Let’s face it, fat. Nobody likes you. You give us muffin tops, cellulite, heart disease, and sadness. But what if there was more to fat than we’ve given fat credit for? What if, benieth that simple yellow exterior, there was something deeper?
Gluttony and sloth are commonly thought of as the cause of obesity. In healthcare we often talk about energy balance as a simple math equation. That is, if you eat more calories than you burn in a day, the rest will be stored as fat. Common logic is that if you over-indulge (gluttony) and don’t move enough (sloth), you get fat. Not only do we think of fat people in these terms, but I believe we have come to see fat tissue in much the same way. We see fat as “extra” tissue, just weighing us down and getting a free ride while muscles and other organ systems do all the work. In personal training we like to show clients models of 1lb of fat and 1lb of muscle and repeatedly remind them that muscle is more metabolically active than fat. It is true that muscle cells burn more energy than fat cells, but it doesn’t mean that fat cells aren’t active.
Adipose tissue (fat tissue) serves several important functions beside the obvious storage of fat. Vitamins, like any other chemical, can either be fat soluble or water soluble. Water soluble vitamins such as B vitamins get to hang out in the blood, which is mostly water. Such vitamins need to be consumed regularly because there is little to no storage in the body- any extra you might have will get filtered by the kidneys and excreted in the urine daily. Fat soluble vitamins such as A, D, E and K, however, can be stashed away in the liver and adipose tissue. Fat soluble toxins such as DDT, PCBs and hexachlorobenzenes are stored in adipose tissue, liver and reproductive tissue in a similar manner . It is thought that the release of toxins back into the bloodstream with fat loss may be part of the reason many people hit a weight loss plateau . As you lose weight (fat) from adipose tissue you are also releasing whatever is stored in that tissue. If this includes high levels of toxic substances your body may not be able to cope with the inflammatory load, resulting in slowed mitochondria function and metabolism. In a way, your body may thwart it’s own attempts at weight loss because it simply can’t keep up with the toxins .
Adipose tissue is not the benign, inactive beast we often think it is. Fat has a half-life in the blood stream of only about 2-3 minutes. Similarly, the fat in each adipose cell is renewed every two to three weeks . Adipose tissue even makes it’s own hormone called Leptin. While we are only just starting to learn about leptin, it is understood that this hormone signals satiety (fullness) to the brain. Leptin levels increase in direct proportion to the amount of fat tissue, which brings us to an interesting point. If obese people have more leptin than skinny people, shouldn’t they feel more full and therefore not be as obese? I believe that this catch-22 of physiology is due to leptin resistance at the neurological level, but that topic deserves it’s own blog post. In any case you can now see that adipose tissue isn’t just chillin’ out in our thighs. Fat is a dynamic creature that is participating in our daily lives more than we ever gave it credit for!
Now that we’ve talked a little bit about the inner workings of fat, perhaps we should shift focus and think about what outside forces act on adipose tissue. After all, adipose tissue is just as connected to your body as any other organ system, so there must be some body-adipose cross-talk happening.
Several hormones are known to have a direct effect on adipose tissue and fat metabolism and storage. Namely, insulin is the chief hormone that acts on adipose tissue. Insulin (and glucose itself) activate Lipoprotein Lipase, the enzyme that promotes the storage of fat in adipose tissue . At the same time, insulin inhibits enzymes that stimulate fat breakdown (lipolysis and beta-oxidation), ensuring that metabolism moves in an anabolic (storage) direction. Insulin also promotes the intracellular enzymes that facilitate the storage of excess glucose and amino acids into fat . On the other side of the spectrum are catecholamines like epinephrine (adrenalin) and norepinephrine, and hormones such as thyroid hormone and growth hormone. These hormones oppose insulin and promote fat release from adipose cells and fat breakdown via beta-oxidation, as well as inhibit the enzymes that would normally store fat (lipogenesis) [3,4]. Epinephrine and norepinephrine are chiefly responsible for the increase in fat mobilization seen with strenuous exercise. These two catecholamines stimulate Hormone-Sensitive Lipase, the enzyme that promotes the release of fat from adipose tissue.
So, what is the take-away from all of this? It’s not necessarily the calories that you consume that make you gain weight- it’s how those calories affect your body through your hormones. Low sugar, low carbohydrate diets such as the paleo diet and the Atkins diet work by decreasing insulin and glucose surges. My advise to anyone who is trying to lose weight is simple. Don’t stress over calories. Rather, eat a diet and behave in a way that will positively influence your hormones. Reducing insulin surges is like removing your foot from the brake pedal of your weight loss efforts. Stop hindering your own ability to lose weight and let your hormones do the rest.
 The Textbook of Functional Medicine, 2010
 Mark Hyman “Systems Biology, Toxins, Obesity, and Functional Medicine”
 Guyton and Hall. Textbook of Medical Physiology 11th edition.
 Burton, Cerny. Exercise Physiology for Healthcare Professionals.
 Silverthorn. Human Physiology and Integrated Approach.