Tuesday, April 29, 2008

Cancer and animals

Cancer experiment on monkey

Cancer relates to questions of animal ethics in two major ways:

1) Animal experimentation

2) Human nutrition and lifestyle.

Let’s start with animal experimentation. This broad field branches out into two main areas in association with cancer:

a) animal testing of carcinogenicity (cancer-inducing quality) of substances

b) cancer research on animals to find cures for humans.

Animal testing of carcinogenicity

Carcinogenicity studies on animals are used for all kinds of compounds, in particular synthetic substances, pesticides, food additives and all sorts of other chemicals. They, especially pesticides tests, have been largely instigated by the environmentalist movement, which has created, since Rachel Carson’s book Silent Spring onwards, a public hysteria about a phantasmic connection between human cancer and man-made chemical substances in the environment.

The crude reality is that animal tests are a totally inadequate means of finding out whether a substance causes cancer in human subjects not just because of the important obstacle represented by species difference but also, more specifically, because of the extremely high dosages to which lab animals are subjected over a short period of time, as opposed to the low levels (mostly residues) to which humans are exposed over a long time.

Half of all the substances administered to animals at these near-toxic levels are carcinogenic in the test subjects, purely because of the local damage they cause in virtue of their massive amounts. Many of these chemicals are well-known for not causing cancer in humans at all.

What increases the risk of cancer in humans is something completely different, and we’ll get to that when we later discuss nutrition and lifestyle.

Of all the substances in our environment, one of the most seriously and lethally carcinogenic is asbestos, and here animal experiments have continuously misled researchers into believing that asbestos was safe simply because lab animals subjected to it did not develop the deadly form of cancer that we have known for decades to plague asbestos workers: mesothelioma. So, thanks to animal research, legislative measures to ban asbestos were delayed in the West by several decades, while workers and their families kept getting ill with asbestosis and tumors which could not be replicated in animals and therefore, so researchers thought, animal experiments had not “validated” the asbestos-mesothelioma causal connection.

Cancer research on animals

Cancer research on animals consists in taking healthy animals, mostly rodents, and trying to make them ill with cancer by various artificial means, sometimes successfully and sometimes not, in order to test on them possible treatments designed for humans. When researchers “luckily” succeed in making a healthy animal develop cancer, the tumor is not the same as the human one that it is supposed to model.

First of all, the aetiology of the disease is completely different. The causal mechanisms that induce cancer in humans are practically impossible to reproduce in a lab using animals. The most frequent causes of human cancer by far, as we shall see in more detail when we examine lifestyle, are smoking habits, bad nutrition choices, alcohol-drinking, lack of exercise, and all of these causal factors accumulate over a long period of time, often a lifetime, gradually and slowly. Lab animals, on the other hand, have to be made sick quickly, and they do not naturally indulge in all those cancer-risky lifestyle habits of which so many humans are so fond. So the means to induce cancer in them are necessarily artificial, different from the human causes, and designed to produce a rapid response.

Some common human cancers, like prostate, rectal and colon cancers, are rare in rats and mice, the cancer researchers’ favourite (most used) species. So experimenters have to labour particularly hard to inflict these tumours on rodents.

Regardless of the causes, moreover, cancer is not the same disease in different species of animals, human included. Cancer is not, strictly speaking, a disease, but an umbrella encompassing several ailments, according to the distribution of the various cancer sites. But animal tumours are not the same entities as human ones, even when they affect the same sites or are given, for reasons of convenience, the same name.

For instance, human bowel cancer affects a different part of the intestines (the colon or large bowel) from rats’ bowel cancer (the small bowel). And the mechanism of colon cancer in the two species is dissimilar: humans die because the cancer metastasizes, namely spreads to other parts of the body, whereas rats die because the colon is obstructed.

So, basically cancer researchers are studying something completely different when they use animals. The latter are not models of human cancer at all.

As a consequence, it should come as no surprise to learn that many of the various cancer treatments making the headlines, which have been tested on animals and found to be effective in them, turn out to be, when later administered to human subjects, ineffective or even harmful.

Human nutrition and lifestyle

We do not yet know how to cure cancer. Despite some improvement in therapy, this often fatal disease remains elusive to understand and refractory to cure. However, we know an awful lot about the risk factors that increase the probability of contracting cancer. Of all the areas of cancer research, the greatest progress has been made in cancer prevention. To stop cancer from developing in the first place remains the best option that we have.

