Have you been told that potatoes are unhealthy and cause weight gain? Do you love potatoes but feel guilty eating them? Read on. This article may change your whole attitude to this wholesome and scrumptious vegetable.
In December 2022 the results of a study from the Louisiana State University’s Pennington Biomedical Research Center were published comparing the effect of a diet low in calories and high in either potatoes or beans (pulses) on the control of blood glucose levels in people with insulin resistance. (1)
The study was an 8-week randomized, parallel design, controlled feeding study which compared a diet containing potatoes with a diet containing beans. Both diets provided 50 to 55% carbohydrate, 30 to 35% fat and 15 to 20% protein. Thirty-six overweight or obese people (BMI between 25 and 40) aged between 18 and 60 and with insulin resistance were enrolled in the study. Compliance with the diets was very high at 87 to 88%. Results showed that both diets reduced insulin resistance by an equivalent amount. There was also a reduction in body weight from both diets during the 8-week study with the potato-containing diet decreasing weight by 5.6% and the bean-containing diet by 4.1%. The conclusion of this research was that the consumption of either potatoes or beans can be effective in reducing insulin resistance and promoting weight loss. (1)
In considering these study results, the first attribute of both potatoes and beans that comes to mind is that they are foods that are nutrient dense but low in calorie content. This is important because people can physically eat only so much food at one sitting. Satiating foods like potatoes and beans fill up the stomach and satisfy the appetite before too many calories have been consumed compared with eating calorie dense/nutrient poor foods such as processed foods. At the same time they provide a bounty of healthy nutrients to those that eat them. It is no wonder that both these vegetables encourage weight loss. But there is much more to learn about beans and potatoes. (2)
Beans are widely considered to be a nutritious food, and rightly so. They are a great source of high-quality protein. They are rich in fiber. They are abundant in minerals including iron, calcium, magnesium, phosphorus, potassium, zinc, copper, manganese and selenium. They are high in the vitamins B1, B6, folate, E and K. Their content of polyphenols, health-promoting bioactive compounds, is outstanding. To top it all off, their consumption is associated with better cardiovascular health; reduced risks of cancer and type-2 diabetes; and improvement in gut health (3,4,5).
Sadly though, through no fault of their own, potatoes have been much maligned. Fewer people are aware that potatoes are also plentiful in beneficial nutrients. These include fiber (including resistant starch); high-quality protein; minerals (potassium, manganese, magnesium, phosphorus); vitamins (C, B6, niacin and folate); and health-producing bioactive compounds (flavonoids, carotenoids, phenolic acids, chlorogenic acid, cathechins, lutein and glycoalkaloids. In addition, their intake is associated with healthy blood sugar control; increased cardiovascular health; better digestive health; and support for weight loss. (6,7,8)
Remarkably, potatoes have a notable quality in that they are a source of resistant starch. When potatoes are cooked and then cooled for consumption at a later time, their starch transforms into resistant starch. This type of starch passes undigested all the way through the small intestine and is delivered to the large intestine where its fermentation (digestion) finally takes place. The fermentation of the resistant starch is performed by healthful microbes residing in the gut microbiome which use the starch for their own energy and, in the process, short-chain fatty acids (especially butyrate) also result. Butyrate has far-reaching health effects throughout the body. Some of the known benefits of resistant starch are (9,10);
- decreasing after-meal blood sugar and insulin responses and improving whole body insulin sensitivity, revealing the possibility that resistant starch may be useful for managing diabetes
- lowering of blood cholesterol and triglyceride concentrations
- reducing fat storage
- improving markers of gut health
- increasing satiety
Butyrate is also associated with the prevention and inhibition of colorectal cancer and ischemic stroke. In the intestine itself, butyrate keeps the intestinal lining healthy, reduces inflammation and prevents gaps from forming in the intestinal lining that can allow bacteria, undigested food particles and toxins to directly enter the bloodstream (leaky gut). The mechanisms of action for these effects from butyrate are varied but many are related to its potent effect on the regulation of gene expression. (11)
A review from 2022 concluded that resistant starch, including the type found in cooked and cooled potatoes, acts separately through several different pathways to reduce the severity of and exert better control on type-2 diabetes. (12)
A study from 2005 illustrated that eating 30 grams of resistant starch daily for four weeks increased insulin sensitivity by 33%. (13)
In late 2022, data from a continuing study reported that resistant starch intake can result in a 60% reduction in the risk of developing a hereditary cancer in people with Lynch Syndrome. Lynch Syndrome predisposes people to colon cancer, gastric cancer and several other cancers. This randomized, double-blind study has been ongoing for decades. Almost 1000 people are taking part, ingesting 30 gm of a resistant starch supplement daily for an average of two years. The protective potential of resistant starch in this study appears predominantly in the upper digestive tract (cancers of the stomach, bile duct, pancreas and duodenum). The protective effect emerges during the first ten years of resistant starch intake and continues on for at least ten years after stopping its regular intake. The mechanism for this effect has not yet been determined but the researchers hypothesize that the gut microbiota are an important part of it. Once again, it has to do with the production of the short-chain fatty acid butyrate when microbes in the lower gut break down resistant starch. Butyrate is known to suppress the growth of cancer cells and induce cancer cell death. This is promising science, however further research is needed to establish the cause of this effect and answer the question of whether the same protective effect from resistant starch affects people who don’t have Lynch Syndrome. (14)
So, is there really a problem with potatoes? The answer boils down to the method that is used to prepare potatoes and the ingredients that are added to them.
