Evolution and obesity

As I indicated in my recent post on Rob Brooks’s Sex, Genes and Rock ‘n’ Roll: How Evolution Has Shaped the Modern World, Brooks devotes some time to the issue of obesity. Rob has also blogged about obesity and published a paper with Steve Simpson and David Raubenheimer on it (although the book covers more ground).

First, why is obesity an evolutionary problem? In his book, Brooks set out why:

Some researchers use the fact that the obesity crisis emerged so recently as a reason to reject or ignore evolutionary or biological explanations for the crisis. After all, they argue, evolution takes thousands of generations. While they are certainly correct that we are not evolving to become fatter, obesity certainly has deep evolutionary roots among its causes. …

The combinations of genes that we inherited from our ancestors are adapted to the environments where those ancestors lived and bred, not the environments we inhabit today.

For most of our evolutionary history, humans ate a diet high in protein and fat, with some complex carbohydrates. With the neolithic revolution, some populations increased the proportion of their diet that consisted of carbohydrates. Over the last 50 or so years, the level of simple carbohydrates in diets has soared. Humans are not adapted to this modern diet and populations that have only very recently been exposed to this modern diet are more likely to face problems. This can be seen in the high rates of obesity on many Pacific islands or the high rates of diabetes and alcoholism among indigenous populations.

One of the arguments as to why the modern diet poses a problem is the protein leverage hypothesis. The basic idea is that humans have a stronger propensity to regulate protein intake than non-protein calories. As humans have a basic daily protein need – we eat until we satisfy our protein requirements. If the food we are eating has low protein content, we need to eat more before hitting that satiation point. These extra calories are what make us obese.

Brooks and his paper co-authors then took this question into the modern supermarket and looked at the prices of protein and carbohydrates. In his book, Brook’s summarises their findings:

I did a quick assessment of the costs of 111 common foods in my local supermarket and takeaway outlets. I was amazed that every megajoule (1000 kilojoules or 239 calories) of energy from protein adds US$3.26 to the average price of a food, but every megajoule of carbohydrate actually reduces the cost of food by 38 cents. …. Because sugars and starches are cheaper relative to protein than at any other time in human history, economic costs are likely to bias the foods we buy and eat toward energy-rich yet protein-poor diets. Within industrialised societies this effect is likely to be most extreme for poor people who have access to a wide range of foods but who are constrained in which foods they can afford to buy.

This led them to estimate that to cut kilojoule intake by 1,600 kilojoules (the estimated jump in calorie intake since the early 1970s) would require a subsidy of US$0.72 per person per day. This is around $262 per obese person per year, or around one-fifth of the estimated annual medical spending due to obesity.

It provides a case for government action, with the benefits well excess of the cost. Brooks puts it as follows:

One possibility is to subsidise high-protein foods such as lentils, lean meat and fish. Another is to reduce subsidies or tariff protection on sugar and cereal staples. An alternative to the politically perilous business of intervening in commodities markets is to tax products that clearly generate a large part of the public health burden. Reductions in carbohydrate intake might more effectively be achieved by raising the price of carbohydrate energy than by lowering the price of protein. Products like soft drinks, cordials, fried potato products and ice cream constitute a large proportion of the energy intake of adults and children at risk of obesity but contain little or no protein. Special taxes on cheap carbohydrates could well prove to be particularly effective.

Getting rid of subsidies and tariffs is an excellent idea, but I am not sure this is a one-way street for obesity reduction. Sugar quotas in the United States raise the price of sugar. Or take high-fructose corn syrup. Corn prices are artificially inflated by the ridiculous ethanol related subsidies in the United States. Would a truly unsubsidised, free market in corn raise or lower the price of corn syrup? I’m not sure, although that is one experiment I would like to see.

On the subsidisation of high protein foods, I am not sure whether this would succeed. Assuming the subsidisation occurred at the point of sale, we would see an increase in demand for these products and some substitution from carbohydrate heavy foods to these subsidised foods. However, we would also see an income effect, whereby the person could use the extra income freed up by the lower price of protein to buy more ice cream. We might also see underlying protein prices increase, with increased demand leading to much of the subsidy going to the fixed factor – the primary producer of the protein.

I’d be more optimistic about the effect of a tax on high-sugar products. There is reasonable evidence that soft-drinks and the like have a high price elasticity (demand is responsive to changes in price). However, there is also likely to be an income effect, whereby reduced income caused by the higher price of sugar might cut protein consumption. I would not expect the reduction in protein purchases due to reduced income to be larger than the incentive to substitute protein for sugars, but we should consider it.  This is particularly the case where obesity is most concentrated in the low socio-economic income groups.

A good step would be to test this by running some randomised trials (if they haven’t already been done) to see if the tax converts into reduced obesity. The evidence on food labelling and calorie disclosure is that it is ineffective, while there is a long history of sin taxes successfully reducing “sinful” consumption. However, I’m wary of these sorts of ideas as there are always unintended consequences. Sin taxes hit a wide number of people who are using the product sensibly. I’d like to see an estimate of the cost of their loss of enjoyment. Even among those who are obese, a substantial part of their life enjoyment might come from eating high-sugar foods. Perhaps they have decided it is worth the cost of obesity (and if you consider that they should not be allowed to impose the costs of their decision on the health system – don’t let them).

