There's a take-off of the industry slogan, "Beef: It's What's For Dinner" - "Beef: It's What's Rotting in Your Colon." I saw this on a shirt once with some friends and I was such the party pooper--no pun intended--explaining to everyone that meat is fully digested in the small intestine, and never makes it down into the colon. It's no fun hanging out with biology geeks.

But I was wrong!

It's been estimated that with a typical Western diet, up to 12 grams of protein can escape digestion, and when it reaches the colon, it can be turned into toxic substances like ammonia. This degradation of undigested protein in the colon is called putrefaction, so a little meat can actually end up putrefying in our colon. The problem is that some of the by-products of this putrefaction process can be toxic.

It's generally accepted that carbohydrate fermentation--the fiber and resistant starches that reach our colon--results in beneficial effects because of the generation of short-chain fatty acids like butyrate, whereas protein fermentation is considered detrimental. Protein fermentation mainly occurs in the lower end of colon and results in the production of potentially toxic metabolites. That may be why colorectal cancer and ulcerative colitis tends to happen lower down--because that's where the protein is putrefying.

Probably the simplest strategy to reduce the potential harm of protein fermentation is to reduce dietary protein intake. But the accumulation of these toxic byproducts of protein metabolism may be attenuated by the fermentation of undigested plant matter. In my video, Bowel Wars: Hydrogen Sulfide vs. Butyrate, you can see a study out of Australia showed that if you give people foods containing resistant starch you can block the accumulation of potentially harmful byproducts of protein metabolism. Resistant starch is resistant to small intestine digestion and so it makes it down to our colon where it can feed our good bacteria. Resistant starch is found in cooked beans, split peas, chickpeas, lentils, raw oatmeal, and cooled cooked pasta (like macaroni salad). Apparently, the more starch that ends up in the colon, the less ammonia that is produced.

Of course, there's protein in plants too. The difference is that animal proteins tend to have more sulfur-containing amino acids like methionine, which can be turned into hydrogen sulfide in our colon. Hydrogen sulfide is the rotten egg gas that may play a role in the development of the inflammatory bowel disease, ulcerative colitis (see Preventing Ulcerative Colitis with Diet).

The toxic effects of hydrogen sulfide appear to be a result of blocking the ability of the cells lining our colon from utilizing butyrate, which is what our good bacteria make from the fiber and resistant starch we eat. It's like this constant battle in our colon between the bad metabolites of protein, hydrogen sulfide, and the good metabolites of carbohydrates, butyrate. Using human colon samples, researchers were able to show that the adverse effects of sulfide could be reversed by butyrate. So we can either cut down on meat, eat more plants, or both.

There are two ways hydrogen sulfide can be produced, though. It's mainly present in our large intestine as a result of the breakdown of sulfur-containing proteins, but the rotten egg gas can also be generated from inorganic sulfur preservatives like sulfites and sulfur dioxide.

Sulfur dioxide is used as a preservative in dried fruit, and sulfites are added to wines. We can avoid sulfur additives by reading labels or by just choosing organic, since they're forbidden from organic fruits and beverages by law.

More than 35 years ago, studies started implicating sulfur dioxide preservatives in the exacerbation of asthma. This so-called "sulfite-sensitivity" seems to affect only about 1 in 2,000 people, so I recommended those with asthma avoid it, but otherwise I considered the preservative harmless. I am now not so sure, and advise people to avoid it when possible.

Cabbage family vegetables naturally have some sulfur compounds, but thankfully, after following more than a hundred thousand women for over 25 years, researchers concluded cruciferous vegetables were notassociated with elevated colitis risk.

Because of animal protein and processed food intake, the standard American diet may contain five or six times more sulfur than a diet centered around unprocessed plant foods. This may help explain the rarity of inflammatory bowel disease among those eating traditional whole food, plant-based diets.

There's a take-off of the industry slogan, "Beef: It's What's For Dinner" - "Beef: It's What's Rotting in Your Colon." I saw this on a shirt once with some friends and I was such the party pooper--no pun intended--explaining to everyone that meat is fully digested in the small intestine, and never makes it down into the colon. It's no fun hanging out with biology geeks.

But I was wrong!

