I went over to my brother’s yesterday and had a “Bee Sting”. A delicious piece of cake/slice heaven filled with cream and sugar and other delightful things. I know that if I didn’t use up all the sugar then it’s possible for fat to be created. So what then? Where does the fat go once I start using it for energy?
The short answer – this article, which is a review of a fascinating video on YouTube featuring Ruben Meerman. Watch it here if you want to get the full picture – highly recommended.
First we don’t actually lose fat – we expel it. While fat does “burn” it does not transmogrify into energy – energy is a by product of the burning of fat. And obesogens and other esoteric compounds are not the cause of our obesity epidemic.
Put simply, when we eat **sugars, carbohydrates and fats the excess is stored as fat in the body through a variety of mechanisms. For carbohydrates this process is called de novo lipogenesis.
**Since writing this article I have found this statement to be misleading – see Richard Hardings comments below.
Fat is made up of fatty acids and glycerol – which are composed of the elements carbon, hydrogen and oxygen (C, H and O – see graphic below).
In order to work out where fat goes we can look at how the elements of C, H and O in fat move in the body. Check out the following diagram.
This shows us that fat in our bodies, plus the oxygen we breathe in, gives us carbon dioxide, water and energy (via some marvellous chemical reactions).
This biochemical process enables us to get up in the morning and do all the things we love to do – feed the cat, annoy our partners etc.
We can see here that carbon (C) in the fat part of the equation ends up in carbon dioxide. And how do we get rid of carbon dioxide? Basically by breathing out – if you are a walking talking human being.
(Note that there is no fat in the energy component. We measure fat in grams because it has mass. We measure energy in joules).
We know from research that when fat is oxidised (put to work in our bodies) 84% is converted and excreted as carbon dioxide via the lungs – i.e. breathing out and the rest becomes water which is eliminated mostly through your back end.
So fat (grams) is not magically burned away or disappears as energy (joules) and it is not converted into muscle and doesn’t all ooze out as sweat.
The fundamental understanding is: we get fatter because we make more fat (through eating protein, sugar, carbohydrates and fats) than we end up expelling through our breath.
And how do we increase our breathing and get rid of fat? By doing work – we take the dog for a walk, we fidget at the breakfast table, we climb up mount Fuji.
Even thinking a lot and watching television is “working”. Yes it is possible to lose weight by watching the tele – just eat very, very little. That’s tough because eating and the tele go hand in hand. It’s a marriage made in fat heaven.
Does this mean to lose weight all you have to do is breathe faster. Well, not really because standing still and breathing quickly for a long time may lead to hyperventilation so that’s not recommended.
The big conundrum is the amount of exercise one needs to do to forego the weight gain that would occur through eating say a Mars Bar (or the aforementioned Bee Sting). Apparently one has to do 25 minutes of freestyle in the pool – non stop.
Better get to the pool.
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When I responded to your comment that “when we eat sugars and carbohydrates the excess is stored as fat”, I was hoping that you may be interested in learning that this is not the case. Excess sugars and carbohydrates are stored as glycogen – not fats. Carbohydrates are not converted to fats. Irrespective of your beliefs, it simply dos not happen.
Consider what my friend, Professor Stewart Truswell, professor of Human Nutrition at University of Sydney, has to say: “In some animal species, carbohydrates in excess of requirements are converted to fat via the pathway of lipogenesis. […]. Other than in the experimental situation of gross carbohydrate overfeeding, conversion of carbohydrate to stored lipids does not occur to any appreciable extent in humans.”
Marc Hallerstein, professor of Nutritional Science at Berkeley: “Fat cannot be converted to carbohydrate in animals because animals lack the enzymes of the glyoxylate pathway, and carbohydrate is not converted to fat because of a functional block of uncertain cause.” 
He also states, “Under most dietary conditions, the two major macronutrient energy sources (CHO and fat) are therefore not interconvertible currencies; CHO and fat have independent, though interacting, economies and independent regulation.” 
A research team at University of Lausanne: “These findings challenge the common perception that conversion of CHO to fat is an important pathway for the retention of dietary energy and for the accumulation of body fat.” 
Perhaps you could explain why adding ADDING 12 slices of white bread (at 70 calories a slice) or high-fiber bread (at 50 calories a slice) to existing diet of overweight participants( a diet that resulted them in being overweight in the first place), resulted in an average weight loss of 9 kg over a period of 8 weeks. There was no change in their physical activity or exercise. 
