Genetics and Fat Loss

Endocrinology, the branch of physiology and medicine that researches the endocrine glands and the substances they produce, (hormones), has revealed several important discoveries over the last two decades or so. Among these were the identification of two hormones, leptin and grehlin, that have a pronounced effect on human body composition, namely, how fat or how lean one is. The health implications in an era of increasing obesity in both children and adults could well be profound.

First, let’s define what a healthy body composition is in terms of body fat percentage. That refers to what percentage of our bodyweight is fat mass. There are several methods available to get this percentage including caliper testing, bioelectrical impedance and hydrostatic weighing. These three methods all have varying ratings of accuracy and should be used as a relative gauge of body composition. The only method considered to be 100% accurate involves the burning of the cadaver, and of course, you don’t get your result back!

A consensus on what constitutes a healthy body fat percentage range is debatable, but generally speaking, a male should be under 25%, a female under 30%. Obesity is defined as over 26% for males, 31% for females. There are numerous variables that affect this percentage.

These include:

1. Genetics-this broad category reflects hormonal and physiological factors that include:
   1. Number and location of adipose (fat) cells. You are born with a certain number, usually distributed in similar location(s) as one or both parents.
   2. Endocrine output and efficiency. The amount of various hormones and their circulation and utilization.
2. Activity level
3. Dietary intake
4. External factors including environment and socio-economic status
5. Adequate sleep, for most this means at least 7 hours

We can manipulate and, for the most part, control activity, sleep and diet, and to a lesser extent environment and socio-economic status. You cannot (at the time of this writing) go back and choose different parents.

Leptin and Grehlin, known collectively as the “hunger hormones”, are relatively new, with Leptin identified in 1994 and Grehlin in 1996. Leptin, produced primarily in adipose (fat) cells, suppresses hunger, while Grehlin, produced primarily in the gastrointestinal tract, stimulates appetite.

Leptin’s primary function is regulation of fat stores and is released when fat cells are at or near capacity for fat storage. Receptor sites on the hypothalamus, the part of the brain that controls energy homeostasis, signal the brain when stores are at or near capacity, and a reduction in appetite follows. Paradoxically, obese individuals have high levels of Leptin, indicating a resistance to Leptin much like Type II diabetics are insulin resistant.

Grehlin is released when the stomach is empty, stimulating the urge to eat, and ceases when the stomach is stretched. Additionally, Grehlin stimulates an increase in gastric acid secretion to prepare the digestive tract for digestion.

An interesting correlation between sleep deprivation and reduced Leptin levels/increased Grehlin levels has been observed. Some researchers speculate there may be a connection between increasing obesity levels and decreasing sleep levels over the last several decades.

Though we cannot manipulate genetics to any large degree, the variables we can control are inter-related: diet, activity and sleep. Nothing has changed in my lifetime, optimal health  still requires proper nutrition, exercise and recovery.