Is red meat bad? (Part II – IGF-1, risk of cancer and more)

Is meat bad for you

Let’s continue our discussion that we started in Part I and see if there really is any association between meat and cancer.

It’s different if you already have a pathology

It is often implied that high-protein diet causes damage to your kidneys by “overloading” them with nitrogen by-products of protein digestion (that they naturally metabolise and excrete) – but as a healthy individual, you will have difficulty overconsuming protein, since your body has natural regulatory mechanisms that drive the desire for protein-containing foods.  So you are unlikely to ever eat too much.

But is it correct to say that eating any amount will put a strain on your kidneys?  Should you specifically reduce protein consumption to avoid damaging them?

The answer is – very unlikely.  If you already have a kidney disease – increased protein consumption can definitely contribute to their pathology.  But if you are healthy – you probably don’t have anything to worry about (read this article by Chris Kesser).


Meat contains a complex array of several amino acids.  One of these amino acids is methionine – and recent studies have suggested that it’s this specific amino acid that may be responsible for increased oxidative stress and the ultimate link between meat, IGF-1 (see below) and cancer.

If you recall our discussion on organ meats – you will remember that methionine is balanced by glycine – another amino acid contained in large amount in bone broth, gelatin and organ meats – which helps your body metabolize and neutralize potential harmful effects of methionine. What follows is that if you balance your intake of methionine with your intake of glycine (by consuming collagen/gelatin, organ meats, bone broth, etc.) – potential harmful effects of overconsuming muscle meat can be greatly reduced.

IGF-1, cancer and proteins

Now is when this is getting interesting.  A large part of associative studies that tie meat-eating with cancer, single out one factor that seems to be the cause – elevated IGF-1.

IGF-1 (Insulin-like Growth Factor-1) is an anabolic hormone molecularly similar to insulin (hence the name) that is secreted by the liver when stimulated by Growth Hormone.  Proteins and lipids seem to increase IGF-1 levels, while carbohydrates seem to reduce them.

The primary function of IGF-1 is to modulate cell growth and survival.  IGF-1 is not inherently bad.  As is the case with many hormones and biologically active compounds – the poison is in the dose.  IGF-1 is necessary to support normal growth and development (including bone growth and density), and promote neurogenesis in the brain.  In fact, low levels, just as high levels are associated with all-cause mortality and cancer mortality specifically.

But when there is too much of it, things get a bit more uncertain.  By this time you probably already know that free radicals, exposure to toxins and a few other risk factors increase the risk of incidence of malignant cells in your body.  Healthy cells have several built-in tumor-supressing mechanisms to stop the proliferation of cancerous cells by either triggering apoptosis or shutting down cell growth and division.  The presence of IGF-1 appears to suppress these natural anti-cancer defenses and, thus, provide better conditions for cancerous cells to proliferate.  So much so, that IGF-1 levels are considered potential determinants of lifespan.

Low protein intake is associated with major reduction in IGF-1 – at least until the age of 65 – after that, the trend actually reverses.

So hereby lies the dilemma for bodybuilders and anyone who cares about growing at least a bit of a muscle mass (this is a good thing).  IGF-1 is necessary to promote muscle growth – this is why nutrition – especially animal products – play a key role in muscle building (you can’t just do this with exercise alone).  On the other hand – it may seem that you have this increased cancer risk.  What do you choose – performance, or general longevity?

You can actually choose both, believe it or not.  The key is to keep in mind the following few important points:

  • While having normally functioning tumor-supressing mechanisms that are uninhibited by excess IGF-1 provides extra insurance against something going terribly wrong, the best strategy is to prevent the formation of cancerous cells in the first place. Of course, it is easier said than done but, thanks to modern science and research, we know at least a few factors that promote cancer – those are, in no particular order – increased number of reactive oxygen species, high exposure to environmental toxins (which, ironically, are often found in some commercial drugs), less than stellar dietary practices that result in consumption of a lot of pro-inflammatory foods, stress (which significantly weakens the immune system), etc.  If you reduce the risk of cancerous cells forming in the first place, you will have less to worry about in terms of not letting those that already formed propagate and take over.
  • A great strategy to reduce the exposure to IGF-1 is doing resistance exercise. Exercise significantly improves the uptake of IGF-1 in muscle tissue and, thus, leaves less available for other cells.
  • Another important factor is reduced carbohydrate intake. While limiting carbs may not trigger a decrease in circulating IGF-1 as much as a reduction in protein does, studies show that overconsumption of carbohydrates and the resulting overactivation of insulin pathways increases the expression of IGF-1 receptors in tumor cells. In other words, by restricting carbs, you are indirectly reducing IGF-1 availability for tumor cells reducing their chance of survival.  We have been talking about the necessity to limit the consumption of carbohydrates  many times – this is another reason to do so.  Remember that – as much as too much IGF-1 may potentially increase the risk of some cancers, excessive carbohydrates have no lesser ability to do so, given that glucose – which is what all carbohydrates are ultimately reduced to – is a perfect fuel for cancer cells.

