Despite a slight anti-meat message, it was a surprisingly balanced documentary with a fairly sensible conclusion. However, some of the issues are poorly explained or represented; the studies were not evaluated properly; some important information is omitted; and, Dr Mosley’s “high meat diet” self-experiment was badly executed, and therefore entirely misleading.
The high meat diet
Dr. Mosley decides to focus on red meat and processed meat, because these are most closely linked to an increased risk of cardiovascular disease (heart attacks and strokes) and cancer.
To start off the programme, Dr. Mosley initiates his own “high meat diet”, almost doubling his (red and processed) meat intake from 70g to 130g/ day. He undergoes some basic blood tests, and gets weighed. He will be re-tested at the end of four weeks of filming.
On his journey he is joined intermittently by Dr. Ali Khavandi, a cardiologist from Bath who seems well informed and sensible; a Senior Heart Health Dietician (whatever that is) from the British Heart Foundation; and, a Nutrition Scientist from the British Nutrition Foundation.
Very early on, the programme points out some important nutrition facts about meat, and red meat in particular – it is high in protein (including some essential amino acids that are very difficult to get from plant-based foods), zinc, iron and vitamin B12. When they analyse meat versus the vegetarian alternatives, we see that the latter are particularly lacking in many of these nutrients. This is one important reason why I think we should include at least some meat in our diet.
Next up, Dr. Mosley speaks to Dr. Gary Fraser, the first of four experts that he talks to about data from their own large studies. Dr. Fraser has spent his life studying over 100,000 7th Day Aventists in California. Because of their close community, generally healthy lifestyle, and the fact that around 50% of them are vegetarian, they provide a fairly unbiased way of comparing vegetarians with omnivores. In this group, omnivores all have higher risks of being overweight and developing high blood pressure, diabetes and heart disease. In fact, according to Dr. Fraser, eating beef 3x per week supposedly doubles the risk of heart disease. However, he does admit that he doesn’t have data on how long these people live, and that all of his data is “observational”.
Importantly, the documentary rightly points out that most of the “evidence” discussed is from observational studies. In this type of study, people are given questionnaires about how they eat, and then they are “observed” to see what happens to them over time. Though this can give us an idea of what might be going on, observational data can never be used to prove that one thing in the diet causes a certain disease. In contrast to Dr. Fraser’s study, some other well-controlled studies show that health-conscious omnivores do not have an increased risk of heart disease or death compared to vegetarians or vegans. And, in one meta-analysis (study of many studies) of over 1 million people, fresh, unprocessed red meat did not increase this risk of heart disease or diabetes.
Our cardiologist, nutritionist and dietician then offer up some potential reasons for the effect of meat on health. Firstly, they declare saturated fat (such as that from meat and dairy products) as “the lord voldemort of the dietary world”. However, Dr. Mosley then speaks to Dr. Ronald Krauss. He is one of a number of researchers that have recently found that saturated fat is not actually associated with an increased risk of cardiovascular disease. Though the programme seems to maintain an anti-fat agenda, this acknowledgement is important and will resonate with many researchers and groups (such as the paleo audience) who have been on the pro-saturated fat bandwagon for years.
Once it is discussed that that saturated fat is no longer being associated with an increased risk of cardiovascular disease, the “expert” nutritionist and dietician suddenly seem completely out of their depth, and have little to add. Awkward.
If it’s not the fat, what part of red meat could be increasing our risk of death? Dr. Krauss continues by talking about potential factors in the meat itself, such as L-carnitine. L-carnitine is produced in the body because it is an essential part of normal fat metabolism, and is also found in muscle meat. L-carnitine is converted by certain gut bacteria into a chemical called TMAO, which some researchers have suggested is associated with an increased risk of heart disease. However, there is very little evidence that TMAO causes heart disease at all. I won’t cover the details here, but in short, the problems with the association between TMAO and heart disease involves changes to the gut microbiome associated with a generally unhealthy lifestyle, as well as some very poor study design. I recommend this summary by Chris Masterjohn. More interestingly, TMAO production is most increased when people eat seafood, and nobody is suggesting that seafood causes heart disease. Even Dr. Krauss acknowledges that the “carnitine hypothesis” is still unproven.
