The Evolution of Human Diet: A Scientific Perspective

[Yashbhatt]

Recently, I read an article in a magazine which said that if all people turn vegetarian, the Earth will be a better place to live. It explained that some energy is lost at each trophic level. So, due to conservation of energy, if we directly consume plants, we will get more energy for some particular mass. In this way our food requirement will lessen. So, we can get rid of the problem of food scarcity.

So, here's the question : I agree that our food requirement will be less because we will obtain more energy for less food. But I think digesting plants directly requires more energy than digesting meat. I want to know if this notion?

 

[SteamKing]

Well, one thing is certain. If everyone goes completely vegetarian, there will eventually be fewer people to worry about. It will be more difficult for people to live in places without sufficient arable land from which to grow enough crops for sustenance, and any increase in population above sustainable levels could be potentially catastrophic for such communities, although the duration of these imbalances could be brutally short as enough die off to bring about a rebalance in the number of consumers versus the amount of food available for consumption.

Say goodbye to places like Japan, which gets a significant proportion of its dietary protein from fish, because there is not enough arable land in the mountainous Home Islands to support the numbers of Japanese currently living there. Say goodbye also to a lot of people living in tropical or very arid climates, as these areas are very poor candidates for farming. Ditto for people living near the arctic circle, since growing seasons there are very short.

One mistake you make in your energy calculation is that kg for kg, a plant diet contains more calories than a diet of meat or other food. This is not true.

A lot of the mass of vegetable matter is undigestible fibre, from which no nutrients or energy are extracted by the human gut. Animals like cows have specially adapted digestive tracts to allow them to survive on an all-plant diet. Even with these specially adapted digestive tracts, cows and other ruminants rely on bacteria living in their gut to ferment the plant matter so that digestion can be completed:

http://en.wikipedia.org/wiki/Ruminant

An all-plant diet has to be carefully monitored to make sure enough of the proper minerals and vitamins are consumed to maintain health.

 

[Yashbhatt]

What I read was that it does not contain more calories but if we directly consume the producers, the energy lost in conversion of energy will be less and so our food requirement will lessen.

But as you said, plants are hard to digest. So, if in future somehow we find a way to completely digest the substances found in plants, then would the claim be true?

 

[SteamKing]

Perhaps, but short of genetically re-engineering the human digestive tract, I don't see us giving cows and other ruminants much competition eating grass.

 

[Monique]

Perhaps, but short of genetically re-engineering the human digestive tract, I don't see us giving cows and other ruminants much competition eating grass.

1) We don't eat grass, 2) Humans cook food, which makes food more easily digestible. People eat spinach (and other vegetables) for the nutrient content.

Yashbhatt is right about the energy conversion thing, it's in the textbooks.

I can't answer the question "But I think digesting plants directly requires more energy than digesting meat. I want to know if this notion?" What energy are you talking about?

 

[Monique]

Say goodbye to places like Japan, which gets a significant proportion of its dietary protein from fish, because there is not enough arable land in the mountainous Home Islands to support the numbers of Japanese currently living there.

Japan could use the sea to grow protein-rich vegetables:
Seaweed: An alternative protein source

from article: Researchers have previously shown that protein-rich red seaweeds such as Palmaria palmata (common name Dulse) and Porphyra (common name Sleabhac or Laver) species may potentially be used in the development of low-cost, highly nutritive diets that may compete with current protein crop sources such as soya bean.

Indeed when I was in Okinawa there were seaweed farms off the coast.

 

[Pythagorean]

A lot of the mass of vegetable matter is undigestible fibre, from which no nutrients or energy are extracted by the human gut.

That's true, but fiber actually helps aid digestion in several important ways:

http://en.wikipedia.org/wiki/Dietary_fiber#Effects_of_fiber_intake

In fact, the low-fiber diet of modern day has been associated with obesity and diabetes!

 

[Pythagorean]

To the OP, "Better world" is a bit of a glorification of the vegetarian diet; when you make such an all-encompassing statement, you have to be careful to consider the economic and social consequences, too. There are certainly benefits, but there are also risks associated with a vegetarian diet. While protein isn't really a problem like most people think it is, B12 is one of the micronutrients that you can only get from animal products.