And this, from many viewpoints (except perhaps if you consider laziness, addiction and force of habit), is extremely good news. Because all the major causes, or risk factors, of cancer are entirely under an individual’s control. They all pertain to a person’s lifestyle.

First comes tobacco, by far the major contributing factor to cancer incidence rates.

Then comes diet. We know very well what a cancer-preventing nutrition (and preventing other major diseases too) should be. Medical authorities and health experts advice is simple: avoid completely certain kinds of meat (namely, cured or processed meats like bacon and sausages), eat as little red meat as possible, reduce all types of meat and animal fats, replace them with proteins and fats of vegetable origin, and eat more fresh fruits, vegetables and grains.

And here we come to the other connection between cancer and animal ethics.

It looks like both our health and our morals point in the same direction. There is no real conflict of interests: what is good for us is also good for other animals, who could be spared the life-long torture of imprisonment in factory farms and the short but agonizing experience of the slaughterhouse.

Friday, April 11, 2008

Thalidomide tragedy, side effects, history

Drug testing on animals

What is Thalidomide

Thalidomide was one of the greatest cases in history of a drug disaster tragedy being caused by animal research.

First of all, Thalidomide had been tested on animals extensively prior to its marketing.

Even now, despite the clinical evidence to the contrary, British health authorities like the Medical Research Council maintain that the vast bulk of evidence from laboratory and animal tests is against thalidomide having any genetic effects.

The tragedy caused by Thalidomide in the 1960s was due to its teratogenic effects, ie effects on the foetus. Teratological effects of drugs were little known then. They were brought to public attention because of the Thalidomide tragedy on humans, therefore only after it. How on earth could animal researchers have thought of those effects before the disaster?

Even after the Thalidomide caused birth deformities in humans, researchers tried to reproduce the same effect in dozens of species of lab animals without success.

Take a look:

"As a consequence to the thalidomide tragedy there has been a marked upsurge in the number of animals used in testing of new drugs. Also drugs are now specifically tested on pregnant animals to supposedly safeguard against possible teratogenic effects on the human foetus. Vivisector's claim that if such tests were carried out prior to thalidomide's release, birth deformities in humans would have been discovered. This is of course sheer nonsense. 'In pregnant animals, differences in the physiological structure, function and biochemistry of the placenta aggravate the usual differences in metabolism, excretion, distribution and absorption that exist between species and make reliable predictions impossible.' (15) (Dr Robert Sharpe, former senior research chemist.)

"In fact when the link between human foetal abnormalities and thalidomide was established (through clinical observation), the world-wide explosion of animal testing, using a large range of species, proved very difficult to duplicate the abnormalities. (16) Writing in his book Drugs as Teratogens, J.L. Schardein observes: 'In approximately 10 strains of rats, 15 strains of mice, eleven breeds of rabbit, two breeds of dogs, three strains of hamsters, eight species of primates and in other such varied species as cats, armadillos, guinea pigs, swine and ferrets in which thalidomide has been tested teratogenic effects have been induced only occasionally.' (17) Eventually after administrating high doses of thalidomide to certain species of rabbit (New Zealand White) and primates could similar abnormalities be found. However researchers pointed out that malformations, like cancer, could occur when practically any substance, including sugar and salt, be given in excessive doses. (16)" [my emphasis]

Thalidomide's history in the USA

Some apologists of animal experimentation say that the reason why Thalidomide was never approved by the FDA (Food and Drugs Administration, the US agency responsible for drugs licensing) in the US is that the FDA reviewer had previous experience in animal research and had refused to clear the drug for sale until better documentation of its effects were provided.

The reality is that the FDA reviewer in question, Frances Oldham Kelsey, had doubts about Thalidomide's safety because of side effects shown in human clinical trials.

The FDA website is very clear on this. In Frances Oldham Kelsey: FDA Medical Reviewer Leaves Her Mark on History it says:

"In December of 1960, three months after Richardson-Merrell submitted its application, the British Medical Journal published a letter from a physician, Leslie Florence, who had prescribed thalidomide to his patients. Florence reported seeing cases of peripheral neuritis, a painful tingling of the arms and feet, in patients who had taken the drug over a long period of time." [emphases added]

And here is another biographical note on Frances Kelsey:

"Dr. Kelsey continued to resist, pointing out in February 1961 that a study in England had indicated the new product caused 'a serious side effect on the nervous systems of patients who took the drug repeatedly,' so she asked for assurances that such side effects wouldn't occur. By May she had developed a theory that if thalidomide caused paralysis of the peripheral nerves, the drug probably would cause greater damage to the developing embryo." [emphasis added]

Better control

The answer is: better control of the effects of medicines after they have been marketed.

