The human body is made up of many types of cells that are each uniquely suited to their jobs. One such type of cell is the fat cell, a.k.a. adipocyte. Obesity is defined as excessive fat tissue in the body, as compared to lean tissue. Although fat can be stored in the liver and muscle, it is most abundantly stored in adipocytes.
How Fat Cells Work
In addition to storing calories after eating for later use between meals, fat cells manufacture chemical messengers such as leptin and adiponectin, which work to regulate weight and appetite on a long-term basis. On a day-to-day basis, calories are continually flowing in and out of fat cells based on signals from the blood as calories are taken in and expended.
Storing Calories as Fat
When you eat more calories than you burn, those calories are stored in your fat cells, as fat. This calorie saving takes place after meals and is one way the body manages calories eaten at meals to be used between meals. With a conventional bank account, the ideal is to grow and build your savings and maintain a positive balance. If you do a good job at this, you become rich. On the same principle, if you build your fat account, you gain weight and may eventually become overweight or obese.
Withdrawing Calories
After a brief period of not eating, fats are moved out of the fat cells to other tissue where they can be "cashed in." This short-term, day-to-day deposit-and-withdrawal is part of our short-term regulation of calorie intake and thus, weight. Longer periods of extreme calorie reduction can be counterproductive, however, predisposing the fats cells toward fat deposits.
Diet and Fat Cells
Soon after eating or drinking, the hormone insulin is released. Insulin tells your body to go into storage mode. The result is that proteins are made, muscle is built, and carbohydrates and fats are stored. Foods high in sugar cause the greatest increase in insulin, which may make weight loss harder. According to research published in the Journal of Academic Dermatology, high levels of insulin may increase the number and size of fat cells. On the other hand, research done by Boqué, as reported in the Journal of Physiology and Biochemistry, has suggested that a high fat diet, especially of trans fats, can encourage increased fat depositions and increase appetite, too.
The Weight Loss Paradox
On a long-term basis, fat cell size is regulated even more by hormones that are made, guess what--by the fat cells themselves. One of these signals, leptin, tells your body to decrease food intake and increase calories spent. Unfortunately, this hormone level goes down with weight loss, thus indirectly triggering increased appetite, which may be part of the reason fat cells are so resistant to shrinking and staying shrunk.
The Solution
The best way to lose weight and keep it off is to follow a modest calorie-restricted diet that limits trans fats and sugars and includes healthy fats and whole grains, fruits and vegetables, lean protein and low-fat dairy. Ultimately, fat cell size seems to be the result of calories eaten and calories spent.
References
- "Journal of Physiology and Biochemistry"; Influence of dietary macronutrient composition on adiposity and cellularity of different fat depots in Wistar rats; N. Boqué, et al.; March 2009
- "Clinical Chemistry"; The perfect storm: obesity, adipocyte dysfunction, and metabolic consequences; de Ferranti S, Mozaffarian D; June 2008
- "Journal of Biological Chemistry"; The response of lipoprotein lipase to feeding and fasting. Evidence for posttranslational regulation.M H Doolittle, O Ben-Zeev, J Elovson, D Martin and T G Kirchgessner; March 1990
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