It's been estimated that with a typical Western diet, up to 12 grams of protein can escape digestion, and when it reaches the colon, it can be turned into toxic substances like ammonia. This degradation of undigested protein in the colon is called putrefaction, so a little meat can actually end up putrefying in our colon. The problem is that some of the by-products of this putrefaction process can be toxic.

It's generally accepted that carbohydrate fermentation--the fiber and resistant starches that reach our colon--results in beneficial effects because of the generation of short-chain fatty acids like butyrate, whereas protein fermentation is considered detrimental. Protein fermentation mainly occurs in the lower end of colon and results in the production of potentially toxic metabolites. That may be why colorectal cancer and ulcerative colitis tends to happen lower down--because that's where the protein is putrefying.

Probably the simplest strategy to reduce the potential harm of protein fermentation is to reduce dietary protein intake. But the accumulation of these toxic byproducts of protein metabolism may be attenuated by the fermentation of undigested plant matter. In my video, Bowel Wars: Hydrogen Sulfide vs. Butyrate, you can see a study out of Australia showed that if you give people foods containing resistant starch you can block the accumulation of potentially harmful byproducts of protein metabolism. Resistant starch is resistant to small intestine digestion and so it makes it down to our colon where it can feed our good bacteria. Resistant starch is found in cooked beans, split peas, chickpeas, lentils, raw oatmeal, and cooled cooked pasta (like macaroni salad). Apparently, the more starch that ends up in the colon, the less ammonia that is produced.

Of course, there's protein in plants too. The difference is that animal proteins tend to have more sulfur-containing amino acids like methionine, which can be turned into hydrogen sulfide in our colon. Hydrogen sulfide is the rotten egg gas that may play a role in the development of the inflammatory bowel disease, ulcerative colitis (see Preventing Ulcerative Colitis with Diet).

The toxic effects of hydrogen sulfide appear to be a result of blocking the ability of the cells lining our colon from utilizing butyrate, which is what our good bacteria make from the fiber and resistant starch we eat. It's like this constant battle in our colon between the bad metabolites of protein, hydrogen sulfide, and the good metabolites of carbohydrates, butyrate. Using human colon samples, researchers were able to show that the adverse effects of sulfide could be reversed by butyrate. So we can either cut down on meat, eat more plants, or both.

There are two ways hydrogen sulfide can be produced, though. It's mainly present in our large intestine as a result of the breakdown of sulfur-containing proteins, but the rotten egg gas can also be generated from inorganic sulfur preservatives like sulfites and sulfur dioxide.

Sulfur dioxide is used as a preservative in dried fruit, and sulfites are added to wines. We can avoid sulfur additives by reading labels or by just choosing organic, since they're forbidden from organic fruits and beverages by law.

More than 35 years ago, studies started implicating sulfur dioxide preservatives in the exacerbation of asthma. This so-called "sulfite-sensitivity" seems to affect only about 1 in 2,000 people, so I recommended those with asthma avoid it, but otherwise I considered the preservative harmless. I am now not so sure, and advise people to avoid it when possible.

Cabbage family vegetables naturally have some sulfur compounds, but thankfully, after following more than a hundred thousand women for over 25 years, researchers concluded cruciferous vegetables were notassociated with elevated colitis risk.

Because of animal protein and processed food intake, the standard American diet may contain five or six times more sulfur than a diet centered around unprocessed plant foods. This may help explain the rarity of inflammatory bowel disease among those eating traditional whole food, plant-based diets.

Foods of animal origin in general naturally contain hormones, but cow's milk may be of particular concern. The hormones naturally found even in organic cow's milk may have played a role in studies that found a relationship between dairy products and human illnesses, such as acne, certain cancers and male reproductive disorders. Milk consumption has also been associated with an increased risk of early puberty and endometrial cancer in postmenopausal women, but "hormonal levels in food could be particularly dangerous in the case of vulnerable populations, such as young children or pregnant women. To this critical population, even a small hormonal intake could lead to major changes in the metabolism."

If you check out my video Why Do Vegan Women Have 5x Fewer Twins, you can see that children are highly sensitive to sex steroids. Because their levels of sex steroids are very low, even a small variation would account for a major change in the total activity of the involved hormone. Because no lower threshold for estrogenic action has been established, caution should be taken to avoid unnecessary exposure of fetuses and children to exogenous sex steroids, even at very low levels.