"We need to encourage doctors and drug companies to watch for, report and take note of side effects in order to protect patients properly. If proper drug surveillance techniques had been available in the 1960s the thalidomide problem would have been picked up much earlier. We still don't have proper post marketing trials in place." (from the source above)

Testing on humans is going to happen anyway, because any new drug which is marketed is an unknown, due to the unreliability of previous animal testing.

Let me repeat: you cannot make an unreliable method reliable by counterexamples.

Even if you happen to encounter cases where animal tests results have not been refuted by their application to humans, this does not alter the unreliable status of the method.

There are cases where there is a correspondence between human and non-human animals. But how do we know that? Because we transferred the results of animal testing on humans. That is, for all practical purposes, we tested them on humans.

It is an unavoidable fact.

Tuesday, April 08, 2008

The greatest scientific event of the millennium

Toxicity test rabbitNever before have I had such a clear feeling that animal experimentation has its days counted, and that supporters of vivisection have started seeing the writing on the wall.

As important as penicillin, double helix and computers

The most prestigious scientific body in the world, which advises the US government on scientific issues, the National Research Council of the U.S. National Academy of Sciences, has released in June 2007 a report entitled “Toxicity Testing in the 21st Century: a Vision and a Strategy”.

The report was commissioned by the Environmental Protection Agency (EPA), another US federal body, responsible for thousands of safety (toxicity) tests on animals each year.

It is nothing short of revolutionary, and whoever knows the facts about animal experiments will realize its immense importance. Especially for people who know how much the American scientific establishment has historically been the most staunch supporter of animal research, this new report will be a blow.

The report’s authors convey very well its revolutionary meaning and the feeling that we have reached a turning point in biomedical research, in the very way they start it:

“Change often involves a pivotal event that builds on previous history and opens the door to a new era. Pivotal events in science include the discovery of penicillin, the elucidation of the DNA double helix, and the development of computers. All were marked by inauspicious beginnings followed by unheralded advances over a period of years but ultimately resulted in a pharmacopoeia of life-saving drugs, a map of the human genome, and a personal computer on almost every desk in today’s workplace.

Toxicity testing is approaching such a scientific pivot point. It is poised to take advantage of the revolutions in biology and biotechnology.”
[emphases added]

The report says:

“Advances in toxicogenomics, bioinformatics, systems biology, epigenetics, and computational toxicology could transform toxicity testing from a system based on whole-animal testing to one founded primarily on in vitro methods that evaluate changes in biologic processes using cells, cell lines, or cellular components, preferably of human origin.” [emphasis added]

Non-animal methods outperform animal tests

The superiority of non-animal methods of testing substances for toxicity to humans, compared to animal methods, is acknowledged by the report:

“The envisioned change is expected to generate more robust data on the potential risks to humans posed by exposure to environmental agents and to expand capabilities to test chemicals more efficiently. A stronger scientific foundation offers the prospect of improved risk-based regulatory decisions and possibly greater public confidence in and acceptance of the decisions.” [emphases added]

The report admits that the current animal method of testing has not been evaluated for its usefulness but rather used by inertia:

”The current system is the product of an approach that has addressed advances in science by incrementally expanding test protocols or by adding new tests without evaluating the testing system in light of overall risk-assessment and risk-management needs. That approach has led to a system that is somewhat cumbersome with respect to the cost of testing, the use of laboratory animals, and the time needed to generate and review data.” [emphases added]

There is acceptance in the report of the well-known problem that the extremely high levels of doses to which lab animals are subjected are a further element of unreliability and lack of predictive value of animal tests, given the huge discrepancy with the actual, much lower, doses of chemicals to which humans are exposed:

“Moreover, the vision will lead to a marked reduction in animal use and focus on doses that are more relevant to those experienced by human populations.” [emphasis added]

The report’s vision is that eventually non-animal strategies will completely replace animal-based toxicity tests and revolutionize safety testing.

