Obesity is the fifth leading cause of death worldwide,
and fourth leading cause of death in Europe. To lower our body mass index and
to raise our self-esteem, we need to know the molecular aspects of weight loss!
This article complements the previous article called: Obesity: a giant problem.
Cells require a
constant supply of energy to generate and maintain the biological order that
keeps them alive. This energy is derived from the chemical bond energy in food
molecules, which thereby serve as fuel for cells. The intermediary molecules
that the body uses to store energy is called Adenosine triphosphate, or ATP for
short. Excess energy is also stored in chemical bonds, mainly those of fatty
acids, the main components of our fat tissue.
There are three distinct types of food that we can digest, and a vast majority
of our energy supply comes from one of them: proteins, lipids or fats, and
polysaccharides or sugars. All of them must be broken down into smaller
molecules before our cells can use them, either as a source of energy or as
building blocks for other molecules. The breakdown processes must act on food
taken in from outside, but not on the macromolecules inside our own cells.
Stage 1 of the enzymatic food degradation is therefore
digestion, which occurs either in our intestine outside cells, or in a
specialized organelle within cells, the lysosome. In either case, the large
molecules comprised of multiple units (polymers) in food are broken down during
digestion intoindividual subunits (monomers)—proteins into amino acids,
polysaccharides into sugars, and fats into fatty acids and glycerol—through the
action of enzymes. After digestion, those small monomers enter the the cell
where they get disassembled further by oxidation.
Figure 1: breakdown
of large macromolecules into simple subunits.
In stage 2, a
chain reaction called glycolysis converts each sugar molecule into two
smaller molecules of pyruvate and subsequently into Acetyl-CoA, producing ATP.
Amino acids and fatty acids skip this step and directly undergo a process
called the citric acid cycle, which is the third and final stage in the
energy production process and occurs only in mitochondria.
schematic view of glycolysis and the citric acid cycle. The whole process can
be simplified by approximating the pathways as such: amino acids get broken
down and mostly used as building blocks, unless there is a shortage of sugars
and fatty acids. Sugars undergo glycolysis, produce pyruvate and subsequently
Acetil-CoA, which enters the citric acid cycle, and produces the most amount of
energy in oxidative phosphorilation, in the form of ATP. Fatty acids get
directly broken down into Acetyl-CoA, and continue on the same pathway as
As our diet changes
to contain more of one of those three types of food, our body adapts to be more
efficient in breaking it down. This happens in stage 1 with the help of various
enzymes, and takes the body approximately three weeks to fully adapt to the
change. A common example of miracle diets is to cut carbohydrates (or carbs,
sugars) and shift the diet towards mostly protein-based nutrition. The body, which
had a majority of its derivates be carbohydrates until now, and had the enzymatic
profile appropriate for that diet, suddenly finds itself without its primary
energy source. Regardless of the amount of other energy sources, it is not able
to produce sufficient energy from the up until recently auxiliary sources, due
to lack of appropriate enzymes. This results in weight loss coupled with
digestion problems and extreme overload of liver, which tries to compensate for
the missing enzymes. After the aforementioned three weeks, the body gradually adapts
to the new regime, and the yo-yo effect occurs. Unless, we do it all again by
changing our diet back to „normal“.
Apart from cell and organ starvation, this method carries a significant risk of
liver and kidney damage, or even their failure.
energy cycle can be of great help in combating obesity as it prevents
Value of food
of food is often disregarded while talking about diets. In contrast to the
energetic value, which gives us the estimate energy our body can produce from
certain food and is measured in calories or joules, nutritive value is the
amount of vitamins, minerals and other helpful chemical entities found inside, which
help the body function properly and execute all of its functions such as
hormone secretion, digestion and general homeostasis. If the energetic value is
the gas to our engine, the nutritive value is the oil, the brake fluid, coolant
WHO reports more
malnutrition every year in countries where obesity is most prevalent. A
sentence contradictory to itself several decades ago has become a rising
concern, especially for children under five years of age. We are used to the
notion that malnutrition equals low body weight and insufficient food intake.
