Sweet Potatoes, Potatoes May Spike Blood Sugar; Nutritionist Warns of Diet Pitfalls

Contrary to the common belief that root vegetables like sweet potatoes, potatoes, and corn are inherently healthy and do not significantly impact blood sugar, a nutritionist warns that certain preparation and consumption methods can lead to sharp glucose level increases. Cai Zhengliang, a nutritionist, highlights that while these are natural starches, their effect on post-meal blood sugar is not always stable. He advises avoiding four common pitfalls: cooking them until too soft, roasting them to excessive sweetness, blending them into soups, and consuming overly large portions.

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Natural does not mean that post-meal blood sugar is always stable.

Cai explains that the impact on blood sugar depends on various factors beyond the food itself, including the starch's structure, fiber content, degree of gelatinization, whether the skin is consumed, and the cooking method. He also points to the formation of resistant starch when cooked starches are cooled. Resistant starch resists digestion in the intestines, slowing the release of glucose into the bloodstream. Therefore, eating these starches cold, after refrigeration, can be more beneficial for blood sugar control than eating them hot.

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The starch structure, fiber content, degree of gelatinization, whether it is with skin, and cooking method all affect blood sugar.

He further elaborates on the types of starch, distinguishing between amylose (straight-chain starch, digested slower) and amylopectin (branched-chain starch, digested easier). Gelatinization, which occurs when food is heated, makes starches softer, hotter, sweeter, and more easily digestible, leading to faster blood sugar spikes. For sweet potatoes, which have a higher proportion of amylopectin, baked versions can raise blood sugar more quickly due to water loss and increased sweetness. Boiled or chilled sweet potatoes, especially with the skin on for added fiber, are more ideal.

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Resistant starch means that after the starch is arranged, it forms crystals and is not digested and absorbed by the intestines, reducing the release of glucose in the small intestine.

For potatoes, mashed potatoes, fries, and au gratin dishes are more likely to cause rapid blood sugar increases due to high gelatinization. Cold potato salads offer a more stable option due to increased resistant starch. Whole corn kernels are digested more slowly due to their fiber content and intact structure, but processed forms like creamed corn or corn flour can accelerate sugar absorption. Taro, when consumed in块状 (block form), is preferable to purees or in sweet soups. Pumpkins, due to their high gelatinization, can be absorbed faster than expected if cooked too soft or made into soup. Cai's general advice for stable blood sugar is to consume these starches with their skin on, in whole or block form, and preferably after cooling.

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The softer, hotter, sweeter, and more gelatinized the food, the easier it is to digest and absorb, and the faster the blood sugar usually rises.