Resistant starch is a topic that is starting to make the odd appearance in some corners of the world of health and fitness, with some people boldly claiming it could be the key to both health and fat loss. So what exactly is resistant starch, what are its proposed benefits and where exactly in the diet do we get it from?
Resistant starch occurs when conventional starches convert into a form that cannot be digested and absorbed in the small intestine. This is important for two reasons, firstly this means that they do not contribute to energy intake in the same way as conventional starches or sugars (two versus four calories per gram) and secondly resistant starch acts much like soluble fibre, which the bacteria in the colon use to ferment and produce numerous compounds, one of which, a type of short chain fatty acid called butyrate, is strongly associated with the intake of resistant starch and soluble fibre and has gathered a lot of interest in both the medical, nutritional science and health communities for a number of reasons.
Firstly, butyrate is a metabolic fuel for the cells of the intestines, helping to support their normal function. This includes the proper absorption of nutrients and water, whilst creating a barrier preventing waste products, pathogens and other unwanted nasties entering into the body via reabsorption. It has been hypothesised and demonstrated in animal models, that diets that produce high amounts of butyrate have lower incidence of colon cancers and other diseases of the large intestine. It also appears that by promoting the growth of good bacteria this has a positive impact on the local immune response and has even shown wider impacts on the immune system throughout the body through a number of interconnected pathways.
This relationship has also been established in humans as well being shown to have links with obesity. Obese people tend to show lower levels of butyrate with some people suggesting that this is a causal factor in obesity, however it is still not known if this plays a role in the causes of obesity or as a result of poor dietary habits… I suspect the latter.
The important message here is that as long as we include a variety of fibre rich foods in the diet, then it is unlikely that specifically targeting foods that contain resistant starch is necessary and in fact many foods we consume do in fact contain resistant starch either directly or through conversion of regular starch by various mechanisms which can occur naturally or through cooking.
So where do we get resistance starch from? The ‘classical’ example of resistant starch is bananas. When they are green they contain plenty of resistant starch then as they ripen they convert to starch and sugars under the action of enzymes. We also know that cooking starchy carb sources such as potatoes and rice and then letting those cool causes this same conversion through a process called retrogradation. This changes the linear structure of the carbohydrate to a more crystallised form that by its nature is resistant to digestion. The final source is found in grains, seeds and nuts and these are naturally occurring alongside fibre within the cell walls, making them super-resistant to digestion.
So is it worth targeting increases of resistant starch in the diet? My initial hunch is that if you consume a diet full of fruit, vegetables and whole grains then trying to actively consume more resistant starch is not on the whole necessary, however much like fibre, if we can include more resistant starch sources in the diet this is not going to be a bad thing and might help with fat loss by promoting fullness and supporting a healthy digestive system.
Thanks for reading.