Monday, March 17, 2008

Two urges to eat

As a biologist, in a lifetime attempt to lose weight, I have always wondered about the fascinating nature of eating. I will begin with a general overview on eating and later discuss our conscious part in it.
To physically live, we need two major ingredients - food and breath. Comparing the utilization of these two assets seems different; the eating appears to be volitional while continuous breathing feels essential. However, more accurate observation reveals that they are in principle rather similar; both have a volitional aspect and an essential aspect. However, they differ in their proportions. If we decide to stop breathing it will take at most a few minutes before we are naturally forced to restart breathing. When we decide to stop eating it takes much longer before we finally eat, regardless of our decision. The evolutionary rationale for this type of behavior is easy to understand. Oxygen is almost always present in our surrounding air and it is unnecessary to develop oxygen reserves in our body, therefore we need to breath continuously. Food on the other hand has not always been available, making it crucial to develop fat reserves and making it unnecessary to eat all the time.
It is interesting to watch dolphins who, like us, breathe air but live in the sea where air is not available. They manage air more like we manage food, dolphins decide when to breath and they can also hold their breath for long periods of time.
It is no wonder that dolphin models are useful in yoga, as yoga is based greatly on breathing.
It is not coincidental that I have introduced yoga here. Evolution has led us to develop both eating and breathing with major autonomous (non-voluntary) regulators. It can therefore be concluded that if we wish to control our eating, we need to develop “yoga type” dexterities.
This also explains why most diets fail, as well as diet pills usage (after 2-3 years). Note that the mammalian energy interface (regulating our eating) is related to about 25% (in mice) of the genes, thus trying to skirt it is pointless. Genes are associated with the lean component of our body mass as well. The main issue is that obesity is a very complex disposition, e.g. a core network module in humans and mice was identified that is enriched for genes involved in the inflammatory and immune response and has been found to be causally associated to obesity-related traits.

I will clarify, how long term effects on our nutrition, requires taking into account the bodily holistic physiological goals as well as its intricacy. Furthermore, affecting these goals intelligently (e.g. good night sleep preferably without headaches, or via physical activity, preferably with music) can lead automatically to smart eating habits and weight loss, without too many struggles. Overeating, rather than the obesity it causes, is the trigger for developing metabolic syndrome.
Note that these special efforts are essential only at our wealthy times, e.g. when Cuba was hit with serious food shortage and people had to walk or cycle wherever they needed to go, health was drastically improved...(today, with better economics it is worse again).

The major point I want to emphasize here is that the need to eat, as well as our satiety, are regulated by two unrelated urges. One is our daily energy expenditure and the other is the need to accumulate energy for the future (our bodily worry).
Which urge we choose to fill, depends on our genetics and condition.
If our body feels that there is no need to worry, we will be satiated once we eat approximately the averaged total energy that we expend daily. This was nicely demonstrated when healthy people were asked to drink various caloric shakes and they drank more or less to reach the same caloric total regardless of the shake.
Recently, scientists from Chicago have demonstrated how the brain integrate information from multiple domains and assesses hunger or satiety. We also have mechanisms to evaluate the caloric value of our foods. Scientists from Duke university have shown that calorie-rich nutrients can directly influence brain reward circuits that control food intake independently of palatability or functional taste transduction. Recently it was shown that the ghrelin hormone can change how we see and smell food, there is no doubt that multiple factors affect our satiety.

On the other hand, if our body feels “worried” (economically not emotionally), the second urge to eat will be initiated, an urge that will subside only when the worry disappears.
Note the multiple reasons for this bodily worry (detailed later); if indeed a quarter of the genes are associated with our weight, it is no wonder that so many reasons are relevant.
The obesity related second urge is manifested not only via the unending urge to eat, but also via bodily "saving policy" [see the top sketch, no water (=calories) is wasted]. Is obesity associated with lower body temperatures?
This obesity related policy prohibits dealing with health issues, promotes no-exercise and leads as much energy as possible to the fat storage. It naturally explains why obesity is associated with so many maladies (e.g. The stress cytokine IL-6, induces obesity related insulin resistance). At old age this "saving policy" is manifested via sarcopenia (loss of muscle mass) which is frequently associated with fat accumulation and varoius disorderly conditions (via renin-angiotensin system?).
What was once a smart temporary strategy to overcome food deficiency, more recently has become a steady limiting strategy that causes the fat to become fatter and sicker. Even obese children find food more reinforcing than do nonoverweight children.
It is, therefore, easy to conclude why obese people can/want to consistently eat more, why they eat quickly (to eat more per time), why satiation is impaired, why they stop eating only when they are full, why they eat more on weekends or when served with smaller bags of potato chips , why they behave differently at buffets, why they stop eating due to technical reasons (e.g. no food left on the table), why there is no relationship between eating pattern and sensations of hunger or fullness and thus why recommending healthy eating is usually futile.

A note for the non-obese reader - It will be difficult for the non-obese to empathize with the obesity behaviors as he is mainly acquainted with the first eating urge. It is not a problem for the non-obese to meet his energy needs and thus to follow healthy nutrition guidelines . The obese, in comparison, is eating due to the second urge and thus is rarely satiated or filling his energy needs as most energy is reffered to storage. For a laugh (and to better understand) see this "getting fat" youtube.

Some of the reasons for bodily worry (besides the trivial reason of lack of food):
* Lack of physical activity (or muscles...) - it raises the question of why didn’t we move (not enough energy?) and possibly assumes that eating might supplement the energy required for movements. Note that exercising reduces the urge to eat... or also another study from well as affects our mitochondrial coupling. Indeed muscular strength is inversely and independently associated with death in men.
* Overeating - Digestion of the eaten food, requires abundance of efforts. Thus overeating will cause temporary lack of attention from most other bodily functions (we might feel tired). This evolutionary smart mechanism that was ideal when dealing with sporadic food abundance, is hazardous today when food abundance is constant. It also may explains why fasting is healthy; all the digestive effort can be forwarded to other essential functions. This btw gives a sense of abundance and I will speculate and suggest that thus it does not promote bodily worry. It is no wonder that fasting has become a "hot" issue, e.g. Fasting-Induced Hormone FGF21. Note that in contrast to fasting, diet foods lead to obesity as they promote its economic Saving policy.
See also how energy restriction induces extension of life span in obese but not in lean mice.
* "Thinner" fat cells metabolism (results of diets). Fat cells that have lost their stored fat, induce “catch-up” processes which promote the second urge of eating. Note how manipulating fat cells can increase the body’s metabolism. Also known, visceral adipose tissue promotes obesity.
* Stress, ADHD (attention deficit hyperactivity disorder) and other psychological disturbances (e.g. depression) are associated with obesity. Note that stress is a complex issue, I have tried to define "muscle/body worry" vs. "emotional worry" as different stress "shippers" and to which we do not respond equally. e.g., “muscle/body worry” promotes eating while “emotional worry” represses eating.
I propose to interpret the association between emotional stress and overeating as a decreasing ability to control overeating and not as if the emotional-stress promotes overeating. Indeed, obesity (initial increased overeating) is associates with the emotional-stress over eating, while leanness is more likely to be associates with eating reluctance under stress.
* Lack of sleep is also associated with obesity... btw, singing could help a silent night...
and not to mention (here, as the article is already too long...) lack of love , body image or mind-body attitude.
and of course other reasons that you might want to add…

Final words
Be smart if you wish to lose weight… rid yourself of your bodily worry ...

Don’t Muscle Worry, Be Happy. aps Observer, 21(4), April, 2008
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