Are yellow potatoes healthier than white? And what about glycoalkaloid toxicity?
The high glycemic effect of potatoes can increase the risk of type 2 diabetes, possibly by overstimulating insulin-producing cells in the pancreas. In my last two blogs, I explained how to reduce the glycemic impact of white potatoes by eating them cold, cooling them and reheating them, or by adding broccoli, lemon juice, or vinegar. What else can we do?
Yes, the pigments of the brightly colored berries can act as starch inhibitors, as you can see below and at 0:38 in my video. The Healthiest Kind of Potato.
So, if you’re going to eat a food with a high glycemic index, you might be able to balance its impact, for example, by spreading raspberries on your toast, adding strawberries to your cornflakes, or sprinkling blueberries on your pancake batter. I’m not saying you should put berries on your baked potatoes, but given that the natural coloring compounds in fruit can slow down the digestion of starch, what about colored potatoes?
Even a common yellow potato like a Yukon gold may be preferable to a white, but the best may be a purple potato—not just a red potato but a purple potato. If you’ve never seen purple potatoes, they’re amazing—they almost have a neon-blue glow, which you can see below and at 1:14 in mine. video.
And not only do they look cool, but purple potatoes cause less insulin spikes and lower blood sugar than yellow potatoes, suggesting that switching from yellow or white potatoes to purple “could have a huge impact on public health.”
How do we know that the pigs themselves are responsible, there are other differences between different types of potatoes? The researchers tried using a control made from berries in a potato starch gel, but that method seems to add more variables. In a test tube, purple and red potato extracts can act as starch inhibitors. Therefore, if you extract and purify the purple potato pigments, you can remove any other effects of the potato variety by adding those purple pigments to the yellow potatoes. And look, compared to plain yellow potatoes, this causes blood sugar suppression and insulin spikes. Instead of an overreaction, where blood sugar can drop below fasting levels, you get a small rise and fall in blood sugar that you would expect from a low glycemic diet, as you can see below and at 2:25 for me. video.
The authors suggest that purple potato extracts can be produced to make supplements or functional foods, but it may be too expensive to obtain these compounds from eating purple potatoes themselves.
Purple potato pigments may also affect inflammation. The Potato Association of America likes to label potatoes as an anti-inflammatory food, but what they don’t tell you is that this benefit may be limited to colored potatoes. When study participants were randomized to eat a small white potato every day for six weeks versus a yellow or purple potato, those in the purple potato group had significantly lower levels of inflammation compared to those in the white potato group, measuring both C-reactive protein and interleukin-6, shown below and at 3:13 in mine. video.
The consumption of pigmented potatoes also changes oxidative stress. Within hours of eating a large purple potato, you get a nice 60% boost in the antioxidant capacity of your blood, and this translates into less free DNA damage. If you compare the antioxidant activity of white potatoes, yellow potatoes, and purple potatoes, Yukon gold has about twice the antioxidant capacity of white potatoes, but purple has 20 times more antioxidants. That is compared to what you can see in berries. Half a purple potato has about the same polyphenol antioxidant content as half a cup of berries.
Purple potatoes can increase the antioxidant capacity of our blood, while the starch in white potatoes can act as a pro-oxidant and reduce it. Eat a purple potato, and, for the next eight hours, the amount of antioxidants in your blood increases. Conversely, if you eat white, colorless potato starch, you can end up worse than where you started, as you can see below and at 4:12 in mine. video.
Okay, but does this translate into different physical effects? Yes, of course. When people ate purple or white potatoes for two weeks, the purple potatoes had some hardening of the arteries, while the white potatoes did not improve. And this leads to a decrease in blood pressure, even in those who are already taking drugs for high blood pressure, suggesting that purple potatoes are an effective way to lower blood pressure.
But what about the toxic glycoalkaloid compounds found in potatoes? The toxic human dose starts at about 2 to 5 mg/kg of body weight, and the lethal dose is not far behind. But the average amount of total glycoalkaloids found in most potatoes, however, is less than 100 mg/kg; therefore, for an average American weight of 180 pounds, the toxic dose is equivalent to four to nine pounds of potatoes. What happens when you approach that amount? You may experience nausea, vomiting, or diarrhea that can easily be confused with something like gastroenteritis or food poisoning. Some people may become ill at 1.25 mg/kg of body weight or even become symptomatic at 1 mg/kg. That would be about two pounds of potatoes in the standard American weight. It is also possible that glycoalkaloids can start to accumulate if you eat potatoes every day. But what about those people who go on a fad to eat potatoes and eat three or four kilos a day? They can do that without risking illness if they peel their potatoes, which removes almost all the glycoalkaloids.
Doctor’s Note
This is the last in a series of five potato videos. If you missed any of these, see:
You may also be interested in The Best Way to Cook Sweet Potatoes.
The video is about the berries I mentioned Finding Starch Takes a Very Contradictory Approach.
