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People who are overweight and wish to lose weight, often do so because they are concerned about looking too big. Their increased size is attributed to an increased volume of fat.

When people try to lose weight however, they often quantify their goals in terms of weight, not volume.

So my question is, is the volume of an adipocyte cell always directly proportional to the weight of the fat stored within the cell?

If not, what factors would increase/decrease the size of the adipocyte cell for a given mass of stored fat?

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3 Answers 3

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Chris asked, "what factors would increase/decrease the size of the adipocyte cell for a given mass of stored fat?"

For an obese person, subcutaneous and visceral fat is composed of 40% immune cells, while that number is ~10% in lean individuals. There is much interplay between adipocytes and immune cells via adipokines and cytokines. Examples include ADIPOQ (adiponectin) and IL1 (interleukin 1). Thus, agents that reduce the inflammation state of the adipose tissue are also likely to have an effect on adipocyte size. This nonetheless is secondary to diet and diet composition as an adipocyte is nearly all lipid droplet and that lipid droplet stores fat - either from the diet directly or converted into fatty acid from simple carbohydrates in the diet.

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Thanks, interesting points made! –  Mew Oct 3 '12 at 21:46
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Is the volume of an adipocyte proportional to the mass of fat that it stores?

The answer is: yes.

Since fat is stored in a lipid droplet within the adipocyte, it is already in the densest form possible. In other words there is no way to make the stored fat more compact, so that a given mass of stored fat takes up less volume.

Response to comment from Chris:

I think you are perhaps being a little pedantic here. Anyway the graph below conveys my view, together with your refinement. So yes, adipocyte volume changes in proportion to mass of fat stored. (The line on my graph should be at 45 degrees, but I drew it by hand so it may be a little out.) There is no way to escape the increase in volume when fat is stored.

enter image description here

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Adipocyte volume isn't directly proportional to adipocyte fat content. Because this would mean 0 fat = 0 volume. But even with no fat, adipose cells still exist and occupy volume. Are you however suggesting the change in adipocyte volume is proportional to the change in fat stored within? –  Mew Oct 3 '12 at 0:31
    
Thanks for your modified answer. –  Mew Oct 3 '12 at 21:48
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Adipocytes (fat cells) change in size quite a bit with nutrient and particularly fat uptake.

Take a look at this paper which is about identifying adipocyte sizes from histological slides.

figure 1 shows how the rat fat cells were swollen after a high fat diet. In the cross section they are sometimes 10+ times larger. When you add depth to the equation there is quite a bit of range in the fat cell must be substantial.

On the other hand, white fat cells do multiply and it is thought that when fat cells are engorged, they secrete growth factors that encourage adipocyte division.

So its not just the adipocytes getting larger, but there are also more fat cells over time if there is extra fat storage needed.

Its particularly of note that Insulin like growth factor 1 (IGF-1) is one of the factors identified that signals adipocytes to divide, coupling fat tissue multiplication with metabolic factors just as you might expect, possibly participating in the development of insulin resistance as the tissue expands.

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Very interesting! –  Mew Oct 3 '12 at 21:49
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