I. Visceral fat vs subcutaneous fat?
There are two main types of fat in the body, subcutaneous fat and visceral fat.
Subcutaneous fat lies directly underneath the skin in a region called the hypodermis. Since subcutaneous fat lies over the muscle, you can grab and feel subcutaneous fat with your hands. Subcutaneous fat can look unattractive and will reduce muscle definition, but is considered to be mostly harmless from a health perspective.Visceral fat is the fat that surrounds the organs in the belly and cannot be seen except through the use of an MRI or CT scan. Visceral fat is extremely dangerous from a health perspective and is correlated with a large number of chronic diseases. BMI and waist circumference often serve as indirect measurements of visceral fat, but both only loosely correlate with visceral fat. For example heavier individuals generally have higher levels of visceral fat, but 25% of individuals with a normal BMI (18-25) are considered to be metabolically obese and have unhealthy levels of visceral fat.
II. What are the health implications of visceral fat?
There has been significant research done over the past 70-80 years correlating visceral fat with an increased risk for stroke, heart attack, and diabetes. Numerous studies have demonstrated that individuals with high levels of visceral fat have high cholesterol, increased blood pressure, and increased insulin resistance. Furthermore, when visceral fat levels are reduced, individuals see significant improvements in their cholesterol, blood pressure, and diabetes leading to major reductions in heart attacks and strokes.
More recent research has also suggested that high levels of visceral fat are correlated to dementia and cancer. A study, by Dr. Whitmer, of 6,500 members of Kaiser Permanente's patients in Northern California, saw that individuals with larger waist size, a rough measurement of visceral fat, had higher risk for dementia than those with smaller waists. Another recent research study done in mice showed that mice who had their visceral fat surgically removed had significantly reduced rates of cancer compared to mice who received a sham surgery.
III. Why might visceral fat be so unhealthy?
The exact details of why visceral fat is so unhealthy are not fully understood, but recent research has demonstrated that visceral fat is extremely metabolically active and secretes large amounts of hormones. These hormones have profound impacts on our health in a variety of ways.
For example, visceral fat cells secrete significant amounts of cytokines (e.g., interluken 6, tumor necrosis factor) that are similar to hormones released by the immune system. These hormones cause chronic low grade inflammation in our body that may lead to increased insulin resistance and plaque formation. Similarly, visceral fat cells secrete leptin. Too much leptin may cause your body to become desensitized to leptin leading to hindered appetite regulation and difficulties with learning and memory. Visceral fat also suppresses the production of adiponectin, a hormone found to have anti-diabetic, anti-inflammatory, and anti-oncogenic functions.