The conclusion of the Saris paper that you reference states: “An overwhelming amount of evidence
shows that the ratio of fat to carbohydrate in the diet is the primary factor in the macronutrient composition of the diet that easily causes passive over-consumption of energy and thus leads to
weight gain. In contrast, high-carbohydrate diets seem relatively benign, regardless of the type of carbohydrate.”  I will repeat the last sentence – “high-carbohydrate diets seem relatively benign, [in regard to weight gain] regardless of the type of carbohydrate.”
It is a commonly held belief in the general population that carbohydrates are converted to fat, but that is not the way the human body works. Excess carbohydrates are not consumed are converted to glycogen. There is no dispute. Your comment that “There is a large volume of evidence for sugars and carbs to be stored as fat in the human body via the well known process called de novo lipogenesis.’ is simply unfounded as the experts above testify.
“We get fat through caloric surplus. Simple.” Incorrect because it does not take into account the much, much, much higher energy costs of digesting carbohydrates, the extraordinary complex feedback mechanisms involved in digestion and the other complexities of real-world nutrition.
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You reference the You Tube clip, The Mathematics of Weight Loss presented by Ruben Meerman. The source of this material was the paper that I referred to in my first response – that is, When somebody loses weight, where does the fat go? in the BMJ Open Access journal. Same material, same author, same errors.
Meerman is a physicist and is treating the body as a calorimeter – an apparatus for measuring the amount of heat created in a chemical reaction. He is so focused on the chemistry that he completely ignores that realities of digestion.
Carbon dioxide that we exhale is also created during oxidisation of glucose – which is why blood sugar and glycogen stores are lowest early morning. Meerman makes the fundamental mistake of assuming that the carbon dioxide we exhale is produced only from the metabolism of fats.
The energy required to digest carbohydrates is much greater than that of fats. Meerman completely ignores this reality. That is why people on a whole-food, plant-based diet have a higher body temperature than others. People on a ketogenic diet have a reduced body temperature.
Fats are oxidised in the mitochondria which involves a complex series of steps where the fatty acids are converted to acetyl CoA and then enter the tricarbonoxylic acid cycle. It is nothing like the extraordinarily simplistic equation that Meerman presents. The rate of oxidation of fatty acids varies greatly and is controlled by other feedback mechanisms (such as the Randle cycle) which Meerman does not consider.
As one comment on the the BMJ website noted, “From a physics/chemistry point of view the article might be right but it’s the most inaccurate article I have read in a long time.”
Meerman’s conclusion is, “losing weight requires unlocking the carbon stored in fat cells, thus reinforcing that often heard refrain of ‘eat less, move more’.” This advice has never been shown to be effective method for losing weight.
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If I knew this issue was going to be so confronting, I probably would not have responded. I thought you would be interested in helping to dispel the common perception that carbohydrates are converted to fats.
As I mentioned in my first response, a whole-food, plant-based diet is by far the best diet for our own health, the health of the planet and the animals that we share it with.
A whole-food, plant-based diet is high in carbohydrates, antioxidants, fibre and low in fat, saturated fat, protein. The concept of demonising fats becomes irrelevant.
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 Mann, J. & Truswell, A. S. (eds.) (2017) Essentials of Human Nutrition. Fifth Edition. London: Oxford University Press.
 Hellerstein, M. K. (2001) No common energy currency: de novo lipogenesis as the road less traveled. The American Journal of Clinical Nutrition. [Online] 74 (6), 707–708.
 Hellerstein, M. K. (1999) De novo lipogenesis in humans: metabolic and regulatory aspects. European Journal of Clinical Nutrition. 53 (1), s53–s65.
 Acheson, K. et al. (1982) Glycogen synthesis versus lipogenesis after a 500 gram carbohydrate meal in man. Metabolism. 31 (12), 1234–1240.
 Mickelsen, O. et al. (1979) Effects of a high fiber bread diet on weight loss in college-age males. The American journal of clinical nutrition. 32 (8), 1703–1709.
 Saris, W. H. (2003) Sugars, energy metabolism, and body weight control. The American Journal of Clinical Nutrition. [Online] 78 (4), 850S-857S.
 Meerman, R. & Brown, A. J. (2014) When somebody loses weight, where does the fat go? BMJ. 349 (dec16 13), g7257–g7257.