 

[Monique]

While protein isn't really a problem like most people think it is, B12 is one of the micronutrients that you can only get from animal products.

Actually B12 comes from bacteria, so it can be cultured without animals. Also, vegetarianism still includes animal products and thus a source of B12.

 

[russ_watters]

There's a big flaw in your premise:

So, due to conservation of energy, if we directly consume plants, we will get more energy for some particular mass. In this way our food requirement will lessen. So, we can get rid of the problem of food scarcity.

The world doesn't have a general food scarcity problem. What it has is people living in paces where food is tough to grow and political problems that prevent surplus food from other areas from getting to them.

 

[Yashbhatt]

@Monique I mean that we need to spend some amount of energy in converting one form of energy to another. So, as the plants molecules are more complex as compared to meat, don't we need more energy in transforming the complex molecules present in plants to simpler ones?

@Pythagorean You are right. But here by better world I meant world without food scarcity.

 

[Pythagorean]

Actually B12 comes from bacteria, so it can be cultured without animals. Also, vegetarianism still includes animal products and thus a source of B12.

But do any humans actually get B12 from bacteria? As far as I know, animals are the only human-available source. I know yeast can be fortified with B12, but it was my impression that this fortification was through animal products.

I know vegetarians consume milk/eggs, but that doesn't seem relevant to the OP's proposition.

 

[Monique]

@Monique I mean that we need to spend some amount of energy in converting one form of energy to another. So, as the plants molecules are more complex as compared to meat, don't we need more energy in transforming the complex molecules present in plants to simpler ones?

Plant molecules are more complex? I don't think so.

But do any humans actually get B12 from bacteria? As far as I know, animals are the only human-available source. I know yeast can be fortified with B12, but it was my impression that this fortification was through animal products.

For a fact vitamin B12 can only be synthesized by certain bacteria, the bacteria live in the guts of animals and that's how it gets into animal products.

Scientific breakthrough reveals how vitamin B12 is made

from the article: Vitamin B12 is pieced together as an elaborate molecular jigsaw involving around 30 individual components. It is unique amongst the vitamins in that it is only made by certain bacteria.

 

[Pythagorean]

I know B12 is only made by bacteria, but that still doesn't address my point. As far as I know, animal products are the only way humans get it (in sufficient quantities).

 

[Yashbhatt]

@Monique They may not be that complex but they are certainly more complex than glucose and we need to convert all food to glucose to obtain energy.

 

[Monique]

I know B12 is only made by bacteria, but that still doesn't address my point. As far as I know, animal products are the only way humans get it (in sufficient quantities).

Obviously if it is produced by bacteria, one can grow the bacteria and harvest the vitamin. Also, one can use the bacteria to ferment food. Indeed, vitamin B12 is present in fermented vegetables: Vitamin B12 content in Korean fermented foods and some popular foods. I'm interested to find out whether humans are able to live in symbiosis with the bacteria, I've never seen research on it.

@Monique They may not be that complex but they are certainly more complex than glucose and we need to convert all food to glucose to obtain energy.

Considering that vegetarians don't need to eat double the amount of food, I don't think it is an issue. I don't have the knowledge or sources to back it up. Your statement that all food needs to be converted into glucose is too simplified, metabolism is very complex.

Let's take an example and compare beans with meat, I think the cooked beans are more easy to digest. Actually they contain carbohydrates that are easily converted into sugar. Just take a bean into your mouth: it tastes sweet due to carbs being digested by your saliva. I think a steak will take longer to be digested, but don't have an appropriate source.

 

[Pythagorean]

Obviously if it is produced by bacteria, one can grow the bacteria and harvest the vitamin.

It's mostly a question of economic viability. Can you produce enough B12 to replace B12 from animal sources? Your own article acknowledges in the abstract that "the apparent nutritional imbalance in the traditional semi-vegetarian diet raised a special attention, especially on vitamin B12 status, supplied by animal foods" and notes the Korean fermented foods as an exception.

But, keeping with the thread topic, we're still left with the question of viability of such alternative B12 sources.

