Glycemic index is commonly used. In using 10 subjects (presumably on a Standard American diet), it is the measured rate of which foods cause the level of glucose in the blood to rise over a 2-hour period, as compared to the affect of a reference food that is usually pure glucose.
But many question the relevance of the glycemic index. In terms of health, it matters little whether your blood sugar rises over a period of less than or more than 2 hours because the carbs eventually are digested and absorbed. Some argue that an extended and sustained rise of blood sugar is more harmful than a quick boost that goes away quickly. Too much glucose for too long in the blood is toxic — one might say that it’s a heavy load. The body has to deal with the glucose one way or another, either burning it as fuel or storing it as fat.
That is why some prefer glycemic load. It is determined by taking the glycemic index of a food, multiplying it by the net grams of carbohydrate in a standard serving size (e.g., 100 grams), and dividing that by 100. So, it is taking into account the total amount of available carbs in the food. “Glycemic load appears to be a significant factor in dietary programs targeting metabolic syndrome, insulin resistance, and weight loss; studies have shown that sustained spikes in blood sugar and insulin levels may lead to increased diabetes risk” (Glycemic load, Wikipedia). Keep in mind that most Americans have some component of metabolic syndrome: obesity, diabetes, fatty liver, heart disease, etc.
This, of course, ignores satiety. The same serving size of one food won’t be equally satisfying as another food and depending on what it is eaten with as part of a total diet. Neither glycemic index nor glycemic load measures the impact of blood sugar on how much the typical person would eat of a particular food, such as spinach compared to popcorn. Some argue a single serving of potato every day or every other day is healthy for most people, but they don’t take into account that few people would ever only eat one serving of potatoes and eat few if any other carbs for the rest of the day. Even foods with moderate glycemic index and load, if snacked on all day, would keep blood sugars higher than is optimal for long term health. That is the real world impact that gets ignored.
Furthermore, consider the insulin index, which some consider more important than glycemic index or glycemic load. It can be misleading, though, with some foods. Foods high in protein will raise insulin higher than many foods because of gluconeogenesis (protein turned into glucose), but the body only does so to a limited degree and it is an extremely short term spike and then, particularly on a low-carb diet, this is followed by insulin stabilizing at a much lower level. Fatty foods will also kick up insulin levels, although once again not a problem on a low-carb diet. By the way, fat is a complicating factor. Even though fat raises insulin, fatty foods overall have a lower insulin response than non-fatty foods, whether comparing 2% milk and skim milk or a regular cook to a low-fat cookie. This partly has to do with fat moderating the absorption of carbs, but it also has to do with how companies will add sugar to low-fat foods in order to make them taste better.
Anyway, temporary spikes from protein or fat alone are not generally problematic, assuming it’s not part of an otherwise unhealthy diet. Metabolic syndrome is more determined by the sustained increases of insulin, not temporary rises. But the problem with the Standard American diet is that it combines protein and fat with massive amounts of refined carbs, and because many carbs like grains and sugar are addictive this eating pattern is repeated as continuous meals and snacks all day long. There is a reason why, to ignore protein, one can lose weight on both a low-carb diet and a low-fat diet. It’s the combination of the macronutrients in highly processed foods that has such consequences to the metabolic system and, to add to the fire, a high-carb diet is inflammatory as are the industrial seed oils that are used in junk food, fast food, and sadly packaged ‘health foods’.
Still, even these short term spikes can be problematic for diabetics trying to maintain insulin levels. But for non-diabetics, it’s less relevant. As we have glycemic load to show which foods have a sustained rise in blood sugar, we likewise need an insulin load to measure the extended impact of insulin over longer periods. This is particularly important for insulin resistance, as seen in diabetes and what some consider central to metabolic syndrome. It is where the body has to keep raising insulin because the body’s response becomes muted. It’s the constant raising of insulin that causes this muting, not brief occasional spikes.
Also, left out is that blood sugar by itself doesn’t necessarily tell us much. Metabolic syndrome is a disease of insulin, not of blood sugar. But as I said, looking at insulin alone doesn’t necessarily help either. Insulin is a hormone that works with other hormones to maintain the metabolic system. We can only know how an individual is responding, in terms of metabolic health, by measuring the insulin to glucagon ratio. Glucagon can detect diabetes sometimes decades before it otherwise would show up. Any doctor could measure glucagon, although few do.
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Let’s look at a specific food as an example.
Potatoes may seem healthier, but they are still a carbohydrate. Potatoes have a higher glycemic index (high 80s to low 90s) than table sugar (59), although slightly below pure glucose (100). “Sucrose (table sugar) has a GI of 59. It is a disaccharide (two sugar) molecule—it’s made up of one glucose molecule and one fructose molecule. Fructose is processed differently in your body than glucose, and it doesn’t affect your blood sugar as much” (Why Do Potatoes Have a Higher Glycemic Index Than Sugar?). As further comparison, bread has a GI between 40 and 95, depending on the kind.