Thankfully, I’d be reasonably immune from these taxes as I like to stick to the edges of the supermarket. I’d encourage anyone to do this. However, this makes me even more reluctant to support a sugar tax. One should be wary of advocating intrusive actions when the intrusion is not on yourself.

Brooks, R., Simpson, S., & Raubenheimer, D. (2010). The price of protein: combining evolutionary and economic analysis to understand excessive energy consumption Obesity Reviews, 11 (12), 887-894 DOI: 10.1111/j.1467-789X.2010.00733.x


  1. Subsidies are mentioned in regards to ethanol (demand for corn), but don’t the subsidies to produce corn (supply of corn) work in opposition to the subsidies for ethanol that you state are inflating corn prices? Unscientifically analyzing the result I would note that corn is such a cheap energy source that, in addition to the proliferation of HFCS, we also use it to feed the majority of our “high protein foods” because it is cheaper than allowing them to graze on their natural diet of grass.

    Too man band-aids on top of band-aids already IMO.

    1. I agree. There are plenty of policies that pull in each direction. It would be interesting to know what the relative prices would be in the absence of all these countervailing subsidies. Rip those bandaids off.

  2. Besides subsidies, the government, the medical establishment and environmentalists actively promote high starch diets. This is not going to change, and the obesity epidemic will continue regardless of subsidies.

    1. One thought in the back of my mind when I wrote this post was a carbon price – what would be the relative price effects on protein and simple carbohydrates? My guess would be that protein would become even more expensive on a relative basis.

  3. Hey,
    I find your reasoning interesting, but have had several problems with the recent high-protein diet recommendations (just as I had problems with the high carbohydrate, low fat diets popular 10-15 years ago). First, there was no empirical evidence that there is a difference in satiety or satisfaction or weight loss in diets with different macronutrient composition tp://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763382. Second, carbohydrates speed up the metabolism by increasing the conversion of thyroid hormones in their more active form (t4 to t3)
    Why carbohydrate restriction might really work is rather frightening: you get into a similar metabolic situation as diabetics, where ketones are used instead of carbohydrates. This can end up in ketoacidosis and diabetic coma… Also, a high protein intake leads to a larger production of urea and thereby demands much more of the kidneys.
    Personally, I find it funny how proteins were recommended in the 70ies, carbs and low fat inthe 90ies and now its proteins again. At the same time, the recommendations of the scientific societies remained pretty constant at around 45-55% carbs, 30% fat and 15-25% protein…
    In my opinion, too many dietary recommendations destroy our “feeling” for food, we stop listening to our body (infants are usually very good at picking the right food) and end up thinking about food all the time. That makes us eat more and misuse food as an emotional regulator…

    1. I think your last line is the key point – what is our feeling for food? I’d be interested to see a study where these different diets were tried without the instructions for calorific restriction used in the study you referenced. Rather, the study subjects could be instructed as to the categories of food they can eat. That would seem to allow a test of the main implication of the protein leverage hypothesis – that protein moderates hunger.

  4. To refer to a ‘sin’ tax completely misses the point about the unhealthy influence big business (big sugar, big salt, big peanut, big fructose syrup, etc) on the legislative processes in America. With three times the lobbyists than politicians in Washington and better funded by orders of magnitude the relationship the US government has with big business is extremely porous and is one reason of many that action to tackle obesity in the US at least will be limited, at least through this generation.

    Understanding how the social world works develops an awareness that the emerging generation can learn from the mistakes of their ancestors and this is not an evolutionary suited problem, but a cultural and social scientific one. It’s not only generation-effects evolutionary theory struggles with, also genres and trends. Stephen Jay Gould called culture ‘the Lamarckian Juggernaut’ and even Richard Dawkins lectures that culture evolution moves at speeds a million times faster than genetic evolution, and evolutionary thinkers on culture Boyd & Richerson have written more fully on culture’s speed in a paper ‘Built for Speed’.

    The move to sedentary occupations hasn’t helped as well as the advent of the TV which has turned sitting down into a profound lifestyle culture for many, many people. The mass production of industrialised food amongst a population has seen deep changes to diet away from fresh produce and more towards convenience food, canned food and fast food. If you haven’t seen the documentary ‘Food Inc.’ it’s worth watching with the quite alarming statement that most of the stuff that Americans consumer isn’t technically food, but food substitute.

    There is a lot of cherry-picking going on here to try and make an even weak evolutionary argument for the current obesity crisis. Industrial foods stuffs are geared more towards value and the profit motive and people’s health is of secondary consideration for manufacturers who all too often hide behind the increasingly hollow “people are free to make their own decisions” lame statement. If capitalism really believed people were free and beyond influence in any shape or form then they wouldn’t spend billions and billions on advertising, not spend 100s of millions lobbying politicians to dilute or dismiss legislation that affects big business, or pass legislation that results in new streams of corporate welfare and subsidies for big business.

