Last Friday’s blog featured a study presented recently at an American Diabetes Association symposium. It found that in a group of individuals with type 2 diabetes, a low-carb diet led to statistically significant reductions in weight, as well as blood sugar and triglyceride levels compared to a low-fat diet. In this blog, I also attempted to put the findings of this study in the context of published research which, taken as a whole, supports the notion that controlling carbohydrate intake has considerable merit to enhance health.
Go back to this post and you will see that it is followed by a response by ‘Chris’, whose previous comments inform me is a dietician. The main point of her comments, it seems, is to draw our attention to a study which purportedly links low-carb eating with colon cancer. The message appears to be that restricting carb is putting people in mortal danger – it’s a common theme put about by low-carb detractors.
So, today, I thought I’d take moment to have a good look at the study supposedly linking low-carb eating to colon cancer, to see if the facts stack up.
Because the study is unpublished (a problem in itself, see point 8 below), I haven’t been able to discern its precise design. I’ve gleaned what I can from the Rowett Research Institute in the UK (where the work was conducted) website here.
From what I can make out, the participants in this study comprised a group of 19 men, who were fed 400 g of carbohydrate each day for 3 days, followed by 160 g of carbohydrate a day for a month, followed by 24 g of carbohydrate for another month. Samples were taken to assess levels of certain bacteria in the gut (not specified in the report) as well as levels of butyrate – a substance made by gut bacteria that is linked with reduced risk of colon cancer in lab experiments.
It seems that the levels of certain gut bacteria and butyrate after feeding individuals160 and 24 g of carb were compared to those found after feeding the men 400 g of carb a day.
Basically, it appears (again, I cannot be sure because the report is less than transparent) that eating 24 g of carbs per day, compared to eating 400 g per day, led to a ‘four-fold reduction’ in levels of the type bacteria being measured. The report also states that butryrate levels reduced too, but neglects to tell us by how much, and if the reduction was statistically significant.
Nevertheless, Professor Flint (the lead researcher in this study) is quoted in reference to low-carb diets that: In the long run, it is possible that such diets could contribute to colorectal cancer.
The report does tell us that two of the diets led to loss of body weight and fat, but (curiously) neglects to tell us which of the three diets these were.
Never mind, let’s now focus more specifically on some other specifics that I think need to be borne in mind when interpreting this piece of ‘science’.
1. The very low-carb group were allowed just 24 g of carbohydrate a day. This barely more that is permitted in the induction phase of the Atkins’ diet, and a level of carb consumption that individuals will generally not sustain – nor would generally be advised to sustain (not even on ‘Atkins’) in the long term.
2. The highest carb intake of participants in this study was 400 g per day. This is substantially higher carb intake than is conventionally recommended. It’s therefore not a benchmark against which to measure the effects of carbohydrate restriction.
3. Butyrate is believed to be what is known as a ‘surrogate marker’ for colon cancer. We do not know if lower butyrate levels (unspecified) would actually lead to an increased risk of colon cancer in the long term. And even if this is the case, how do we know that other effects of carb restriction won’t offset this risk or even reduce overall risk? The answer is, we don’t.
4. Butyrate is found in generally high quantities in foods traditionally permitted on low-carb regimes (e.g. butter and cheese).
5. Professor Flint’s quote that: In the long run, it is possible that such diets could contribute to colorectal cancer is nothing but hypothesis/opinion. I suggest we all remain mindful of the fact that study did not actually show that eating a low-carb diet increases colon cancer risk. It showed that a very low carb diet after an extremely high carb diet led to reductions (unspecified) in the level of a substance which appears in lab experiments to reduce colon cancer risk.
6. Lower carbohydrate eating has been found to be beneficial for weight reduction and for the reduction in markers that would expect to reduce the risk of diseases such as type 2 diabetes and heart disease.
7. Higher carbohydrate diets have been linked with an increased risk of some forms of cancer.
8. And last but not least: Professor Flint’s study is unpublished. This makes it impossible to appraise properly. Though, even on the limited facts he has shared with the press, there is much about this study that is clearly inadequate from a ‘scientific’ perspective.
So, in summary, I’d be disinclined to let this sort of poor and unpublished science to ‘scare’ individuals off a dietary approach which has, it seems, very broad benefits for health.
This Professor-led Rowett Research Institute study is, to my mind, a classic example of the sort of quite rubbishy science that is dredged up by those keen to discredit the concept of low/controlled carb eating.
My sincere hope is that when ‘Chris’ uses this research to inform and educate her dietetic clients, she at least points out its manifold deficiencies and puts it in the context of existing evidence.
