Lately, I’ve heard a variety of health experts suggest that it’s healthy to eat potatoes if they are first cooked, and then refrigerated. Let’s break down this claim, and see how much holds true.
First, let’s address resistant starch.
Resistant starch is starch that you can’t digest. It passes through your intestinal tract without being absorbed and your gut bacteria feed on it, breaking it down and fermenting it into short chain fatty acids (such as butyrate), thus feeding and supporting healthy gut bacteria. These short chain fatty acids also support your large intestine, even decreasing your risk for colon cancer.
Sources of resistant starch are beans and lentils, green bananas, rice, oats, and potatoes (sweet and purple potatoes have a bit more resistant starch than white potatoes).
Next, how does chilling a potato impact the glycemic load (sugar load) of eating a potato?
Potatoes have a high sugar load. This is true if we look at the glycemic index (which is the amount of sugar in your bloodstream after consuming 50 grams of carb from a food) and glycemic load (a far more practical measure, which is the amount of sugar in your bloodstream from eating one serving of food).
When you chill a cooked potato, the structure of some of the starch is changed and this process increases the resistant starch load by about 2%, increasing it from 3.3% to 5.2%. So although a 1.9% increase isn’t a big change in overall potato starch, it does increase the resistant starch content by 55%. So if you are going to eat a potato, it makes sense to chill it after cooking, then reheat it, or eat it cold.
Studies have shown that the glycemic index in chilled potatoes is about 25-35% less than in freshly cooked potatoes that are still warm. Keep in mind that 50 grams of carb in a potato is about 1.5 medium sized red potatoes, which is only about 1/3 to 1/2 of a cup—not a very big serving. So if you ate such a small portion, it would lower the glycemic index from high to medium for that food. If you eat a normal sized portion of potato (I’d say at least one cup), the glycemic index would be less if it was chilled before you ate it, but it would still have a high glycemic load and raise your blood sugar level significantly.
What about the type of potato and how to cook it?
White potatoes that are baked and mashed have the highest glycemic load, as they have a glycemic load that is equal to table sugar. Boiled potatoes have 20-25% less glycemic load than baked and baked potatoes. Sweet potatoes and purple potatoes also have about a 20-35% lower glycemic load than white potatoes, and a russet potato has the highest glycemic load of all.
Further, small potatoes have a higher ratio of skin to flesh. Since potato skins have a much lower glycemic load than the flesh, eating small potatoes means getting a lower glycemic load.
Eating your potato with protein and fat can also decrease the glycemic load by another 10%. Again, not a big reduction, but every bit helps.
When you compare a potato with other vegetables, notice the difference in glycemic load in the table below: (Below are 1 cup portions)
Glycemic load from 0 to 9.9 is low, 10 to 19.9 is medium, and 20 and above is high:
Food: Glycemic Load:
Bell pepper 2
Small, purple potato, boiled 14-18
Sweet potato, baked 20-22
Boiled large white potato 21
Baked large white potato 26-33
If you are considering whether to eat potatoes or skip them, hopefully this table will guide you to make the best choice that works for you. Eating other vegetables is still by far the better choice!
If you do eat potatoes on occasion, it is better if they are small instead of large, purple or sweet potato instead of white potatoes, and chill the potato first in the refrigerator and serve it cold or hot later.
Keep in mind that potatoes are also on the dirty dozen list, so if you buy potatoes, be sure to buy organic!
Here is how my wife, Nicole, and I on occasion use potatoes at home. We often make a soup of the week on weekends and eat it for lunch during the week. If we choose to include potatoes in the soup, we buy small, organic purple or red potatoes, and cook them in the soup (boiled). We store and refrigerate them in glass containers, and we likely only get one-quarter of a cup of potatoes per lunch serving. We add lots of other vegetables and either cooked beans or other clean animal protein to the soup as well, allowing a few delightful potato bites, but with an overall low glycemic load, and loaded with fantastic flavors.
What about selecting and chilling other sources of resistant starch, such as beans, oats, rice, and pasta?
If you are disappointed that even chilled potatoes have a fairly high glycemic load, keep in mind that beans, oats, and unripe bananas have a lower glycemic load than potatoes, and they are also a good source of resistant starch. So if you’d like to benefit from eating more resistant starch, then eat more beans, oats, and unripe bananas.
Glycemic Load and Resistant Starch Content of Other Foods: (1 cup serving)
Glycemic Load 1st # and then Resistant Starch Content (grams/100 grams food)
Steel-cut oats 9 11
Beans 10 3-6
Brown rice 22 2-3
Boiled potato 21 3
Boiled, cooled, white potato 16-17 5
Banana (unripe) 10 5
Whole grain pasta 15-18 2-3
Chilling beans, rice, and pasta lowers the glycemic load of these foods as well. Thus, serving chilled beans, pasta, and brown rice that has been chilled and then served in a salad or re-heated in a stir fry will lower the glycemic load as well.
I wish you the best of health!
Steven Masley, MD, FAHA, FACN, FAAFP, CNS