There has been much debate over the past year or so in particular over whether meat or generally animal products are bad for you. In light of films like The Gamechangers and the nature of social media, people are often all too quick to jump on the bandwagon with these trends. That is why now more than ever it is important for people to have an open mind on the information they read and listen to. In this post, we will delve into what the actual scientific research says on the matter with no biases.
There is considerable observational evidence and mechanistic evidence to suggest that low level, chronic elevations in inflammation may contribute to various diseases. These diseases include cardiovascular disease, type 2 diabetes, and others.
So what do the controlled trials say about meat and inflammation? Well, there is some evidence that substituting red meat with soy protein sources reduces inflammation as well as a few other studies showing similar outcomes. However, on closer inspection, we see that one of the biggest drivers of inflammation is actually weight gain, and vegans consume over 600 calories LESS per day than omnivores. This is a huge reason why the vegan diet is associated with better health outcomes. As such, a cohort study examined the relationship between red meat, BMI and inflammatory markers in 1223 subjects. They did indeed find that red meat intake was associated with markers of inflammation. But, when they corrected for the differences in BMI, the associations between red meat and inflammatory markers were no longer significant, while the associations between BMI and inflammation were. This suggests that inflammation is driven by increases in body fat, not necessarily red meat. Interestingly, a systematic review of over 1100 studies demonstrated that there was no difference in inflammation in healthy subjects who consumed more than 9oz of red meat per week than subjects who ate less than 9 oz red meat per week.
Additionally, none of these studies controlled total calories. Perhaps even more relevant was a recent randomized control weight-loss trial where researchers had type 2 diabetic subjects split into two high protein (30% of total calories from protein) weight loss groups. One consumes protein predominantly from animal protein and another group consumes protein from plant protein. These diets contained the same total calories, protein, carbohydrates, and fats. The only differences were the protein sources. Both groups lost the same amount of weight and low and behold both groups DECREASED inflammation to the same extent. This suggests that the anti-inflammatory benefits of a vegan diet are likely simply due to vegans consuming less total calories than meat-eaters. However, meat-eaters can likely enjoy the same health benefits so long as they do not consume too many overall calories and live a healthy lifestyle.
As we have already established, meat-eaters tend to eat more calories, gain more weight, and be more prone to heart disease. But as we demonstrated with the data on inflammation, this is a problem of excess energy intake and its associated weight gain, not because animal protein is somehow inherently inflammatory. What about CVD? While fatty meats are associated with increases in total cholesterol and LDL, lean meats do not have the same effect of increasing blood lipids. There is also evidence that fish, even fatty sources of fish such as salmon which contain the essential fatty acid omega 3, may decrease CVD risk. Further, consumption of lean beef (113g per day) as part of a healthy overall diet has been demonstrated to decrease cardiovascular risk and improve blood lipids. Interestingly, a Mediterranean diet (high protein from lean meats, low saturated fat, moderate carbohydrate and fat intake) has been demonstrated to improve CVD markers in a recent review of over 45 studies.
Many people who argue that Meat causes cancer state that Leucine, a type of amino acid found in meat, stimulates muscle anabolism through a complex known as mTOR (mammalian target of rapamycin). Inhibiting mTOR is one of the therapies out there for cancer. In fact, rapamycin is an anti-cancer agent. This is a really large leap of logic however, that has many holes in it. The first is that the leucine stimulation of mTOR is brief, lasting only a few hours before returning to baseline. This is very different than chronic, long term elevations in mTOR that may be linked to cancer. A great comparison is inflammation in response to exercise. We know that chronic inflammation is a very bad thing. However, about of exercise will drastically increase inflammation (as well as blood pressure, reactive oxygen species, heart rate and a whole host of other metrics thought to be ‘bad’ for health) in the short term. But when we take measurements of inflammatory markers in people who exercise they are lower than the average non-exercising person. This is because there is a big difference between an acute response and a chronic response. Additionally, resistance training increases mTOR stimulation for DAYS post-exercise. If their claim of mTOR and leucine were legit we would expect to see people who resistance train have higher rates of cancer as well, but we don’t. People who exercise have LOWER rates of all issues that cause mortality including cancer.
Vegans also have a higher rate of ‘health-seeking behaviours.’ That is, a vegan diet is already a very restrictive diet, and people who select it are much more likely to pursue other healthy behaviours like limiting their calories and exercising. In contrast, people who eat high amounts of meat tend to eat more calories (~600 more per day on average), exercise less, eat fewer fruits and vegetables, eat less fiber, and engage in other non-health seeking behaviours, like smoking. This makes it difficult to determine if the increased rates of disease are caused by meat, or by these other parameters.
Fortunately, there are studies that attempted to control for these confounders in an elegant way. One such study in the UK recruited 11000 health-seeking vegetarians and health-seeking non-vegetarians by recruiting them from health shops and various societies. In a 17 year follow up they found no difference in the mortality rates between health-seeking vegetarians and non-vegetarians. This suggests that it is the health-seeking behaviours like calorie control and exercise that improve health and protect against disease, not the omission of meat. Indeed, in another massive study examining mortality rates of over 243000 people age 45 and older, the researchers found that there were no differences in mortality rates between vegetarians and non-vegetarians. In perhaps one of the most rigorous systematic reviews ever conducted examining the association between meat and cancer in 56 studies with over 6.1 million participants concluded: “The possible absolute effects of red and processed meat consumption on cancer mortality and incidence are very small, and the certainty of the evidence is low to very low”. Meaning that the strongest associations between meat and cancer are found in the lowest quality studies with the lowest level of control. In studies that are more tightly controlled and account for confounding variables, the association is minimal or non-existent. Further, on the off chance that meat intake does directly cause cancer (unlikely based on the data), the effect would be extremely small based on the data.
In summary, based on scientific evidence, eating good quality meat has not been found to be a direct cause of disease as many would have you believe. Eating more vegetables is a better message for most people not to stop eating meat altogether. By all means, if you choose to for ethical or religious reasons or just that you feel better don’t let anyone tell you otherwise but do not blindly believe everything you’re told. Instead do your research, site factual evidence and then make your own judgement.