The report recommends advanced non-animal methods using in vitro human cell lines in combination with computational methods and epidemiological studies. These new methods should also be employed in other areas of biomedical research currently using animals, and there is reason to hope that the new report may influence that development too.

The reference in the report to “paradigm shift” as the description for the new vision outlined there echoes Brute Science: Dilemmas of Animal Experimentation (Philosophical Issues in Science), a revolutionary book written by a philosopher and a biologist. The book uses science historian Thomas Kuhn’s concept of “paradigm” to explain the “sticky” nature of scientific enquiry, the prevailing scientific dogmatism which often makes change in normal scientific activity between “revolutions” so difficult. That echo seems to indicate that this report has taken on board criticisms made by the anti animal experimentation camp, to which the book generally belongs.

The future has already started

This milestone report comes at a crucial moment in the history of toxicity testing. The European Union has last year approved a new Regulation called REACH (Registration, Evaluation and Authorisation of Chemicals) which will require the largest mass animal testing programme in Europe’s history. It has just started and will see the testing of 30,000 chemicals on an estimated 10 to 50 millions animals.

This programme is closely watched by the US and the rest of the world as a pioneering enterprise. So it is the right moment for Europe to introduce the new methods and the new vision that this report so clearly recommends. Otherwise REACH could be an incalculable waste of money, time, resources without any benefit but possible harm to humans, and a totally pointless, immense source of animal suffering. Non-animal tests would provide more reliable data, produced more quickly and at an enormously lower cost than animal tests.

The “Toxicity Testing in the 21st Century: a Vision and a Strategy” report, which has the purpose of guiding future research policy, has already had a momentous application: a Memorandum of Agreement was signed by the Environmental Protection Agency, the National Toxicology Program and the National Institutes of Health on 14th February 2008 aiming to end animal testing of chemicals and drugs.

Another cause for much happiness is that the hugely influential anti-visection Italian-Swiss author, the great Hans Ruesch, who wrote Naked Empress or, the Great Medical Fraud and many other books on animal experimentation, was able to see what appears like the beginning of the end for animal experimentation before he died on 27th August 2007, aged 94. He started me on this path when I was 17 years old and read his books.

This post is also a tribute to his memory. He can rightly be called the founder of the modern scientifically-based anti-vivisection movement. We will continue the fight that he began.

Saturday, April 05, 2008

Vegetarian cats

With cats, giving them a meat-free diet is more difficult, whereas it is relatively easy to have vegetarian dogs. But it is not impossible to convert cats to vegetarian nutrition either.

A vegetarian lioness

In the case of felines as well, we have a "wild" model to look to. In America, in the '40s, there was a clamorous case of which the whole country and the world press talked. A lioness, Little Tyke, kept with other animals by a family in a ranch in Washington state, refused to eat meat. Georges Westbeau, her "adoptive father", in the book Little Tyke (A Re-quest book) (originally published by Pacific Press Pub. Assoc., 1956 and now reprinted) recounts that she was an extraordinarily tame animal, who lived in domestic peace with the herbivores of the ranch.

Little Tyke was also exceptionally healthy: one of the most experienced American zoo curators visited her and called her "the best specimen of the species" he had ever seen. The Westbeaus were still worried, because scientists kept saying that a lion cannot survive without meat. But despite their prolonged efforts, they could never make their lioness eat it. When in 1955 Tyke appeared live on the TV programme You asked For It, all America got emotionally involved in this modern tale of the Gubbio wolf. Unusual as the case of Little Tyke is, it clearly shows that even the most carnivorous of animals can live well without meat (and prefer it to boot).

Domestic cats' nutrition requirements

But what about domestic cats? It has long been thought impossible to convert these not easily deterred meat-eaters to vegetarianism. Many of those who accept a meat-free nutrition for dogs do not consider it suitable to cats. In this field we must thank Barbara Lynn Peden, an American supporter of a vegan diet for dogs and cats, who did not give up but started a really pioneering work. The book she wrote, Dogs & cats go vegetarian, documents the struggle she fought with tenacity and determination to solve the problem of finding a balanced diet for domestic felines without resorting to animal foods.

