It’s widely accepted that having too much fat increases your risk of diabetes. But if the job of fat is to store energy and produce necessary hormones, why is it so bad for us?
First off, I want to address what many people see as a paradox, but is really just a difference in degree. Fat (and I’m specifically talking about “white fat” here. To learn about brown fat, click here) is necessary for our survival. In fact, we all need a minimum amount of body fat for our bodies to function properly. For men, that minimum is about 3%, and for women the minimum is about 12%. Problems arise not from having body fat, but from having too much body fat. Men begin accumulating excess body fat when about 21% of their mass is attributable to fat. For women, that number is 31%. Once you reach 30% body fat for men and 40% body fat for women, the health risks are extremely high.
Looking at the first chart, we see that having either too little fat or too much fat poses health risks. In both conditions, our bodies are not able to function properly. I want to really drive this point home because having a healthy relationship with body fat is essential to reaching our body fat goals. Having a healthy relationship involves recognizing that fat itself is good. It’s too much or too little fat that is bad.
The good, the bad, and the fat
Fat serves important functions including storing energy for times when food is scarce and producing hormones like leptin, adiponectin, resistin, and steroid hormones. These hormones regulate metabolism, affect hunger and feeding behavior, and influence immune functions.
According to the lipostatic hypothesis, fat tissue’s production of these hormones is proportional to the amount of fat in the body.
Consider leptin. Leptin regulates (and actually reduces) appetite and feeding behavior. It also increases energy expenditure and provides feedback to the brain about the status of your body’s energy reserves. The amount of leptin produced is directly related to the amount of body fat someone has. So more body fat = more leptin and less body fat = less leptin. Having too little body fat, and thus only a small amount of leptin, will cause your body to reduce it’s energy expenditure and signal that you are hungry. Having adequate body fat, on the other hand, produces adequate amounts of leptin to regulate hunger and energy expenditure in a healthy way.
You may be thinking, if leptin is good for appetite and metabolism, wouldn’t excess fat and therefore excess leptin also be good? The short answer is a resounding NO. The long answer is that when we have too much body fat and too much leptin, we become leptin resistant. So we no longer get the positive effects on appetite and energy expenditure. In other words, we feel more hungry and burn less calories at rest. The result? More body fat, leptin resistance, and decreased adiponectin (discussed next).
What about adiponectin? Adiponectin increases the liver’s and muscles’ sensitivity to insulin. Why is this good? Insulin helps transport glucose from the blood to the liver and muscles for storage and energy. If your muscles and liver are sensitive to insulin, blood glucose will transfer more easily. If your muscles and liver are resistant to insulin, it’s harder for glucose to leave the bloodstream. Having elevated blood glucose increases our susceptibility to diabetes and heart disease. Therefore…ding ding ding…adiponectin helps reduce our risk of diabetes and heart disease.
The amount of adiponectin produced by fat tissue, like leptin, is related to the amount of body fat we have. But, unlike leptin, the relationship is inverse, meaning less body fat = more adiponectin and more body fat = less adiponectin. Excess body fat causes production of adiponectin to slow or even stop, contributing to insulin resistance and increasing risk of diabetes.
Resistin. Not much is known about the role of resistin in diabetes. But it’s suspected that resistin contributes to insulin resistance. Resistin also appears to increase inflammation and atherosclerosis (which leads to heart disease).
Having an adequate amount of body fat results in healthy production levels of leptin, adiponectin, and resistin. This helps regulate appetite and energy expenditure and, importantly, promotes insulin sensitivity.
Having too much body fat leads to leptin resistance, decreased adiponectin, and possibly increased resistin. This ultimately results in insulin resistance leading to diabetes and other health problems.
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