This might have been possible, but a simple calculation shows that this is unlikely. A man who is 100 kg too heavy and 50 years old, to a first approximation ate 2 kg per year too much. Two kilograms of fat is 1400 Cal and thus comparable to what one eats in 4 days to one week, depending on your, height, weight and level of activity. In other words, this man ate only about one or two percent more than he should have. You may increase this number somewhat to account for the fact that a larger body also needs more energy. Still the additional amount eaten by an overweight person is small and will be hardly noticeable in day life.
In the times that humans were hunters and gatherers, it should have been easily possible to eat a few percent more than usual. The year to year variability in the availability of resources is large; on the negative side think for instance of floods, droughts and grasshopper plagues. A human that is able to survive in a bad year, should easily be able to hunt or gather double his need in good years. One would expect the maximum amount of food a person can find is much more than a few percent more than the average needed. Otherwise, a human with a bit of bad luck would soon starve to death and be removed from the gene pool.
This may be illustrated by numbers from other animals. Ecotravel states about lions that: “If suitable prey is available, lions eat every 3 to 4 days, but can go without food for more than a week. They average about 5 to 7 kg meat daily, but can consume about 25% of their body mass if necessary. An adult lion will kill in the region of 15 animals per year.” Such a lion has some spare time to hunt more often. The same was most likely also the case with early man.
Not only should it be very easy to eat more than a few percent more than you need, then and now. It should be very difficult to estimate within a few percent how much food is needed and how much energy is in the food eaten. Thus, there is bound to be a feedback mechanism that keeps the energy stores not too low (starvation, reserve for bad luck and illness), but also not too high (slows one down, more attractive prey). As I have illustrated above, this feedback mechanism was always already needed. This feedback would use information on how much energy is stored in the body, similar to a thermostat using the room temperature and not an estimate of how much the heating warms and is lost through the windows and walls.
Thus looking for a cause of obesity, we should have a look what we do differently now that may break such a feedback mechanism. The most straight forward change is that we are continuously eating carbohydrates (bread, pasta, potatoes, etc.). As the stores for carbohydrates (glycogen) are small, carbohydrates are used first for fuel. Someone who eats carbohydrates day in and day out does not use his fat burning capabilities. Just as with muscle, bones and your brain, the saying “use it or lose it” is likely also true for the metabolic system for fat. Enzymes for fat burning that are not used, are produced less, just as any other enzyme. If the enzymes are missing, the body no longer notices the large fat stores; these stores no longer provide sufficient energy when needed.
Another obvious change is that we are less active, which together with eating carbohydrates, means that the glycogen stores are often full to the brim. This may lead to problems with blood sugar at the next carbohydrate-rich meal or snack. The blog Marks daily apple has much more background information on the difference between then and now and how we can mimic past behaviour to achieve better health.
More posts on paleo (diet and lifestyle topics inspired by evolutionary thinking).
- Paleo and fruitarian lifestyles have a lot in common
- A comparison of the main ideas and recommendations of these two lifestyles.
- Natural cures for asthma?
- Some ideas for natural ways, which helped me cure or reduce asthma.
- Sleep and diversity
- Differences in sleeping times, from early bird to night owls, may provide security advantages.
- Freedom to learn
- Forcing children to learn stifles their innate motivation to teach themselves and may thus be counter productive.
- The paleo culture
- After the Ancestral Health Symposium 2012, as discussion started about the sometimes self-centred culture of the paleo community