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Hunger seems like a simple topic, but really it is a relatively complex issue. It involves hormones, perception, psychological components and more! Hunger is a signal to warn the body of potential starvation. In a culture where food is scarce, hunger is an important signal. In our culture where food is abundant, hunger can be a little misleading. Also, when you are changing your diet, especially by eating fewer calories, you will experience more hunger due to hormones and other factors.
Leptin and Ghrelin are two hormones that signal hunger and fullness in the body. There are other hormones that influence satiety, but these are the two we will focus on.
Leptin – Leptin is a hormone produced by fat that signals fullness when it is released and sensed by the brain. It tells the brain you do not need to eat anymore. Leptin impacts metabolism by influencing thyroid hormone release. It’s designed was to prevent starvation when food was scarce. Your brain cells can become resistant when levels are elevated over time, which means the signal of fullness is not perceived in the brain.
Factors that affect leptin levels/sensitivity:
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Crash diets [significant rapid reduction in calories] – reduced levels cause hunger
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Obesity leads to increased levels – but also leads to resistance.
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Insulin Sensitivity – people who are Insulin resistant are often leptin resistant, so the brain never senses fullness.
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High-carbohydrate meals, particularly high fructose corn syrup containing foods, cause increased release (along with insulin)
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Reduced sleep release of leptin by fat cells, increasing appetite/hunger (reduced activation of the parasympathetic nervous system which improves
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Gender – women tend to be more sensitive to leptin than men, possibly due to estrogen
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Increasing Omega 3 containing foods cause increase in leptin and may increase the brain’s sensitivity to the hormone
Ghrelin is a hormone released by the stomach and stimulates hunger/appetite when the stomach is empty. As the stomach stretches, ghrelin production is reduced.
Factors Affecting Ghrelin Levels/Release:
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Dieting – reduced food and calorie intake leads to increased ghrelin levels, thus increased hunger and appetite.
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Physical activity may increases ghrelin, with the exception of high intensity interval training.
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Stress increases the release of ghrelin by the stomach. Do you notice you are more hungry when stressed?
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Sleep debt/restriction causes elevations of this hormone.
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Growth hormone release may cause differences in ghrelin release in women vs. men.
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Increasing Omega 3 containing foods cause decrease in ghrelin and may increase the brain’s sensitivity