Consuming these types of food can spike your blood sugar and lead to metabolic dysfunction. Here’s why—and what to eat instead.

What you eat has a powerful impact on your metabolic health. Nutrient-dense whole foods supply energy to your cells and provide molecular instructions to your body to help it repair tissues, fight infection, produce hormones, and stimulate bone and muscle growth. The compounds in foods can also activate specific genes that protect against inflammation and build immunity. Consuming a  diverse, whole-food diet is critical for building a metabolically healthy body.

There are certain foods, however, that jeopardise your metabolic health by spiking blood sugar, raising levels of cholesterol and triglycerides, or simply adding too many calories devoid of essential nutrients. In addition, some foods contain chemical additives and added sugars that promote inflammation. The typical  “Western” diet is filled with them, and many experts believe that plays a key role in our nation’s metabolic health crisis.

It’s important to note that metabolic health is about long-term trends, not single meals. Your body can adapt to the occasional fast food meal or high-carb food. But how those meals affect us—spiking our blood sugar or leaving us feeling fatigued—is essential feedback that helps us avoid unhealthy trends or repeated behaviours over time.

#1: Sugar (in all its forms)

There are good reasons why some experts advocate regulating sugar in the same way we regulate alcohol. Repeatedly eating too much of any kind of sugar can cause several forms of damage to the body. Whether consumed in “natural” foods such as honey, fruit, or milk, or as added sugar, your body breaks down the carbohydrates from food into smaller sugar molecules (such as glucose, galactose, and fructose). Glucose is then sent directly into the bloodstream. There, it triggers the pancreas to release insulin, which shuttles glucose into your cells for immediate fuel, or into your muscle or fat cells for storage, where it becomes glycogen, so that your body can call upon it when circulating glucose is low. Foods high in sugar and carbohydrates, especially in the absence of fibre, protein, and fat, tend to cause sharper elevations in blood sugar and subsequent insulin responses that can be damaging over the long term when eaten frequently. Fructose impacts your body differently, as it does not raise blood sugar or trigger insulin release immediately, but it can still be damaging. Fructose is metabolized in the liver, where it’s converted to fat and stored.

#2: Wheat Flours

Wheat flours are another form of easily-digestible carbohydrates. Unlike whole grains, which retain the germ, bran, and endosperm of wheat, wheat flour is milled, a process that removes the germ and bran. As a result, they lack the fibre, fat, and other nutrients that occur naturally in whole grains.

This is true even of whole wheat flour. While it does contain some fibre (it’s added back after milling) to help slow digestion slightly, whole wheat flour, just like all wheat flours—including bread flour, pastry flour, all-purpose flour, and cake flour—has a high glycemic index (GI), a measure of how quickly and how much a food raises your blood sugar. That rapid digestion means it will likely spike your blood sugar levels. According to a 2021 systematic review comprising observational studies involving more than 36,000 people, diets composed of foods with a high GI increase the risk of metabolic syndrome—a cluster of metabolic risk factors that, together, are associated with a significantly increased risk of Type 2 diabetes and cardiovascular disease.

#3: Ultra-Processed Foods

More than 70 percent of foods sold in grocery stores in the U.S. are ultra-processed, research shows. These foods include frozen meals, packaged snacks, granola bars, sodas, and cereals that contain few whole food ingredients, have little nutritional value, and are full of fat, sugar, sodium, and other additives and preservatives to improve texture or flavor or extend shelf-life. Especially dangerous are hot dogs, deli meats, and bacon. In a meta-analysis of data from three studies that examined dietary habits and health outcomes of around 200,000 men and women over 14 to 28 years, researchers observed that consumption of unprocessed and processed red meats—particularly those high in nitrites and sodium—was positively associated with risk of Type 2 diabetes, with relatively higher risk associated with processed meats. In one study, consuming these ultra-processed foods doubled diabetes risk for the highest consumption versus the lowest consumption.

Ultra-processed foods may also contain trans fats created during the manufacturing process. Despite research showing trans reduced HDL cholesterol and increased inflammation and that a high intake is associated with Type 2 diabetes and cancer, they were once widely used in many packaged foods like cakes, cookies, breads and crackers, ice cream, and snack foods. However, trans fats are now acknowledged as so dangerous that the US Food and Drug Administration recently banned adding them to foods, predicting that doing so could “prevent thousands of heart attacks and deaths every year.” Always read ingredient labels and look for “trans fats” or “partially hydrogenated fats,” which indicates their presence. Avoid foods that contain them.

Ultra-processed foods also often contain refined wheat flour and added sugar, which may spike blood sugar, disrupt the gut microbiome and promote inflammation. People who eat fewer processed foods tend to have healthier gut microbiomes and be more metabolically fit.

#4: Vegetable Oils and Refined Seed Oils

Many refined vegetable and seed oils are high in omega-6 fats, which have been linked to poor metabolic health in some observational research, especially when consumed frequently. The omega-6 fatty acid that has metabolic health experts most troubled is linoleic acid. Although it has long been considered essential for health, many researchers are beginning to question linoleic acid’s benefits, pointing to animal studies showing it causes insulin resistance. There is also some evidence that a diet high in linoleic acid increases inflammation, elevates the risk of cardiovascular disease, and stimulates appetite. Some researchers suspect a causal link between high linoleic acid consumption and obesity and diabetes.

Oils containing more than 20% linoleic acid and that are best AVOIDED include:

  • Safflower Oil
  • Sunflower Oil
  • Corn Oil
  • Cottonseed Oil
  • Soybean Oil
  • Sesame Oil
  • Rice Bran Oil
  • Peanut Oil
  • Canola Oil

#5: Fast Food

By their very nature, most fast foods are ultra-processed (see above) and loaded with refined flours, fats, salts, and hidden sugars—often engineered to be potentially addictive. According to CGM data from Levels users, McDonald’s and Chick-Fil-A are two of the worst foods for blood sugar spikes and no wonder. Whether you choose a chicken sandwich or a cheeseburger, you’re getting a dose of added sugar in every bite (you’ll find it in the buns, chicken, and condiments). Recent research from Asia reveals what happens when a population starts rapidly increasing the amount of fast food in their diets: The diabetes rate skyrockets. A 2015 research review directly implicated frequent fast-food consumption with abdominal fat gain, impaired insulin function, and systemic inflammation: key markers for metabolic disease.

And consider this: The raw ingredients used to make cheap fast food are rarely, if ever, sourced from producers whose primary concerns are organic, sustainable, humane, or ethical farming and husbandry practices—and that can have important implications for your health. A recent research review linked organic food consumption to better metabolic health, including reduced incidence of high BMI and metabolic syndrome. The study authors say longer-term studies on the health benefits are needed to determine why this is the case.

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