In the AMA's Pediatrics Journal, the Chair of Boston Children's Hospital's Obesity Prevention Center along with the chair of Harvard's nutrition department questioned dairy industry recommendations that children should drink three glasses of milk a day. Dairy milk evolved to promote the growth of grazing animals at high risk for predation when small, so they needed to put on a few hundred pounds quickly in the first few months of life.

The consequences of lifetime human exposure to the growth factors in milk have not been well studied. "Milk consumption increases serum concentrations of insulin-like growth factor 1, which is linked to prostate and other cancers. In addition, modern industrial methods maintain dairy cows in active milk production throughout their pregnancies, resulting in a milk supply with high levels of reproductive hormones."

Pregnant cows excrete significantly higher levels of sex steroids into their milk than non-pregnant cows. The subsequent consumption of such dairy products from pregnancy results in additional consumer exposure. And it's not just dairy. Although dairy products are an important source of hormones, other products of animal origin must be considered as well. All edible tissues of animal origin contain estrogen. This may explain why, in a study of over a thousand women eating plant-based diets, vegan women have a twinning rate that is one fifth that of vegetarians and omnivores.

Twin pregnancies are risky pregnancies, with much higher complication rates. Many parents and physicians underestimate the negative consequences of multiple pregnancy, but "women with a multiple pregnancy face greater risks for themselves and their infants." Twin babies may be ten times more likely to die at birth. To avoid these complications, the research team writes, "women attempting conception should avoid milk and dairy products."

In response to concerns raised about the toxicity of Monsanto's roundup pesticide, which ends up in GMO foods (See Is Monsanto's Roundup Pesticide Glyphosate Safe?), Monsanto's scientists countered that these in vitro experiments used physiological irrelevant concentrations, meaning dripping roundup on cells in a petri dish at levels far above what would be realistically found in the human body.

Sure, it's probably not a good idea to mix up your alcohol with your roundup and chug the stuff, or try to commit suicide by drinking or injecting it. And there are rare cases of Parkinson's reported after getting directly sprayed with it, or working for years in a pesticide production plant, but that's not your typical consumer exposure.

As shown in my video GMO Soy and Breast Cancer, some of the researchers responded to the accusation claiming they used the kinds of concentrations that are used out in the fields. Therefore every little droplet we spray worldwide is above the threshold concentration they found to cause adverse effects. Monsanto's folks responded saying, "Yes, that's the concentration we spray, but that's not the concentration that human cells are bathing in. Once it gets into drinking water or food, it's highly diluted." And, they're quick to point out, if we look at people with the greatest exposure--pesticide workers--the vast majority of studies show no link between the use of Roundup and cancer or non-cancer diseases. There are a few suggestive findings suggesting a link with non-Hodgkin's lymphoma. One study of pesticide applicators suggested an association with multiple myeloma, and one study of the children of pesticide applicators found a tentative association with ADHD, but again these are folks experiencing a much greater exposure level than the general population that may just get a few parts per million in their food. But there had never been any studies done on the tiny levels found circulating in people's bodies, until now.

In a study out of Thailand, the maximum residue levels were set at parts per million (the concentrations found within human bodies is measured in parts per billion). The study found glyphosate can activate estrogen receptors at a few parts per trillion, increasing the growth of estrogen receptor positive human breast cancer cells in a petri dish. These results indicate "that truly relevant concentrations of the pesticide found on GMO soybeans possesses estrogenic activity."

That may be because most GMO soy in the U.S. is fed to chickens, pigs, and cows as livestock feed, whereas most of the major soy food manufacturers use non-GMO soy. Or it could be because the benefits of eating any kind of soy may far outweigh the risks, but why accept any risk at all when we can choose organic soy products, which by law exclude GMOs.

The bottom-line is that there is no direct human data suggesting harm from eating GMOs, though in fairness such studies haven't been done, which is exactly the point that critics counter. This is why we need mandatory labeling on GMO products so that public health researchers can track whether GMOs are having any adverse effects.

It is important to put the GMO issue in perspective though. As I've shown (See Lifestyle Medicine: Treating the Causes of Disease), there are dietary and lifestyle changes we can make that could eliminate most heart disease, strokes, diabetes, and cancer. Millions of lives could be saved. A healthy enough diet can even reverse our number one killer, heart disease. So, I'm sympathetic to the biotech industry's exasperation about GMO concerns when we still have people dropping dead from everything else they're eating. As one review concluded "consumption of genetically modified food entails risk of undesirable effects... similar to the consumption of traditional food." In other words, buying the non-GMO Twinkie isn't doing our body much of a favor.