Not also, this issues that have arisen so far with B12 synthesis. The B12 produced by cyanobacteria like in Spirulina is well known for being a pseudovitamin. The B12 it produces is useless to humans:

http://www.ncbi.nlm.nih.gov/pubmed/17959839

I'm interested to find out whether humans are able to live in symbiosis with the bacteria, I've never seen research on it.

You might be interested in this paper I came across during our discussion here:

We now show that at least two groups of organisms in the small bowel, Pseudomonas and Klebsiella sp., may synthesise significant amounts of [B12].

http://www.nature.com/nature/journal/v283/n5749/abs/283781a0.html

 

[Yashbhatt]

So, till we don't find a way to completely digest plants we can say that being completely vegetarian would be no better than present?

 

[Monique]

So, till we don't find a way to completely digest plants we can say that being completely vegetarian would be no better than present?

Why would you say that?

*edit* Here, does this answer your question?

Climate benefits of changing diet. Climatic Change (2009) 95:83–10

Abstract
Climate change mitigation policies tend to focus on the energy sector, while the livestock sector receives surprisingly little attention, despite the fact that it accounts for 18% of the greenhouse gas emissions and for 80% of total anthropogenic land use. From a dietary perspective, new insights in the adverse health effects of beef and pork have lead to a revision of meat consumption recommendations. Here, we explored the potential impact of dietary changes on achieving ambitious climate stabilization levels. By using an integrated assessment model, we found a global food transition to less meat, or even a complete switch to plant-based protein food to have a dramatic effect on land use. Up to 2,700 Mha of pasture and 100 Mha of cropland could be abandoned, resulting in a large carbon uptake from regrowing vegetation. Additionally, methane and nitrous oxide emission would be reduced substantially. A global transition to a low meat-diet as recommended for health reasons would reduce the mitigation costs to achieve a 450 ppm CO2-eq. stabilisation target by about 50% in 2050 compared to the reference case. Dietary changes could therefore not only create substantial benefits for human health and global land use, but can also play an important role in future climate change mitigation policies.

 

[256bits]

Up to 2,700 Mha of pasture and 100 Mha of cropland could be abandoned

To put that in perspective:
The world has a total land mass of 149,000,000 km^{2}.
1 square kilometre contains 100 hectares.

2,700 Mha = 27M sq km of pasture ( roughly the size of Morth America )

for the cropland:
100Mha = 1M sq km or roughly the size of South Africa, or Canada and Australia combined

Worldwide:
17,298,900 square kilometres of world land is cultivated.
15,749,300 is used for replanted food crops such as wheat, rice, corn.
1,549,600 is used for other agricultural food crops and industrial plant products such as fruit and rubber trees.

If we ate veggies:
% reduction in cropland worldwide ie replanted cropland = 1,000,000 / 15,749,300 = 6.35%

( I suppose that means that 93.35% of food crop land use is already used for human consumption )

http://en.wikipedia.org/wiki/Land_use_statistics_by_country

No breakdown on the pasture land usage at wikepedia.
Although this site might be able to provide some correlation,
http://data.worldbank.org/indicator/AG.LND.ARBL.ZS

 

[Curious3141]

It's mostly a question of economic viability. Can you produce enough B12 to replace B12 from animal sources? Your own article acknowledges in the abstract that "the apparent nutritional imbalance in the traditional semi-vegetarian diet raised a special attention, especially on vitamin B12 status, supplied by animal foods" and notes the Korean fermented foods as an exception.

But, keeping with the thread topic, we're still left with the question of viability of such alternative B12 sources.

Not also, this issues that have arisen so far with B12 synthesis. The B12 produced by cyanobacteria like in Spirulina is well known for being a pseudovitamin. The B12 it produces is useless to humans:

http://www.ncbi.nlm.nih.gov/pubmed/17959839

Most of the B12 derived from algal sources is a pseudovitamin. However, a small proportion (around a sixth) is biologically active in humans. Here's a reference: http://www.ncbi.nlm.nih.gov/pubmed/10552882

Now that having been said, educated vegans will not rely on spirulina for their B12 needs. They will look to fortified vegan foods like Marmite, cereals and soy milk. The source for the B12 here is industrially synthesised from bacterial cultures. There are tons of bacteria in large chemostats just pumping out B12, which goes to fortify vegan foods and produce vegan supplements. Clearly, this is cost-effective because the process can be done on a large industrial scale, and there is an actual demand from people who choose to be vegan for ethical and/or other reasons.

