It is becoming increasingly important to maintain a balanced body weight. A correct weight is crucial for a good health - and not just for a good appearance. The food of our days is not only consumed in large quantities but is also loaded with fattening substances that are degenerative to the circulatory as well as digestive system and to the whole organism. Fats and sugars are in abundance and not for giving us excitement but for a matter of choices of the food industry that knows well how to make profit. The gain to the food businesses is made at the cost of our health. We are a population of overnurished, yet ill-nourished people.
So many of us are committed to drop the extra pounds, because we are asked by our clothes, increasingly tight, and by the mirror, increasingly severe, and because we have been recommended by our doctors. But often, even with the iron will that we think we are employing, after the first few kilos we fail and we can’t lose more than a little.
There is a simple physiological explanation for this, that the diet industries hide from us: the more we lose fat, the more the body is put under conservative mode thus hunger is increased and metabolism is decreased to avoid a ‘collapse’ which at first glance would seem risky to our body: lack of food could be lethal ...
That would be ok if we were still in the bush in search of roots or along the beaches in search of mussels. Unfortunately, our evolutionary system, designed in a very refined and complex way to keep us alive even when resources seem to wane, has not yet adapted to the current abundance of food on the shelves, the super equipped kitchen, the over-full pantries. So, when we force our body to sustain itself in the presence of "less" (but not "little") food, it believes it is in front of a crisis of resources and puts the brakes on energy expenditure while increasing hunger so that we eat any calorie is present to avoid death.
How does this survival mechanism work?
The hypothalamus is the part of the brain that is capable of detecting body weight and keep it in a narrow range. The hypothalamus is also involved in other regular unconscious impulses and reflexes as basic as sex, aggression, drinking, body temperature etc. This part of the brain is used to maintain all physiological balance. Coming back to weight, our bodies are able to adjust food intake in order to regulate appetite and energy consumption, based on the amount of energy supplied by the food, on its volume and the information on body weight.
In turn, what gives information about weight to the hypothalamus is a hormone called leptin, produced by fat cells in our adipose tissue. When we gain weight, the amount of fat increases and leptin is released to a greater extent. This protein reaches the hypothalamus which responds by lowering appetite and increasing energy expenditure.
And therein lies the key of the deception of diets. When you start to lose fat, different neural and hormonal signals are involved to try to curtail the loss of energy storage: the lower leptin released from the reduced fat mass signals for lower metabolic rate and increased impulse to feed, the survival signals that do not allow us to lose too much weight.
This is the inevitable truth concealed by the industries of dietary products. Even liposuction is not the ultimate solution because it reduces the fat and then triggers the mechanisms of "defense" as during a slimming.
You cannot escape this law: the more you lose weight and the less you’ll manage to lose.
In addition to the leptin signals, there are other hormones such as neuropeptide Y and orexin that control the states of hunger and satiety. The control system is very complex and not fully explained by science. However, the result is always that losing a lot of weight and keeping it off is a very difficult action precisely because of this complex circuit of homeostasis (balance).
But if these hormones control the drop and gain of weight, what is it that controls appetite at mealtime?
What drives us to start a meal is not the drop in blood sugar as previously thought but rather socio-cultural and environmental signals: when the table is set or when the clock shows the typical time we rush to eat. And what tells the brain that we are satisfied at the end of a meal is not leptin but different signals, such as stomach distension and the chemical composition of the food ingested. Highly proteic food for example will send a message to stop eating way before sugary food: stopping to eat after a baked salmon is much easier then stopping after the first slice of cake.
In addition to these complex neural and hormonal mechanisms, weight loss is also made more difficult by the circuit of pleasure that is triggered by food, such as it is triggered by smoking, drugs, gambling, alcohol, sex, etc. When we eat, the part of the brain that controls pleasure is stimulated and the hormone dopamine is released into the blood. Evolution has thought to connect the act of eating to pleasure because it is the most important action keeping us alive! Obviously, different foods produce different levels of dopamine release; also, the amount of this hormone decreases with food intake: the more you eat, the less you enjoy the food ingested. When leptin circulates in abundance (when there is a good fat accumulation) dopamine release is slowed down, so there is less instinctual drive to find pleasure in food. But in rare cases there is a real addiction to food and food intake is controlled more by this addiction than by energy needs. However, it must be remembered that we always have a 'choice': the addiction to food, such as to drugs, alcohol or whatever does not eliminate this possibility.
Similarly, we can always use will to manage the unconscious impulses that drive us to eat more when the low level of leptin tries to fill in the lost fat. If the consequences of being overweight become quite threatening to the individual, some people may learn to stop such instincts that make them eat in excess. Trying to lose a large amount of weight needs nevertheless a fight of millennia of evolutionary pressure against weight loss. It takes an iron will!
But it is really only a question of will?
Studies on the neural circuits that control food intake led to the discovery that as much as 80% of the variation in weight is determined by genes. For example, some obese people assume greater quantity of food because their circuit of hunger or that of pleasure are not fully functioning due to genetic variations that change the amount of hormones or their receptors. Specifically, 1% of obese people shows that they have a deficiency of leptin production, so even if they are fat, their hunger does not subside.
However, let us never give too much importance to the genes (in fact we mentioned only 1% in the case of obese): the environment and gene-environment interactions play an important role in determining the weight of an individual. For example, we know that the environment and the foods to which the fetus is exposed in the womb are partly responsible for the final body weight.
The circuit of pleasure is widely used by the food industry which focuses to produce foods and drinks that stimulate the most pleasure so that we over-eat and over-consume. To create foods that are able to strongly activate the pleasure circuit in order to outweigh the signals of satiety and adiposity, the industries of food use the knowledge of ancestral eating habits of the early humans. Originally, the human diet varied according to the habitat but it was basically a mostly vegetarian, low-fat and very little sugar- diet. There were few sweet flavors (mature fruit and honey), the meat was rare and very lean, salt and savory flavors were rare except for groups that inhabited the coasts. Famines were frequent and, when present, the rare but highly energetic fatty and sugary foods were consumed in abundance whenever found in order to survive the lean times. For this reason, fatty foods and sweets activate the system of pleasure to the maximum extent. They are our life-buoy in case of incumbent ‘famine’.
Unfortunately, as happens with drugs, the most intense pleasurable stimuli are those that give more addiction. Maximum pleasure and addiction come from foods that combine fat and sugar and salt, and this the food industry knows very well. But in order to create irresistible foods, mixing fat, sugar and salt, is not enough. It is also important to create foods that combine contrasting flavors and textures (spicy chicken, sweet pumpkin ravioli, pork chop with mashed apples - sweet ‘n spicy, greasy and salty, spicy and salty).
In addition, the weight game is also influenced by stress. A moderate level of stress stimulates appetite and change the circuits of feeding and pleasure. The ‘fight-or-flight’ response triggers hormonal mechanisms that tend to release all the reserves of fats, proteins and sugars in the blood to increase the energy capacity for the fight or the escape. The hormone corticosterone then leads to overfeeding to replace reserves that should be used in the run. As a result, strategies for reducing stress are also effective in reducing overeating.
Weight gain exposes to health problems such as diabetes, cancer, sleep disorders, cardiovascular problems and others. Fortunately, a drop of a few kilos (ex. from 5 to 10 kg) already brings significant benefits to health. So, although it is difficult to lose a lot of weight, it is best to lighten your body mass even slightly, or, even better, not to gain weight. Eating a healthy and balanced diet and doing a daily physical activity are simple rules for the long-term maintenance of good health and a lean look!
David Linden The compass of pleasure, 2011
Cheesecake-eating rats and food addiction, a commentary