    Darwin wrote himself a number of times that natural selection was “much diminished” in civilised societies. He also wrote something much more telling. Letter 2931 Darwin to Lyell, Charles 28 Sept 1860

    “I quite agree with what Hooker says that whatever variation is possible under culture is possible under nature; no that the same form would ever be accumulated & arrived ay be selection for man’s pleasure, & and by natural selection for the organism’s own good.”

    Read that and read it again, there are some crucial points made here by Darwin.
    (1) It’s not true to say that whatever variations that culture makes that nature can make, that’s simply not true. Nature doesn’t make computers, cars, books or satellites. Indeed, the human social world is made up of trillions of artifacts that nature could never make, and looking at the corrosive effect some of the processes in making these artifacts have had on the natural world, that’s no bad thing.

    (2) Artificial/human selection is for man’s pleasure writes Darwin. In ‘Origin’ he writes artificial selection is for man’s use and man’s fancy. We can contrast this with ‘natural selection’ (preservation) which has no foresight and is only does ‘for the organism’s good’.

    Is anyone seriously proposing that obesity and all its associated health problems is for the human organisms own good? It’s to do with man’s use/pleasure/fancy which at this time is unhealthy shaped by the idea (and for some an ideal) of free market capitalism. To understand culture is to understand the causative behavioural software it enables to shape human thought and action. Currently (and that is no metaphor) capitalism has a hold but it has been exposed as deeply flawed now that we know that capital is finite, meaning that not all people can benefit from this system. Moreover, in the surge to create the capital we have at present this had such a destructive effect on nature’s aggregate that we can see this instability registered across a range of indicators.

    Again, one system is for the good of the organism, the other for man’s pleasure and fancy. Human current fancy is held by capitalism but this will change, it has to or as James Lovelock (Gaia author) fears we won’t finish this century with more than one billion people. This is not just a problem, but the problem of all problems.

    I’ll leave you with the words and beliefs of Michael Shermer, the dogmatic who asserts that the economy of humans ‘mirrors’ the economy of nature. There has been no accepted theory of culture and mind from the evolutionary perspective over the last 152 years. That is a fact. There have been 10+ schools of thought on this task and they have not managed to generate this accepted theory of culture and mind. Due to the number of attempts its important for evolutionary theory to realise this but all we have are narratives on a range of phenomena where there is also a sociological and cultural reason which is being overlooked. A true sign of pseduo-science.

    In Shermer’s most recent book ‘The Believing Brain’ in section 9 – Belief in Aliens’ he writes:

    ‘What happened to those big-brained culture-generating Homos: habilis, rudolfensis, ergaster, erectus, heidelbergensis, and neanderthalensis? If big brains are so great, why did all but one of their owners go extinct?
    Historical experiment after experiment reveals the same answer: we are a fluke of nature, a quirk of evolution, a glorious contingency.’

    Wow. This is some admission from Shermer who sure spends a lot of time writing and coining new terms to convince the reader that despite being a ‘fluke’ and a ‘quirk of evolution’ that we still apply to all those evolutionary imperatives that he (and I’ll include Rob Brooks in this as well) and his colleagues would try and convince you still apply to humans, the fluke and quirk of evolution. He can’t have it both ways, and evolutionary theory will struggle on trying to explain this species who are ‘a glorious contingency’.

    Google ‘freaks of nature’ and you’ll be able to read an article from the UK Guardian newspaper quoting from research carried out by the Royal Society B publication (B stands for biology) and looking at comparable mammals the result was that humans were more than 38,000 times more ecologically unbalanced. I’m saying the reason for this is that culture and mind(s) enable humans to over-ride nature, and that means over-riding natural selection and the economy of nature, although their are often broad limits to this.

    If you believe in freedom you can’t also believe that genes control human behaviour, they are different propositions.

    The real sin is the one that Charles Darwin noted on his beagle voyage:

    “if the misery of our poor be caused not by the laws of nature, but by our institutions, great is our sin; ”

    The misery of the poor is indeed caused primarily by social institutions and this is the real sin that the ‘developed’ world needs to awaken to. We’re focusing on huge numbers of the developed world becoming obese while billions are malnourished and in desperate poverty. To use ‘sin’ in referring to a tax in order to get fat Americans thinking more about their diet is shameful. Truly shameful.

    1. I’m not using “sin” because I want to get people thinking about obesity. Rather, it is because the taxes are being imposed by some people for the “good” of others, when I prefer to believe that (excepting clear cases such as mental illness, childhood etc) that people are best able to decide for themselves.

      However, on your broader point, I don’t disagree – and if you reread my post, you will note that the very point made in the article is that humans have not evolved to their new diets (i.e. cultural evolution is faster). The obesity “crisis” is clearly a result of social and institutional frameworks. But why is it that we get fat when we eat sugar and other simple carbohydrates rather than proteins and fats? Evolution can give some insight into that. Why do some groups of people suffer from higher rates of diabetes or alcoholism? Again, evolution offers insight.

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