Feedback regulation of food intake

The physiological regulation of the food intake has two kind of feedback signals: long-term and short-term. The long-term feedback signals are derived from the adipose tissue and reflect the size of the adipose tissue stores. The short-term feedback signals originate from the gastro-intestinal tract and influence satiation and satiety. The signals are received in the hypothalamus and are integrated with emotional stimuli (mood), cognitive stimuli (thinking), hedonic stimuli (liking), influencing hunger, appetite and food seeking behavior.

On food intake, the immediate distension of the stomach (stretching) will send the feeling of fullness. The food entry on the gastro-intestinal tract will inhibit the release of the hunger hormones and stimulate the release of the satiety hormones (cholecystokinin - CCK AND glucagon-like peptide 1 -GLP1). The entry of glucose and amino-acids into the blood stream will activate the nutrient sensing cells from hypothalamus.

Long-term regulation - the leptin hormone produced by the fat tissue (the production and the blood levels of leptin are proportional to the amount of fat mass, converging the feeling of satiety, sending signals to the satiety cells in the hypothalamus. Lack of leptin due to the genetic disease will lead to extreme hunger, massive overfeeding and obesity. While the animals tends to have a relative stable body weight, the human's body fat tends to increase with age.

When we fast, we release hunger hormones, the low levels of nutrients in blood will also decrease the leptin production, triggering the hunger cells in the hypothalamus. Raising an effective hunger response and being effective at storing body fat is critical for survival.

Let's see a bit more about the feedback regulations from adipose tissue. When we have a body fat gain, the increased leptin release will stimulate the satiety cells in the hypothalamus, decreasing the food intake, decreasing the energy storage. When we lose body fat, the decrease of the leptin will trigger the hunger cells from the hypothalamus, increasing the food intake and increasing the energy storage.

The adipose tissue( fat ) has a central role in the long-term regulation of food intake. The leptin reduction during weight loss is one of the reasons of being difficult to maintain the weight loss.

The next post will be about the energy value of nutrients, maybe after i come back home.