While that might still be true in some underdeveloped countries, more recent
studies place the prevalence of malnutrition in those countries lower than in
some developed countries. It is not uncommon to find under- or malnutrition
coexisting with obesity within the same country, the same city, or even the
All of this sums
up a disturbing notion of modern cuisine: people, but especially children, are
exposed to high-fat, high-sugar, high-salt, energy-dense, and
micronutrient-poor foods, which tend to be lower in cost but also lower in
nutrient quality. These dietary patterns, in coupled with lower levels of
physical activity, result in sharp increases in childhood obesity while
under-nutrition problems remain unsolved.
A simple way to
loose weight is to exercise, a practice known from the dawn of time. Physical effort
of any kind escalates our metabolic needs, and our fat reserves are used up to
combat the rising energy needs during exercising. Yet, entire fields of study
are dedicated to the notion of exercise and weight loss, not only in scientific
terms, but also in form of cosmetics, gyms, supplements, devices, diet plans,
advisors and others, in a far greater quantity. Why is it so hard to loose
weight (for most people, at least), when there is a simple formula for doing
, we gain weight. If input<output
, we loose weight. This is related to the energetic value
of food: if we consume more calories than we spend, we gain weight, and if we
spend more than we take in, we loose weight. The reason there is a limit to the
amount of fat a body can store is the ever-increasing energy demand for
maintaining that weight. Although body fat is relatively inert, its cells still
need a constant maintenance in terms of nutritive and energetic value.
contribute to the difficulty of the task, but the major problem lies with the
two hormones, leptin and serotonin. Serotonin awards every decision that
prolongs and secures our homeostasis, that is, our body's well-being, and
loosing weight and depleting energy reserves is certainly not on that list. So,
as the pangs of hunger claw deeper and the energy reserves deplete, lack of
serotonin associated with food intake increases. Leptin, on the other hand,
while initially positive in terms of weight stabilization, is linked to
serotonin's function, and will succumb to its relentless nagging for that 1
a.m. ice cream. You giving in to the temptation of a chocolate cake is not for your
lack of perseverance, but for the lack of serotonin. Several studies linked
personal happiness with lower body weight and healthier lifestyle.
include the prevalence and abundance of high-fat, high-sugar, high-salt and
energy-dense food served at every fast food restaurant and stall. People are generally
lazy as a function of energy conservation, and if something is available now, they
will get it now. Prevalence and availability of energy-dense food leads to
prevalence of obese people. Related to this is is the already mentioned lack of
nutrient. Needing nutrients, we feel the urge to eat. But if the food is
nutrient deficient, obesity is imminent. Lack of exercise is, however, the
biggest obstacle in any attempt to loose weight.
Diets as a way of
the negative dietary concepts, let's now focus on the positive ones and try to ease
the burden of weight loss.
First and foremost, some sacrifices will have to be made. Change comes when the
aspects of future are more desirable than those of the present, and if we want
for the future us to be healthier, leaner and feel better, we need to adjust
the present in a sustainable way. To help with the process, we need to view
diets as a permanent state, and not just a phase or an ordeal to overcome. The
sooner we understand this, the easier it becomes.
It also takes
time. As discussed before, three weeks is the minimum amount of time our body needs
to adjust to change. We also need to keep in mind that this change comes in
small, sustainable steps, and we should adjust the diet to be just as
sustainable. Slow and steady wins the race.
We can manipulate
our input-output equation on both ends to achieve the desired input<output
state: we can reduce
the calorie intake into our body, and increase the output values by exercising.
The best results are achieved by doing both.
Reducing the input
of calories doesn't mean eating less and being hungry: it means eating energy-poor
foods rather than energy-rich ones. A device such as a calories counter could
be of great help in this regard.
The same rule applies for exercising: slow and steady wins the race, and
exercising less in more frequent intervals will always be preferable to an
occasional, extremely hard sweat.
Controlling the input and output of energy can be a
daunting goal, but one worth pursuing. Not only does loosing weight prevent
diabetes, cancer, osteoarthritis, and cardiovascular diseases, but it also
raises self-esteem, and lifts a big burden made of fat from our backs, in both
a literal and proverbial sense!
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