The China study

The last bastion of defense for those who shun meat and animal products is the book that summarizes a study of seemingly epic proportions and appears to eliminate any doubt that meat is bad for you – “The China Study”.

This book, describing and elaborating on the results of a 19-year-long study done on 6500 adults in rural China, has become a bible for vegans and a seemingly unbeatable argument against eating any animal foods.

There have been numerous cases of very good critique and analysis of both the conclusions drawn in the book and the raw data used for the book – if you are interested in reading very detailed (but clear) analyses – you can read any (or all) of the following:

The China study: fact or fallacy?

“The China study” – formal analysis and response

One Year Later: The China Study, Revisited and Re-Bashed

The China Study, Wheat, and Heart Disease; Oh My! (this article might also help you understand the direct correlation of heart disease rates observed in the study with wheat consumption, rather than animal protein)

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The Truth about the China Study

Tuoli: China’s Mysterious Milk Drinkers (this, Along with A Closer Look at the China Study: Dairy and Disease will explain how even for those who consume a lot of dairy there is no correlation between the consumption of dairy – let along other animal proteins – and cancer and how, based on raw data used for the China Study, there is no correlation between meat consumption and any disease (in fact, meat even seems to have some protective effect).

If you are only interested in key points, here is what you have to remember: while The China Study raises some important questions (for instance, drawing attention to aflatoxins so prevalent in peanuts and peanut butters, as well as some other crops), the final conclusions it draws regarding meat should be assessed from the following critical angles:

