Dear Pharmacist: I'm frustrated and happy at the same time because last week you taught me about a blood test called leptin and how it relates to obesity. I've been the same weight for five years and can't lose anything, yet I eat very little. Please share more. -- A.S., Gainesville, Fla.

Leptin and leptin resistance may explain why you eat nothing and hold on to weight.

Leptin is your stop sign at the dinner table. This hormone is released while you're eating. Special fat cells in your body secrete leptin, which sends a message to your brain saying, "Stop eating, you're full now!"

Erratic fluctuations of leptin (and the hormone ghrelin, which makes you feel hungry) complicate your ability to lose weight and triggers intense hunger. The imbalanced leptin hormone can impede weight loss even in the presence of proper levels of estrogen, progesterone and thyroid. Some of you have adequate leptin, but your body doesn't care because it is desensitized to the hormone and resistant to leptin. This is called leptin resistance and unfortunately for your waist line, there's no stop sign at the dinner table anymore! You'll eat more than you should, and more frequently than others. You're hovering over the fridge at all hours of the day. Yo yo dieting creates the problem, and makes it much worse.

This begs the question, "Why have I become leptin resistant?" There are many causes. A common one is because, long ago, you followed your taste buds too long because the food was so yummy. Perhaps your portions were too big and you ate until your stomach hurt. There's no blame here. The typical American diet of processed foods contains ingredients that are delicious, if not addictive, so there's a strong crave for these meals.

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Some of you wolf down your food down. It takes 10 to 15 minutes for your brain to get the leptin "stop sign," so if you eat too fast, then you'll eat too much! Slow down when you eat to allow the leptin signal to be heard. Also, avoid going to bed on a full stomach.

How can you tell if you're leptin resistant? The hallmark sign is that you can virtually starve yourself and still not lose weight! That's a sign leptin resistance has been going on a long time. Diet pills won't help you, but exercise will. You can have a blood test done to determine leptin levels. If you can normalize it, your body will start burning fat. It helps if your thyroid hormone is optimized. Leptin resistance occurs years before insulin resistance and full-blown diabetes.