If your last smoothie left your energy crashing an hour later, you might want to consider how some so-called healthy foods cause rapid glucose spikes.
Nutritionists stress the importance of keeping blood sugar levels steady throughout the day. “If your blood sugar spikes too quickly, you can get a ‘sugar high,’ followed by a sugar crash, which can lead to fatigue, moodiness and cravings,” said registered dietitian nutritionist Chelsey Amer.
It’s not always easy to balance, experts say. “Management of blood glucose levels is like the bedtime story of Goldilocks,” said RDN Toby Smithson, senior manager of nutrition and wellness at the American Diabetes Association. “If levels are out of range for extended periods of time, it means you won’t feel your best, and, long term, can even increase the risk of complications from diabetes.”
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What does it actually mean to have blood sugar spikes? Jessie Inchauspé, biochemist, author of “Glucose Revolution” and founder of Glucose Goddess, explained it this way: “When we give our body some glucose, everything goes great. Our blood sugar is steady, and we feel it: good mood, sharp focus. But if we give our body too much glucose, then blood sugar increases too fast, and then after a spike, there’s a crash when you feel tired, hungry, craving more sugar or caffeine, sometimes anxious or irritable.”
Two Terms To Learn: GI And GL
A lot of phrases are tossed around when we’re talking about blood sugar and nutrition, including GI (glycemic index) and GL (glycemic load). RDN Sharon Palmer, author of “The Plant-Powered Plan to Beat Diabetes,” explained what’s going on: “Healthy people have a tightly regulated system to control blood glucose, also known as sugar. Glucose rises in the blood after eating, then the pancreas responds by providing the hormone insulin to usher that glucose (energy for the body) into body cells and tissues.
“The GI is a scale that ranks carb-containing foods and beverages by how quickly they raise blood sugar levels after eating,” Palmer said. “High GI foods tend to increase blood sugar faster than low GI foods. The GI of foods can change based on serving size, fiber content, method of cooking and if they’re combined in a meal or snack.” A low GI is considered 55 or less, and that’s the rating given to most vegetables, fruits, nuts and minimally processed grains. High GI foods are rated between 70 and 100, and they include candy, cookies, breakfast cereal, potatoes, rice and bread.
Palmer said of GL: “It’s a more accurate reflection of how foods impact glucose, as it takes into account the amount of carbs in a food, too. For example, watermelon is high in GI, but low in GL, because it has relatively little carbohydrates in a serving.”
According to the University of Sydney’s Glycemic Index Research Service, which originally developed the GI concept and maintains the world’s leading food database on the subject, low-GL foods are those with less than 10 grams of glucose per serving.
‘Healthy’ Foods That Are Known To Raise Blood Sugar
“Many foods marketed as ‘healthy’ can cause big spikes if eaten alone,” Inchauspé said. She suggested shifting the focus of those foods from “healthy” to “pleasurable.”
“It’s fine to eat them, but we need to put them back where they belong: in the dessert category,” she added. Here are some top “watch outs” from nutrition experts:
Beverages: “Many plant-based milks, especially oat and rice milk, contain naturally occurring or added sugars that raise blood sugar more than people realize,” said registered dietitian Marissa Karp. As she noted, portion size makes a big difference: “Oat milk may not be an issue when it’s just a splash in your coffee, but if you’re having a full latte, you might be better off choosing regular milk or an unsweetened nut milk.” A serving of oat milk has a GI of 49.
RDN Dawn Jackson Blatner mentioned sports drinks (65 to 100 GI) and kombucha as other beverages with a high GI. There’s no standardized number for kombucha, but one small study showed kombucha consumption can lower the GI of a high-glycemic meal, such as one with rice.
Protein bars: “They can be a sneaky source of blood sugar spikes, especially if there are hidden sugars,” Amer said. “Many of these bars don’t contain enough protein, or an adequate balance of carbs, protein and fats, to prevent a blood sugar spike.” One study of snack bars found GIs in the 43 to 56 range, depending on formulation. In another study, PowerBars were shown to have GI ranges from 56 to 58.
