Correlation vs Causality

If you start reading into nutrition and what is the best diet from a health perspective, it can quickly become overwhelming. Separating fact from opinion and science from fiction is no easy task. The level of emotion in the argument is comparable to political or religious debates. Coupled with that emotion is the confusion around what is correlation vs causality and how sampling and statistical analysis can be used to prove and disprove points of contention.

If you tried really hard and were selective enough in your sample size and normalizing the data, you could probably find some level of correlation between consumption of wet cardboard and the chances of winning the lottery. An absurd example, but important to understand when you wade into the world of nutrition and what is presented as absolute fact. When you dig into it, often correlation is used as absolute proof that eating this or that will result in some adverse consequence. In reality the level of burden in proving causality is much higher. Think back to the tobacco debates – nothing changed for years until causality between smoking and detrimental health consequences could be proved and then the world was left with no other choice than to share this information with consumers.

Going into this year I decided to try a vegan diet more from the humane treatment of animals angle. Nutrition wasn’t the motivational force. That said, two months in eating vegan certainly feels like it has some health benefits, but I am no nutritional expert (nor a large enough sample size…). So I won’t pretend to have any irrefutable proof for you.

This week instead of sharing recipes, I’ve done something a bit different and instead detailed a summary of key resources discovered throughout February.

Over the last month I have started to read into the nutritional impacts of a vegan diet based on recommendations from friends and reading other vegan blogs and podcasts. Sobering insights (if the research is to be believed) that link consumption of animal products with increased incidence of chronic diseases ranging from cancer to diabetes to multiple sclerosis to name just a few. Correlation or Causality? You be the judge…

If you’ve come across these resources, would love to hear your views in the comments section. Similarly if you have recommendations on other resources arguing either side of the debate, let me know.

1. The China Study

I can recall sitting cross legged on the floor in primary school growing up in Australia listening to our teacher explain the food pyramid. A simple graphical depiction of the secret to good health that we all needed to follow to live a long and healthy life. The genesis of the food pyramid is linked to nutritional food guidelines that the US Department of Agriculture (USDA) issue every five years. This pyramid has evolved over the years to factor in new views and research around what constitutes an ideal diet. For many of us growing up the food pyramid was taken as undisputed proof that consuming animal products was fundamental to good nutrition.

Dr T. Colin Campbell in this book (co-authored with his son Dr Thomas M. Campbell II) describes his four decades of nutritional research as a biochemist at Cornell University. Dr Campbell disputes many of the USDA guidelines, advocating instead for a Whole Food Plant Based (WFPB) diet which excludes all animal based products. Various research studies by Dr Campbell are described in the book, providing insights into the impact of consuming meat, dairy and fish on the likelihood of contracting chronic disease such as cancer, heart disease, diabetes, dementia or autoimmune diseases including multiple sclerosis.

While the book is called the China Study, there is actually only one chapter in the book that covers this study. The China Study is referred to as one of the most comprehensive nutritional studies ever undertaken on humans comprising ~6,500 individuals across China. The study was conducted over a 20 year period and was a joint effort between the Chinese Government, Oxford University and Cornell University. The study looked at the incidence of many of these chronic diseases and how that varied regionally across China. The relevance of this last point being diet tended to be quite regionalised in China providing helpful comparison groups to observe the incidence of these diseases with varying levels of animal product consumption in diet. The findings from the study supported many of the research findings Dr Campbell conducted in laboratories on animals over the years and were offered as proof of the benefits of consuming only a WFPB diet.