Her research starts with the recognition that cats do have special nutritional requirements. First of all they cannot transform beta-carotene, which is found in plants, into vitamin A (as do humans and dogs); therefore they need a pre-formed source of vitamin A. This problem has not presented great difficulties, though, because, even if a direct vegetable source of vitamin A does not exist, it's easy to find it as a nutrition supplement in tablets.

More complicated has been the question posed by taurine, an amino acid not essential for humans, whose body can synthetize it, but essential for cats. After months of research and toil among scientific literature, transoceanic conversations with biochemists and discussions with vets and dietologists, the obstinate Barbara has succeeded in finding a totally vegan source of taurine, first in an petroleum by-product and then in an organic, renewable resource.

The other two nutrients which have demanded a special enquiry and a series of trial and error attempts have been the arachidonic acid, a fatty acid which generally mammals (but, alas, not cats) synthetize from linoleic acid, and another fatty acid of the series ¤ë3 (omega 3). Both are present in the seaweed Ascophyllum.

How to turn cats vegetarian or vegan

So, after all the obstacles had been overcome, Barbara Lynn Peden has put together these substances in one supplement, and called it "Vegecat". This only needs to be added to the pussy's meal. Furthermore, to make it even more precise, Barbara and her husband have developed a series of recipes on the computer, using a model of 47 nutrients taken from the latest knowledge on cats' nutrition (the same has been done for dogs). They have selected easy to find ingredients, like soya, rice, hazelnuts, wholemeal bread, oats, oil, vegetables, brewer's yeast, and have come out with a variety of recipes suited to every kind of vegetarian nutrition: lacto-vegetarian, ovo-vegetarian, vegan and crudist. The nutrients which were not to be found easily in the foods themselves have been added to the supplement Vegecat, so that to use the latter and to follow the recommended recipes guarantees a balanced and complete diet. Vegecat can be ordered from the Vegan Society or directly from the American producers.

Kitties, as everyone knows, are a bit fussy about food, and it's not easy to get them to change even a tinned food brand. Vets call the attachment to a particular food "fixed nutrition preference", and recommend a gradual change to something new. The ideal would be to add some of the new food to the old one, and then increase the dosage little by little, until one is totally replaced with the other over a few days.

Barbara Peden has the following advice to give: "One recipe may be preferred over another. Our own cat ate her lentil-based food just fine for many months, until we tried chickpeas. We found that she likes chickpeas so well that, if we gave her lentils after that, she'd 'hold out' for chickpeas. So, try different recipes until you find one he likes".

Although many are still perplexed, the view that cats, respecting the due precautions, can be vegetarian is now accepted by various scientific literature, among which a recent report of the United States' National Research Council, which says: "A pure source of taurine can be added to vegetable diets... A much higher level of zinc is needed if a dietetic regime of vegetable protein is followed".

UK government’s animal experimentation cover-up is unlawful, court rules

Making decisions on animal research is impossible if the relevant information is not disclosed. This is true for decisions to be made both in public policy and by the so-called people in the street.

This is why this recent event is an important victory.

The UK’s Information Tribunal on 30 January 2008 ruled that the government’s
withholding the details of the animal experiments it licenses in the country is against the law
because it violates the Freedom of Information Act (FOI), introduced in January 2005.

The case was brought by the BUAV (British Union for the Abolition of Vivisection) after the Home Office refused to reveal basic information about animal experiment licences: experiment’s purpose, what is to be done to the animals, how the applicants proposed to limit animal suffering and, crucially, how they proved it was essential to use animals rather than alternatives in their intended experiments. The BUAV was not looking for information on who is involved or where the research is occurring.

This ruling now means that the government will have to disclose much more information about what is done to laboratory animals, for what purpose, and what consideration has been given to non-animal alternative methods.

Andre Menache said in an interview:

“The other difficulty especially in the UK is this obsession with secrecy. The Freedom of Information Act came into effect in 2005 with respect to animal experimentation. I can tell you that the Home Office simply laughs in your face when you try and obtain information from them about animal experiments using the Freedom of Information Act. They simply say, ‘Sorry we have this information but we can't give it to you because of the activities of a small group of people who may endanger the safety of the researchers and institutions.'

“All this talk about transparency I'm afraid it's not happening and if it is happening then it's not happening fast enough. I would say transparency is a good thing but it's like passing a law which sounds good but it's unenforceable.”

Maybe now we can be a bit more optimistic than that.

