Beans, other legumes, seeds, nuts and mushrooms are perhaps the commonest sources of protein for non-meat and -fish eaters, and some of the other vegetables and grains provide a bit extra. Most vegetarians have no problem getting enough protein if they have a varied diet including these items. Beans and lentils are known around the world as poor man’s meat, containing as they do all the key amino acids necessary to make protein inside the body. All of them are complex foods and protein is just one of the many ingredients that can affect our health and our microbes. Many vegetarians have turned to soy and its fermented product in the form of curds – known as tofu and sometimes called by its less organic name, ‘textured vegetable protein’ – as a different source of protein that can also come from grains. The demand for alternative-meat products has grown rapidly over the last few decades, especially in fast-food restaurants in the form of veggie-burgers. More recently sales of meat-free products have begun to drop off, perhaps because of health concerns and the resulting media attention.
Soy-hormone burgers and cancer
Soy protein was first produced from the soybean in the 1930s, and strange as it seems was used as a fire-fighting foam before its edible properties became apparent. Like other beans it is a mix of carbohydrates, fats, vitamins and protein. Although most beans have 20–25 per cent protein, soy is the champion at 36–40 per cent.
Hardened meat eaters dismiss soy and tofu as fake meat only eaten by the Japanese and vegetarians. What is not so well known is that Americans and Britons now consume nearly as much soy as the Japanese. This is not because of dramatic changes in our habits but because soybeans (or more commonly their protein extracts) are an additive used in two-thirds of processed foods. Many ‘non-soy eaters’ unwittingly get a detectable dose from milk and dairy products from ruminants fed on soy.1 In the US, as for corn (maize), there are billion-dollar subsidies for soy farmers and the country is the world’s largest producer of this genetically modified industrially produced crop. Most of the $4.5 billion US soy market actually goes to feed livestock which we then eat.
Soy is one of the most controversial topics in nutrition, with strong arguments on both sides for it being either the ultimate health food or a major cause for concern. Soy and tofu have been part of the natural Asian diet for centuries, and all soy products depend on a complex fermentation process that involves bacteria, fungi and yeast. There is now reasonable evidence of soy’s mild protective effect against breast cancer and possibly also in reducing recurrences of the disease.2 Similar but weaker findings are suggested for prostate cancer.3
Inconsistent evidence from observational and trial data suggests it also offers protective properties against dementia and Alzheimer’s disease in Asians, but so far there’s no similar evidence for Europeans. Soy in Asia is consumed differently: there it is more often eaten as the fermented product, which alters its properties and could account for some of the health differences encountered. Some of the many longstanding health claims have now been disproved: for instance, it is no longer believed to be of any obvious use against menopausal symptoms or osteoporosis.4
As we have noted before in this book, the same foods can have very different effects in different people. Even when considering a single soy product, we have found that its effect in Europeans appears different from its effect in Asians. Soybeans contain unique antioxidant chemicals called isoflavones which are converted in the gut into active compounds known as endocrine disruptors (such as genistein); these mess up your hormone pathways and can modify your genes. This group of chemicals is thought to act like a type of mild oestrogen that could potentially increase cancer risk. Early in my career I enthusiastically explored this hypothesis, and I also published another observational study that linked global soybean consumption to national rates of pancreatic cancer.5 This proved to be yet another demonstration of a false epidemiological association due to bias, and there is currently no good evidence of an adverse effect on the pancreas.
We now know that the isoflavones in soy don’t affect oestrogen levels directly but do stimulate oestrogen receptors and have gene-modifying (epigenetic) effects. Thus they have the capacity to switch our genes on and off and subtly alter our hormone responses, possibly and worryingly modifying fertility, sperm counts and infant development. Given the very large doses many of us are unknowingly ingesting in processed foods or knowingly giving our babies in soy milk, we should be doing more serious studies on potential long-term side effects.
