An analysis of 18 studies from Denmark found that vegetable, but not potato, intake is associated with a lower risk of type 2 diabetes (Diabetes Care, 2023;46(2):286–296). Studies of 54,793 people, aged 50 to 64, found that 7,695 (14 percent) were diabetic. Those who ate the most vegetables, particularly leafy and cruciferous ones, were least likely to have type 2 diabetes or to be obese.
Some of the 18 studies included potatoes in their analysis of vegetable consumption, while others did not. From the studies that included potatoes, participants who ate the most total potatoes had a nine percent greater risk for being diabetic than those who ate the least. Furthermore, if they avoided fried potatoes, potato chips and potatoes mashed with butter, they were not at increased risk for diabetes. Potatoes are the fourth most important staple food crop in the world, behind wheat, corn and rice. Potatoes can be healthful, but that can depend on how you cook them and what you add to the potatoes or eat with them.
How Vegetables May Help to Prevent Diabetes
Vegetables are low in calories and high in soluble fiber, phenols and nitrates that help to prevent diabetes. Soluble fiber passes unabsorbed through your upper intestines to your colon. In your colon, healthful bacteria break down soluble fiber to form short-chain fatty acids (SCFAs) that pass into your bloodstream. SCFAs help to treat and prevent diabetes by lowering high blood sugar, high blood pressure, and the bad LDL cholesterol (Am J of Clinical Nutrition, Nov 1, 2017). Soluble fiber also reduces inflammation by helping to increase the mucus layer that prevents harmful bacteria from getting into the cells lining your inner colon. The healthful bacteria increase in number when you eat plenty of fiber-rich foods, and this reduces the number of harmful bacteria because they have difficulty passing through the mucus to get their food from the cells lining your inner colon.
What you eat determines which types of bacteria grow in your colon. Eating a plant-based diet encourages the growth of bacterial species that help to break down resistant starches and other soluble fiber that:
• help make the vitamins biotin, folate and vitamin K
• stimulate your immunity to protect you against infections
• help prevent diabetes by lowering blood levels of sugar and insulin
• lower blood levels of cholesterol and triglycerides
• produce butyrate that may help to reduce your chances of developing cancer or inflammatory bowel disease
Potato Cooking Methods
When you cook a potato with water, the sugar in it combines with the water to produce energy, carbon dioxide and water as the end products of digestion, all of which are safe and healthful. (Baked potatoes are “steamed” — cooked in the water trapped inside their skins). On the other hand, when you fry potatoes in oil, the sugar combines with protein to form advanced glycation end products (AGEs) such as acrylamide, that have been linked to cancers in animals and may increase cancer risk in humans. Eating a lot of foods that are high in AGEs can also prevent cells from responding to insulin, which can lead to diabetes (Crit Rev Food Sci Nutr, 2016;56(6):989-98) and make it harder to control existing diabetes (Diabetes Care, January 2014;37:88-95).
Cooking potatoes at high temperatures converts their resistant starches that are not absorbed until they reach your colon bacteria into carbohydrate molecules that can be easily absorbed and can cause a high-rise in blood sugar. When your blood sugar rises too high, your body first tries to store the sugar in the liver, muscles and fat. This is only a small amount and then the excess sugar is converted to fatty triglycerides. So blood triglyceride levels rise and are carried to the liver by the healthful HDL cholesterol, so blood HDL levels drop. The liver fills up with fat and a fatty liver can prevent the body from responding to insulin, and blood sugar levels can rise to high levels and cause diabetes. Having high blood triglyceride levels above 150 mg/dL (1.7 mmol/L) puts you at increased risk for diabetes, heart attacks, strokes, and heart valve disease, even if your blood cholesterol levels are normal (Eur Heart J, Dec 2021;42(47):4791-4806).
Other Studies of Fried Potatoes
A study of 4400 North American men and women, ages 45 to 79, followed for eight years, showed that those who ate fried potatoes two or more times a week were at increased risk for dying during the study period, compared to those who ate fried potatoes occasionally. Those who ate potatoes that were not fried had no increased risk of death (Am J Clin Nutr, Jul, 2017;106(1):162-167). I can find no data to show that eating French fries on occasion, such as once a week, increases risk for any disease. However, several studies have shown that people who eat fried potatoes frequently are at increased risk for:
• obesity (Am J Clin Nutr, Aug 2016;104(2):489-98)
• high blood pressure (BMJ, May 7, 2016;353:i2351)
• colon cancer (Nutr Cancer, May-Jun, 2017;69(4):564-572)
• diabetes (Diabetes Care, Mar 2016;39(3):376-84; Am J Clin Nutr, Feb 2006;83(2):284-90)
My Recommendations
I believe that everyone should eat lots vegetables. Among their many benefits, vegetables help to prevent many diseases by increasing colonic bacterial production of SCFAs that reduce inflammation. Potatoes can be included, but try to use the more healthful cooking methods (steaming, baking, boiling or microwaving) and limit the favorite high-fat, high-calorie additions: butter, cream, sour cream, gravy and so forth. Restrict potatoes if you are diabetic or overweight.
