Overweight: Why can’t we stop eating, even without an appetite?

Appetite control is our body’s main way of determining how much food we need. However, this mechanism is not perfect, because certain foods full of bad fats disrupt this control and cause us to overeat and therefore gain weight.

Appetite control takes place primarily in the hypothalamus, a tiny region at the base of the brain that has two “watchdog” centers that constantly listen for information about the body’s energy level. For example, sugar level

blood sugar (glycaemia) is constantly measured by the hunger center and a drop, even slight, immediately triggers the alert and the stimulation of the appetite. When you feel a drop in energy, irritation or even stomach gurgling, it is because these mechanisms are at work and signal to you that it is high time to eat. If the signals of hunger are quite easily recognizable, those which command the cessation of food ingestion are much more complex and can sometimes be more difficult to interpret.

The first control point is located in the wall of the stomach, where nerve fibers detect the state of distension of the organ induced by ingestion, which allows the brain to estimate the volume of food brought to the stomach. body. These nerve fibers are activated long before the stomach is filled to capacity, so as to avoid the negative effects that an overload of food can have on the digestive process.

However, any greedy person knows that it is possible to override these signals and eat more than the amount allowed by our brain.

Several hormonal mechanisms also play an extremely important role in signaling to the brain that the process of food assimilation is underway and that consideration should be given to stopping eating to avoid overloading the system. The two most important are hormones called leptin and insulin, each of which has the role of informing the brain about the state of energy stores in the form of sugar and fat. When the levels of these hormones reach a certain threshold, the brain emits a series of signals signaling that the energy supply is sufficient and that the meal should be ended to avoid a calorie overload.

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Palmitate: a fatty acid that disturbs our feeling of satiety

Even if these control systems are generally very efficient, their effectiveness can however be considerably reduced depending on what we eat. For example, a recent study showed that palmitate, a saturated fat present in large quantities in meat, in dairy products, in palm oil and therefore in all industrial foods, acts directly on the neurons of the hypothalamus. involved in the detection of leptin and insulin.

The impact of this interaction is spectacular: in animals which have a diet rich in palmitate, the mechanisms involved in the transmission of the signal of these hormones are disturbed during the three days following the meal, with the inevitable consequence that these animals eat more than necessary and gain weight.

Change fat to eat less and gain less weight

Interestingly, this appetite disturbance is not observed when animals are fed oleic acid, a monounsaturated fat found in large amounts in olive oil.

These observations suggest that the high amount of saturated fat present in the Western diet, naturally but more industrially, could thwart our internal appetite regulation mechanisms and thus contribute to the current obesity epidemic. The simple fact of replacing saturated fats with monounsaturated fats, using olive oil, for example, could neutralize this effect and thus participate in maintaining a healthy weight.


Benoît et al. Palmitic acid mediates hypothalamic insulin resistance by altering PKC-sub-cellular localization in rodents. J Clin Invest, 119:2577-89.


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