So what else could it be? Next we talk to Dr. Walter Willett, who is deservedly referred to as “the father of nutrition epidemiology”. He runs some of the largest observational studies of diet and health, such as the Nurses Health Study, out of Harvard University. In his studies, those with the highest red meat intake have higher risks of cancer and heart attacks, and they die earlier. Compared to fresh meat, processed meat is several times worse.
However, this ignores the fact that all the processed foods that Dr. Willett lists (such as hot dogs and burgers) are usually eaten with a hefty dose of bread and French fries, particularly in America, where this study was carried out.
Additionally, though it is meticulous in its data-collection, scientific articles published on the data from the Nurse’s Health Study are also affected by two large problems:
1. All studies from the Nurse’s Health Study data suffer from “healthy user bias”. Namely, the people that eat the most red meat also smoke more, are less active and eat fewer fruits and vegetables. This is also an issue for Dr. Fraser’s study of the 7th Day Aventists.
2. The data is analysed by splitting people into five groups, and comparing the 20% that eat the most red meat (for example) with the 20% that eat the least red meat. When you take the outer edges of data from large groups of people, you will mainly be working with the exceptions to the rule – those people that eat amounts of meat that most people would never even consider, or those people that have the greatest genetic (or lifestyle) susceptibility to cancer or heart disease in the face of a high meat intake.
In short, these sorts of study provide a cute way of manipulating data to more easily give a certain result. If you instead looked at the middle 60% of meat eaters (which would include most of us), you would find that consumption of red meat has little or no effect.
Some EPIC results
Back in the UK, Dr. Mosley investigates the results of some data from the European Prospective Investigation into Cancer and Nutrition (EPIC), which followed over 500,000 people for 12 years. This study found that moderate fresh meat intake had no effect on cancer or mortality. In fact, the study authors found that eating some meat was better than being a vegetarian, potentially because of the vitamins and nutrients mentioned above. However, the same could not be said for processed meats, which were still associated with an increased risk of death and cancer. Cut to our cardiologist, who says that the “red meat argument is slightly less clear at the moment”, and Dr. Kathryn Bradbury, a Nutritional Epidemiologist at Oxford, who says she is “not as confident that there is real association between eating red meat and early death”.
It is also worth mentioning that America and European studies may differ in their results because American meat production is far less regulated, and allows a greater number of additives, antibiotics and hormones.
Now that Dr. Mosley has failed to find a real association between red meat and disease risk, he turns his attention specifically to processed meats. After a trip to St. Thomas’ hospital (nicely nostalgic for me after I spent two years working there as a junior doctor) to see some potentially cancerous polyps in a colon, we hear that Dr. Jeremy Sanderson (consultant gastroenterologist) eats red meat at least twice per week, but would recommend cutting down on the processed stuff to reduce the risk of colon cancer.
Dr. Mosley then makes his own bacon, whilst discussing the potential links between processed meats and cancer risk. Doing so, he uses salt and sodium nitrite, both of which he immediately suggests are bad for your health. Though the salt in processed food does appear to increase our risk of high blood pressure, there is no evidence to suggest that salt added to home cooking is bad for you. The story surrounding nitrites is also much more complicated than the programme leads us to believe. Though nitrites are present in bacon, we actually produce far greater quantities of nitrites ourselves when we eat vegetables that are rich in nitrates (notice the difference of a single letter there). In fact, one of the touted health benefits of beetroot is as a result of the nitrates it contains being converted to nitrites by the bacteria in your mouth; these nitrites lower your blood pressure.
However, there are some potentially damaging compounds that can be produced from meat, and these can have a negative impact on your health, and increase your cancer risk:
1. The added nitrites in processed meat can react with amino acids (protein) to form N-nitroso compounds, which damage DNA. This is first step in some cancers. This reaction is greatly accelerated when processed meat is cooked at a high temperature.
2. Cooking any protein (including meat) at a high temperature can produce aromatic hydrocarbons (PAHs), and a similar group of chemicals known as heterocyclic amines (HCAs).
This could be why, particularly processed meats (containing extra nitrites, and often grilled or fried), are associated with health issues. However, the production of these compounds is greatly reduced if you marinade meat first (olive oil, red wine or lemon juice, for example), or cook your meat on a low heat (like in a stew). So as long as you are sensible about your cooking methods, this risk can be almost completely prevented.