You can read more about it here: http://www.vegetarian.org.uk/factsheets/b12factsheet.html There is a list of references in the peer reviewed literature at the bottom.

The relevant quote:

The industrial production of vitamin B12 for the fortification of foods involves fermentation with bacteria. Large-scale production is carried out using a number of bacterial species, including for example Pseudomonas denitrificans, Propionibacterium freudenreichii and Propionibacterium shermanii. Bacterial cultures are grown in huge vats for the extraction of B12.

B12 can be obtained from many everyday food items that are fortified such as veggie burger and sausage mixes, yeast extracts, vegetables stocks, margarines, breakfast cereals and soya milks. See below for guide to how much B12 is contained in a range of these foods.

 

[Pythagorean]

Hi Curious, thanks for you post. That article was careful to reference things except for when it brought up production! so I dug up a paper on microbial production:

http://www.ncbi.nlm.nih.gov/pubmed/11935176

Looks like pretty good production rates. I was just curious whether it could replace the world demand for B12; not just vegan's (which make up about 3% of the US taking the average from wiki's pool):

http://en.wikipedia.org/wiki/Vegetarianism_by_country#United_States

 

[Yashbhatt]

@Monique I just wanted to know if it's easier to digest plants than to digest animals. You already answered that. So, thanks.

 

[Curious3141]

Hi Curious, thanks for you post. That article was careful to reference things except for when it brought up production! so I dug up a paper on microbial production:

http://www.ncbi.nlm.nih.gov/pubmed/11935176

Looks like pretty good production rates. I was just curious whether it could replace the world demand for B12; not just vegan's (which make up about 3% of the US taking the average from wiki's pool):

http://en.wikipedia.org/wiki/Vegetarianism_by_country#United_States

Thanks for your reference - it certainly "supplements" this discussion.

Sure, I believe that it's possible to generate enough microbial B12 to sustain the entire human population on a vegan diet. There just has to be a massive demand for it. When that's accomplished, the supply part is not difficult - large scale industrial operations are eminently scalable.

 

[Evo]

Everything you wanted to know and more...and more...and more.

Most nations in the West, as well as Japan, have already seen saturations of per capita meat consumption: inexorably, growth curves have entered the last, plateauing, stage and in some cases have gone beyond it, resulting in actual consumption declines. Most low-income countries are still at various points along the rapidly ascending phase of their consumption growth curves, but some are already approaching the upper bend. There is a high probability that by the middle of the 21st century, global meat production will cease to pose a steadily growing threat to the biosphere’s integrity.

Killing animals and eating meat have been significant components of human evolution that had a synergistic relationship with other key attributes that have made us human, with larger brains, smaller guts, bipedalism and language. Larger brains benefited from consuming high-quality proteins in meat-containing diets, and, in turn, hunting and killing of large animals, butchering of carcasses and sharing of meat have inevitably contributed to the evolution of human intelligence in general and to the development of language and of capacities for planning, cooperation and socializing in particular. Even if the trade-off between smaller guts and larger brains has not been as strong as is claimed by the expensive-tissue hypothesis, there is no doubt that the human digestive tract has clearly evolved for omnivory, not for purely plant-based diets. And the role of scavenging, and later hunting, in the evolution of bipedalism and the mastery of endurance running cannot be underestimated, and neither can the impact of planned, coordinated hunting on non-verbal communication and the evolution of language.

Rational meat eating is definitely a viable option.