Gut microbes might be the key to producing the active soy compounds in our bodies as well as regulating how quickly they are eliminated. Asians, who have a different gut-microbe composition from Europeans, can break down the soy internally so as to produce greater amounts of its active isoflavone compounds.6 7 In the US the soy food lobby (already heavily government-subsidised) managed, on the basis of rather shaky observational evidence, to get a health claim approved for soy protein being protective against heart disease. However, to get sufficient health benefits from soy you will either need to eat lots of processed or junk food or regular Japanese-style portions of miso soup, edamame or tempeh three times a day (roughly 100 grams in total).
Now, when it comes to modern processed foods, the problem is knowing what exactly they contain. If you are very lucky the label may give you some clues. Like other beans or legumes, soy is complex and has hundreds of ingredients. Some of these such as phytates are toxic and prevent the uptake of nutrients, while many others are potentially healthy (like fibre and unsaturated fats). But industrial processing often strips the soy down to its protein, which can then be reduced further to its component parts. Too much concentrated soy protein without the other natural parts of the bean could produce adverse effects; the truth is we really don’t know. It could overwhelm your microbes, which expect to be interacting with the many complex components of the natural bean.
Soy milk sales have been increasing rapidly in many countries and are now the commonest soy product consumed. It is a good source of protein for children allergic to cow’s milk, although the cure is rapidly becoming the problem: allergies to soy are also increasing, and soy alternatives are now available. The other components of soy such as endocrine disruptors like genistein, mentioned earlier, are regularly contained in infant feeds in amounts large enough to be a potential worry. Concern here is because the first three years of life are crucial for the normal development of a child, when the genes are constantly changing and fine-tuning their functions so as to produce new proteins.
Given that the isoflavones in soy have such significant and usually beneficial epigenetic effects in cancer, we should be more cautious when considering whether to give soy to susceptible babies. When you combine the epigenetic effects of soy with other known endocrine disruptor chemicals like bisphenol (BPA), which is in many babies’ plastic bottles, you could be preparing a dangerous cocktail.8
Seaweed suppers
An unusual source of protein is seaweed, although to get health-giving amounts you would need to spend your day in sushi bars, since protein makes up only about 2 per cent of the content of marine algae; the rest is hard-to-digest carbohydrate starch. Seaweed comes in many flavours and colours, is an important source of iodine in preventing thyroid disease, and contains potentially beneficial antioxidants. It is another beautiful example of our human ability to adapt our digestion to accommodate new sources of food. This is a change that has happened in our recent history, brought to our attention thanks to the Japanese love of sushi.
Japanese who lived on or near the coast for centuries enjoyed eating seaweed in many different forms, for instance as additives to soups or salads or to wrap their raw fresh fish in. Like most Europeans, they originally lacked the enzymes to digest seaweed’s complex carbohydrate starch. This meant it would pass straight through the gut without liberating any calories for the human or any nutrients for the microbes. Fortunately, the microbes in the guts of regular seaweed eaters gradually acquired the ability to digest it and obtain energy and nutrients from it.
The average Japanese has now made seaweed a regular part of their diet, and they consume an amazing 5 kg per person per year. This is nearly three times their consumption of dairy, which they digest poorly. Other Asian countries have also become hooked, and over two billion tonnes of seaweed are harvested each year for food. Edible seaweed is usually the brown variety such as kelp and wakame, and the red type such as nori is mainly used in sushi and as a massage gel and skin toner. Here is another example of the human capacity to adapt to different environments, once again demonstrating to us that our bodies may be programmed differently from others’.
Algae and GM humans
We may well wonder at the flexibility of our microbes in their capacity to digest plants. Just one single species of bacteria, Bacteroidetes thetaiotaomicron, contains an amazing arsenal of over 260 specific enzymes for breaking down different plant structures and over 200 related genes. In contrast, we human hosts have a puny store of less than thirty enzymes, showing how dependent we have become on our microbes.
