Of Microscopes and Myopic Hypotheses
Surely somewhere somehow in your life you've used a microscope. If this was in grade school, perhaps the teacher set it up for you, but most do not escape high school or college, even as non-science types, without using one at some point. Here is your basic microscope you might encounter in a biology or forensic chemistry lab or such.
The light shines up from the bottom, through your sample, up through the objective lens that magnifies the image and through the eye tube to your eye. The eyepiece usually adds additional magnification (10X). A choice of three objective lenses that can be "dialed in" is quite common. Note the different lengths of these. The shortest lens is the lowest magnification lens and is often called the low power objective. As lens length increases so does the magnifying power of the lens. The technique for using the microscope is pretty universal and begins with something that sounds rather silly: Finding your sample when you look through your microscope! If there's dust on the lens or the stage, etc., depending on what you're looking for, you might find yourself looking at something other than your sample. Dumb as that sounds, it's far more common than you might think, especially if what you're looking at is a hair or a fiber to begin with! The focus knobs work to adjust the vertical height between the sample and the objective lens -- this is called the working distance -- within the range of heights you see your sample, outside that range you basically see nothing. The working distance is the longest for the low power objective and can be very small indeed for the higher power objective (which, incidentally, tends to be the most expensive and delicate of the objectives)
And so, good practice is always to use the lowest power objective first. For one thing it will allow you to "find" you sample most rapidly, but it will also reduce the risk of damaging/contaminating the lens and/or your sample by bottoming the lens out onto your sample. The lowest magnification is also the most forgiving one. Unless your microscope is totally out of whack from the last user, your chances of seeing at least something of your sample on first peek is generally pretty good. But if not, you would use the coarse focus knob and without too much trouble you locate your sample and adjust the fine focus to see a clear image. At this point you are looking at a circular area of your sample. This may appear to be a large circle to you, but the actual area on the sample will be rather small. We call this the field of view. You are only viewing a small portion of your sample, even at this low magnification. Generally the image at this point is of insufficient magnification to see the detail you are ultimately after. So, now you would rotate the next higher power objective into place, then you may require a little coarse adjust, but the fine focus might do the trick to clarify this more magnified image. When you increase the magnification you are decreasing, dramatically, the size of your field of view. And if you proceed to the highest power objective the field of view gets even smaller still.
Now, let's say you have a smear of cells from a biopsy and you get cocky and decide you're just going to get the thing into focus at the diagnostic magnification (whatever is required to distinguish cancer cells). You are looking at a teeny part of the whole sample. Even if you scan back and forth and side to side (more advanced microscopes have knobs that move the stage in these directions for just this purpose), you are so focused in you can easily miss something. If you're following proper procedures, on the other hand, you get the sample into focus on low mag and scan the full sample to look for areas of interest. Once the entire sample is assessed for "areas of interest", you zoom in on each one to see what's really going on there.
Hence both the low power and the eventual diagnostic power objectives serve a purpose. The low power objective is good for seeing the full picture -- not missing any cancer cells in our analogy -- but it is useless for anything more than identifying where there might be a problem. The diagnostic (higher) power objective is instrumental for viewing a small area in detail sufficient to find tell-tale signs of cancer cells, but it would be rather useless for scanning the entire sample, and you would be far more likely to miss something by trying.
Where am I going with this? Well, to this whole discussion of "fat tissue regulation". Gary Taubes wants to look at a close-up of fat tissue metabolism -- that is only at the cycling of the triglyceride/fatty acid cycle within or in and out of the fat cell -- and extrapolate the regulatory events in play there to be representative of overall regulation of fat tissue in the body. So far, he's gotten away with it in certain circles. But Taubes is using a high power lens, and thus he doesn't see what goes on elsewhere, and he doesn't want you to see it either. To do so would mean having to discuss what is out of his myopic field of view. Now it's nice to know the biochemistry of the TAG/FA cycle and how it is regulated within the fat cells themselves, but this is not by any means the right way to go about looking at the overall regulation of fat tissue mass in the body as a whole. For that we need the low power lens to find the "interesting" phenomena going on throughout the body in conjunction with several high power images.
Just a small case in point, let's look at the diagram on p. 149 of my ebook version of WWGF:
And let's compare that even to the depiction in the 2003 Reshef et.al. article referenced in GCBC.
So the image in WWGF ignores the liver. What else does this ignore? Dietary triglycerides. The relatively huge loads delivered by chylomicrons a couple hours or so after a meal -- whether or not carbohydrates are ingested. Look at the diagram at right. It's a bit blurry, but the green in the bars on the bottom is triglyceride content of the various lipoprotein particles. Chylomicrons have a higher percent triglyceride content. The balls indicate the relative sizes of lipoproteins. The chylo is more than 3X the diameter of a VLDL particle, the main conveyor of triglycerides produced in the liver. The volume of a sphere is V = (1/6)πd3. Therefore a typical chylo delivers over 30X the fatty acids in the form of triglycerides to the adipose tissue if the trig content by percent is equivalent for all particles. But the delivery load is even greater still given the higher proportion of triglycerides in chylo vs. VLDL.
In WWGF, Taubes reiterates a common statement of his:
... anything that works to promote the flow of fatty acids into your fat cells, where they can be bundled together into triglycerides, works to store fat, to make you fatter. Anything that works to break down those triglycerides into their component fatty acids so that the fatty acids can escape from the fat cells works to make you leaner.
He wants you to look through his "cool and learned" high power objective lens to see the truth, and yet he focuses his microscope on only the part he wants you to see. But it is interesting that we are guided to stop thinking (rightly) of the fat cells as passive depots for fatty acids, but rather as metabolically active entities. And yet, we are equally encouraged to largely ignore the all of the hormones (of which leptin and ASP are but two) secreted by the adipocytes themselves. The very active behavior observed that has elevated adipose tissue the level of endocrine organ.
There is little doubt that Taubes has the part about the triglyceride/fatty acid cycle at the zoomed in level of the fat cell correct. Insulin is the primary regulator of this continual cycle and the balance of it in the post-absorptive state -- that is some hours after a meal through the fasted state until the next one. At that time, the balance is regulated by basal insulin levels to ensure adequate fatty acid supplies to meet energy needs. But this is the big picture of a small part of whole picture. But its like focusing in on a high power image of a biopsy tissue sample, seeing no cancer cells and declaring an "all clear". How about that cell over there, out of the field of view?
In my next post I'll address the whole picture. The regulation of total fat tissue levels is a much more complicated thing than the myopic focus on just the triglyceride/fatty acid cycle.