The Hungry Brain is a new (2017) book by Stephan Guyunet on how to “outsmart” the instincts that make us overeat. “Outsmart” is a good word, because he doesn’t advocate pure willpower as the answer. There were a few observations that I found of special interest.
1) Leptin is a protein that’s made in the fat cells, circulates in the bloodstream, and goes to the brain. It is a way of telling you that you are not underweight. Some people have leptin deficiency and
Unlike normal teenagers, those with leptin deficiency don’t have much interest in films, dating or other teenage pursuits. They want to talk about food, about recipes.
Starvation has a similar effect in normal people. Patients who were put on a semi-starvation diet for months were hungry of course, but also:
their conversations, thoughts fantasies and dreams revolved around food and eating. They became fascinated by recipes and cookbooks. Their mental lives gradually began to revolve around food.
This indicates to me that people’s drives and emotions at any particular point in time drive thoughts and interests and not just the other way around.
2) Stephan also talks of the finding in obesity that the hypothalamus was inflamed, and he says that this made sense.
Previous research had already implicated chronic inflammation in insulin resistance–a condition in which tissues like liver and muscle have a harder time responding to the glucose controlling hormone insulin -and this process had already been linked to increased diabetes risk.
So it wasn’t a major leap to suppose that there was resistance to leptin as well in inflammation, and therefor more leptin would be needed to inform the hypothalamus that the body is not starved, and therefore more fat cells (or bigger fat cells) would be needed to create that leptin.
Even worse, but the inflammation (and other damage) in the hypothalamus is caused by too much fattening foods, (perhaps by putting too much leptin in the blood that overwhelms the leptin receptors in some way).
So there is a positive feedback in obesity.
This means that people who already eat too much are harming a part of the brain that would normally say “enough”, so that their normal weight set point increases (like the set point of a thermostat being turned up).
I asked the author via email why, if there is damage to the hypothalamus, there isn’t damage to other parts of the brain.
He gave this idea as a possibility:
Parts of the hypothalamus (the parts that get inflamed) have a leaky blood-brain barrier, presumably because the hypothalamus is designed to sense the metabolic state of the rest of the body. So anything that’s circulating in the bloodstream can impact the hypothalamus more than other parts of the brain, e.g. if a person overeats and experiences excessive circulating levels of nutrients.
I also asked him if a damaged hypothalamus would affect other processes in the body. He gave this interesting answer:
The hypothalamus regulates many things, and many are linked to energy status. Four of them that are altered in obesity are blood glucose regulation, sexual maturity onset, reproductive function, and blood pressure regulation. There is some evidence that the neuronal changes that accompany obesity can contribute to poor blood glucose regulation. Sexual maturity onset is linked with leptin levels and this probably explains why puberty onset has been getting earlier lately as the population has been gaining fat. …There is evidence that obesity-related hypertension is caused by excess leptin acting in the hypothalamus, so that could be an indirect effect of hypothalamic inflammation (hypothalamic inflammation -> leptin resistance -> fat gain -> high leptin -> hypertension).
An acquaintance of mine who was dramatically overweight had an operation to make his stomach smaller, and not only did he lose weight, but his diabetes was cured. I found this hard to believe at the time, but after reading the “Hungry Brain”, it starts to make sense.