High Meat Diet – The results
When Dr. Mosley then returns to have his second health check, we see that he does not have an increase in N-nitroso compounds in his stool sample after eating extra meat for four weeks, and this is attributed to his very high fibre and vegetable intake. Meat and vegetables… that sounds pretty good to me! In fact, it is very similar to what I have previously suggested people base their diet around.
The man delivering the test results is Dr. Gunter Kuhnle, who also works on the EPIC study, and was my lab supervisor when I did my undergraduate thesis (for the really geeky, you can read this paper we published together). Dr. Kuhnle tells Dr.Mosley that his cholesterol has increased from 6.2 to 6.8 after four weeks on a “high meat diet”. Dr. Mosley tells us this is not good, and mostly because the increase was in his “bad” LDL cholesterol. We also learn that he has gained 3kg of fat, and his blood pressure has gone up from 118/69 to 141/81. Uh oh…
What are we missing?
The effects of Dr. Mosley’s “high meat” diet are the most misleading part of this whole documentary:
1. On more than one occasion he is seen increasing his meat intake by eating a burger or pulled pork, which comes a large portion of fries and/or onion rings, and a big slab of bread. At no point does he consider how these processed carbohydrates (fried in vegetable oils) could affect his health. Heated vegetable oils and processed carbohydrates are very good at increasing your risk of atherosclerosis and heart disease.
Indeed, Professor David Spielgelhalter, a Cambridge statistician, tells us that 2 rashers of bacon a day could shorten our lives by 2 years. This conclusion entirely ignores the shortcomings of the studies behind the statistics (discussed above in relation to the Nurse’s Health Study, for example). I also suspect that the apparently “lethal” bacon is usually accompanied by sugary ketchup and white bread (with a side of onion rings if you’re Dr Mosley).
2. Secondly, we return to the fact that LDL cholesterol is “bad”, which we know is a huge oversimplification. The type of LDL also matters. I imagine Dr. Mosley would have increased his “bad LDL” type (in particular his LDL particles), but more likely due to his intake of onion rings and extra bread. However, the programme neglects to mention this.
3. In fact, if you calculate the protein and fat he would have eaten if he only added 70g of extra meat a day to his diet, it would have been almost impossible for him to gain as much weight as he did without all those extra processed trimmings.
4. They take his blood pressure after scaremongering about his “bad” cholesterol, and weight gain. That added stress is almost certainly going to have affected the single blood pressure measurement that they took!
The documentary also omits to cover the need to balance intake of methionine and glycine (two amino acids, the building blocks of protein). High levels of methionine are found in muscle meat, but rarely found in plant sources (beans and legumes). Glycine is found in connective tissue and organ meats, as well as in plant sources of protein (such as nuts and seeds). It is becoming clear that the balance of these two is important for health. Focusing on just eating muscle meat, while ignoring offal and plant sources of protein, could be causing a problem. Our ability to process methionine is also very variable, and may even be determined early on pregnancy, based on epigenetic factors from our mothers.
Take Home Messages
Despite the poorly conducted “high meat” diet experiment, there are some good take home messages from the documentary:
- It suggests that our diet should be largely plant-based, and supplemented with meat.
- Helpfully, Dr. Mosely also advises that vegetarians and vegans make sure they get enough protein, iron, zinc and B12. And that you don’t replace meat with foods high in processed sugar and carbohydrates.
- Though not unhealthy, the documentary says that saturated fats are also “not a health tonic”. However, this largely dependent on the source. As many additives and hormones tend to end up in the fat of the meat, it is probably best to avoid eating too much of the fat if you are eating meat of a poor quality.
So, meat presents no health dilemma whatsoever, if you:
- Eat a diet based around whole-foods with plenty of vegetables.
- Ensure your meat is of the highest quality that you can afford.
- Cook meat in ways that minimise the production of harmful compounds.
- Also eat organ meat (liver, kidneys, heat, brain) and the connective tissue stuff (for example bone broths)
- Include some plant-based proteins (legumes and/or nuts and seeds).
Previous articles summarising the effects of diet and health; Eat Real Food and It's Not About The Diet.
I have also written a shorter, summary version of this article for Paleo Britain.
Finally, if you want to watch a documentary looking at meat and fat intake from the other side of the coin, I recommend that you watch Cereal Killers.