When somebody loses weight, where does the fat go?

[Kisito]

http://www.bmj.com/content/349/bmj.g7257

 

[mkrnhr]

Hi Kisito,
Can you summarize the article?

 

[Mikey]

Here's the gist:

When somebody loses 10 kg of fat (triglyceride), 8.4 kg is exhaled as CO2. The remainder of the 28 kg total of CO2 produced is contributed by inhaled oxygen. Lungs are therefore the primary excretory organ for weight loss. (This calculation ignores fat that may be excreted as ketone bodies under particular (patho)physiological conditions or minor amounts of lean body mass, the nitrogen in which may be excreted as urea)

 

[monotonic]

How would deep breathing and the change in VQ ratio on a ketogenic diet affect the CO2 coming out from the lungs?

 

[herondancer]

Thanks for posting this interesting bit of information. A little science for the metabolism geeks, but not so much as to intimidate the casual reader. Nice graphic too. Here's the conclusion:

Our calculations show that the lungs are the primary excretory organ for fat. Losing weight requires unlocking the carbon stored in fat cells, thus reinforcing that often heard refrain of “eat less, move more.” We recommend these concepts be included in secondary school science curriculums and university biochemistry courses to correct widespread misconceptions about weight loss.

However, it still reinforces the idea that a calorie is a calorie, without taking into account the ways in which human metabolism can be modified, or that different fuels, carbs vs fats, give different results. The body won't really mobilize fat stores until carbs are drastically reduced in the diet. The body has to deal with the sugars they become as a priority, and won't get around to the triglycerides until they are gotten out of the way. Standard diets never get to that point.

 

[trendsetter37]

Thanks for posting this interesting bit of information. A little science for the metabolism geeks, but not so much as to intimidate the casual reader. Nice graphic too. Here's the conclusion:

Our calculations show that the lungs are the primary excretory organ for fat. Losing weight requires unlocking the carbon stored in fat cells, thus reinforcing that often heard refrain of “eat less, move more.” We recommend these concepts be included in secondary school science curriculums and university biochemistry courses to correct widespread misconceptions about weight loss.

However, it still reinforces the idea that a calorie is a calorie, without taking into account the ways in which human metabolism can be modified, or that different fuels, carbs vs fats, give different results. The body won't really mobilize fat stores until carbs are drastically reduced in the diet. The body has to deal with the sugars they become as a priority, and won't get around to the triglycerides until they are gotten out of the way. Standard diets never get to that point.

This thought crossed my mind as I read this as well. The mechanism is interesting but one thing they don't mention is that you will not be able to unlock those fat stores if your insulin is perpetually high from high carb consumption. Also I guess this could be another explanation as to why going keto sometimes increases the need to relieve yourself. Could losing water weight be attributed to this theory in some form or fashion?

 

[Carl]

This thought crossed my mind as I read this as well. The mechanism is interesting but one thing they don't mention is that you will not be able to unlock those fat stores if your insulin is perpetually high from high carb consumption. Also I guess this could be another explanation as to why going keto sometimes increases the need to relieve yourself. Could losing water weight be attributed to this theory in some form or fashion?

True that keto helps tremendously, but it's not that simple and I wouldn't be so categoric. A whole lot of the keto weight loss is water weight yes. So much so that I can lose or gain 3kgs just by swapping from paleo to keto or vice versa.

Some people can also lose fat just fine without going keto, and conventional diets do work (if only temporarily). Based on a lot of reading, anecdotes and self experimentation I would guess that the biggest thing that affects weight loss, gain, and body fat levels are hormones. Changing calories or macro-nutrients seems to be just a way to force the hormones into doing what you want. That's why someone can take kinds of steroids or other hormones/drugs and either become leaner or bigger without stepping foot in a gym or altering their diet.
Keto is great for the insulin lowering effect but the weight loss seems to 'run out of steam' eventually. This is helped by a few re-feeds of higher protein or carbs.