Obesity part 2

Yup, another post about obesity. See my earlier post for BIOC3004 here.

The obesity epidemic-definition and prevalence

See earlier post: Obesity

Health issues associated with obesity

The metabolic syndrome

See earlier post: Metabolic Syndrome and Fat Metabolism

Properties of adipose tissue

Adipose tissue is often simply thought of as a storage organ for fatty acids, but it can do much more than that. Aside from the storage and release of free fatty acids, it can also store and release leptin, adiponectin, renin, angiotensin, glucocorticoids, sex steroids and pro-inflammatory cytokines. Pro-inflammatory cytokines can cause macrophage migration, which is why obesity is sometimes thought of as a "chronic, low-grade inflammatory condition."

Factors contributing to obesity

Thermogenesis

Around 2/3 of our resting metabolic rate is used on maintaining our body temperature. If our core body temperature is higher, we will use more energy for thermogenesis, and vice versa. The next question is this: can we increase thermogenesis to increase energy expenditure?

As mentioned here, children and some adults have brown adipose tissue, which burns energy to create heat. In fact, as little as 50g of brown fat could use up to 20% of our basal energy needs. Interestingly enough, there is an inverse relationship between BMI and detectable brown fat, so brown fat might represent a potential target for obesity treatment. Fibroblast growth factors (FGFs) and bone morphogenic proteins (BMPs) may both help to stimulate brown fat proliferation. BMP-7 has already had some promising effects in mice, but we need to wait and see if it will have the same effects in humans.

Circadian rhythmicity

You've probably heard of the Circadian rhythm- an adaptation to the 24 hour light-dark cycle that controls many physiological processes. The main controllers of the Circadian rhythm are the "central clock" located in the suprachiasmatic nucleus, directly linked to the retina, as well as several "peripheral clocks" in metabolic organs. There are strong links between the Circadian rhythm and metabolism, as many metabolic hormones such as insulin and leptin display rhythmic secretion patterns. Eating at abnormal hours, when our organs are not "primed" for feeding, may be problematic.

Knocking out "clock genes" in mice has been shown to cause abnormal metabolic phenotypes. Knocking out Clock leads to hyperphagia, obesity and hormonal imbalances associated with metabolic syndrome, whereas knocking out Bmal1 leads to extreme weight loss. Interestingly enough, feeding rodents a high-fat diet appears to alter the activity of hepatic clock genes.

Melatonin, a hormone usually secreted at night by the pineal gland, has been examined as a potential treatment option. It might be able to decrease weight gain, improve lipid profiles and insulin sensitivity, and have anti-oxidative and anti-inflammatory effects. It might also help to "re-set" the Circadian rhythm for shift workers.

Metabolic programming

See earlier post: Developmental programming of adult health and disease. Offspring of rats fed a high-fat diet were more likely to become obese, even if they ate a normal diet throughout their life. In other words: babies born to obese mothers appear to be predisposed to obesity.

Treatment options and directions for the future

Another treatment option that has been examined is omega-3. Omega-3 may help to lower the inflammation that is present in obesity (remember, obesity is considered to be a "chronic low-grade inflammatory condition"). A lot more research is still being done in this area, though.