It seems that the change in bodyweight should be a strictly increasing function of calories eaten minus calories spent. The first caveat to this claim is that calories in the food eaten do not equal the calories absorbed, which is what matters for weight gain. People differ in the efficiency of their digestion – that is what bariatric surgery relies on. Also, food labels use calories measured by the burn method (dry the food, burn it, measure the heat output), which ignores for example that coarsely chewed food chunks pass through the digestive tract relatively unchanged, thus contribute few nutrients to the organism. An extreme example is wholegrain flax (linseeds) that remain undigested due to a waxy coating. In nature, seed dispersal by birds relies on the indigestibility of the seeds.
Even if calories absorbed could be accurately measured, the type of food eaten would still matter for weight gain due to imperfect willpower. Some foods are more addictive than others, notably those rich in refined carbohydrates – an easy example is drinks that are essentially sugar-water. Consuming a given amount of calories from high-glycaemic-load sucrose makes people eat more sooner on average than ingesting the same calories from slowly digested whole grains or unsaturated fat. Similarly, ignoring willpower limitations is why abstinence-based programs to prevent sexually transmitted infections, which naively might be expected to be 100% effective, are in fact ineffective (Underhill et al 2007, doi:10.1136/bmj.39245.446586.BE).
There are various tricks to circumvent limited willpower to win the game against one’s future tempted self. To reduce temptation, food should be out of sight outside mealtimes (in cupboards, drawers, fridge) and unhealthy snacks should not be bought at all. Even seeing dishes and cutlery may trigger cravings, in which case these too should be placed out of sight when not in use.
Avoiding grocery shopping while hungry is an old piece of advice, which may be taken further by having someone else buy your food. Two people can even agree to grocery-shop for each other according to shopping lists exchanged beforehand. Online ordering may be a solution, but of course the merchants want customers to buy more, so advertise tempting foods with photos on their website. These ads can be blocked with some effort. A more sophisticated solution is to have one’s own user interface (front end) interact with the merchant’s website – scrape the data on inventory and prices, send commands to buy.
Democracy picks the leader who is best at getting elected, not necessarily the best at leading the country. The ability to become a leader differs from the ability to lead. For example, populism and overconfidence in oneself may help one’s election prospects but harm performance at governing.
Even if there was some very accurate way to select the best leader (e.g. test their honesty, intelligence, work ethic, in addition to electability), it may be not be feasible in practice to make this person govern for long. The reason is the political economy constraint that someone better at obtaining power can depose the best leader (one whose government would maximise social welfare, however defined). The disruption resulting from the coup may even harm society more than the difference between being governed by the best leader as opposed to the best power-grabber. In this case, the leadership of the most electable person may maximise welfare, subject to assumptions like „the best power-grabber is also good enough at retaining power, preventing coups once in government”.
The skills of getting elected and organising a revolution probably differ, so an elected government has some of the same vulnerability as the best leader. The political economy constraint of preventing a coup may then favour making the strongest dictator or the most dangerous revolutionary lead the country. However, this may not be the best system for selecting leaders due to a tradeoff between the ability to govern and the ability to overthrow a government. The welfare-maximising selection system subject to the political economy constraint would pick the person who is best at governing among those who can successfully resist a coup. Democracy may be such a compromise, choosing reasonably popular leaders who have a low probability of being overthrown and are adequate at governing. On the one hand, democracy may avoid a ruthless dictator whose rule is very stable, but harmful, and on the other hand a saintly leader who would be deposed quickly.
Animals may evolve a preference for a varied diet in order to get the many nutrients they need. A test of this on mice would be whether their preference for different grains is negatively autocorrelated, i.e. they are less likely to choose a food if they have eaten more of it recently.
Variety is perceived mainly through taste, so the mechanism via which the preference for a varied diet probably operates is that consuming a substance repeatedly makes its taste less pleasant for the next meal. Spices and other flavourings can make the same food seem different, so may interfere with variety-seeking, essentially by deceiving the taste. A test of this on mice would flavour the same grain differently and check whether this attenuates the negative autocorrelation of consumption, both when other grains are available and when not.
If seasonings reduce variety-seeking, then access to spices may lead people to consume a more monotonous diet, which may be less healthy. A test of this hypothesis is whether increased access to flavourings leads to more obesity, especially among those constrained to eat similar foods over time. The constraint may be poverty (only a few cheap foods are affordable) or physical access (living in a remote, unpopulated area).
A preference for variety explains why monotonous diets, such as Atkins, may help lose weight: eating similar food repeatedly gets boring, so the dieter eats less.
Overconsumption of salt is a significant public health problem. People are reluctant to reduce the saltiness of their food, because it would taste bland. Eventually, preferences adjust so that a diet without added salt tastes normal and salted foods are perceived as too salty. The only question is how quickly tastes adapt.
My experience of stopping adding any salt to my food was that the bland taste lasted less than 3 days, after which I had fully adjusted to the new reduced level of saltiness. An easier way to adapt may be to gradually reduce the amount of added salt, as opposed to suddenly cutting off all of it, as I did. In that case, there may be no perceived taste difference, especially if the reduced salt is accompanied with increased amounts of other seasoning, like pepper. Given the smallness of the adjustment cost and the health benefit of cutting salt consumption, doing it is a clear and easy win.
There are at least two potential explanations for why students from group A get a statistically significantly higher average grade in the same course than those from group B. The first is discrimination against A in admissions: if members of A face a stricter ability cutoff to be accepted at the institution, then conditional on being accepted, they have higher average ability. One form of a stricter ability cutoff is requiring a higher score from members of A, provided admissions test scores are positively correlated with ability.
The second explanation is discrimination in favour of group A in grading: students from A are given better grades for the same work. To distinguish this from admissions discrimination against A, one way is to compare the relative grades of groups A and B across courses. If the difference in average grades is due to ability, then it should be quite stable across courses, compared to a difference coming from grading standards, which varies with each grader’s bias for A.
Of course, there is no clear line how much the relative grades of group A vary across courses under grading discrimination, as opposed to admissions bias. Only statistical conclusions can be drawn about the relative importance of the two opposing mechanisms driving the grade difference. The distinction is more difficult to make when there is a „cartel” in grading discrimination, so that all graders try to boost group A by the same amount, i.e. to minimise the variance in the advantage given to A. Conscious avoidance of detection could be one reason to reduce the dispersion in the relative grade improvement of A.
Another complication when trying to distinguish the causes of the grade difference is that ability may affect performance differentially across courses. An extreme case is if the same trait improves outcomes in one course, but worsens them in another, for example lateral thinking is beneficial in a creative course, but may harm performance when the main requirement is to follow rules and procedures. To better distinguish the types of discrimination, the variation in the group difference in average grades should be compared across similar courses. The ability-based explanation results in more similar grade differences between more closely related courses. Again, if graders in similar courses vary less in their bias than graders in unrelated fields, then distinguishing the types of discrimination is more difficult.