Patrick Holford, 24 Mar 2015
I have had some somewhat aggressive responses to this from fans of low-carb, high protein/fat diets and ‘paleo’ diets so I thought it best to address these criticisms and qualify some of the points about this study.
The first comment was that the study does not show a 75% increased risk for meat eaters compared to fish-eating vegetarians (we shall call them fishitarians). Actually, it does. While the figure given is that fishitarians have a 43% reduced risk if you express the risk as the increased risk for meat-eaters it comes out at 75%. For example, if there were 100 cases of cancer in meat eaters and 50 cases in fishitarians we can say either that fishitarians have half the risk (50%) or that meat-eaters have double the risk (100%).
The next comment was that this is the relative risk, while the absolute risk is very small. This is partly true. In this study there were 40,367 vegetarians overall (all categories of vegetarians inc fish eaters) and 252 cases of colorectal cancer among them over a 7 year period, e.g. only 0.62 % got colorectal cancer. There were 37,292 meat-eaters overall and 238 cases of colorectal cancer so only 0.64% got colorectal cancer. When adjusted for fibre intake and weight (given that less fibre and more weight means more risk, so that the two groups were weighted equally in this respect) the vegetarians were 22% less likely to get cancer. This ‘relative’ risk increase was statistically significant (P>0.01) and even more so when comparing the meat eaters with the fishitarians. Their relative risk reduction was 43% (p>0.003).
The absolute risk for a meat-eater getting colorectal cancer in this study was around one in a hundred and fifty. This might sound small, but it is not that small. For example, one in a hundred people have schizophrenia. Also, this was only over a 7 year period and included anyone over 25 years old. Let us say that the average person lives at least for 49+25=74 years then, if the study had followed people for 49 years eg 5 times as long, you would expect the incidence to be 5 in a 150, or 1 in 30. If you have a population of 50 million this equates to 1.67 million deaths in total for that population followed over their lifetime from age 25. That would be an average of 34 thousand deaths a year.
The next comment was that this is an American study and they probably are eating processed meat, injected with hormones, lots of sugar and other processed foods – unlike an intelligent low carb high protein/fat enthusiast who eats healthy meat and no sugar.
There is an element of truth in this but this was a study of Seventh Day Adventists who are actually quite health conscious, do not, for the large part, eat processed meat or junk food. Their intake of sugar overall, in both vegetarians and meat-eaters, was much below the US average. Also, the meat-eaters did not eat that much meat, certainly less than a Banting/Atkins dieter is likely to do. On top of this Seventh Day Adventists largely shun smoking and alcohol, both of which increase cancer risk.
Also, the study authors controlled for these kind of variables in different ‘models’, all of which still showed that meat-eaters had a much higher risk than fishitarians.
Previous studies have found that a) high red and processed meat; b) carcinogens created when meat is grilled, fried, barbecued – the crispy, burnt stuff and the fat that drips onto a barbecue fire, ignites and sends carcinogens back into the meat; c) cured meats that introduce nitrosamines formed from the nitrates used in the curing process; and d) slow gastric transit time eg constipation all contribute to increased cancer risk.
A low carb high meat/fat dieter could mitigate these hazards by never eating crispy or burnt meat/fat, ideally eating raw or semi-raw meat, and avoiding cured meats. This would indeed by more consistent with early diets of homo sapiens.
While the vegetarians overall had a reduced risk the fish-eating vegetarians had by far the lowest risk. The study cannot say why this is. It is just an epidemiological survey. It is likely, however, that the extra omega-3 from fish, plus the fact that very little fish is ever eaten with ‘burnt’ flesh, and possibly the high B12 and selenium level in fish, all add to its cancer protective effect.
The final criticism was more personal. I want to be clear here that I am only reporting on the actual study. “Don’t shoot the messenger!” I am not against meat-eating per se. My cookbooks have meat recipes. I just think, overall, meat should be a very small part of our diet for reasons such as the above.
I do also totally accept that there are some people whose lives have been saved by eating a high-meat low carb diet. It can cause tremendous loss of excess weight, reverse diabetes and heart disease. I just do not think it is the best way to live once health has been restored.
My low GL approach carries none of the risks associated with high meat diets and is equally effective in reversing diabetes, heart disease and obesity. So, there is an alternative.
I do also totally accept that we are all different. Some people who react very badly to sugar and carbs may do better cutting them out completely. Some people feel great on meat, and prefer it. Others feel worse and get immediate health problems on a high meat diet (eg worse arthritis, headaches, constipation, kidney problems). Some people just don't like eating meat. It is the right of people to find their own way and what works best for them. My job is simply to give you the facts to make an informed choice.
Matthew M, 24 Mar 2015
Hello Patrick, I agree with what you have posted here.
We have got to make choices in this world. I have made the choice with very helpful advice recommended here on the site and the newsletter and certain blood tests that have showed intolerance's to milk and fish (white fish) and gluten also.
That and other recent major issues you have talked about (GM and organic farming) have again made me consider if it is better to turn away, not from just the dairy products and meat (like yourself ) but fish and eggs too.
Which I know you are not recommending from a recent blog post.
Matthew M, 24 Mar 2015
LowCarb Paleo diet camp leaders also seem very closed minded and ignore evidence like this. Tim Noakes is diabetic I think and yet his Paleo diet is not working for himself maybe he should GL diet or
low fat diet soon.
Vegans do make strong arguments against fish and egg eating though.