In addition to the research, the book also includes interesting views (or a conspiracy theory depending upon your position in the debate) around the USDA, specifically the funding and composition of this and other peak US bodies that develop nutritional guidelines. In the finance world, if you own shares in a company and publish a research document advocating others invest in it, you need to disclose a conflict of interest. Dr Campbell claims the same principles don’t necessarily apply in the realm of nutritional advice. USDA as it turns out advocates on behalf of the animal agriculture industry and receives funding from these groups. The guidelines the USDA issues Dr Campbell argues are therefore inherently biased, a point he argues is evidenced by the fact that money the USDA spends on developing materials for school classrooms has to be classified as a marketing rather than educational expense as an acknowledgement that the materials are not so much fact based as they are designed to create life long animal product consumers. Insert explosive twitter, blog and social media debate around this point…

Dr Campbell also describes in the book his encounters with Dr Caldwell Esselstyn a former heart surgeon at the Cleveland Clinic who moved away from traditional heart surgery to treating heart conditions with diet, namely the WFPB diet. Dr Esselstyn argues that many of the modern heart surgery techniques do little to address and reverse the causes of heart disease, whereas a WFPB diet he claims is more effective at this in his clinical experiences.

While certainly an interesting book, at 400+ pages it is not light reading. My mistake was also trying to ‘read’ this as an audio book. Given the data focused nature of the book, suggest reading rather than listening to it would be a better approach. I give it a 3 out of 5 based on the audio book experience, but probably would have given it a 4 out of 5 if I read a hard copy and could follow the detailed tables and visuals that an audio book version struggles to communicate.

2. Forks Over Knives

A documentary by Lee Fulkerson (2011) that explores the same research of Dr Campbell and Dr Esselton described in the China Study. An easier format to get across the key messages from the China Study, but as it is a movie length documentary, it can only cover a subset of what is detailed in the China Study. Nonetheless provides some interesting insights that brought much of the nutritional debate into the mainstream through a more approachable format than the 400+ page China Study. I give it a 4 out of 5.

3. What The Health

A documentary by Kip Anderson (2017) that explores the linkages between diet and various chronic diseases in the US. Covers similar content to Forks Over Knives and the China Study, including an exploration of the conspiracy theory angle around the financing of America’s top nutritional advice bodies by large animal agriculture and pharmaceutical companies.

Some of the data points the movie presents that stood out to me:

  • In the next 25 years one in three Americans will likely have diabetes;
  • One serving of processed meat per day increases the risks of developing diabetes by 51%;
  • Countries with the highest rates of dairy consumption have the highest rates of osteoporosis; and
  • The pharmaceutical industry sells 80% of all antibiotics produced in the US to to animal agriculture.

If you like a good conspiracy theory and are ok with a lower budget style approach to cinematography, this is fairly easy to watch and provides some interesting statistics to consider. I give it a 4 out of 5.

4. Cowspiracy

Another documentary by Kip Anderson (2014) explores the environmental impact of the meat and dairy agricultural industry. Takes on a conspiracy theory angle around the absence of reference to the impact dietary choice has on the environment.

Specifically, it explores the statistics that demonstrate animal agriculture is the leading cause of climate change yet key environmental activists are silent on dietary choice as a key means of addressing climate change.

Some of the data points the movie presents that stood out to me:

  • Animal agriculture is accountable for 18% of greenhouse gas emissions, more than the combined exhaust from all transportation;
  • Agriculture is responsible for 80-90% of US water consumption;
  • 2,500 gallons of water are needed to produce 1 pound of beef, 1,000 gallons for a gallon of milk, almost 900 gallons to produce 1 pound of cheese, and 477 gallons for 1 pound of eggs;
  • 1-2 acres of rainforest are cleared every second;
  • 70 billion farmed animals are reared annually worldwide. More than 6 million animals are killed for food every hour;
  • Throughout the world, humans drink 5.2 bilion gallons of water and eat 21 billion pounds of food each day. Worldwide, cows drink 45 billion gallons of water and 135 billion pounds of food each day;
  • 1.5 acres can produce 37,000 pounds of plant-based food, or 375 pounds of beef; and
  • Each day, a person who has a vegan diet saves 1,100 gallons of water, 45 pounds of grain, 30 sqft of forested land, 20 pounds of CO2 equivalent, and one animal’s life.

An infographic is also available at the film’s dedicated website and shown below.

Cowspiracy infographic

A little clunky in parts and given I watched it after watching ‘What The Health’ it felt repetitive (although chronologically this movie was released first) as the format and conspiracy theory style approach are identical. I give it a 3 out of 5.

Key resources

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