Good Fat, Bad Fat

Obesity first ages us and then kills us

Posted Feb 07, 2011

We need fat. Fat is frequently the largest organ in our bodies. Fat is important in defending our bodies from pathogens such as bacteria and viruses, it contributes to our immunity and helps us recover from injury. Once, a really long time ago, we needed our fat depots because food was not always available. Fat can accommodate wide swings in nutrient availability because it is capable of rapid changes in size, especially our subcutaneous fat which is not subject to the size constraints. We can simply keep packing on the fat cells for a future time when less food might be available - thus improving our chances of survival.

I was recently honored by an invitation to give a TED talk on this topic.  The video is available here.

In humans, fat is purposefully located beneath the skin and around our vital organs, where it can protect our body against infection and trauma. Bacterial and fungal infections of fat are uncommon and cancer is rare; this is likely related to the high local concentrations of fatty acid that are lethal to pathogens and non-fat cells that might be metastases. Fat is also critical for thermoregulation by preventing heat loss by acting as insulation and by generating heat in brown fat. Fat provides mechanical protection and forms a buffer that dissipates pressure over skeletal prominences, thus preventing skin collapse at vulnerable spots on our limbs.

As we are all too aware, our fat mass increases throughout middle age; then, it starts to decline in old age. As we pass middle age, our fat is being redistributed into different depots; it is moving from subcutaneous depots to visceral depots around our vital organs. Sadly, the percentage of fat in our diet that is stored in subcutaneous depots is lower in older than younger men and women. Due to this redistribution waist size tends to increase by 1.5 inches every 9 years in adult women. To make matters even worse, as we age our fat is also being redistributed into our bone marrow, muscle and liver. The loss of subcutaneous fat is often associated with the development of the infamous "metabolic syndrome" which is characterized by glucose intolerance, insulin resistance, visceral obesity and hypertension. When present in the elderly, this condition impairs cardiovascular function and accelerates cognitive decline. Some of us inherit a tendency to redistribute our fat at an earlier age, and at a faster rate; when this happens, it is associated with a reduced life span.

Unfortunately, standard liposuction is not going to help. Removing large amounts of subcutaneous fat does not improve insulin sensitivity. Indeed, having larger amounts of subcutaneous fat might actually be protective if you are obese. In contrast to the removal of subcutaneous fat by liposuction, the removal of visceral fat actually enhances insulin sensitivity and extends maximum life span. Indeed, maintaining a high ratio of subcutaneous fat to visceral is associated with enhanced longevity. The reason is that all fat depots do not behave similarly; visceral fat is more inflammatory than is subcutaneous fat.

Obesity and aging are both associated with chronic, low-grade, body-wide inflammation and insulin resistance. Fat dysfunction associated with obesity is now thought to reproduce many of the same metabolic conditions that underlie the aging process itself. Essentially, obesity is an accelerated form of fat tissue aging and obesity predisposes us to diseases that are common in old age, including depression. For this reason, obese people often respond poorly to anti-depressant therapies.  But you do not have to be obese in order to suffer from the consequences of fat. Even skinny older people who possess relatively more visceral fat than subcutaneous fat are at increased risk for diabetes and mortality.

The surgical removal of visceral fat is not an option, thus the only solution available to us is to simply eat far less food. Caloric restriction is the only valid, scientifically proven dietary intervention that has been shown to slow the aging process and improve health. The reason we hear so little about this approach is because no one stands to make a profit on all of us eating less food.

© Gary L.Wenk, Ph.D., author of Your Brain on Food (Oxford, 2010)