Let’s say you really need to find reliable information about the best diet – for high blood pressure – or heart disease – or diabetes. Where do you go? Do you go to a website sponsored by Big Pharma that wants to sell you pills to fix your problem?
Or, do you want to treat the cause?
Welcome to the NutritionFacts podcast – with the latest peer-reviewed research on the best ways to eat healthy – and live longer.
Today, we take a close look – at a multi-faceted and often understood root vegetable.
And, we start with a little trick about lowering their glycemic impact.
If you systematically pull together all the best studies on potato consumption and chronic disease risk, an association is found for the risk of type 2 diabetes and hypertension. Yeah, but that was for French fries. Consumption of boiled, baked, or mashed potatoes was not associated with the risk of high blood pressure, but there was still a pesky link with diabetes. Overall, potato consumption is not related to the risk for many chronic diseases, but boiled potatoes could potentially pose a small increase in risk for diabetes. That’s one of the reasons some question whether they should be counted as vegetables when you’re trying to reach your recommended daily servings of fruits and vegetables.
If you look at other whole plant foods—nuts, vegetables, fruits, and legumes (which are beans, split peas, chickpeas, and lentils)—they’re associated with living a longer life. Significantly less risk of dying from cancer, dying from cardiovascular diseases like heart attacks, and 25 percent less chance of dying prematurely from all causes put together. But no such protection is gained from potatoes for cancer, heart disease, or overall mortality. So, the fact that potatoes don’t seem to affect mortality can be seen as a downside. Now, it’s not like meat, which may actually actively shorten your life, but there may be an opportunity cost to eating white potatoes, since every bite of a potato is a lost opportunity to put something even healthier in your mouth— something that may actively make you live longer.
So, potatoes are kind of a double-edged sword. The reason that potato consumption may just have a neutral impact on mortality risk is that all the fiber, vitamin C, and potassium in white potatoes might be counterbalanced by the detrimental effects of their high glycemic index. Not only are high glycemic impact diets robustly associated with developing type 2 diabetes, but current evidence suggests that this relationship is cause-and-effect.
A front group for the potato industry called the Alliance for Potato Research and Education funded a study that found that intake of non-fried potato does not affect blood sugar markers, but that’s compared with the likes of Wonder Bread; so, that isn’t really saying very much. Foods with a glycemic index (GI) above 70 are classified as high-GI foods, high glycemic index foods, and those lower than 55 are low-GI foods. Pure sugar water, for example, is often standardized at 100. White bread and white potatoes are way up there as high glycemic index foods. When you compare them to an intact grain, like barley groats (also known as pot barley), a super-low GI food, you can see how refined grains and potatoes are simply no match.
Is there any way we can have our potatoes and eat them too, by somehow lowering their glycemic index? Well, if you boil potatoes and then put them in the fridge to cool, some of the starch crystallizes into a form that can no longer be broken down by the starch-munching enzymes in your gut. However, the amounts of this so-called resistant starch that are formed are relatively small, making it difficult to recommend cold potatoes as the solution. But when put to the test, you actually see a dramatic drop in glycemic index in cold versus hot potatoes. So, by consuming potatoes as potato salad, for instance, you can get nearly a 40 percent lower glycemic impact. The chilling effect might, therefore, also slow the rate at which the starch is broken down and absorbed. So, individuals wishing to minimize dietary glycemic index may be advised to precook potatoes and consume them cold or reheated. The downside of eating potatoes cold is that they might not be as satiating as eating hot potatoes. But you may get the best of both worlds by cooling them and then reheating them, which is exactly what was done in that famous study I profiled in my book How Not to Diet. The single most satiating food out of the dozens tested was boiled then cooled then reheated potatoes.
There’s actually an appetite-suppressing protein in potatoes called potato protease inhibitor II, but the way you prepare your potatoes makes a difference. Both boiled and mashed potatoes are significantly more satiating than French fries. That was for fried French fries, though. What about baked French fries? Folks had a big drop in appetite after eating boiled mashed potatoes, compared to white rice or white pasta, which is right where fried French fries were stuck, as well as baked French fries. So, though they may be your BFF, they’re not very satiating.
In our next story – broccoli, vinegar, and lemon juice are put to the test to blunt the glycemic index of white potatoes.
White potatoes have a high glycemic index, and consumption of high glycemic impact foods may increase the risk of diabetes. Normally after a meal, we’d like our blood sugars to just gently, naturally rise and fall. But with high glycemic foods like potatoes, you get an exaggerated blood sugar spike, which leads your body to over-compensate with insulin, forcing your blood sugars lower than when you started, which results in negative metabolic consequences––such as a rise in triglyceride fats in the blood. However, potatoes are a good source of potassium, vitamin C, and polyphenols, which may counterbalance the glycemic impact. This may explain why potatoes appear to have a neutral effect when it comes to lifespan, unlike other whole plant foods that have been associated with actively living longer.
I teach my nip-and-nuke method, where the act of chilling potatoes can dramatically lower their glycemic index, even if you then reheat them in a microwave. How else might we reduce the glycemic impact of white potatoes? The answer is the same way you make anything better in your nutritional life—add broccoli. The co-consumption of two servings of cooked broccoli with your mashed potatoes would certainly do it, immediately cutting the insulin demand by nearly 40 percent. In contrast, adding chicken breast makes things worse, and adding tuna fish makes things even worse still, nearly doubling the amount of insulin your body has to pump out.
Why does plant protein make things better, but animal protein make things worse? Because decreased consumption of branched-chain amino acids improves metabolic health. I cover this in my book How Not to Diet as well as my video on the topic.