- Unfortunately, the vast majority of potatoes that people eat have been deep-fried or turned into potato chips.
- Other favourite recipes bring in elements such as butter, sour cream, cheese and bacon.
- Potatoes are often peeled during their preparation. Note that the skin of the potato contains more nutrients than its flesh and most of its fiber.
Such cooking methods and added ingredients turn potatoes from nutrient dense/calorie poor vegetables into calorie dense/nutrient poor ones.
It’s an easy solution. If potatoes are boiled, baked, roasted, pressure-cooked, slow-cooked or air fried, they are allowed to shine as a delicious and nutritious food to be enjoyed without any guilt at all. (15)
For an easy and delicious potato recipe, keep an eye out for my next blog entitled “Rosemary Roasted Potatoes”.
1 Rebello, C.J., Beyl, R.A., Greenway, F.L., Atteberry, K.C., Hoddy, K.K., Kirwan, J.P. Low-Energy Dense Potato- and Bean-Based Diets Reduce Body Weight and Insulin Resistance: A Randomized, Feeding, Equivalence Trial. J Med Food. 2022 Dec; 25(12): 1155-1163. Doi: 10.1089/jmf.2022.0072. Epub 2022 Nov 11. PMID: 36367708; PMCID: PMC9805852.
5 Ganesan, K., Xu, B. Polyphenol-Rich Dry Common Beans (Phaseolus vulgaris L.) and Their Health Benefits. Int J Mol Sci. 2017 Nov 4; 18(11): 2331. Doi: 10.3390/ijms18112331. PMID: 29113066; PMCID: PMC5713300.
9 Higgins, J.A. Resistant starch: metabolic effects and potential health benefits. J AOAC Int. 2004 May-Jun; 87(3): 761-768. PMID: 15287677.
10 Lockyer, S., Nugent, A.P. Health effects of resistant starch. Nutrition Bulletin. March 2017; 42(1):10-41.
11 Canani, R.B., Costanzo, M.D., Leone, L., Pedata, M., Meli, R., Calignano, A. Potential beneficial effects of butyrate in intestinal and extraintestinal diseases. World J Gastroenterol. 2011 Mar 28; 17(12): 1519-28. Doi: 10.3748/wjg.v17.i12.1519. PMID: 21472114; PMCID: PMC3070119.
12 Rashed, A.A., Saparuddin, F., Rathi, D.-N. G., Najihah, N. et al. Effects of Resistant Starch Interventions on Metabolic Biomarkers in Pre-Diabetes and Diabetes Adults. Front. Nutr., Sec. Nutrition and Sustainable Diets. 12 January 2022; Volume 8: Doi.org/10.3389/fnut.2021.793414.
13 Robertson, M.D., Bickerton, A.S., Dennis, A.L., Vidal, H., Frayn, K.N. Insulin-sensitizing effects of dietary resistant starch and effects on skeletal muscle and adipose tissue metabolism. Am J Clin Nutr. 2005 Sep; 82(3): 559-567. Doi: 10.1093/ajcn.82.3.559. PMID: 16155268.
14 Mathers, J.C., Elliott, F., Macrae, F., Mecklin, J.-P., et al. Cancer Prevention with Resistant Starch in Lynch Syndrome Patients in the CAPP2-Randomized Placebo Controlled Trial: Planned 10-Year Follow-up. Cancer Prev Res (Phila). 2022; 15 (9): 623–634. https://doi.org/10.1158/1940-6207.CAPR-22-0044.
When you said the potatoes are cooked and cooled do you mean they have to be both cooked and cooled?… My trouble with potatoes is the butter I like to put on them. Looking forward to your recipe for Rosemary Roasted Potatoes. ( I think I have had the pleasure to have had yours before).
Yes, it is after the potatoes have cooled that some of their starch turns into the resistant starch. And yes, butter and other calorie dense toppings are definitely reduce the healthfulness of potatoes 🙂