Are yellow-fleshed potatoes healthier than white potatoes? And what about glycoalkaloid toxins?
The high glycemic effect of the potato can increase the risk of type 2 diabetes, perhaps through chronic overstimulation of insulin-producing cells in the pancreas. In my last two blogs, I explained how you can reduce the glycemic impact of white potatoes by eating them cold, freezing them and then reheating them or adding broccoli, lemon juice or vinegar. What else can we do?
Well, pigments in 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 moderate 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 blueberries in your baked potato, but since the natural coloring compounds in fruit can slow reduces starch digestion, what about colored potatoes?
Even regular yellow potatoes like Yukon gold may be preferable to white, but the best can it is purple potatoes—not just purple-skinned potatoes but purple-fleshed potatoes. If you’ve never seen purple potatoes, they’re remarkable—they have an almost blue glow, which you can see below and at 1:14 in my video.
And not only do they look cool, but purple potatoes too cause less of a spike in insulin and a smaller spike in blood sugar than even yellow-fleshed potatoes, suggesting that switching from yellow or white potatoes to purple “could have great potential in maintaining public health.”
How do we know that the pigments themselves are responsible and not other differences between different potato varieties? The researchers tried using a berry-on-potato-starch jelly control, but that approach seems to add even more variables. In a test tube, purple and red fleshed potato extracts can act as starch inhibitors. So if you extract and clear the purple potato pigments, could you remove any other effect of different potato varieties by adding these purple pigments to yellow potatoes. And lo and behold, compared to plain yellow potatoes, this results in blood sugar suppression and insulin spikes. Instead of an overshoot reaction, where blood sugars can drop below fasting levels, you get the milder rise and fall of blood sugars that you would expect from a lower glycemic index food, as you can see below and at 2:25 in my video.
The authors recommend Purple potato extracts could be produced to make supplements or fancy functional foods, but it may be more economical to get these compounds from eating purple potatoes.
The purple pigments in the potato may also affect inflammation. The Potato Association of America likes it color potatoes as an anti-inflammatory food, but what it doesn’t tell you is that this benefit can be limited in colored potatoes. When study participants were randomized to eat a small white potato every day for six weeks versus a yellow- or purple-fleshed potato, participants in the purple potato group achieved significantly lower levels of inflammation compared to those in the white potato group, measuring both C-reactive protein and interleukin-6, as shown below and at my 3:13. video.
Eating colored potato as well alters oxidative stress. Within hours of eating a large purple potato, you’ll have a nice 60% boost in the antioxidant power of your bloodstream, and that translates into less DNA damage from free radicals. If you compare Antioxidant activity of white potato, yellow potato and purple potato, Yukon gold has about twice the antioxidant power of white, but purple has 20 times more antioxidants. This is comparable to what you can see in berries. Half a purple potato has about the same polyphenol antioxidant content as half a cup of blueberries.
Purple potatoes maybe increase the antioxidant capacity of our blood circulation, while pure white potato starch can act as a pro-oxidant and reduce it. Eat a purple potato and, for the next eight hours, the antioxidant capacity of your bloodstream increases. Conversely, if you eat white potato starch with no coloring, you may end up worse than where you started, as you can see below and at 4:12 in my video.
OK, but does this translate into different physiological outcomes? Yes, indeed. When people he ate either purple potatoes or white potatoes for two weeks, purple potatoes improved a measure of arterial stiffness, while white potatoes did not. And this translates in lowering blood pressure, even in those already taking high blood pressure medication, suggesting that purple potatoes are an effective blood pressure-lowering agent.
But what about the toxic glycoalkaloid compounds? I establish in potatoes? The toxic human dose starts about 2 to 5 mg/kg body weight and the lethal dose is not far behind. But the average amount of total glycoalkaloids I establish in most potatoes, however, it is less than 100 mg/kg. So, at the average American weight of 180 pounds, a toxic dose is like four to nine pounds of potatoes. What happens when you get close to that amount? You may have nausea, vomiting, or diarrhea that could easily be mistaken for something like gastroenteritis or food poisoning. Some people can start to get sick with as little as 1.25 mg/kg body weight or even experience symptoms at 1 mg/kg. That would only be about two pounds of potatoes at the average American weight. Glycoalkaloids are also likely to initiate accumulation if you eat potatoes day after day. But what about those people who are on a trendy potato diet and eat three or four kilos a day? They can do this without risking getting sick if they do peel their potatoes, which removes almost all the glycoalkaloids.
Doctor’s note
This is the last in a series of five videos about potatoes. If you missed any of the others, see:
You may also be interested The best way to cook sweet potatoes.
The berry video I mentioned is Take the starch to take the path of greatest resistance.