Oatmeal: “While many brands of oatmeal contain some fiber, oatmeal alone tends to raise blood glucose levels more than you would expect,” Smithson said. Oatmeal GI indexes range from 42 for steel-cut oats, 55 for rolled oats and 74 for instant or quick oats. “Shop for oatmeal that’s highest in fiber per serving and doesn’t contain added sugar,” Smithson advised. “Include a source of lean protein to eat with the oatmeal, like eggs, low fat cheese, nuts or nut butter.”
Sushi: “It can often be an unexpected cause of blood sugar spikes,” Amer said. The index lists a GI for basic sushi of 45 to 55, but that number will vary quite a bit based on the type you order, the sauces you add and how much you eat. One serving of sushi rice alone has an 85 GI. The short grain and stickiness make it easier to digest and raise blood glucose more quickly.
Sauces and dressings: “Foods with hidden sugars like pasta sauce (23 to 35 GI) and salad dressings (55 to 69 GI) can be a problem,” Smithson said. “It’s important to check the total grams of carbohydrate on the nutrition facts, aiming for 1 gram of carbohydrate or less per 2-tablespoon serving.” If a pasta sauce or dressing has lots of added sugar, its GI could be higher.
Smoothies and protein shakes: “They may have nutrient-dense ingredients like fruit, milk, yogurt, oats and honey, but all those ingredients are carbs, and they add up very quickly,” Smithson said. “That will raise blood glucose levels more quickly than when choosing one or two carb foods with a lean source of protein.” When it comes to protein shakes, Karp noted: “They can be a culprit if they’re made with sweetened powders or blended with banana, honey or flavored yogurt.”
The GI of smoothies can vary quite a bit, but recent research noted that the types studied ranged from 35 to 40 GI. Naturally, smoothies made without added sugars are likely to have a lower GI, especially if they include fiber-rich fruits or seeds. Many commercial smoothies and protein shakes are not included in major GI databases, like the University of Sydney GI database or peer-reviewed GI tables.
Rice cakes: “Yes, they’re light and low in calories, but they’re high on the glycemic index, so they can cause a quick spike in glucose,” Karp said. Rice cakes have a GI of about 85, classifying them as high GI.
Quick Tricks To Keep Blood Sugar Stable
Reading labels is always a good idea, Karp said. “Check both the total and added sugar content, since even foods that seem healthy, like granola, yogurt or smoothies, can pack a surprising amount of sugar.” (The American Heart Association recommends limiting added sugars to no more than 6% of calories each day. For most American women, that’s no more than 100 calories per day, or about 6 teaspoons of sugar. For men, it’s no more than 150 calories per day, or about 9 teaspoons.)
Also pay attention to whether the food contains protein, fat or fiber, because those nutrients help slow how quickly sugar enters your bloodstream. A food that’s high in carbohydrates but low in these balancing nutrients is more likely to cause a spike.”
RDN Jerlyn Jones also suggested reading food labels carefully. “To avoid blood sugar spikes, examine the percentage of added sugars and avoid foods with added sugars higher than 20% of the total weight of the product,” she said. Foods with more than 20% added sugar are considered “high sugar.”
There’s another easy way to keep yourself in balance. “One of the best things you can do to avoid a blood sugar spike after eating is go for a walk or do some light activity,” Amer said. “This helps your body use the carbohydrates you consume.”
Jones agreed: “I advise my clients to get up and move 10 to 15 minutes after eating to help with digestion and lower blood sugars.”
The Negative Long-Term Effects Of High-GI Foods
Those high-GI foods may lead to afternoon crashes now and then, but it’s important to know they can have a detrimental effect long term, too. “In the short term, occasional spikes make you tired, unfocused and snacky,” Blatner said. “But over time, frequent glucose surges may contribute to inflammation, weight gain and potentially insulin resistance.”
While eating a high-GI food may make you feel temporarily sluggish or weak, making a habit of eating like this can have a long-term effect. “When your blood sugar stays balanced, your body has a consistent supply of energy and your mood, focus and metabolism function smoothly,” Karp said. “But when it rises and falls too quickly, those repeated surges put stress on your system.”
Jones added other long-term concerns: “Research has shown that the long-term consequences of blood sugar spikes are pro-inflammatory and may lead to free radical damage, which has been linked to cancer, heart disease and aging.”
“As a general rule, we want to eat in a way that helps us feel good and energized, not sluggish or sleepy,” Karp concluded. “When you keep your blood sugar steady, you feel more energized and focused.”
