Is obesity caused by too many fat cells, each one of which is “normal” sized, or fat cells that are each one too fat? Yes, both. But the critical issue in trying to answer this question is measuring the size of fat cells. Then once you have the sizes and number of fat cells in a sample of fat tissue you can multiply that times the other measures of volume and weight of fat stores in the body to get the total number. Obviously this involves cutting out a piece of fat tissue.
There are chiefly 3 ways of measuring fat cells in a lump of fat and each way gets a different answer. In the first method the tissue sample is fixed in formaldehyde and embedded in paraffin and then sliced and stained to make slides and then the cells are viewed and measured and counted by looking at them under the microscope. This can be automated to some extent by computer scanning but it still requires a lot of slow human tedious looking. The second method involves digesting the sample with an enzyme, collagenase, that loosens each cell into a suspension. Those cells, which are still alive, can then also be counted under the microscope but this method has the draw back that the smaller cells don’t float apart as well and big cells are fragile and easily damaged. In the final method a sample of collagenase digested fat tissue is fixed and stained with osmium tetroxide and then that can be fed into a cell counter machine like the ones commonly used to count cells in blood samples. This method allows you to easily count more cells and so might be more representative of the actual situation but the osmium tetroxide has been shown to swell the cells by about 25%.
This month’s issue of the journal Obesity has the report of a study that simultaneously used all three of these methods on samples from 60 women who were of various sizes and shapes, but mostly on the heavy side like women are these days, aged 35 to 60 years old, who were getting a hysterectomy at Laval University Medical Center in Quebec, Canada, but were otherwise healthy and hadn’t lost or gained weight in the last year. (1) A chunk of fat tissue was taken from two spots, under the skin of the abdomen and inside around the intestines. That is subcutaneous and omental samples respectively, the two parts of the visceral fat stores generally recognized to be problem fat. They also measured distribution of body fat, cholesterol and triglycerides and insulin sensitivity in the women to see which of these standard metabolic risk factors was best correlated to the fat cell size distributions.
All three techniques did show that fat cell size average was correlated with the overall size and shape of fat in these women. Also increased average fat cell size correlated with worsening metabolic risk factors. But the tightest correlations was with the osmium fixation technique. That’s good because that’s the easiest, most automated method and can be done in batches. But it’s a problem because since this method significantly enlarges the cells, the overall number will be reduced and number estimates are also an important predictor of metabolic issues. (2)
Other interesting things were that subcutaneous fat cells were fatter than omental fat cells and the first method of fixing and staining fat counted a simple even normal distribution from small to big cells but the other two methods showed two populations in the size distribution, two peaks, a smaller one for small cells and and a bigly peak for big cells. The biologic relevance of more or less of the small cells was not teased apart in this study – they were just averaged together. It might be that small cells are baby fat cells that will later grow up to be part of the problem, so more of them is also bad. Higher average fat cell size was also accompanied with higher leptin and adiponectin levels. These two hormones, made by fat cells, are good for you because leptin signals the brain to stop eating and adiponectin has beneficial effects on fat and sugar metabolism.
So there you have way more information about measuring and counting fat cells than you can possibly cope with.
John DiTraglia M.D. is a Pediatrician in Portsmouth. He can be reached by e-mail- firstname.lastname@example.org or phone-354-6605.