Throughout my book, The Potato Hack: Weight Loss Simplified, I discuss a special type of fiber known as resistant starch (RS). I’ve written loads about this amazing prebiotic here in The Potato Hack Chronicles, as have hundreds of other bloggers and researchers…just Google “resistant starch,” and you’ll find a treasure trove of articles and scientific papers.
Please keep in mind as you read on that an all-potato diet contains more resistant starch than any other diet you could possibly eat, and all from real foods…no supplements needed!
Occasionally researchers will look at mounds of data on a particular topic and write a review paper. In January 2017, the British Nutrition Foundation released a nutrition bulletin for food producers and medical professionals. This paper, “Health effects of resistant starch (Lockyer and Nugent, 2017),” is a review of hundreds of research papers written over the past 20+ years. In this blog post, I will “review the review” and point out some interesting findings. Let’s start with Lockyer and Nugent’s bottom line. Please read this carefully:
There may be a lot still to be discovered in terms of the health benefits of RS. At present, most RS research relates to RS2. A wider spread of evidence relating to all RS types, via the testing of whole foods, would be useful in informing innovation, the selection of grains/varieties of RS-rich foods and perhaps in future, a recommended intake value for RS.
From the 2017 review, Health effects of resistant starch.
The paper is divided into sections based on current research, please click and review if you have time. Find here a description of the sections, and the “key points” noted by the authors, but first a short video released by the British Nutrition Foundation:
Section 1. Resistant Starch Overview:
- Starch types;
- Methods of analysis;
- Challenges in developing high RS foods;
- Labeling and health claims.
Key Points 1 –
- RS is a type of dietary fibre.
- It passes through the small intestine intact and is then fermented in the large intestine, producing SCFAs.
- RS provides ˜2 kcal/g.
- There are five different types of RS (RS1, RS2, RS3, RS4 and RS5).
- RS is present in grain products, seeds, pulses, bananas, potatoes and in commercially purified forms, which can be added to food products.
- RS intake is estimated to be around 3 g/day in the UK and is likely to be similar in other countries with Western-style diets.
Section 2. Resistant starch and colonic health, studies reviewed:
- Short-chain fatty acid production;
- Influence of resistant starch on gut bacteria and the microbiome;
- Pre- and probiotics;
- Colon cancer;
- Conditions associated with disturbances in gastrointestinal function;
- Oral rehydration solutions.
Key Points 2 –
- RS increases the production of SCFAs in the gut but there appears to be significant inter-individual variation in responses.
- RS modulates the composition of gut microbiota, specifically those involved in amylose breakdown and butyrate and methane production, but responses are variable and health implications remain to be elucidated.
- There is some evidence that RS can counteract the detrimental effects of high red meat intake on colorectal cancer risk.
- Emerging evidence suggests a role of RS as an ingredient in oral rehydration solutions.
Section 3. Role of resistant starch in metabolic responses – lipid and glucose metabolism, insulin resistance and prevention of cardiovascular disease, type 2 diabetes and metabolic syndrome, studies reviewed:
- Influence of resistant starch on other markers of metabolic health;
- Proposed mechanisms/sites of action of resistant starch.
Key Points 3 –
- It is well accepted that postprandial glycaemic responses to RS are reduced compared with digestible carbohydrates.
- In the EU, there is an approved health claim that baked products containing at least 14% RS in place of digestible starch reduce postprandial glycaemia.
- There may be synergism between RS and other fibre types in reducing glycaemic responses.
- More long-term studies are required to fully ascertain the effect of RS consumption on plasma lipids.
Section 4. Resistant starch and appetite regulation, studies reviewed:
- Dietary fibre and satiety;
- Resistant starch, satiety and acute energy intake;
- Resistant starch and bodyweight;
- Other health benefits of resistant starch.
Key Points 4 –
- There is some evidence that RS can decrease appetite and short-term food intake.
- Potential mechanisms include an increase in the release of gut hormones that promote feelings of satiety, stimulated by SCFAs.
- There is little evidence that RS can decrease adiposity in humans.
- RS may have a role in treating chronic kidney disease.
Theirs (emphasis mine):
…current evidence points towards RS as a dietary component with several potential health benefits and no harmful effects, besides possible gastrointestinal symptoms in some individuals at high intakes.
…wealth of evidence linking RS to reduced postprandial glycaemic responses has resulted in an EU-approved health claim.
It is clear from animal and in vitro studies that RS modulates many outcomes related to gut health but there is difficulty in translating this to humans…
There is evidence that RS can increase the production of SCFAs in the human gut but there appears to be a significant degree of variability in response to RS intervention, most likely influenced by differing gut microbial compositions between individuals, habitual intake, RS type and presence or absence of other RS and other fibre types.
There is good evidence that RS influences gut microbial communities involved in amylose breakdown and butyrate and methane production, but there is a significant variability in responses.
There is some evidence that RS can positively influence satiety and short-term food intake and plausible biological mechanisms have been demonstrated, but results have not been consistent.
This review pointed out several of the inconsistencies I’ve been talking about for many years, that each individual will react a bit differently when increasing the RS in their diet. But besides some unwanted gas, there is only good to come of increasing RS in your diet.
This review pointed out poor study design in many RS studies, ie. too short, no acclimation period, or the wrong type of starch was used.
This review demonstrated that large benefits of RS come from RS2 in supplemental form. While it is great to think we can get all of our fiber needs from the foods we eat, this is not always the case. This does not suggest, however, that we should rely on fiber and RS supplements for all of our needs. My advice has been, and always will be, to eat lots of high fiber, high RS foods and to take a fiber/RS supplement if you so desire.
Still to be determined: Exactly how much and what type of RS is best for inclusion in the human diet. Until a governing agency tells us exactly what we need, we are on our own here.
For an amazing, in-depth review of resistant starches, please see, Resistant Starch Sources, Applications, and Health Benefits (2013).
Food Sources of Resistant Starch & The Potato Hack
A 2008 study, Resistant starch intakes in the US, found that most Americans ingest about 5 grams of RS per day. This RS is mostly in the form of RS3 from bread, pasta, and other wheat products. Other sources are from potato chips, beans, and rice. Studies find that the benefits of RS are seen at much higher intakes of 20-40g per day.
The Potato Hack is a short-term intervention where one eats nothing but potatoes for several days in a row. Eating 3 pounds of potatoes provides 30-40g of RS. If one cooks and cools their potatoes, that number doubles!
Unripe bananas (still mostly green) contain about 15g of RS2 per medium banana. A 1/3 pound (150g) raw potato contains about 20g of RS2. These two food items can be eaten daily as a source of RS2.
Supplemental Sources of Resistant Starch
While it’s possible to get 20-40g of RS per day from your food, one would need to consume several pounds of bread or pasta prepared to be high in RS or several pounds of cooked then cooled potatoes, beans, or rice. Researchers use concentrated forms of RS2 when studying its effects on humans or animals. This type of RS is easily and cheaply purchased, for instance:
These three cooking ingredients may be used to supplement RS, the recommended dosage is 1-4TBS per day.
I’ll be reviewing the new studies that come out this year and writing about them frequently. I think sometimes we tend to make things more difficult than they need to be, so keep in mind that if you just take a spoonful or two of one of the RS sources mentioned above, you’ll be getting double or triple the RS that the average person gets. It’s my belief that this should be done long term. RS and “fiber” are two separate things, I believe that newer research will show that we have a requirement for raw starch granules to keep our guts in tip-top shape, and we also need other types of fibers to keep things moving, reduce cholesterol, etc.