For more on the public health implications of genetically engineered crops in our food supply, check out the these videos:

Researchers out of Norway described the amount of pesticide residues found in GMO soy as high compared to the maximum allowable residue levels. The legal limit for glyphosate in foods had been set at 0.1-0.2 mg/kg; so these exceed the legal limits by an average of about 2000%, whereas organic and conventional non-GMO soy both had none.

So what did Monsanto do? Did the industry ditch the whole GMO thing, go back to using less pesticides so that residue levels wouldn't be so high? Or, they could just change the definition of high. What if they could get authorities to raise the maximum residue level from 0.1 or 0.2 up to 20? Then the residue levels won't look so high anymore. And this is exactly what they did. The acceptance level of glyphosate in food and animal feed has been increased by authorities in countries that use Roundup-Ready GM crops. In Brazil, they went up to ten, and the U.S. and Europe now accept up to 20. In all of these cases, the maximum residue level values appear to have been adjusted, not based on new evidence indicating glyphosate toxicity was less than previously understood, but pragmatically in response to actual observed increases in the content of residues in GMO soybeans--otherwise it wouldn't be legal to sell the stuff.

What evidence do we have, though, that these kinds of residues are harmful? For 12 years we've heard that Roundup interferes with embryonic development, but that study was about sea urchin embryos. For 14 years we heard that Roundup may disrupt hormones, but that's in mouse testicles.

Blogs will dish about concerning new studies implicating Roundup in male fertility, but if we look at the study, it's about rat testicles. Some blogs cite studies with disturbing titles like "prepubertal exposure alters testosterone levels and testicular shape," but they're talking about puberty in rats, though that doesn't make as catchy a blog title.

Why not use human tissue? Women are having babies every day--why not just experiment on human placentas, which would otherwise just get thrown away? In 2005, researchers did just that. And despite all the negative effects in rodents, glyphosate, the active ingredient in Roundup didn't seem to have much of a toxic effect on human cells even at high doses, or have much effect on a hormone regulating enzyme, leading Monsanto-funded reviewers to conclude that regardless of what hazards might be alleged based on animal studies, "glyphosate is not anticipated to produce adverse developmental and reproductive effects in humans."

But pure glyphosate isn't sprayed on crops, Roundup is, which contains a variety of adjuvants and surfactants meant to help the glyphosate penetrate into tissues. And indeed when the study was repeated with what's actually sprayed on GMO crops, there were toxic and hormonal effects even at doses smaller than the 1 or 2% concentration that's used out on the fields.

Similar results were found for other major pesticides. It took until 2014, but eight out of nine pesticide formulations tested were up to one thousand times more toxic than their so-called active ingredients, so when we just test the isolated chemicals, we may not get the whole story. Roundup was found to be 100 times more toxic than glyphosate itself. Moreover, Roundup turned out to be among the most toxic pesticides they tested. It's commonly believed that Roundup is among the safest, though, an idea spread by Monsanto, the manufacturer. However, this inconsistency between scientific fact and industrial claim may be attributed to the huge economic interests involved.

It's the dose that makes the poison, though. Do we have evidence that the levels of Roundup chemicals not only found on crops, but also in our bodies after eating those crops actually have adverse effects? That's the subject of the video: GMO Soy and Breast Cancer.

Commercial interests can have a corrupting effect on the science of nutrition and hold sway over institutions that are supposed to operate in the public interest. See for example:

As I discussed in the video, Are GMOs Safe? The Case of BT Corn, genes from GMO crops were found in pregnant women. There is debate on the direct threat of the inserted genes, but the real danger may come from pesticides associated with genetically modified foods. As stated in an article published in Science and Engineering Ethics, "genetically engineered seed biotechnology typically has not been used to increase crop yields, nutrition, or drought tolerance but instead for profitable pesticide-resistant products... 80% of GMO crops are bioengineered only for pesticide resistance. Not surprising, given that the top five biotech companies are chemical companies that manufacture pesticides."

This allows farmers to spray herbicides directly onto the crops, raising a theoretical possibility that the levels of herbicide residues on food we buy at the supermarket may have increased. Or at least it was theoretical... until now.