Friday, April 04, 2008

Animal experimentation public opinion. An Update

Painful experiment on dog
A mixed bag of updates on the front of public opinion on animal experiments.

UK opinion polls on animal research

A UK national public opinion poll conducted by YouGov and published on 23rd July 2007 showed that 80 per cent of the British public supports a ban on experiments which cause suffering to animals.

The poll was sponsored by PETA (People for the Ethical Treatment of Animals). Before regarding this as a victory for the anti-vivisection movement, we should consider that results of opinion polls tend to vary according to on whose behalf the research is conducted.

A similar UK national poll conducted by TNS and commissioned by the BUAV (British Union for the Abolition of Vivisection) in 2003 revealed that 76 per cent of the British public thinks that the Government should, as a matter of principle, prohibit experiments on any live animals which cause pain, suffering, distress or lasting harm.

At the same time that the BUAV survey was conducted, other vivisection opinion polls were giving very different results. The reason of these variations lie in the way questions are formulated and how sympathetic to a certain cause the questioner is, because this latter fact influences the respondent’s answer by creating a certain expectation.

Besides, on the subject of animal research the people who have definite views - always against or always in favour - are few, with the absolutely favourable ones being fewer than the absolutely opposed. The vast majority do not have enough knowledge of the topic to develop an informed opinion, and therefore are particularly susceptible to the wording of the question because in that wording a certain amount of information is perceived to be hidden and a guide to the answer is found. Usually questions on complex issues like this are preceded by a statement, which gives away the position of the questioner but at the same time is used by the people polled as a help in making up their mind.

Consider this question:

“Non-animal research methods have replaced many tests previously done with animals. These are used if the Government judges them to be as good or better than animal methods.
The organisation PETA (People for the Ethical Treatment of Animals) estimates that the Government spends up to £10 million each year on developing non-animal research methods and that the Government's total science research budget is around £5,000 million per year.
On the basis of this information do you think the Government should:
Increase the allocation of funds for developing non-animal research methods
Leave the funding unchanged
Decrease the allocation of funds for developing non-animal research methods
Don’t know”.

Now consider this:

“How strongly do you agree or disagree with this statement: I agree with animal experimentation for all types of research where there is no alternative?”

The first gives ample information that strongly suggests that animal experiments could be replaced if only there were a political will. The second does not seem a “leading question” as the other does, but it is exactly that, only more subtly, because it assumes, and conveys the impression, that there are cases where no alternative to animal experimentation exists, whereas this is entirely to be demonstrated; however, only a respondent who has devoted time and effort to study the issue would spot that (or a respondent intelligent enough to understand that the question’s underlying assumption is wrong in principle, even before one knows the relevant facts).

The lesson to learn from all this is that public opnion on this issue is not easy to assess without a bias inherent in the method of assessment which will skew the results (who is familiar with Heisenberg’s uncertainty principle in quantum mechanics will see here another example of the observer’s interference with the subject). So, when for instance animal experimenters and their apologists make statements about widespread public support for animal research, we must remember that the members of the public are only responding to the sort of data (or pseudo-data) that they are feeding them.

USA opinion polls on health charities and animal research

Meanwhile, on the other side of the Atlantic, in July 2005 another poll conducted in the USA found that 67 percent of people said they were more likely to donate to a health charity that has a policy of never funding animal experiments than to one that does and 57 per cent said they would never donate to a charity that finances animal experiments.

Again, though, the sponsor of this investigation was an organization which opposes animal experimentation, the Physicians Committee for Responsible Medicine (PCRM).

Two more surveys had been previously conducted on the same subject. All three were held by Opinion Research Corporation International of Princeton, New Jersey, on behalf of PCRM. The percentage of people giving the above answers had increased regularly over the past 10 years, and the highest increase had been among the older generation, since the youngest were already mostly supporting humane donations even in previous polls.

The generation gap is a welcome result, showing that younger people are more opposed than others to animal experiments and therefore indicating a future trend away from support to vivisection.

This age-related difference in response to questionnaires on animal research very probably explains why opinion polls conducted online regularly favour anti-vivisectionist views in comparison with offline ones. The demographics of internet users, who belong disproportionately to younger age groups, are at work here.

This result is in harmony with what we know, i.e. that youngsters are more sensitive to animal issues generally, as other data show, for instance in the much higher percentage of vegetarians among teenagers and people in their 20s than in other age groups.