  • As many studies that attempt to vilify meat, fat or other commonly blamed dietary bad habits, the China Study – despite its massive proportions – is a correlative, not a causative Protein-eating (and meat-eating, specifically) was never isolated as a single important factor in disease – because other factors were not properly eliminated.  For instance, one observation mentioned in the book was that although the areas with the highest consumption of peanut butter had the highest incidence of liver cancer in the Philippines, it was the children of the “best-fed families,” who consumed the most protein, who were getting liver cancer – however, whether those families ate the many staples of modern affluent diets like refined breads and sugars isn’t mentioned.
  • A lot of the data on dietary habits was collected from questionnaires – and, therefore, depended on whether the facts were properly recalled and truthfully represented. Even so, some questions were lacking in necessary details – for instance, questions about the frequency of consumption of sea food, meat, eggs, and milk were included, but questions about organ meats and insects were not included on the questionnaire, nor was fish differentiated from shell fish, despite the very different nutrient profiles of these foods.  Why are organ meats important?  Because they contain a lot of vitamins, minerals and glycine – which balances out methionine, as discussed above;
  • Although the studies began with using aflatoxin as cancer initiator and casein (one of milk proteins) as the promoter protein and the results of the China Study seem to corroborate the earlier results of other researchers (i.e. – a dose-response curve existed for aflatoxin and some other initiators, such as hepatitis B, and cancer on a 20% casein diet, but disappeared on a 5% casein diet) – this article will explain how the same low-casein diet that protected the rats against aflatoxin-induced cancer dramatically increased the vulnerability of these rats to the acute toxicity of aflatoxin. Moreover, high-casein diets provided the rats with dramatic protection against cancer when they were fed before or during the aflatoxin dosing rather than after.
  • Casein behaved exactly like plant proteins when the limiting amino acid of the specific plant protein was provided, as would occur on a normal diet of mixed foods (as opposed to high-dose isolated casein powder). Most of the generalizations in the book that associated cancer risk with any animal protein were based on cases of isolated casein fed to lab animals.  Keep in mind casein is only one type of animal protein (and not the most prevalent in a typical normal diet, unless you just consume a lot of dairy).  In fact, the other prevalent protein in milk – whey protein – has protective effect against different cancers (and other benefits, such as promoting the synthesis of glutathione by the liver).  Any effect of casein, then, cannot be generalized even to other milk proteins, let alone all animal proteins.
  • Once again – just as with processed meat we discussed in Part I, a question that remains unanswered is what effect different types of processing have on casein’s capacity to promote tumor growth. Pasteurization, low-temperature dehydration, high-temperature spray-drying, and fermentation all affect the structure of casein differently and thereby would affect its physiological behavior.
  • The book fails to address the problems of vitamin A depletion from excess isolated protein, unsupported by the nutrient-dense fats which accompany protein foods in nature.
  • The conclusions in the book are highly selective – we have covered in the past the role of excessive carbohydrates (plant foods) in promoting diabetes and other metabolic diseases – nevertheless the book concludes that “high-fiber, whole, plant-based foods protect against diabetes, and high-fat, high-protein, animal-based foods promote diabetes”. The book fails to mention that excessive fructose consumption (from plant foods) causes insulin resistance and how the increase in high fructose corn syrup consumption has paralleled the increase in diabetes.  Similarly, the possible role of cow’s milk (an animal food) is discussed in causing Type 1 diabetes via an autoimmune reaction but no mention is made that wheat gluten (a plant food) has been implicated in Type 1 diabetes by a similar process.
  • The China Study reiterates the myth that dietary fat and cholesterol contribute to Alzheimer’s (stating that “Eating foods that contain any cholesterol above 0 mg is unhealthy.”) (which, as we previously discussed, really is just that – a myth) and discusses the potential protective effects of plant foods, but does not mention the protective effect of DHA, an animal-based nutrient, that has been known for years;
  • As you will see reading some of the analysis in the links presented above, raw data obtained from the China Study doesn’t even support the conclusions drawn in the book – that’s without even considering the fact that results from some counties (of the 65 used in the study) were conveniently omitted because they did not fit the pattern presented;
  • Nutrient intakes were determined from food composition tables, rather than measured directly from foods – which raises a question of whether there were differences in nutrient composition of foods in different areas due to soil quality;

The list can go on – but it is already long enough.  Thoroughly discussing all relevant points related to the China Study is beyond the scope of this post (especially given that we have previously already discussed the dangers of veganism in some detail).  But you probably get the idea now – given all these inconsistencies, you definitely cannot rely on the China Study as your dietary guide.


We can be relatively certain that consuming meat eliminates some nutritional deficiencies facing us otherwise.  We can be relatively sure that even if those deficiencies are addressed through extra supplementation and careful meal planning, trying to get the same quality and quantity of nutrients from other foods when meat is out of the picture almost certainly leads to increased consumption of carbohydrates.  What we cannot do is state with certainty, whether meat consumption increases the risk of developing disease or not.  Is there a chance that it does?  There probably is (there is a chance like this with most foods you eat).  Can we then conclude that meat is bad for you?  Probably not – unless you violate the core principles of quality natural and minimally processed food, of course (in which case any food can be bad for you!)

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How can a product that seems to be so good for us be potentially bad?  You have to keep in mind that even if something is completely natural and essential for your body – it may still come with some unwanted side effects.  As a simple (and somewhat unrelated) example – consider cellular metabolism.  Whether your cell uses glucose, fat or ketone bodies for energy – it generates reactive oxygen species (ROS) as a result.  This is just a fact of life – and not always a bad thing – low and moderate amounts of ROS have beneficial effects on several physiological processes including killing of invading pathogens, wound healing, and tissue repair processes.  But excess ROS have also been historically linked to cellular damage and risk of developing cancer.  It almost seems that some mechanism of timed self-destruction is pre-programmed into our DNA.

Whether you believe this or not – or if you, like me, think that by carefully managing our biology we can extend our lifespans significantly – the key to figuring out this dilemma is understanding that completely eliminating meat doesn’t really solve the problem.  Back to IGF-1 discussed above, for instance – if you omit meat and eat a bunch of rice and beans – you might (or might not) reduce circulating IGF-1, but might also increase availability of that lower amount to tumor cells.