Scientists have worked out one way whereby our microbes have managed to maintain this amazing level of diversity: by swapping genes.
Once upon a time there was a marine microbe (also from the Bacteroidetes family) called zobellia, that lived happily by feeding off marine red algae. One day he went on an adventure. From the fish he was riding on, he jumped straight into a human belly, which would become his new home. In the dark human colon he met other microbes, and in return for not eating him he kindly lent them some genes of his own which they lacked.
What this marine microbe was engaged in is known as horizontal gene transfer. The process of swapping genes is very common in bacteria, and accounts for their ability to resist antibiotics and fight off viruses. So microbes in seaweed-eating Japanese colons now acquired the ability to break down the seaweed, which benefited them as well as the human host.9 We don’t yet know how long it would take or how many buckets of seaweed for the average unexposed European to acquire the crucial marine microbes, although a few Welsh and Irish living on the coast may have them already.
We have recently discovered that humans contain at least 145 genes that have ‘hopped over’ in this way from other species, making us good examples of GM animals.10 We may have inherited our blood group genes and some obesity genes from bacteria and algae.
The marine biologists investigating horizontal gene transfer looked for evidence of other aquatic microbe genes now residing in terrestrial gut microbes. Acting like Interpol, they tracked down the unique enzymes of marine species living happily and replicating in human guts in America, Mexico and Europe, sometimes far from the sea.11 Their success proved that the process was not just a one-off, and confirmed the new-found ability of some of us not just to digest seaweed and other algae but to deal with any new food. More interestingly, this ability confers not only an energy and nutrient value, but offers health benefits too.
Seaweed contains a whole range of novel compounds, including proteins and chemicals like our friends the polyphenols, which act in helpful ways with anti-inflammatory, antioxidant and anti-cancer agents that our microbes can unlock. Part of the algae cell wall is important as a source of fibre, and can be broken down into helpful short-chain fatty acids such as propionate. A few small-scale trials in volunteers have suggested that seaweed can assist weight loss, offering the possibility that its fibre content reduces appetite. So eating seaweed may have kept the Japanese healthier and thinner than Europeans and resulted in less heart disease and cancer.12
As mentioned earlier, the Japanese and in particular the Okinawans in the south are the longest-living people on the planet and have the highest proportion of centenarians (743 per million). Their ingestion of seaweed could play a major part in this. The coasts of the UK and Ireland are not unlike Japan’s in that we have over six hundred species of algae, which we know very little about. Unlike the Japanese, Britons have investigated only a few, but we do know that at least thirty are edible. Traditionally, coastal dwellers used to eat seaweed as a rich source of calcium and iodine. A seaweed that is still enjoyed today in Brittany and Wales is laverweed (Porphyra), which when mixed with oats is made into laverbread (in Welsh, bara lawr). In Ireland dillisk is still eaten as a snack, while carrageen (Irish moss) is used for jellies and puddings.
There is a new culinary movement called Gastrophysics that advocates using seaweed in cooking to replace flavours like umami instead of resorting to meat, salt or MSG for the same effect. In the UK and Ireland seaweed farming is attracting commercial interest, as a crop fertiliser but increasingly as food supplements. European and US production remains tiny compared to the industrial scale of seaweed farms in Japan, but demand is growing.
If you or your family are not regular fish eaters and don’t live near the coast, you may not yet have the microbe genes and enzymes to allow you the full benefits of eating seaweed,13 though it is likely that if you were to move to Japan or start eating enough sushi you would eventually acquire them. As always our microbes, which can produce a new generation every thirty minutes, react much faster to food than we can. The story of seaweed illustrates both the ability of the human body to change and the symbiotic relationship we have with our microbes.14
Magic mushrooms and fungi
Mushrooms are hard to classify: traditionally they were thought of as a vegetable although they are not plants, and in that they need to eat to survive they are probably closer to animals. They are part of the fungi kingdom, which also contains yeasts. Mushrooms actually consist of a collection of large microbes that usually settle on decaying matter which they live off to grow and reproduce. As well as also living on soil, plants and fruit, they sometimes live off us humans. They do this in our dark, moist places like on our feet and especially between our toes, as athlete’s foot, or in our armpits or groins (jock rot). They contain no fat and generally have near-equal amounts of protein and carbohydrate. They are full of the healthy antioxidant selenium which mops up potentially toxic chemicals in our cells and they contain vitamin B, and if they have been sunbathing there is sometimes some vitamin D. They go well with meat or can act as a substitute for it as they stimulate the same umami taste receptors on our tongues that inform our brains that we are eating valuable protein.
