Have you seen the recent headlines? 90% of people are reportedly not eating enough fibre, but do you know how much fibre you need?
A recent paper published in The Lancet, a very well recognised medical journal recently reported their findings on dietary fibre intake and health outcomes. I will guide you through the evidence behind increasing your fibre intake. The authors used the results from 185 prospective studies (observing people) and 58 clinical trials (people were given an intervention), with a total of 4635 adult participants1.
The data was combined so that all the prospective, observational studies were analysed together separately from the clinical trials. From the observational data, the authors found that people that ate the highest amount dietary fibre were 15-30% less likely to die of all causes, and less likely to have coronary heart disease, stroke, and type 2 diabetes and colorectal cancer.
There are several problems with observational studies. Firstly, they often rely on patient recall which can be unreliable. If the person incorrectly remembers how much fibre they ate, then the study, however well intended will be inaccurate. Secondly, there is a difference between association and cause. Two things might be associated such as ice-cream consumption and sales of sunhats, since both increase in good weather. However, there is no causal relationship between these items, since an increase in ice-cream consumption does not cause an increase sunhat sales. Observational studies are able to show associations, but unlikely to show causation. Clinical trials are generally needed to determine cause by directly comparing a control group with an intervention group and monitoring the outcome.
These results therefore need to be cautioned given that they are from observational studies, which only enables us to conclude there is an association between high-fibre diet and reduction of mortality / specific chronic diseases / specific cancers.
To address this problem, the authors used data from the 58 clinical trials. Analysing the clinical trials together they found that higher daily fibre consumption was associated with a significantly lower bodyweight, blood pressure, and total cholesterol compared with a low fibre diet. These effects were maximal when dietary fibre was between 25 and 29g per day. Of greatest significance is that a dose-response curve was seen, so that increasing fibre consumption caused an even greater protection against cardiovascular disease, type 2 diabetes, colorectal cancer and breast cancer. This dose-response effect strongly suggests a causal relationship.
Was this protective effect seen with any other food items? Yes a similar effect was seen with consumption of whole grains but the certainty of effect was lower than seen with fibre. No effect was seen on health when the observational data was analysed according to diets characterised by low or higher glycaemic index or load.
Next time I will give you examples of what these fibre recommendations mean for you and your family. Sign up to my mailing list or follow me @healthyeatingdr so you don’t miss out on the next update!
- A. Reynolds. et al.Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet1–12 (2019).