So, what do you do?  Here is one solution – instead of trying to eliminate the dangers associated with consuming meat (which also exist when you consume other foods) – you can try to mitigate it by following these guidelines and tactics:

  • Try intermittent fasting. Even short-term fasting dramatically reduces the amount of circulating IGF-1.  Although longer-term (72 hours or more) fasting has been found to have a far more pronounced effect on lowering IGF-1 and increasing the activity of hematopoietic stem cells (SSC) (at least in lab animals), the emphasis is mainly on “short-term” because longer-term (30 hours and more) may potentially lead to muscle wasting – which you don’t want to get to.  Intermittent fasting is a great alternate strategy of compressing your refeeding window to only about 8 hours and making sure that, during that refeeding window, you consume adequate amount of essential amino acids;
  • Follow a low-carb diet. Studies have shown that people who follow high-fat diets (especially saturated fat) have significantly lower levels of IGFBP-3 (IGF binding protein-3) – which, jointly with IGF-1 is considered another marker for an increased risk of cancer.
  • Restriction in protein (and make no mistake – it is, specifically protein restriction we are concerned with, as simple calorie/energy restriction doesn’t work in humans as well as lab animals doesn’t necessarily mean you will compromise your muscle development or feel hungry. Keep in mind that the amounts of protein used in studies that confirmed significant impact of “moderate” protein restriction on lowering the IGF-1 levels landed on 0.95g per 1kg of body mass (reduced from 1.67g per 1 kg).  This is not a terribly low amount – in fact, this is close to the general recommendations we have been discussing when we were talking about protein intake for muscle growth – and the study referenced above did not focus on competitive athletes – who typically get away with higher amounts of protein as they have higher requirement for it.
  • Incorporate heavy weights into your exercise schedule. Once again this is true for both men and women.  You may not be concerned with bodybuilding per se, but incorporating heavy weights using resistance exercise provides sufficient stimuli for your muscle tissue to adapt and grow.  That growth is supported by IGF-1 – which is taken up by the muscle and, thus, removed from free circulation.  Exercise, therefore, beside all other benefits it provides, is a great insurance policy against too much of IGF-1.   Because muscle tissue synthesis requires protein – you have an added buffer if you consume more protein than necessary.
  • If you are already diagnosed with cancer – to be on the safe side – you might want to reduce protein consumption slightly (also, make sure you read an article on potentially powerful anti-cancer properties of ketogenic diets – which also do not suggest high protein consumption);
  • When selecting animal protein sources, make sure you pick high-quality healthy meats. Factory meat from animals fed low-quality pesticide- and mycotoxin-laden GMO grains – IGF-1 or no IGF-1 – are not suitable for human consumption.  Not only they are potentially exposed to residues of toxic compounds which, incidentally, get stored in their fat tissue which grain-fed animals possess more of – but the fatty acid profile of this stored fat is completely different and unnatural – to an extent that it actually causes chronic inflammation (which is often at the very heart of many diseases, including cancer).  Instead, choose meat from pastured animals humanely raised on organic farms;
  • Having started with highest possible quality of meat – follow through and use low-temperature gentle cooking methods as opposed to open-fire grilling;
  • Being an omnivore is not a ticket to load up on protein and forget about everything else. No matter how big of a meat eater you are – do not ignore your veggies!  Think of your food as mostly vegetable-based, with a side serving of meat.  A good variety of nutrient dense organically grown vegetables can provide necessary minerals, vitamins and, specifically, antioxidants and other beneficial compounds that actually reduce the risk of cancer.  Due to the presence of naturally occurring alkaline ash, vegetables also help regulate pH levels of your blood by buffering the theoretic acidification due to increase in sulfur-containing amino acids from meat,

Personally, I would like to have some middle ground – and that’s why I would adopt a strategy of eating as much meat as necessary, but not more.  This is a vague statement because it doesn’t give you a specific guideline – but the reality is that it shouldn’t.  It really does depend on your goals, your starting point and your tolerance.  I have a view that an adequate amount of meat intake is necessary (and, generally speaking, not harmful if you take care of other important considerations, such as meat quality, source and cooking methods which make sure you do not amplify the effect of any potential biological downside).

Whether you choose to believe it or not is entirely up to you – but at least now you are armed with facts and knowledge that would help you make a better decision.