Perhaps the most important highlight:
Many vegans place great faith in the China Study, and the book of the same name by Professor T Colin Campbell. However, you do not cite results from the study in Vegan for Life, saying that it “doesn’t provide information … on the health of vegans”. Would you care to explain to readers why the findings of the China Study are largely irrelevant to vegans?
Jack Norris: The China Study is an ecological study, which means that it pools information from different populations, in this case different regions of China, and compares the averages among the groups, rather than from individual subjects. There is certainly nothing wrong with doing this - it gives researchers an idea of what about those regions might be useful for further research, looking at individuals rather than regions. We now have a great deal of data on many of the disease markers of actual vegans, and some data on their disease rates, through the Oxford Vegetarian study, EPIC-Oxford, studies of Seventh-day Adventists, and a few other studies. That data, which is highly relevant to vegans at large, is what we focused on in the book.
Ginny Messina: I would add that the findings from the China Study aren’t exactly irrelevant to vegans. Any well-designed study like the China Study that looks at health impacts of animal versus plant foods has relevance to vegans. However, because it didn’t include vegan subjects, the China Study doesn’t speak specifically to the health of vegans. We can’t look at that data and conclude that vegans are healthier than lacto-ovo-vegetarians or pesco-vegetarians, for example. Something that is also a little bit unique to our book is that we wanted to help readers understand that some types of studies carry more weight than others - or that they have different purposes. As Jack pointed out, ecological studies, which include the China Study, generate findings that stimulate further research. But they aren’t the type of studies that allow us to make statements about causal relationships between diet and health.
In fact, there are instances where ecological studies have led us completely astray. For example, the belief that vegans have lower calcium needs than omnivores comes, in part, from an ecological study that compared rates of hip fracture to protein intake around the world. It showed that hip fracture rates were highest in countries with the highest per capita protein intake. The obvious conclusion is that eating protein causes weak bones. But it’s turning out that this conclusion may in fact be wrong. There are other explanations for the differences in hip fracture rates in these countries, all of which are missed in ecological studies.