would be interested in a medium term solution for his non-alcoholic fatty liver disease. You can certainly help NAFLD with a ketogenic diet, and fasting can certainly be an important part of that, but everyone should be aware that if you eat the way you used to eat, your medical condition will return to the way it used to be. It’s not a short, or even medium term solution to the problem. Eating the standard American diet is what got him the fatty liver, why would he ever consider going back to it?

Diet compliance is 99% of diet success. There is a reason only a tiny fraction of people who lose significant weight are able to keep it off for years, and it is because eventually they start eating more calories.

If people believe keto is magic, they might comply better. But I am skeptical that very low carb diets are easier for compliance in the long run, regardless of any real or placebo effects of the difference in macros. We don’t have any good long-term studies on compliance with different diets. But I suspect that for a typical person, the best advice is still the old idea of a modest caloric deficit achieved mostly by reducing dietary fat (depending on where they are now with their macros). We know from psychology that smaller lifestyle changes are easier than big ones, all else being equal. The less something is a “diet” and the more it is just how they eat, the better.

Good point! No, I certainly don’t want that. In fact, I am now afraid of the consequences, and just want to do the right thing and get it dealt with, safely and efficiently.

Thank you all for your input!

Fasting like the op has done (not those various “intermittent fasting” plans), is likely something that would be considered “crash” by most people. YMMV.

Be that as it may, the point is that the evidence for ketogenic as better somehow for NAFLD than any other plan that produces sustained fat loss is not there, and that the current best evidence available is strongest for the Mediterranean Diet. That may change as more evidence is collected.
krondys, FWIW - Richard Parker is spot on and I think Bill Door is making somewhat the same point: “efficient” is less important here than sustainability. Speed is not of the essence; tenacity is. Ketogenic is that lifelong doable nutrition plan for some people and it is a wonderful choice for those individuals. But there is no reason to believe it is better than other approaches specifically for NAFLD.

I lost about 40 lbs 2-3 years ago and have successfully kept it off so far. The main changes I made were switching most of my lunches to either salad or soup (lots of variations in those categories, most of which have fewer calories than lunches like sandwiches or burritos), about half of my dinners to salad or soup, and the vast majority of my snacking to fruit. My breakfast almost every day is 2 fried eggs and a small glass of juice. I also altered my commute to work so that I walk about 12 thousand steps every work day.

Once I shifted my mindset to “I will eat salad or soup for almost every lunch, and half my dinners, and snack on fruit”, and to stick to my commute routine even in bad weather, it hasn’t been terribly difficult to maintain. I still eat junk food and other high-calorie foods, just not very often.

good going! Keep it up!