Likewise, not all potatoes are created equal: “In general, potatoes can range in GI value from 53 to 111, with white potatoes typically showing up lower on the index. Leaving the skin on adds fiber, which can reduce the potato’s effect on glucose. Often, the sweet potato is rated with a GI in the mid-40s.” How they are prepared matters to some degree as well, but that still puts the lowest GI potatoes around the same as table sugar.
The glycemic load, the most important measure, is even worse: “A small study compared the impact 50 grams carbohydrate portion of potatoes versus bread versus pasta had on participant’s blood sugar levels. While clearly none of the foods tested are particularly blood sugar friendly, it’s interesting to note that the potatoes resulted in the most significant rise at the 2 hour mark” (Potatoes and Diabetes: Can You Eat Them?). This also depends on the type of potato with the baked white potato having a high glycemic load of 29 and sweet potatoes around a moderate 19, that is moderate for starchy foods. That is much higher than the glycemic load of bread, from 11 to 16.
The only theoretical advantage to potatoes is resistant starch, but even that is not a net benefit since, “Research has also suggested that increased consumption of potatoes, especially french fries, leads to an increased risk of developing type 2 diabetes.” In case you forgot, type 2 diabetes, like liver disease, are part of metabolic syndrome. So, the basic point is that potatoes don’t contribute to metabolic health and certainly shouldn’t be eaten or at least eaten in extremely small amounts by anyone suffering from any condition of metabolic syndrome.
The author goes on to say that, although it’s true that potatoes have a bit more resistant starch than other high-carb foods, “The problem is that this logic of resistant starch is flawed, similar to the flaws found with the net carb counting method. First, the amount of resistant starch found in a medium potato is about 9 grams, which still leaves around 28 grams of fully digestible carbohydrate available to spike your blood sugar. Resistant starch in and of itself offers health benefits such as improved glycemic control, but in order to eat enough resistant starch (from potatoes, rice, and unripened bananas) you would end up eating an outrageous amount of carbohydrate.”
Let us touch upon the insulin index. Like refined grains, potatoes have a high insulin response. This would vary by kind of potato and preparation method, I’m sure. But interestingly, another factor alters the insulin effect. I mentioned fat above in how it moderates carbohydrate absorption. This is demonstrated by comparing two products that only differ by fat amounts (Forget Calorie Counting; It’s the Insulin Index, Stupid).
A normal potato chips have an insulin index of 45 whereas it’s 51 for 40% reduced-fat potato chips. I don’t know exactly what that means. A low-fat diet can be used to lose weight, but that is a separate issue from the insulin index. Both obesity and high insulin responses contribute to insulin resistance. I guess you could solve this problem by cutting out the potatoes along with most other starchy carbs and then you have nothing to worry about. Potatoes are high insulin response for potatoes, though a bit lower with fat, is still on the higher end of the scale.
The next bit of info comes from an article that seems balanced in the mainstream sense with no particular alternative slant, such as low-carb or vegan. Interestingly, it comes from the Food Revolution Network with their show co-hosted by John Robbins who “was groomed to be the heir to the Baskin-Robbins empire” who left the family business because “He simply didn’t want to devote his life to selling ice cream after realizing it makes people unhealthy.” So, the only bias might be against commercial ice cream.
The author states that, “Potatoes can be a healthy choice for most people…” But… there is always a but: “but three groups might want to minimize their consumption (particularly of white potatoes): pre-diabetics, diabetics, and people who are overweight” (Are Potatoes Healthy? The Surprising Truth About This Controversial Vegetable), and presumably any other condition involving metabolic syndrome/derangement, such as fatty liver. That means anyone who isn’t metabolically healthy should avoid or minimize potatoes in their diet and, as we know, most Americans aren’t metabolically healthy.
On the other hand, “But, in a published in the Journal of the American College of Nutrition in 2014, researchers found that when people followed healthy recipes, they lost weight even while eating five to seven servings of potatoes per week.” So, it’s possible that someone by eating generally healthy, in removing all the common problematic foods, might be able to regain enough metabolic health to eat some starchy foods like potatoes. Still, even then, a serving of potatoes is fairly small. Few people eating potatoes are likely to limit themselves to a single serving, not to mention all the other starchy carbs they are also likely to eat throughout the day.
It goes back to the challenge of modern society. In a few traditional societies, they did eat relatively more carbs as a percentage of their diet. But that is in the context of their diet in general being typically limited and often to an extreme degree with small portions and caloric restriction. That is the key point that goes unspoken. If one is to eat a higher-carb diet or even merely a moderate-carb diet, in any case not low-carb, one should all the more closely follow a traditional diet and lifestyle: pasture-raised animal foods, regular cardio exercise and strength training, etc.
Still, a higher carb diet was rare until the modern era. The highest end of the carbohydrate range of hunter-gather diets at 40% of calories, I like to point out, is what some Western researchers define as part of a ‘low-carb’ diet (Cordain et al, Plant-animal subsistence ratios and macronutrient energy estimations in worldwide hunter-gatherer diets). So, even at the highest amounts for hunter-gatherers, they are still getting most of their energy and nutrients from animal foods. And guess what? Obesity, diabetes, and heart disease is rare among most of these populations — that is as long as they remain on their traditional diets.