How Does Fat Get Converted Into Energy
  • tomlevine1tomlevine1
    Posts: 501
    This is perhaps a little on the 'nerdy' side of questions, but is something I don't quite understand.  It's not really necessary to fully understand it, to follow a 'whole foods' diet, or an 'ssos' lifestyle, but still, I would like to get my head around it. So in that regard...

    I understand that carbohydrates are converted into glucose, which is then used as energy in the body, and whatever energy the body does not use, it then moves into the adipose tissue, with the help of our friendly hormone called insulin.

    I understand that protein gets converted into amino acids, that the body then uses to restore, rebuild, and construct muscle tissue, along with other healthy  tissues throughout the body.  Whatever protein is not used for amino acids, is then moved into the liver, where it is converted into glucose, and at that point, the body can then use this glucose for energy.  Just like our buddy, carbohydrate up above, whatever glucose (that originated from protein) that is not used for energy, can then be shuffled on over to the adipose (fat) tissue, with the help of insulin, where it is stored as body fat.

    Now, with Fat, this is where things get a little confusing, because my understanding, is that fat molecules can not be converted into glucose.  In fact, step 1 on this journey, is that fat is utilized by the body, for fatty acids, which are required and needed for proper metabolism and biology.  Whatever fat is not used for fatty acids, is then converted to triglycerides (do I got that right?), and moves on over to our adipose tissue, where it is stored as body fat.

    So, with that in mind, how does the body convert fat into energy, if it does not convert fat into glucose?  Let me give you an example;  Let's say we have a person who chooses to eat a 100% all fat diet, no protein, and no carbs (not recommending...).  So, if fat is the only food ingested, and dietary fat cannot be converted into glucose, where would this person be getting his energy from?  What if he at 10,000 calories of fat on a given day, well in excess of his caloric needs (I'm not suggesting we count calories, just making an extreme example)...The body would use some of the fat as fatty acids, and then what?  He has no carbs, he has no protein, for glucose?  Does the body reach into the adipose tissue, to generate his energy needs in this example?  If so, what happens with the dietary fat he is eating?  Does it all gets stored as adipose tissue?  Is the adipose tissue sort of an in/out process, where it is giving up glucose for the body, while taking in fat from the diet at the same time?  So, how would this persons body generate glucose?  Does the body store All his fat, or, does the body have some way of removing some of his dietary fat from its' digestive system as waste?

    How does fat get converted into energy?

    Anyone that can answer the question, gets 3 gold stars!  

    Thanks, t
  • JGBJGB
    Posts: 23
    The real problem under the all fat diet is a the complete lack of nitrogen. All amino acids have nitrogen in their structure and they are the only source of nitrogen in a form that can be used to make amino acids (which make up protein). I'll try and shoot for a mid level of detail on the other part about fat metabolism.

    When Glucose is turned into energy by the cell, there are two portions to the process. This is true for any carbohydrate, they just go through a couple of steps to enter the same overall process first. This first stage only makes a little bit of energy, but (when oxygen is present) ends up making a molecule called Acetyl-CoA. This is then fed to the mitochondria in your cells which metabolize it like crazy and make a lot of energy. Fat as it is broken down gets turned straight into acetyl-CoA. It is not possible to run the first process backwards to get sugar out directly. Alternative pathways exist to make things called ketones that can be burned somewhat like sugar in the brain, and as long as there is enough amino acids present the sugar that is needed for cell structures (many proteins have sugars attached to them for a variety of reasons) can be manufactured in less direct ways. As Jon points out this is much less energy efficient than just having the sugar already on hand. A reality that shows up in plants too, I was watching a video from Prof Ford Dennison and he mentioned data showing how at least part of the increase in food yields can be explained by higher carbohydrate content and lower protein content which costs a plant twice as much photosynthetic energy.
  • JGBJGB
    Posts: 23
    PS I typed that kind of fast, so let me know and I can try to add or subtract info.
  • DrCathyDrCathy
    Posts: 1,178
    I like this particular explanation:  not too technical; not oversimplified so much as to miss the point:

    image
  • tomlevine1tomlevine1
    Posts: 501
    Hurray for really, really smart people!!!

    Very generous response, thank you.  (Gold stars are at the bottom of the post).

    @DrCathy, REALLY informative link, THANK YOU!  I will be going back to it again and again.  To try to distill it down, so, here again, we have a very good example of how biology is not math, it's biology.  My previous idea of fat digestion was over-simplifying things.  While I don't fully comprehend all of this, it looks like dietary fat (lipids) are digested and absorbed, and then converted into "lipoproteins", which then move on to a variety of functions within the body, including storage in adipose tissue, and oxidization for energy, but also excretion as waste, and conversion to brain and nerve tissue.  

    So, to look at my unrealistic example of a guy eating 10k grams of all fat, and how his body might metabolize it, I think @JGB might be alluding to the answer, "not very well..."  

    Perhaps what is most interesting to me, from the perspective of 'ssos', is how the body might metabolize extra fat consumed, beyond what it might need as fatty acids, since we aren't really quantifying the consumption of fats in 'ssos', as I understand it.  By comparison, with NSF, we quantify 10+, and with protein, we sort of quantify that a little bit, such as saying 200grams plus, or 1 gram per pound of weight, etc.  But with fats, within  'ssos', we are eating as much 'as to satisfy', but only after good food syntax, such as eating our NSF and 30grams of protein plus, first.  

    Perhaps, a simplified answer, is to suggest that assuming we have an unclogged sink (back to ssos metaphor), we won't  consume more fats than are needed, and the reason why we won't, is because our bodies won't allow us to...With a well-balanced, hormonally unclogged metabolism, our bodies, with the help of hormones, will stop us from over-eating, and keeping ourselves full of NSF and protein, prevents the need for us to over consume fats alone, or in egregious amounts.  Is that fair to say?


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  • llilli
    Posts: 218
    So, I'm trying to interpret that chart and maybe am being overtly obvious lol...but we want less lipogenesis and more of its converse (lipolysis)..either by reducing the process in the chain where acetyl Co A induces lipogenesis or stimulating its opposite (lipolysis), or both.

    Aside from that, for someone like myself who has little understanding of this biological system, I guess it could raise questions. Someone might take a look at the chart and say well..a calorie is a calorie because it all ends up as acetyl Co A which then in turn feeds lipogenesis (fat storage );and the citric acid cycle. Or a calorie is a calorie because it all ends up in the citric acid cycle..But maybe this is just one factor in a system that deals with fat storage and usage. I guess thats where calorie quality (SANEity) comes into play.

    Anyway, interesting and thought provoking even with my limited understanding..
  • DrCathyDrCathy
    Posts: 1,178
    The chart is not meant to be separate from the article cited.  Read that if you're interested in the topic. 

    The key concept is that all of those arrows go at different speeds in different directions depending on a bunch of factors.  Blood glucose, insulin, adiponectin, letpin, grehlin, growth hormone, cortisol,  testosterone, cholecystikinin, peptide Y, somatostatin, motilin, etc, etc, etc.  

    The kinds of foods we eat, and the exercise we do --  drive those hormones in various directions that will either cause overall fat lost or gain.  SANE eating and eccentric exercise will push the cycle in the direction of fat loss.