Body fat content before diet or exercise intervention influence how much muscle or fat you'll lose

Gilbert  B. Forbes has already shown, in the 1980s, that there is an interesting relationship between lean body mass and body fat.  This relationship (albeit adapted from the original publication) is, to this day, still being used in mathematical models that describe the dynamics of weight loss.

Gilbert Forbes highlighted some elegant anthropometric relationships - I just want to quickly point one out.  Gilbert Forbes showed that the amount of body fat that you have before starting with a diet will greatly influence how much fat and lean body mass you will lose during that diet - more specifically the ratio of fat to lean body mass loss.  If you look at the top right data point of the graph below you can see that those individuals described by that specific data point  has about 70 kg body fat and 60 kg lean body mass.  These highly obese individuals when losing weight (move from the top right datapoint along the curve to the left) will lose a substantial amount of fat without losing a lot of lean body mass.  In contrast, if an individual with, say 20 kg fat and 40 kg lean body mass will, with the loss of fat, also lose lots of lean body mass.  This is probably one of the main reasons why it is so difficult to lose that last bit of stubborn fat!  It just shows that a residual amount of fat in one's body is extremely important - so much so, that the body will rather sacrifice muscle than lose that last bit of fat.  Another interesting thing to note is that the function describing this lean body mass and fat relationship is a semi-logarithmic function.

The plot depicted above, copied from the article "Body fat Content Influences the Body Composition Response to Nutrition and Exercise" published in the Annals New York Academy of Sciences, is a plot of lean body mass against body fat content in women 156-170 cm tall.  The women were grouped according to body fat content.  The Semi-log insert plot is of the same data.

Now you may ask, does this mean that, if I have an initial fat percentage of, say, 30% and a weight of 100 kg (220 lbs), I will follow a predetermined loss of lean body mass and fat that can be described by a mathematical function when going on a diet?  Do the magnitude of my caloric restriction and the composition of my food not influence the ratio of lean body mass and fat loss?  What about exercise? I will answer these questions in future posts by discussing some more interesting findings by Gilbert Forbes as well as other scientists.

Calorie intake vs. calorie expenditure

Ever since I can remember I have been struggling with my weight (understatement of the year).  I have read many books on the subject and I even got a PhD in Biochemistry.  I have read thousands of journal articles but here I am, fat yet again.  You see, I don't have a big problem with losing weight but I struggle to keep it off.  For me the recipe for weight loss has always been simple.  Eat less calories than what I expend (read: starve myself) and exercise to increase my calorie expenditure (read: 45 minute jogs every single day).

No wonder the following graph (linked from http://www.hussmanfitness.org which is a good source of information on fitness and diet) has, for so many years, been an extremely valuable reference point in my arsenal of information on weight loss.  This is also why I decided to include it in the first post of this blog.

You can see from this graph that losing weight is actually quite simple.  John Hussman shows without a doubt that your cumulative fat loss will follow the same trend as your caloric deficit does.  The reason he divides his cumulative caloric deficit by 3500 is because it takes about 3500 calories to lose one pound of fat (one pound = 450 grams.  There's about 8 calories in every gram of fat.  Thus, 450 * 8 = 3600 calories).  This all makes sense, this is basic thermodynamics, right?

However, I occasionally stumble upon articles such as those from Richard Feinman the biochemist (not Richard Feynman the physicist) who is credited for doing the first serious research on the Atkins diet.  His work states that a calorie is not a calorie and that the macronutrient ratio of the food you eat is extremely important for weight loss.  Some of the studies he's been involved with, which I will discuss in future posts, are listed below:

"A calorie is a calorie violates the second law of thermodynamics" in the Nutrition Journal (http://www.nutritionj.com/content/3/1/9)

"Thermodynamics of weight loss diets" in Nurition & Metabolism

(http://www.nutritionandmetabolism.com/content/1/1/15)

This is just basic thermodynamics again!  As a biochemist I tend to side with Richard Feinman.  Biochemical pathways are complex and, depending on the macronutrient ratio of the food you stuff in your mouth, the fluxes through these biochemical pathways will cause the energy to be extracted from your food in a slightly different way (I even think John Hussman will agree as he isn't saying that you should stuff yourself with whatever you like, but just make sure you limit yourself to a specific amount of calories).

The study of human nutrition and weight loss are slowly moving into the quantitative realm where, at long last, computational models exist that can even predict the ratio of fat loss and muscle loss of an individual on a specific diet.  New studies even show that the levels of two peptide hormones at the beginning of one's diet, ghrelin and leptin, can be used to predict whether someone will keep the pounds off (yes, I know this is discouraging)!  I will also make an attemp to discuss all these studies in future posts.

However, even though I am a quantitative scientist and everything that Richard Feinman et al. says makes sense to me, I cannot help but remember the picture that John posted on his website many many years ago where he illustrates how fat loss follows cumulative caloric deficit.  Each time I have overly complex ideas about weight loss and nutrition I tend to revert back to that picture.  It makes me feel better as it says the solution might be simple and elegant.

And it does work for me!  But here I am, fat yet again.  Is it inevitable that I will always put the weight back on? I mean, in a sense we are just machines governed by our bodily chemistry.  And don't go tell me that, because you could do it, I can too.  People are different.