Fungi can also live in our guts, as yeasts. We used to think they occurred only in relation to disease, but new sequencing detection methods have shown that in healthy people they make up about 4 per cent of the gut biomass – but about this kind of fungus we know virtually nothing. Fungi are only a problem when they run amok, unchecked by our normal microbes. Many fungi live happily and symbiotically with our microbes and us in our intestines. Some alternative medical practitioners are regularly and incorrectly diagnosing many vague symptoms as being due to an overgrowth of candida and offering bizarre and worthless treatments in an attempt to remove a natural part of our bodies. Our normal bacterial microbes are crucial in fighting off major fungal invasions. When under threat the microbes probably do this by signalling to our immune system. But when we take antibiotics or have immune-system problems we change the delicate balance, and consequently often develop fungal infections such as the yeast candida, commonly seen in the mouth and on the tongue.
Most women develop candida of the vagina (or thrush) at some point in their lives. This is normally kept in check by our bacteria friend lactobacillus, which is found in yoghurt. Thus yoghurt has become a popular internet remedy for candida. There have been few trials of its efficacy, but one Australian study recruited 270 women about to receive antibiotics and followed them for thrush, which a quarter of them later developed. They were randomised to take orally or vaginally lactobacillus probiotics or dummy products. Sadly, the probiotics did nothing for preventing the fungal infection.15 Using full-fat yoghurt in the vagina hasn’t yet been tested properly, but even if it doesn’t work many women apparently find it soothing. Immunologists are currently working on genetically modified lactobacillus strains that will be able to counteract vaginal viruses and reduce infections like HIV/AIDS.16 Whether vaginal yoghurt catches on as a health food remains to be seen, but it clearly has potential.
The Chinese have been using mushrooms as remedies for centuries. Although there have not yet been any human mushroom trials, studies have shown that feeding button mushrooms to mice for six weeks is beneficial. It increases their gut-microbial diversity and their Bacteroidetes species, and protects against gastric infections and inflammation.17 18
One fungus we commonly eat without usually knowing its origin is mycoprotein, more commonly known as Quorn™. This is grown in labs that began by taking the original fungus found in soil (Fusarium venenatum) and domesticating it in the same way that our ancestors did with many plants. Quorn has a high protein content, 44 per cent, and when blended with egg albumin mimics many meat products in texture. In Europe it is the commonest meat substitute.
Quorn had less success in the US, where soy is heavily sponsored, and it was severely criticised. It was marketed to the public as a mushroom-like product whereas it is in fact a completely different, unrelated, form of fungus. Despite the usual media scare stories that any new product faces, there has been no evidence of it doing any harm. Whether we take in the occasional bit of mould with our cheese or a tasty fungus, they are quite likely equally good for us.
In conclusion, for non-meat eaters nature provides a rich source of foods containing protein which, if varied enough, can supply us with nearly all the same nutrients that carnivores get except for vitamin B12. Our ability to digest them and produce the various necessary chemicals and hormones from them varies with our diverse resident gut microbes. Our adaptation for seaweed eating, thanks to our friends the microbes, is a great example of our combined flexibility and the cross-fertilisation of genes across species which makes us all ‘genetically modified’. It is hard to believe, but drinking milk was once as foreign to us as eating seaweed.