How Fat Cells Work

Where's the Fat?
Fat, or adipose tissue, is found in several places in your body. Generally, fat is found underneath your skin (subcutaneous fat). There's also some on top of each of your kidneys. Other locations depend upon whether you are a man or woman:

*An adult man tends to carry body fat in his chest, abdomen and buttocks, producing an "apple" shape.

*An adult woman tends to carry fat in her breasts, hips, waist and buttocks, creating a "pear" shape.

*The difference in fat location comes from the sex hormones estrogen and testosterone.


Your body contains two types of fat tissue:

White fat - important in energy metabolism, heat insulation and mechanical cushioning.
Brown fat - found mostly in newborn babies, between the shoulders; important for thermogenesis (making heat).

Fat tissue is made up of fat cells. Fat cells are a unique type of cell. You can think of a fat cell as a tiny plastic bag that holds a drop of fat:

White fat cells are large cells that have very little cytoplasm, only 15 percent cell volume, a small nucleus and one large fat droplet that makes up 85 percent of cell volume.

Brown fat cells are somewhat smaller, are loaded with mitochondria and are composed of several smaller fat droplets. The mitochondria are able to generate heat. Fat cells are formed in the developing fetus during the third trimester of pregnancy, and later at the onset of puberty, when the sex hormones "kick in." It is during .......

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Metabolism 101

Metabolism- sum of all the chemical changes occurring in a cell, a tissue, or the body.

Reactions occur through various pathways. In these pathways a cascade of events occur as one reaction results in another reaction. Most pathways can be classified as Catabolic( break down of complex molecules into simpler molecules) or Anabolic (complex products are formed from simple precursors). Each pathway is composed of multienzyme sequences, and each enzyme, in turn may exhibit important catalytic or regulatory features.

Catabolic pathways
Catabolic reactions occur to capture chemical energy in the form of ATP from the degradation of energy rich fuel molecules. Catabolism also allows molecules in the diet or nutrient molecules stored in cells to be converted into building blocks needed for the synthesis of complex molecules. Catabolism provides the chemical energy necessary for the maintenance of the living cell. Generally, energy generation from degradation of complex molecules occurs in three stages.

Stages of Catabolism
1) complex molecules are broken down into .......

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Is a calorie just a calorie?

Before finally getting into a discussion of the different dietary approaches out there, I want to adress one of the bigger points of contention in the dieting literature: is a calorie a calorie? Simply put, the debate comes down to this: all that matters is caloric balance (calories in versus calories out) or do the source of those calories matter?

As usual, both sides of the argument can bring lots of data to the table in support of their contentions. Frequently, as you'll see below, they end up arguing slightly different issues. In looking the topic, I want to look at three distinct data sets, each of which generates slightly different results (part of the confusion comes from comparing data from dissimilar studies).

Studies varying protein intake
Most commonly, when folks want to argue that 'a calorie is not a calorie', they will use studies comparing higher and lower protein intakes. With very few exceptions, dietes providing adequate protein intake (for dieters 1.5 g/kg lean body mass or higher would be a minimum) to lower intakes find better results than diets with lower protein intakes. This is especially apparent under dieting conditions with any number of studies support the need for higher protein intake to support muscle growth.

That is, given an identical caloric intake, the group that gets sufficient protein .......

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Fat Loss Debate: Hale vs. Harmony

The following article features a discussion between Susan Harmony Ph.D and myself. Susan sent me an e-mail informing me that I had misrepresented the science concerning exercise and saturated fat. Excerpts from our first debate were featured in last week’s newsletter. In this article I present our second debate. Susan’s comments appear in bold between the quotation marks.

"You obviously have much to learn." If you read my work I think you will find I have learned quiet a bit. Although I would agree I still have much to learn. As long as my brain is functioning I will attempt to keep on learning. Learning should be a life long process. Once an individual admits they have much to learn this process can continue. If a person assumes they have learned enough then learning usually comes to a stop.

"To remove bodyfat you need to use it as fuel. The muscle fibers that are fuelled by fat ('slow twitch' fibers ) are the ones that produce GENTLE movements" You don’t have to learn how to use fuel. Are you aware that you are burning fuel 24 hours per day? When you are sitting doing absolutely nothing you are burning fuel. Many tissues can use free fatty acids for fuel not just slow twitch muscle fibers. Losing bodyfat relies on way more than activity of the slow twitch muscle fibers (how about cal deficit). Do you realize to use slow twitch muscle fibers nervous stimulation is required (CNS requires cals although not fat calories)? High intensity exercise often results in a lower RQ (indicating higher proportion of fat) than low intensity exercise post-workout. Below is a brief description of what occurs during mobilization of stored fat and oxidation of fatty acids: The following is an excerpt from Fat Burning How it Works by Jamie Hale. I added a few additional comments to make the information more precise.

- Bodies 2 major stores of fat that provide .......

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