Due to psycho-emotional stress, the brain signals the adrenal glands to produce cortisol, so that the body can better anticipate stress. If this lasts too long, we speak of chronic stress, leading to a prolonged release of cortisol. This continuously raises blood sugar levels, causing disruptions in energy and insulin regulation. Therefore, stress is harmful in the long term and contributes to the development of metabolic syndrome.
Our brains determine much of our behavior, but not everything. If too much fat tissue develops, this can influence the brain to alter the energy distribution throughout the body.
Just like in prehistoric times, the brain still wants to maintain energy storage in fat tissue for times of possible scarcity. There simply wasn't always food, so when it was available, a lot was eaten. Excess energy was then stored in subcutaneous fat tissue. When there wasn't enough food, the body could break down these fats, and the liver converted them into glucose as an energy source for all organs, including the brain and all cells. The circumstances determine the energy distribution in the body, so that we can flexibly respond to potential threats like hunger, thirst, heat, cold, injury, etc. This system is still the same. We are very sensitive to scarcity; our brain responds by conserving energy. All processes virtually go on the back burner, allowing you to survive with little energy. Because this is no longer necessary (think of supermarkets and a well-stocked refrigerator, so food is always available), the body stores excess energy, which now causes more problems than benefits.
Movement
We also move very little compared to our distant ancestors. The Netherlands ranks second in all of Europe in terms of daily sitting hours, averaging 8-9 hours per day. Among teenagers, this is even 12 hours a day. The 'sedentary lifestyle' is probably the biggest risk factor for overweight.
Naturally, we don't want to waste energy if there is enough available in the body. Look at lions in nature; they only act to search for prey, for the hunt itself, and for reproduction.
The brain responds to hunger and satiety hormones that are sent from the body via the blood.
Leptin and ghrelin
Over the past decade, it has become clear that fat tissue is not merely a storage place for fat, as was previously thought. Adipose tissue secretes numerous hormones (adipokines) that play an important role in fat and carbohydrate metabolism and the biology of vascular complications. It is therefore a complex endocrine organ. Through the blood, hormones from adipose tissue cause other organs in the body to work harder or less hard. Fat cells therefore have a significant effect on other tissues and thus also on the brain.
One of the hormones released by adipocytes (fat cells) is leptin. This hormone signals your brain, specifically the hypothalamus, that you have eaten enough. It further regulates your energy level and how much body fat can be burned. All our organs have receptors for leptin. The brain, immune system, and reproductive organs are most sensitive to this substance.
When leptin is released into the blood in sufficient quantities and reaches the brain, another signaling substance, ghrelin, which typically signals a desire to eat, stops. Ghrelin is also produced by the hypothalamus and stimulates the pituitary gland (a hormone gland in the brain) to secrete growth hormone. Ghrelin also plays a role in the hippocampus, where it stimulates learning ability and adaptation to changing circumstances. It further stimulates fat synthesis and reduces fat breakdown. Lack of sleep can even lead to overweight due to an increase in ghrelin.
So, in a healthy situation, an (empty) stomach releases ghrelin, which reaches the brain via the blood. This makes you feel hungry. Once you've eaten, leptin eventually ensures that your hunger signal stops because enough energy has been consumed, until you've used up this energy again (through basal metabolism and your activities). Then this pattern repeats itself. But when you lie awake for hours at night worrying due to stress, for example, this lack of sleep can lead to an increase in ghrelin, which can ultimately even lead to overweight.
