Food Fat vs Human Fat

When we measure human fat, we measure fat cells. When we measure fat in foods, we measure the fatty acids.

How efficient is the storage of fat molecules in the fat cell? Is the fat in a solution? Do fat cells also have to absorb some solvent molecules for each fat molecule? If there is a solvent, what is it? I know that fats are not soluble in water.

I don’t think that’s exatly right Zot. The only two ways I’ve ever heard of measuring human fat on living peoples are the pinch test and the density test. The pinch test measures the total volume of fat in the target area and the density test works on the fact that lipids (fats and oils) are less dense than virtually any other tissue. Fat cells swell when they are holding large amounts of fat and shrink when the fat is utilised therefore the pinch test and the density test measure total lipid volume not the number of fat cells. You can have near zero body fat and exactly the same number of cells. They’re just empty.

As for storage efficiency I’m not sure what you mean by efficiency. Fats are used for energy storage because they are water insoluble and as such don’t cause osmotic problems. If you tried to store energy as suger you’d either bloat up with water or the cells storing the sugar would cease to function properly beacuse of dehydration. Plants do store energy as starch, but this is beacuse to most plants bloating with watre isn’t a bad thing. The fat in cells isn’t in what you would normally call a solution, although the cells obviously contain water. IIRC the fat exists as triglycerides mainly, which are basically three fatty acids pinned together.
The primary solvents the body uses for fat are the bile salts used as detregents in the gut to break the fat up. Once it’s broken up it passes through the cells of the gut lining fairly easily becasue the cell membranes themselves are mostly lipid. After this it enters the bloodstream until it is absorbed by various cells including fat cells.

I’m not sure I understand this statement. In both humans and mammals, the term fat is really just a convenient way of saying triglyceride or, nowadays, triacylglycerol.

Fatty acids refer to one component of the triglyceride molecule - there are three fatty acids plus one glycerol in every triglyceride molecule. The particular fatty acids used to join with the glycerol vary. Depending on your diet, the fatty acid can be saturated (eg. palmitic acid), monounsaturated (eg. oleic acid), or polyunsaturated (eg. linoleic acid).

BTW, fatty acids are also what are used to join to cholesterol to get the latter into cells. Depending on the type of fatty acid used, eg. saturated vs. unsaturated, there are major differences in cholesterol metabolism.

Very efficient! Evolution is on our side. In fact, by making it hard for sugar to get into muscles (insulin resistance and/or “thrifty genotype”) there is a profound secondary effect that causes even more fat to get into fat cells.

Fat in fat cells is simply triglyceride. Not in solution AFAIK. It got delivered to the fat cells on particles called lipoproteins, and gets into the fat cells via the action of insulin.

Wanna know more?

Thanks KarlGauss and Gaspode. You answered my question.

This may clarify what I was asking:

When you do the pinch test, you are measuring the volume of fat cells. It is only equivalent to measuring the volume of triglyceride, if fat cells are mainly triglyceride. If fat cell function required that the triglyceride remain in a solution that was 50% substance X by volume, then the pinch test is measuring the volume of a triglyceride/substance X solution rather than close-to-pure triglyceride.

The way I was using the term efficiency, I would consider the storage solution that requiring substance X to be half as efficient as storing close-to-pure triglyceride.

Gaspode, Thanks also for explaining the advantage of storing energy as fat rather than sugar.

You’ve satisfied my curiosity. However, if there is anything else you think worth posting, feel free to continue to use this thread. It’s my first. I would love it to go on and on and on…