When I once visited the Western Wall (aka the Wailing Wall) in Jerusalem, I noticed that the cracks in the wall in the women’s section contained significantly more of the prayer notes worshippers insert than in the men’s section. I asked a friend who is supposed to know things like that, and his answer was unequivocal. “Childless Israeli women ask for a child,” he said, “but American women ask for a permanent weight loss.”
He was joking, of course, but there is a grain of truth here: Keeping your weight down takes great willpower. That, plus or minus a prayer to the god of your choice, may do the trick.
But, why is it so difficult?
Blame it on natural selection
Life was not always bountiful as it is today. From the dawn of humanity, about 250,000 years ago, until the advent of agriculture about 8-10,000 years ago, making a living, or even just staying alive, was tough. People had to search wide and long for edible plants, and if they were lucky, some scraps of meat left behind by predators.
Limited food resources is a powerful selective force, and the adaptive response was to increase the efficiency of the metabolism. When we metabolize food, some gets captured as ATP, for short-term use. The rest could get dissipated as heat, which is inefficient.
To increase efficiency, and thereby increase the odds of survival, our metabolism evolved to capture more of the “leftover” energy and store it for a “rainy day,” or in reality, for a period of drought. And the molecule that stores that extra energy? None other than the now dreaded fat.
Times have changed, and we are now blessed with a surfeit of food, and we don’t even walk to the food store. The result? We take in more energy and spend less of it.
Our metabolism is no great help either. It is powerfully geared to store energy as fat rather than waste it as heat.
That brings me to a discussion of fat and fat cells.
The fat cell allowance
In theory, there are two main ways you can increase your body fat:
- You can increase the number of fat cells in your body
- You can increase the amount of fat content per cell
The second option has been amply documented because it is quite easy to demonstrate. All you need to do is take biopsies of adipose tissue before and during the weight gain and measure the fat content in the cells. If you want to really nail it, you take an additional biopsy after weight loss and document the drop in the lipid content of the fat cells.
But what about changes in the number of fat cells? That’s much tougher to measure, for obvious reasons. You can’t do a total body fat cell count. Or, can you?
Fat cells develop, like any other tissue, from undifferentiated stem cells. They, then, undergo a number of cell divisions, each one bringing it closer to the definitive fat cell. Finally, after the last division, the fat cell is fully differentiated.
So if we want to find out how many fat cells we have, we can label the DNA of the terminally-differentiated cells with radioactive carbon. This way we can get their ‘birth date’, and then follow the disappearance of the radioactivity over time and get their life span.
Such studies were indeed done in mice but there are two problems.
- Human and mouse metabolisms are different.
- Incorporating radioactive carbon into fat in humans is problematic because fat turnover is very slow (about 10 years), and the subject would, therefore, be exposed to high levels of total radiation over a long period of time.
How we learned about human fat cells
Kirsty Spalding and her colleagues at the Karolinska Institute in Stockholm had a clever idea.
They knew that although atmospheric levels of radioactive C14 were relatively constant for centuries, between 1955 and 1963 there was a major increase. This is because, in our infinite wisdom, nuclear bombs were tested above ground.
They also knew that a chain of reactions in the body ensures that, at any given time, the radioisotope content of human DNA matches that of the atmosphere. By employing this knowledge, the authors could thus follow fat-cell dynamics in individuals born around 1955–63.
What they found when they studied the dynamics of fat-cell number in some 700 adults, both lean and obese, and combined their data with previous observations in children and adolescents was that fat cells have a high turnover. What that means is that new cells are continually being born to replace their dead predecessors. The average age of a fat cell seems to be about 10 years in both lean and obese individuals.
The number of fat cells as a proportion of all cells remained constant in each weight group. But the total number of new fat cells was higher in obese subjects, suggesting that they are replenishing an existing larger pool.
The number of fat cells increases until adolescence, after which it remains more or less constant. So the finding that obese people have a larger pool of fat cells means that they were endowed with it before adulthood. Pretty discouraging, because it implies that this endowment is the proverbial gift that keeps on giving.
Implications for dieters?
So, can obese people do anything about their weight? After all, they’ve already accumulated a large pool of fat cells in childhood and adolescence. The answer is yes. They can still reduce the volume of their fat cells. But, anybody who ever went on a diet is now thinking, yeah, but that easier said than done.
And, what about the lean among us? Do they still need to worry about dieting? After all, we have fewer fat cells? The answer is yes. Remember, even if you are lucky enough to have fewer fat cells, they can still store larger and larger amounts of fat when presented with excess energy (a.k.a. calories).
What about liposuction?
So, you may be asking…why not reduce the number of fat cells with liposuction and be done with this big fat problem?
This is still not a panacea. As we know from studies of people who had undergone liposuction, they slowly regain their previous weight by storing more fat in their remaining cells.
Liposuction is futile, ladies and gentlemen! Oh well, in that case just pass the foie gras, please!