Monsanto's roundup-ready soybeans are the number one GM crop, genetically engineered to be resistant to the herbicide, Roundup--also sold by Monsanto. This allows farmers to spray fields with the Roundup herbicide glyphosate, which then kills the weeds while leaving the soy standing.

Monsanto maintains that roundup ready soybeans are compositionally equivalent to that of conventional soy, a concept that is used to argue that GMO foods are therefore as safe as non-GMO. Monsanto did not report the level of pesticide residues, however. In fact, some of the comparison tests were done on Roundup-ready soybeans that hadn't been sprayed at all, which is the whole point of having Roundup-ready plants. In contrast to real-life samples from the market, transgenic crops intended for scientific studies are often produced without the application of herbicides or at doses lower than those typically used by farmers. It wasn't until a study published in 2014 when the full composition of ready-to-market soybeans was analyzed.

You can see the analysis in my video, Are GMOs Safe? The Case of Roundup Ready Soy. There was a significant amount of glyphosate found in the GMO beans, along with a glyphosate breakdown product called AMPA. There was no glyphosate or AMPA found in organic soy. What about conventional non-GMO soy where glyphosate is just sprayed on the soil to kill weeds between crop cycles? Also none. So GMO soybeans are really not equivalent, they appear to have substantially more pesticide residues. The debate then shifts from the safety of Roundup ready soybeans, to the safety of Roundup itself.

Recently the prominent science journal Natureeditorialized that we are now swimming in information about genetically modified crops, but that much of the information is wrong--on both sides of the debate. "But a lot of this incorrect information is sophisticated, backed by legitimate-sounding research and written with certitude," adding that with GMOs, "a good gauge of a statement's fallacy is the conviction with which it is delivered."

To many in the scientific community, GMO concerns are dismissed as one big conspiracy theory. In fact, one item in a psychological test of belief in conspiracy theories asked people if they thought food companies would have the audacity to be dishonest about genetically modified food. The study concluded that many people were cynical and skeptical with regard to advertising tricks, as well as the tactics of organizations like banks and alcohol, drug, and tobacco companies. That doesn't sound like conspiracy theory to me; that sounds like business as usual.

We must remember there is a long legacy of scientific misconduct. Throw in a multi-billion dollar industry, and one can imagine how hard it is to get to the truth of the matter. There are social, environmental, economic, food security, and biodiversity arguments both pro and con about GMOs, but those are outside my area of expertise. I'm going to stick to food safety. And as a physician, I'm a very limited veterinarian--I only know one species (us!). So, I will skip the lab animal data and ask instead: What human data do we have about GMO safety?

One study "confirmed" that DNA from genetically modified crops can be transferred into humans who eat them, but that's not what the study found, just that plant DNA in general may be found in the human bloodstream, with no stipulations of harm (See Are GMOs Safe? The Case of Bt Corn).

Another study, however, did find a GMO crop protein in people. The "toxin" was detected in 93 percent of blood samples of pregnant women, 80 percent of umbilical cord blood samples, and 69 percent of samples from non-pregnant women. The toxin they're talking about is an insecticidal protein produced by Bt bacteria whose gene was inserted into the corn's DNA to create so-called Bt-corn, which has been incorporated into animal feed. If it's mainly in animal feed, how did it get into the bodies of women? They suggest it may be through exposure to contaminated meat.

Of course, why get GMO's second-hand when you can get them directly? The next great frontier is transgenic farm animals. A genetically modified salmon was first to vie for a spot at the dinner table. And then in 2010, transgenic cows, sheep, goats and pigs were created, genetically modified for increased muscle mass, based on the so-called mighty mouse model. Frankenfurters!

But back to children of the corn and their mothers. When they say it's a toxin, it's a toxin to corn worms, not necessarily to people. In fact I couldn't find any data linking BT toxin to human harm, which is a good thing since it's considered one of the few pesticides considered so non-toxic that it's sprayed on organic fruits and vegetables.

For more on on the public health implications of genetically modified crops, see:

A common concern about eating a plant-based diet is that it is expensive. I beg to differ. There are ways to purchase food on any type of meal plan that range widely from simple to extravagant, regardless of whether there are animal foods in the mix or not. In fact, you will likely save thousands …