Great reply Richard. Thanks for taking the time and I urge all my readers to read it. I have done some more research and concede that that I am wrong that carbohydrates are notably converted to fat in the human body – it does happen but one would have to eat a hell of a lot of carbs. It’s quite amazing how many scientists believe this popular notion (just google it). I am making a note in my article which will correct that.
As for the video – I will let my readers decide on that. Also I have issue with your statement that the “eat less move more refrain” has never been shown to be effective method for losing weight. Anecdotally I can say that it can be. If I eat less and move more I lose weight – lickety-split and so have a lot of people I have known over the years. But of course I understand that it all depends on what you eat less of.
Hi Richard – Good to hear from you. This article was not to “justify a high fat diet” as you proclaim. Far from it. I think it helps to have people understand that fat doesn’t disappear as energy but ends up mostly as co2 in the breath – I find it fascinating. I have edited it slightly as I understand that it was a little confusing about burning/oxidising fat which you pointed out. (You say I refer to an article – I did not – you must be reading something else?)
Yes I agree with you that we do have a responsibility to get our information correct when advising people. You say “it is impossible for sugars or any carbohydrates to be converted to fat in humans. It just does not happen.”
Seriously? – I can’t believe I reading this statement. There is a large volume of evidence for sugars and carbs to be stored as fat in the human body via the well known process called de novo lipogenesis. It’s just that dietary fat is much easier to convert to fat in the body than carbohydrates. The carbs to fat conversion is very inefficient.
We get fat through caloric surplus. Simple. We need to stop demonising macronutrients. This is one of the better papers I found from the American Journal of Clinical Nutrition – https://academic.oup.com/ajcn/article/78/4/850S/4690057
I read your article, “Where Does Fat Go? The Answer May Surprise You”. Yes – the answer did surprise me.
You state, “I know that if I didn’t quickly use up all the sugar then fat is created.” James – it is impossible for sugars or any carbohydrates to be converted to fat in humans. It just does not happen.
What really happens to sugars that are not used, is that they are stored as glycogen – a carbohydrate that is stored in the liver and muscles Over 1 kg of carbohydrates can be stored as glycogen. It is physically impossible to eat that much. That is why athletes perform “carbohydrate loading”. so they can store glycogen. That is why they hit the “wall” when the glycogen stores are depleted.
You have formula with fats being oxidised to produce energy. You could create a very similar (and meaningless) formula with carbohydrates being oxidised and producing energy since they are also comprised only of carbon, hydrogen and oxygen . But I really do not see why this is relevant.
Your statement, “And fat does not burn [that is, oxidise] away and transmogrify into energy,” is simply not true based on the very argument that you present. Replace the word “burn” with “oxidise” and the statement becomes “fat oxidises and is converted into energy” which is exactly what happens and is is exactly what the formula expresses.
“Fat makes you fat.” It is not that complicated.
The article you refer to in BMJ “When somebody loses weight, where does the fat go?” is a little more over 1 page in length, contain references do not relate to the article and it is “externally peer reviewed” which really means it is not peer-reviewed at all.
As one comment for the article stated, “From a physics/chemistry point of view the article might be right but it’s the most inaccurate article I have read in a long time.”
James, I really not sure what point you are trying to make. I suspect that you wish to minimise the impact of those who advocate a low-fat diet so you can justify a high-fat diet.
The healthiest people on planet Earth with the greatest longevity are not the Okinawans or Japanese, but vegan Seventh-day Adventists who live 10-14 years longer than the average American.
The following two beautiful stories show what can really happen when we eat consciously and with compassion.
and John Robbins amazing story about The Pig Farmer at https://www.johnrobbins.info/the-pig-farmer/
If we are hoping to influence people, we have the responsibility of ensuring what we say is accurate – and helpful.
The diet that has by far the least impact on the environment is a whole-food, plant-based diet. What right do we have to separate a calf from its mother and then slit its throat for some perverse pleasure that is actually doing us harm. Consuming any dairy results in the death of young males. A whole-food, plant-based diet is by far the best diet for our own health, the health of the planet and the animals that we share it with.
If you are interested learning about health, there is a lot of information – with proper references on my website and lots of additional resources. I have had several people reversing type 2 diabetes, recover from rheumatoid arthritis and high blood pressure after reading my book (and making appropriate changes) – and it takes only days to have any effect The results can be so quick that continuing on medication can be detrimental. But most people would prefer to be unwell than change their beliefs or habits.
Colin Campbell’s The China Study and Rohan Milson’s Why Animals Aren’t Food are really good resources.
With many blessings.