Toward Rational Meat Eating

We could produce globally several hundred millions of tons of meat without ever-larger confined animal feeding operations (CAFOs), without turning any herbivores into cannibalistic carnivores, without devoting large shares of arable land to monocropping that produces animal feed and without subjecting many grasslands to damaging overgrazing – and a single hamburger patty does not have to contain meat from several countries, not just from several cows. And there is definitely nothing desirable to aim for ever higher meat intakes: we could secure adequate meat supply for all of today’s humanity with production methods whose energy and feed costs and whose environmental impacts would be only a fraction of today’s consequences.

http://www.scientificamerican.com/article/should-humans-eat-meat-excerpt/

 

[Monique]

from: http://www.scientificamerican.com/article/should-humans-eat-meat-excerpt/
Killing animals and eating meat have been significant components of human evolution that had a synergistic relationship with other key attributes that have made us human, with larger brains, smaller guts, bipedalism and language. Larger brains benefited from consuming high-quality proteins in meat-containing diets, and, in turn, hunting and killing of large animals, butchering of carcasses and sharing of meat have inevitably contributed to the evolution of human intelligence in general and to the development of language and of capacities for planning, cooperation and socializing in particular. Even if the trade-off between smaller guts and larger brains has not been as strong as is claimed by the expensive-tissue hypothesis, there is no doubt that the human digestive tract has clearly evolved for omnivory, not for purely plant-based diets. And the role of scavenging, and later hunting, in the evolution of bipedalism and the mastery of endurance running cannot be underestimated, and neither can the impact of planned, coordinated hunting on non-verbal communication and the evolution of language.

Thanks for the article, interesting read! About the quote above, I always find it silly that something that was important for evolution 6 M years ago is being cited as a reason to eat meat in modern days.

 

[Pythagorean]

Of course, it wasn't just agriculture, it was also animal husbandy, which included the harvesting of animal products. But I agree that evolutionary origins aren't a reason for motivating a particular lifestyle behavior. That's the paleo diet claim, and we know paleo is not the best diet for modern man.

 

[Curious3141]

Of course, it wasn't just agriculture, it was also animal husbandy, which included the harvesting of animal products. But I agree that evolutionary origins aren't a reason for motivating a particular lifestyle behavior. That's the paleo diet claim, and we know paleo is not the best diet for modern man.

Yes, animal husbandry was practised side-by-side with crop farming. But of the two, I believe the latter to require a more stable civilisation. Extant nomadic cultures practice animal husbandry but they are considered to be less advanced than stable sessile civilisations. A nomad who takes his sheep to graze on a nearby grassland or drink from a nearby river never has to think about how he might get that crop to grow in a fixed place that's more convenient to him and his herd, or how he might divert the course of that body of water to his ends.

 

[Pythagorean]

Yes, animal husbandry was practised side-by-side with crop farming. But of the two, I believe the latter to require a more stable civilisation. Extant nomadic cultures practice animal husbandry but they are considered to be less advanced than stable sessile civilisations.

It's hard to know that. You're comparing societies that had both husbandry and agriculture with societies that just had husbandry; it's not a case of comparing just husbandry to just agriculture. Also, "advanced civilization" isn't a word that modern anthropologists use very often. It's typically used by a non-academic groups in an ethnocentric manner to justify occupation, missionary work, and codification.

 

[AlephZero]

2,700 Mha = 27M sq km of pasture ( roughly the size of Morth America )

for the cropland:
100Mha = 1M sq km or roughly the size of South Africa, or Canada and Australia combined

That sort of accountancy ignores the ecological effects of removing the farmed animals from the pasture land. Either they will be replaced by wild animals (which might not be a good idea, if the native replacement species are large and/or dangerous) or the flora will change dramatically when the grazing pressure is removed.

Sustainable agriculture probably needs animals as well as plants. A nice example (up to the 19th century) was the chalk downs in southern England. The landscape is basically a plateau of chalk with a thin soil covering that can only support grass, with a network of deep river valleys. The traditional farming method was to use the grass land for grazing sheep and the valleys for growing crops. Outside of the crop-growing season, the sheep were driven up to the grass land each day and back down the valleys each night, partly for safety and shelter, but more importantly to use their poo and pee as fertilizer.

Of course you could get rid of the sheep and ship in fertilizer from half way round the world - but if you think the sheep are more environmentally friendly, you might as well eat them rather than letting them die of natural causes.