Speaking of How Not to Diet, remember the section on vinegar? Here are the blood sugar and insulin spikes someone with prediabetes can get from eating a bagel. Eat that same bagel with a tablespoon or so of apple cider vinegar diluted in about a quarter cup of water, though; the impact is significantly less. Does it work for potatoes too?
Simply chilling potatoes may cut down on the blood sugar and insulin spikes, but to get significant drops in both, you just have to add about a tablespoon of vinegar to drop levels by 30 to 40 percent. And that was just plain white distilled vinegar.
Is it the vinegar itself, or would any acidy condiment do? In a test tube, lemon juice appeared to have a remarkable starch-blocking effect, but you can’t know if it works in people, until you put it to the test. And indeed, lemon juice reduces the glycemic responses to bread. And not just by a little, but by like 30 percent. Now, the subjects were drinking a half cup of lemon juice, but that makes it even more remarkable that it helped, because that added an extra half teaspoon of sugar, and yet they still had a better blood sugar response. Vinegar is more potent, though. Just one to two tablespoons a day of vinegar diluted in water can significantly improve both short- and long-term blood sugar control in diabetics, which is why clinicians may want to incorporate vinegar consumption as part of their dietary advice for patients with diabetes.
Finally, today – are yellow-fleshed potatoes healthier than white? Let’s find out.
The high glycemic impact of potatoes may increase the risk of type 2 diabetes, perhaps by chronically overstimulating the insulin-producing cells in the pancreas. In my last two videos, I explained how you can decrease the glycemic impact of white potatoes by eating them cold, or chilling then reheating them, or adding broccoli, lemon juice, or vinegar. What else can we do?
Well, if you remember, I had a video a few years back that showed how the pigments in brightly colored berries can act as starch blockers. So, if you’re going to eat a high glycemic food, you may be able to moderate its impact by spreading raspberries on your toast, for example, or adding strawberries to your cornflakes, or sprinkling blueberries in your pancakes. No, I’m not saying you have to put blackberries in your baked potato, but given that the natural color compounds in fruits can slow down starch digestion, what about pigmented potatoes?
Even just yellow potatoes like Yukon gold may be preferable to white, but the best may be purple potatoes: not just purple-skinned potatoes, but purple-fleshed potatoes. If you’ve never seen purple potatoes, they are remarkable; they have almost a neon blue glow. And not only do they look cool, but purple potatoes cause less of an insulin and blood sugar spike compared to even the yellow-fleshed potatoes, suggesting that switching from yellow or white to purple could have a large potential public health benefit.
How do we know it’s the pigments themselves that are responsible, rather than other differences between the different potato varieties? The researchers tried adding a control comprised of berries in a potato starch jelly, but that would seem to add even more variables. In a test tube, extracts of purple- and red-fleshed potatoes can act as starch blockers; so hey, if you can extract and purify out the purple potato pigments—say that five times fast—you could remove any other effects of the different potato varieties by adding the purple pigments to yellow potatoes. And lo and behold, compared to just plain yellow potatoes, you can get a suppression of the blood sugar and insulin spikes. This way, you don’t get that overshoot reaction where your blood sugars can actually drop below fasting like you might get otherwise; instead, you get the gentler up and down in blood sugars you’d expect from a lower glycemic food.
The authors suggest purple potato extracts could be produced to make into supplements or fancy functional foods, but these health-promoting compounds may be more cost-effectively received from consuming purple potatoes themselves.
The Potato Association of America likes to paint potatoes as an anti-inflammatory food, but what they don’t tell you is that this benefit may be limited to pigmented potatoes. If you randomize people to eat a small white potato every day for six weeks versus a yellow- or purple-fleshed potato, the purple potato group achieved significantly lower levels of inflammation compared to the white potato group, measuring both c-reactive protein and interleukin-6.
Pigmented potato consumption also alters oxidative stress. Within hours of eating a large purple potato, you get a nice 60 percent bump in the antioxidant power of your bloodstream, and this translates into less free radical DNA damage. If you compare the antioxidant activity of white potatoes, yellow potatoes, and purple potatoes, Yukon gold has about twice the antioxidant power as white, but purple has twenty times the antioxidants, which is comparable to what you might see in berries. A half of a purple potato has about the same polyphenol antioxidant complement as a half cup of blueberries.
Purple potatoes can increase the antioxidant capacity of our bloodstream, whereas straight white potato starch can act as a pro-oxidant and decrease it. Eat a purple potato, and over the next eight hours the antioxidant capacity of your blood stream goes up. In contrast, if you eat white potato starch devoid of any pigment, you can end up worse off than where you started. Okay, but does this translate into different physiological effects?
Yes indeed. Have people eat either purple potatoes or white potatoes for two weeks, and the purple potatoes improved a measure of arterial stiffness, whereas the white potato did not. And this translates into a drop in blood pressure, even in those already taking high blood pressure drugs, suggesting purple potatoes are an effective blood pressure lowering agent.
But what about the toxic glycoalkaloid compounds in potatoes? The toxic human dose starts around 2-5 mg/kg of body weight, and the lethal dose is not too far behind. But the average amount of total glycoalkaloids in most potatoes, however, 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 approach that? It’s possible you can get nausea, vomiting, or diarrhea that could be easily confused with something like gastroenteritis or food poisoning. Some people can start to get sick at just 1.25 mg/kg of body weight, or even 1 mg/kg. That would only be about two pounds of potatoes at the average American weight. It’s also possible they could start accumulating if you eat them day in and day out. But what about those people who go on a fad potato diet and eat three or four pounds a day? They can do that without risking getting sick only if they peel their potatoes, which removes nearly all of the glycoalkaloids.
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To see any graphs, charts, graphics, images, or studies mentioned here, please go to the NutritionFacts podcast landing page. There, you’ll find all the detailed information you need – plus links to all of the sources we cite for each of these topics.
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